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Author Topic: Stepper motors  (Read 7104 times)

Hellmut1956

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Stepper motors
« on: May 16, 2013, 12:48:59 PM »

Dear Friends

Often I have realized, that many people, even those pretty familiar with electrical motors, do have a very superficial knowledge about stepper motors. I will try to share some of my knowledge, without yet being sure what the best strategy is.

I will start presenting what is a stepper motor.



Here the picture of a typical stepper motor. The name stepper relates to what makes this motor special. It rotates not continuously, as we know it from brushed or brushless motors, but as a sequence of steps. A common value is 200 steps for one 360 turn!



This picture, which I am using based on the written authorization I have from Trinamic.com, owner of the pictures, exemplifies a simple stepper motor that makes a full 360 turn in just 4 steps. The more coils you have within the motor the more steps it is able to make, but that does not mean that for 200 steps you have an equal number of coils!
 
In the center is the rotator which is magnetic. In this picture they have put a compass needle just to visualize it. As you all know, the compass needle will stay stable, as soon as its north pole has a south pole next to it, and vice versa its south pole has a north pole next to it. Now those external north and south pole are generated by the magnetic field that builds up when a current flows through the cable of a coil. Depending of the direction of flow of the current flowing through the coil it will show either a north or a south pole at one of his ends and in consequence define in which orientation the needle will stabilize. The coils come in pairs as shown in the picture and there are 2 pairs. I will not go into the details about Unipolar and bipolar stepper motors to keep it simple. One is called Phase A, the other one, what a surprise, Phase B.





In this picture you can see how the 4 steps for a full turn are achieved by having the coil show either the north or the south pole to the compass needle in the center. Depending on which of those poles are generated by the current flowing through the coil you see how the needle is repositioning itself.

The control of the direction of the current flow depends on the value of the tension applied to the cable that makes up those coils. Remember, one circuit is called Phase A, the other one Phase B!


 
This graphic shows the same facts as the one before, but may be a bit more abstract! To get a better grasp of the message lets look at each 4 the 4 steps represented in this graph. Remember form the 1st picture, Phase A consists of the cable ends next to "4" and "7", Phase "B" of the cable ends next to "3" and "5". Those 4 cable ends are given at any bipolar stepper motor, the more common today, by the 4 cables coming out of a stepper motor. Lets call them Phase A1 and Phase A2 for the one pair of coils made by one cable and its 2 ends and Phase B1 and Phase B2  for the second set of coils made by one cable and its 2 ends.
 
So if you connect the cable Phase A1 to one connector of a stepper motor controller and the cable Phase A2 to a second connector, and so for Phase B1 and Phase B2, you have connected the 4 cables coming out of a stepper motor to the corresponding bipolar stepper motor controller. Lets name those connectors correspondingly A1, A2, B1 and B2.
 
Lets look to the interval 1 of the chart and lets assume as follows:
 
A1 has the value logical "1" of 5 VDC and A2 has the value of logical "0" or ground.
B1 has the value logical "1" of 5 VDC and B2 has the value of logical "0" or ground.
 
As a consequence the 2 lines are showing a value of "1" meaning the current is flowing from A1 to A", respectively B1 to B2!
 
Lets look to the interval 2 of the chart:
 
A1 has the value logical "1" of 5 VDC and A2 has the value of logical "0" or ground.
B1 has the value logical "1" of 5 VDC and B2 has the value of logical "0" or ground.
 
As a consequence the 2 lines are showing a value of "1" meaning the current is flowing from A1 to A", respectively B1 to B2!
 
Lets look to the interval 2 of the chart:
 
A1 has the value logical "0" or ground and A2 has the value of logical "1" or 5 VDC.
B1 has the value logical "1" of 5 VDC and B2 has the value of logical "0" or ground.
 
As a consequence the 1 line, Phase B, has not changed and is showing a value of "1" meaning the current is flowing from B1 to B2" as before,
While Phase A has inverted the direction of current flow.
 
Lets look to the interval 3 of the chart and lets assume as follows:
 
A1 has the value logical "0" or ground and A2 has the value of logical "1" or 5 VDC.
B1 has the value logical "0" or ground and B2 has the value of logical "1" or 5 VDC.
 
As a consequence both lines, Phase A and Phase B have inverted the direction of the flow of current compared to interval 1!
 
Lets look to the interval 4 of the chart:
 
While Phase B has not changed Phase A has inverted the direction of current flow to the same as in interval 1!
 
Result:
 
By just controlling the polarity of the tension applied to Phase A and Phase B the stepper can be made to move from one step to the next!
 
What does this mean to us as model ship builders? Well, a stepper motor has a known orientation at any given time interval, depending from the polarity applied to Phase A and Phase B. We know the position of the stepper motor! Having this knowledge we can use that knowledge to have a stepper motor moving into a defined position and in consequence achieving the action we want!

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john44

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Re: Stepper motors
« Reply #1 on: May 16, 2013, 01:19:29 PM »

I know I might seem stupid to ask,but what speed do these motors go
or would you have to have controls to slow them down as in a servo?

john
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Hellmut1956

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Stepper motors
« Reply #2 on: May 16, 2013, 01:28:03 PM »

Lets continue. The old thread will be deleted and now I will try to prevent this from taking place again.

As this thread about stepper motors is meant for ship modellers, I will try to relate the facts about this motor to our hobby and will try to pass that knowledge to you, that enables you to translate that knowledge into may be completely new uses of stepper motors.

I want to highlight that you can find stepper motors for free cannibalizing old PC equipment or printers, but be aware of, that there may also be unipolar motors, which I am not touching yet, trying to keep things simple. Yet so I want to tell you how to relate cabling from an stepper motor to either phase A or B. The simplest and meaningful way is to look for the datasheet of the motor in the internet. If you find the datasheet you will be told there which color the cables belonging to either Phase A or B have. The other method is to use an instrument to measure resistances, a multimeter set to Ohm, is usually the best way and to set it to either just ring, this means it makes a peep sound when the resistance is very low. The cables corresponding to either Phase A, or the pair corresponding to Phase B, will have the multimeter ring. But it also makes sense to measure the real value of the resistance of the cable that makes up a coil to know the static inner resistance of the Phase. On some stepper motors you will find not 4, but 6 for 8 cables coming out of it. Watch in detail the second picture in this thread. You see that the cable of either Phase A or Phase be are used in the winding of 2 coils. Well, when a stepper motor has 8 cables, guess what, a single cable with it's to ends just is used for 1 coil. As a consequence you have twice the number of cables coming out. For 6 cables, just study the next picture. Here the datasheet is very helpful to identify which cables you need to connect to each other, to make either Phase A or Phase B. But often this is also color coded, i.e. on one of my stepper motors, one cable is white/green, the other one just green. Connecting the 2 is what needs to be done. Going back to measuring the resistance. Each pair belonging together will ring and have i.e. 4 Ohm value as resistance. Connecting the cables of 2 coils together will give phase A or Phase B a value of 8 Ohm!





If the motor is a unipolar motor, they often have 6 cables coming out of it, then there measuring the resistance value, to take the values of the former example, when the resistance value is just 4 Ohm, then just one coil is using that cable pair, if the value is 8 Ohm, then you know which 2 cables are linked together to be either Phase A or B and you just isolate the cable that has just 4 Ohm. The picture might help to understand this and the german terms are similar enough to english ones to capture the meaning, otherwise, just ask!


The last of those picture addresses the possibility to connect the cables in a way, that the coils are either connected in i.e. phase A in series or parallel. This has an impact on the available torque and on the stability of the operation of the stepper motor. This will be explained later and I do plan to make short videos to demonstrate the impact of certain parameters on the operation of stepper motors. This information should help you to identify a stepper motor and the cables coming out of it and how to use and connect those. But lets go on introducing you to this wonderful motors!






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Hellmut1956

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Re: Stepper motors
« Reply #3 on: May 16, 2013, 01:50:35 PM »

@John: Good and helpful question! This motors do not go at any speed! They just move in steps. How many steps you make it do and how many steps make one 360 turn defines at what "speed" the stepper motor goes! I am serious saying that your question is good and helpful! It is the first step and very important step to understand stepper motors and how they are different from what we are used to! They, I know this is not exact, they do not move at any speed! Lets take an example that applies to our hobby, where a stepper motor, taken out of an old CD-ROm drive, is used to make the radar of a ship make its turn, i.e. at 1Hz, means one 360 turn per second!


Those stepper motors usually have about 20 steps for a 360 turn, so you would have to make your stepper motor step 20 steps per second to achieve that "speed"! Let me use this opportunity to introduce the concept of microstepping, as the example chosen is pretty helpful for this! The above 20 steps are also called "full steps". Having the stepper motor step at 20 steps per second, or even slower, will make visible that the turning is not continuous, but done in steps. Microstepping is a technique very common in stepper motor control and which being refined and used to optimize the operation of a stepper motor makes wonders to the capabilities of a stepper motor! The number of microsteps per full steps can be incremented in powers of 2:


20=     1
21=     2
22=     4
23=     8
24=   16
25=   32
26=     64
27= 128
28= 256


So, 0 at the power of 2 gives 1, etcetera. Ff course that requires to increment the stepping rate, as now every step sequence just means 1 microstep, requiring up to 256 of those to make 1 full step! But this is no problem, as the microcontrollers that operate the control circuit for stepper motors operate at millions of "steps" per second!


But applying this to our example of having a radar on the mast of a ship turning at 1 Hz. Now the movement of the stepper for 1 full turn will be:


Number of "steps": 20 (number of full steps per 360 turn) * 256 (microsteps per full step) = 5120 steps per second to achieve 1Hz operation of our radar antenna! But microsteps have a few additional effects that impact the operation of a stepper motor in dramatic ways! But you can imagine, that you cannot visually perceive 5120 microsteps per second. Your impression is that the motor is moving smoothly at 1HZ! Having said this I want to put a number of facts on the table to acknowledge and that you will later understand.


1. A stepper motor is not good to turn fast! Fast meaning up to may be 10k 360s per second!
2. A stepper motor looses its torque  the faster it turns!


Those are negative statements, but make it clear when a stepper motor is not a good choice. For fast turns a brushed or brushless motor are the much better choice! But this facts have a very good and helpful side!


1. The stepper motor has its maximum torque when it is standing still, means just holding position!
2. The stepper motor has implied a "knowledge of its position"!


Using stepper motors as winches in a sailing ship, as I am doing it, means that the stepper motor is capable of offering maximum torque to withstand the pressure of the wind on the sails coming to the drum holding the sheet for sail control. This feature makes it possible to control a sheet for the main sail that can be shortened or lengthened over 8.4 meters making possible to implement something like this. Here a Picture from the original:





Normal winches would have to increase the number of turns, making sensitive control of the sails impossible, but what is much more critical, the principle of the lever applied to what ever technique is used to make longer sheet changes possible, either drum with larger diameter or the pulley principle reduce the available torque so dramatically that large sails on a large sail boat model either become impossible or demand the purchase of special winches that cost up to 400.- to 600.- Euros. Here an early picture showing the huge sails that will be operated on my sailboat:


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Hellmut1956

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Stepper motors
« Reply #4 on: May 16, 2013, 04:20:52 PM »

Next I want to introduce some terms which are relevant to describe the stepper motors and then present one of usual mistakes people make when selecting a stepper motor for an application.


Nominal Current:
This is the maximum current for which the cable that go through the coils we described earlier is made and therefor the motor can withstand without getting to hot and break.
Nominal Tension:
This is the tension for which the stepper motor is having the nominal current flow through its coil.


If we apply this 2 values to the law of Ohm we get the resistance I mentioned earlier can be measured while identifying the cables coming out of the stepper motor.


R = U / I


Holding torque:
This is the torque provided by the stepper motor and which prevents the stepper motor to rotate.


Power:
Expressed in Watt and can be computed by multiplying a current in Ampere with a tension in Volt:


P = U * I


End of the terms and lets dwelf into interesting matters!


Lets compare 2 stepper motors, one with a nominal voltage of 12 VDC and one with 1 VDC, lets assume both motors have a nominal current of 1A:


The nominal power of the first motor, which translates into torque:


P = U * I = 12 * 1 = 12 W



The nominal power of the second motor, which translates into torque:


P = U * I = 1 * 12 = 12 W


The first impression is, the two motors are of identical power and this would fully comply with the perception we have from brushed or brushless motors! Let me tell you that of the 2 I prefer the second motor! Surprising, isn't this true?


Well, lets explain this! The control logic to operate a stepper motor includes a function that is called PWM, or Pulse Width Modulation. This function uses a switch that switches the current ON and OFF a couple of thousand times per second. The relationship between the ON and OFF times is called duty cycle and basically says how much time the switch is ON allowing current to flow and how much time the switch is OFF and the flow of the current is interrupted. This technique is also used to control the speed of a brushed motor i.e.! Well in stepper motor controllers this technique is used to limit the amount of current flowing through the coils normally to the nominal value of the current. Lets explain this on the example of my own sail boat model and the operation of the stepper motor there! I promise that later i will present movies loaded onto YouTube to explain this in a visual manner!


I do have 12 battery cells LiFePO4, each with a capacity of 16AH and with a tension, fully loaded of 3.65 VDC and fully unloaded, 2.0 VDC. That means the battery pack made of the 12 cells will supply a tension that will be below the max value of:


12 * 3.65 = 43.8 VDC


and above the min value of:


12 * 2.0 VDC = 24 VDC


I will use the tension provided by this battery pack to feed the 2 stepper motors I use to control the main and the headsail. lets apply this tension value to the 2 stepper motors introduced above:


First motor:


P = U * I = 12 * 1 = 12 W (nominal values)
P = U * I = 43.8 * 1 = 43.8 W


You see that the power of the stepper motor can be about 3.5 times the nominal value!



Second motor:


P = U * I = 1 * 12 = 12 W (nominal values)
P = U * I = 43.8 * 12 = 525.6 W


You see that the power of the stepper motor can be about 3.5 * 12 = 42 times the nominal value!


You see the second motor has a dramatically higher power than the first motor and it explains why I do prefer the second motor. The lesson i am trying to pass is as follows:


When you have the choice between two stepper motors with the same nominal current, always prefer that one that has a lower nominal tension specified! This says that the second motor is the one of much higher value and better implementation! More generically. Ignore stepper motors with a nominal tension value that is high and choose the one with the lowest possible nominal tension value, but still offering the torque you need and want!


This higher tension applied to the stepper motor has another important effect. It allows the stepper motor to run at much higher step rates and as a consequence at much higher speed loosing less torque as it gets faster! Advanced motors often do specify up to which tensin the stepper motor can be operated, this value being always much bigger than the nominal tension value. I hope you understand now the difference. The manufacturer of the stepper motor is saying with this that due to the way he has designed and manufactured his stepper motor a tension applied to it not higher than this value will not ruin the motor. Remember, the coils are made by winding slim cable and this cable as an isolation coating. if the tension is too high, combined with the nominal current the motor could break somewhere in its design!


Lets explain why a stepper motor can turn at higher step rates without loosing all his torque! By changing the flow direction of the current through the coils in the stepper motor by inversing the tension applied, we explained this above, the coil behaves like one to which an alternate power supply is being applied, as we know from a transformator. Here we have, saying it simple, 2 coils with different number of windings. The AC tension applied to the primary side, the input to the transformator, induces, that is how the effect is called, a tension in the second coil which is higher or lower depending upon if the number of windings on the secondary side, the output side, is higher or lower.


Well in a stepper motor the higher the step rate is, the higher the frequency of the change of polarity is and the higher the induced tension is! This tension has the opposite polarity as the applied tension. Saying it in an equation:


UResulting = UApplied - UInduced


In numbers:


U = 43.8 V - 33.8 V = 10 V


As a result the effective tension responsible for the torque has been reduced to less than 1/4 so the power in the stepper motor and the torque available is also reduced to less than1[size=78%]/[/size]4


This can get to the point where the stepper motor does not have the torque available to even do a step with no load! So applying the higher tension allows the stepper motor to tolerate a higher induced tension before becoming inoperable!

I have been learning a lot while trying to understand the operation of stepper motors and why my stepper motor, with just 12 VDC applied, a nominal tension of 1.6 VDC, did not move. The next issue I want to present to you is a bit complex and better understandable once I have made the videos to explain. Basically the issue is about what parameters do exist that influence the operation of a stepper motor, its degree of vibration, its degree of noise, the amount of torque versus step rate, the connection of the coils in parallel or in series, I have already explained physically what this means, the impact of the microstepping, the impact of the characteristics of the microstepping, the acceleration and deceleration rate of the stepper motor. For all this there is a GUI as part of the IDE supplied for free from www.trinamic.com and a board called StepRocker, which allows to play with this parameters by changing them on the GUI (Graphical User Interface), which is running on a PC to which the StepRocker board is connected via USB. It might sound intimidating, but it is really just getting a rough understanding and starting to play with it!



http://youtu.be/X4X_EUxqKEo


Here the link to a short video that shows how using the right functions to operate a stepper motor can make a big difference! I have used this S-Ramp function, which is just clicking a box in the GUI, being able to accelerate the stepper motor even more. For me, where my stepper motors will be turning a drum for the sheet, this function will make the difference between being able to operate the sails during a turn of the sail boat in fraction of a second, to have it last a couple of seconds, as i get to see it on other implementations!

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Hellmut1956

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Re: Stepper motors
« Reply #5 on: June 10, 2013, 05:57:49 PM »

I will try to continue with the tutorial in stepper motors.  It is apparent, that the knowledge about this motors and their use in our hobby is not well known. The challenge i see is how to pass information so that it can be captured fast, so that the information is of use for our hobby and to make clear how the different parameters do influence the operation of a stepper motor. I started presenting what a stepper motors was and Jon was so kind to ask the right question about how fast a stepper motor is. The overwhelming further questions made clear to me that either I had done an awful job trying to present stepper motors to you, that the information had been too theoretical and as a consequence the use of this motors in our hobby was impossible to perceive.


Well, I will try the next step in this tutorial generating short videos and publish them using the YouTube platform. In analogy to an old saying that one picture explains more than a thousand words, may be a video is another step passing data. Should the information be too boring or theoretical, please forgive me for using this platform to develop the tutorial for stepper motors in our hobby.


Finally again, excuse me for the lack of knowledge of the english language and for my abilities to present the information!


Previously I have presented in an theoretical way data which is key to understand the message of the videos I will present. I will try to summarize this information and generate a video that extends on the subject. As the uploading of videos is a slow process, please forgive me if In the process of generating the contribution the document will be incomplete.


I start presenting the setup that will be used to generate the videos. I am using my brand new, not yet finished electronic workplace and I do take the 24 VDC to feed the stepper motors to start. I have put in series into the positive pole of the power supply a multimeter set to measure up to 10A current. We will see in the videos the current value during the experiments.





I will start working with the large stepper motor that can offer up to 3 Nm torque and can be fed with up to 3A. I have put a piece of tape onto the shaft of the stepper motor, so that its rotation can be perceived better. The black foam I have placed the motor on will be used to address the issue of the noise the motor generates while being operated. Putting the motor onto the wooden surface allows to amplify the noise generated by the motor and to appreciate how low the noise can be when properly operated. Remember, that noise is the effect of the current, the electrical and magnetic fields not working efficient. or to say it the other way around: A silent operation of the motor is the indication that the motor is being operated efficiently resulting in close to no vibration, best torque generation efficiency and best use of the applied energy.





This next picture shows 2 other stepper motors that I will be using. The smallest one was taken out of an old CD drive and did move the laser lens of the read sensor along the radius of the CD. The diameter of this small stepper motor is just 15 mm, or 0.6 inch and it is for free by cannibalizing old computer hardware. The other motor is a small stepper motor with just 28mm, or 1.1 inches.





And finally you have the 2 multimeter I use in parallel, the bigger one to measure the current and the smaller one to measure the tension. You have to know, that a power supply can have the tension supplied drop when a load like a stepper motor is connected to it. This way both values can be measured. The small card is called the StepRocker card supplied by Trinamic which works together with the gratis IDE, development environment and which contains a graphical user interface that allows to set the values of all parameters on the screen of the PC. This is a comfortable environment to test  and I believe ideal for this tutorial. The Trinamic controller and an ARM Controller build onto the card offer the most complete set of functions to control a stepper motor and as a result allows for an efficient use of the stepper motors.



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Hellmut1956

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Re: Stepper motors
« Reply #6 on: June 12, 2013, 08:34:16 PM »

I will continue presenting the IDE, the environment that allows to control the stepper motor functions from a PC.







We use the the function "Direct Mode" which allows to control the motor directly from this interface software on the PC. You can see the "tab" for this mode by the hand icon, the sixth icon from the left.





This picture shows the window with the control interface for the "Direct Mode" and you can see the default as being "1. ROR rotate right". At this selector you have a huge number of options, most used to influence a program written in a special high level control language. I will list the key functions we will be using from this selector, but keeping their numeral:


1. ROR: rotate right
2. ROL: rotate left
3. MST: motor stop
4. MVP: move to position
5. SAP: set axis parameter
6. GAP: get axis parameter


The list continues up to the counter value of 139 offering many choices we would need when programming our own code.


This and the many additional functions represent the elements of a high level language that allows to implement complete functions in the form of self written short programs. In the case of my use of the stepper motor as a winch, whenever I get the angular position of the sail, I will have 1024 positions both for the main and the foque, I will use the MVP instruction to have the stepper motor moving the drum with the sheet in to the proper position as needed for the sail in the current position. This way for example I will never have loose sheet, as the angular sensor provides to the stepper motor controller the target position to make available just the required amount of sheet. Imagine the sailship turning and the main sail moving from a 45 position on one side and I wishing to have the sail stop at the other side in the equivalent 45 position. While the sail is moving from one side to the other, the angular sensor is reporting the boom position which the controller for the stepper motor translates into a target position for the drum. This way it keeps collecting the sheet length now not required. Once the boom on the other side reaches the 45 position, the software knows it has reached the final point and stops providing sheet and this way keeping the sail movement limited to the 45 position it has been instructed to by decoding the data from the receiver that reflects the position of the control stick on the transmitter!


The first 4 instructions are kind of generic as they determine the direction of rotation of the stepper motor, by instructing a continuous rotation, correctly said stepping direction! Or it makes the motor stop or just go to a target position! Lets continue with either "SAP" or "GAP" selection, which we will use to either set parameters and see in short videos the result or to read the parameters currently in place. Lets assume we always choose "SAP" as soon as we have initiated the continuous stepping / rotation of the stepper motor, either left or right!


We now will deal with the selector "Type", the second one, that allows to set or read the value of a parameter, the following list is a part of a total of 254 choices, but we will limit ourselves to those relevant for presenting to you those parameters that have an impact on the operation of a stepper motor and that I will use together with short videos that will show the effect.


0. target (next) position
1. actual position
2. target (next) speed
3. actual speed
4. maximum positioning speed
5. maximum acceleration
6. absolute maximum current
7. standby current
8. target position reached
9. reference switch status
10. right limit switch status
11. left limit switch status
135. actual acceleration
138. ramp mode
140. microstep resolution
160. step interpolation enable / disable


I will go in detail into the different entries of this table as I do demonstrate this by short videos and when I will present the big picture as to how those parameters play together.


The third selector just reflects that 3 of this controllers can be combined and the third selector has the role as to select which of the 3 cards I want to read or write to!


The 4th selector, named "Value", is guess for what? Of Course to enter the value when writing to the controller card. Below are 3 buttons. One called "Execute", which when punched passes the value or the request to the card controlling the stepper motor. The other to are meant to pass the instruction with its type and value to the editor when writing a program to automate the behaviour of the stepper motor.


Next under the title: "Manual Instruction Input", allows to see, read, modify or write the instructions as selected above. This, together with the related buttons is just of interest when writing code.


Finally we see fields under the title "Answer". Here we can see what we send to the card when using the "set axis parameter=SAP" and see the response from the card when using the "GAP" instruction! A valuable source of information to make sure we know always what we have done!


Reading all this might be intimidating at a first glance, but as the tool, together with the attached controller card and the stepper motor, allows to play and see the effect right away and the videos will let you exactly this. That is why I believe it will be very important for you readers, as it was for me, to watch the videos. Should you wish to buy this inexpensive board, called "StepRocker" in the USA, here a link. In the UK, or elsewhere in the world!


The company Trinamic will introduce a new module, I had the opportunity to see at a tradeshow in Germany, that will be even more adequate for us to use in our hobby for stepper motors, which is smaller and allows for higher tensions to be applied to to mare current if required. This will be available in second half this year!


To make sure this is not a promotion package for Trinamic, nor for their products and I have no relationship with them other than loving their products for my hobby. But I got the StepRocker card as a Christmas present from my family and I loved to play with it and by getting a much better understanding of stepper motors I could refine my plans for the use of stepper motors in many very different applications on my sailboat model!



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Mad_Mike

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Re: Stepper motors
« Reply #7 on: June 12, 2013, 09:15:55 PM »

this is all very clever stuff. Probably a bit too clever for me  :embarrassed: To be honest i cant think where i would be able to use such a motor in any of my boats as nothing i have requires this kind of accuracy, therefore ive not experimented with them.
On the other hand these motors would be PERFECT for driving the steering gear of 360 degree azipod and schottel units.
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Hellmut1956

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Re: Stepper motors
« Reply #8 on: June 12, 2013, 09:56:39 PM »

Hi Mike, what about making the radar on a ship turn at the desired rate? What about controlling the cannons on a military ship? Understanding stepper motors allows you to use the stepper motors from old CD drives or old printers to achieve the objective and they are for free! What I have learned to hate is the awful noise servos make when turning! Stepper motors properly setup will make no noise at all! Its what I learned when I studied mechanical engineering at an university here in Germany! The difference between a space rocket and a washing machine is that they use less expensive materials in a washing machine and the tolerances are less tight! But the skill set required for either equipment is about the same! Same applies for stepper motors compared to normal brushed DC motors. Both can be for free or very expensive, both can be controlled to operate fast or slow, precise or not precise. Just stepper motors have abilities due to the way they work which opens interesting fields of use! They have build in the parameter of a position, they can use this data without an additional sensor. Today the only rough equivalent we have is a servo! Awful noise, more expensive than cannibalizing a CD drive from an old PC or an old printer!
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Re: Stepper motors
« Reply #9 on: June 12, 2013, 10:06:55 PM »

i suppose yes but you would need some kind of board to drive the stepper motor right? And if we wanted to run off the stepper motor off a normal radio channel is there a simple plug in and play way of connecting the board to the receiver? For stepper motors to really take off they would need to have a very simple installation as most people in this hobby do not possess the skills or understanding to build their own.
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Re: Stepper motors
« Reply #10 on: June 12, 2013, 10:16:06 PM »

You say that, Mike, but then I read things on Mayhem where people are discussing things to a level I have no experience of - steam engines, for example.

There is (almost!) a plug-and-play method of control using R/C: there are a range of small, cheap and easily available microprocessors that can take pulse inputs (servo channels) and send stepper outputs.

Hellmut's guide is a great introduction to the black art of stepper motors. Hopefully we'll all be programming* stepper controllers to our heart's content as this thread continues!

Andy

* Hopefully this word won't put anyone off! Programming is not difficult and (most importantly!) a pile of fun.
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Re: Stepper motors
« Reply #11 on: June 12, 2013, 10:51:28 PM »

A stepper motor with feedback would be a great way of controlling ballast/trim tanks on a model sub
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Re: Stepper motors
« Reply #12 on: June 12, 2013, 11:06:27 PM »

Great to have both Mike and Andy answering and allow me to answer to both.


If I read the report of buildings from scratch,  if I read the marvells about work in wood, in metall, in glas fiber and epoxy or other plastics, if I read about how some they implement marvellous mechanics in their models, than why electronics needs to be simpler? Then why do electronics just have to be made in China, be plug-and-play, or ready to fly? I do see in our hobby a wide spectrum of different objectives by those dedicated to it, why does electronic just have to be a simple black box? The title of this subforum is:

The "Black Arts!" ( Electrics & Electronics )

The target is to open the pandora box of electronics so it stops being a black box only be used as plug-and-play elements! Electronics require much less than many mechanical activities shown in this forum. I have seen and I have promoted the use of electronics in forums in the Spanish world. It is a bit like legos. if you learn a few elements you can combine them and build whatever you imagine, as long as you map it into what is easy and what not to achieve in electronics. But we are talking about something more equivalent to a build from scratch then to operate a ready to fly model!


I started programing with microcontrollers using the mega8 from Atmel and using a Basic compiler called BASCOM. This compiler has many instructions that already implement the building blocks of what is required to program for our hobby and this compiler is for free!


If I compare brushed and brushless motors with the perception users have about it, the result is they are familiar with what those can do. If I do the same analysis for stepper motors I find that a huge percentage has not a clue about them! This is why I do a tutorial for stepper motors. But as in most areas involved in building from scratch or in building of many kits, nothing is for free! Learning can be seen as something boring, but it also can be perceived as a way to open a door into a whole new world of possibilities. You get to see that with the new 2.4GHz radio control systems the marketing people of the suppliers are using the terms from the old i.e. 40 MHz systems to sell something where those terms do not apply. Why? Because that allows the to charge more and to limit the expectations of their customers and in this way not be forced to open those systems to their real power. But also, because many want to hear the known terms applied, even if that is just marketing "xxxxx"!


Why am I writing this. because I want to use the example of the 2.4 GHz systems to see how lack of knowledge allows the marketing people of the suppliers to stick to the old world! There are no channels in a 2.4GHz system! 2.4 GHz systems are just transmitting a serial stream of data between the transmitter and the receiver. That is totally different from the old systems in the megahertz range! Here every 20 ms i.e. 8 pulses where send, each of the pulses having encoded in its length the position information from the control on the transmitter. So the term "channel" made sense! Every 20 ms 8 pieces of data were transmitted.


So back to the stepper motor tutorial, it is not meant as an alternative for those that only use ready to fly electronics from China! It is for those that might have an interest to engage into the "black art" of electronics! I had prepared to publish a certain number of pictures and videos to illustrate the data given previously. I lost it, so I will have to repeat it and publish it in the near future, if there is an interest in it!
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Re: Stepper motors
« Reply #13 on: June 12, 2013, 11:10:10 PM »

Dear friend from Finland, please explain why and with what objective you need a feedback and why this would be of interest with a stepper motor in a submarine. This is an interesting advice that I would appreciate to understand and it would present an example about how we can discuss on electronics as we do in many other fields of our hobby!
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Re: Stepper motors
« Reply #14 on: June 12, 2013, 11:16:25 PM »

Im interested... I have a shed full of old computers, printers etc :)


I'm not sure if I do mean feedback... This is a little (actually a lot) above my knowledge level


basically I was thinking of stepper motors to control the piston type dive tanks on a submarine one at the front and one at the back.  In order to keep the sub level you would empty or fill one or both tanks.  The stepper motor would give very fine control over the filling of the tanks.
Feedback could be used to report back to a central unit exactly how full each tank is
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Re: Stepper motors
« Reply #15 on: June 13, 2013, 12:49:12 AM »

Something like this movie shows?


http://youtu.be/G8i2x1M3A50
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Re: Stepper motors
« Reply #16 on: June 13, 2013, 09:08:17 AM »

That's pretty much it
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Re: Stepper motors
« Reply #17 on: June 13, 2013, 10:24:34 AM »

Well, as I lost what I had been preparing to publish, lets try once more to get it reedited and published.


So far I have introduced to you the tool, IDE , stands for "Integrated Development Environment", and specially the direct mode graphical user interface that makes it possible to experiment how those parameters influence the performance of a stepper motor. But to understand what I will be showing using short videos that I will make and publish in YouTube, kind of a big picture is necessary for a better understanding, I do believe!





Lets look in detail in the speed profile when a stepper motor moves from a starting position to a target position. Remember, stepper motors do move by advancing in steps, the sequence of steps makes the shaft turn. So when using a stepper motor i.e. to turn a drum on which is the sheet to control a sail, than the stepper will be moving as addressed here form a current position to a new position. In my model I use a drum with a circumference of 400 mm. The sheet length to control the sail can be moved over 8.4 meters. As a result the change in sheet length from the boom of the main, i.e. from the center position to a one perpendicular to it would be achieved by just 21 turns of the drum. Now imagine I would accelerate at maximum rate and decelerate at maximum rate, what a stress would be imposed on the sheet and the blocks! The jerk would either destroy those immediately or their life expectancy would be very low.


So if you look at the speed profile chart it shows you where those parameters selectable and settable as shown in the short list of "types" you can see that it allows me to set how steep the acceleration and deceleration phase speed curve is, it allows to set how high the maximum speed while travelling would be. So to find the proper parameters for my use of the stepper motor as winch for the sheet for my main, I would try to make the acceleration and deceleration phase as little steep as possible, while the maximum speed for the horizontal phase of the movement would have to be slow enough for the stepper motor still to offer the torque required to move the sail against the force generated by the wind blowing against the sail! And finally all this has to happen fast enough to be acceptable. remember, that the faster a stepper motor rotates, the lower the torque is!





Now when you compare the first speed profile chart with this second one you can appreciate the difference! While the first has a trapezoidal form in the second chart those straight lines that represent the speed change during the acceleration and deceleration phases are replaced by curves! This technique is called S-Ramp and allows to soften those faces and so reducing the jerk that would stress the sheet and blocks on a sailboat when used as winch replacement.


http://youtu.be/X4X_EUxqKEo

In this video you can see how a glass, filled 1/2 with water is moved. Once following the trapezoidal speed curve and once using the S-ramp technology! What a difference! Just this feature makes the solution using the Trinamic components or modules worthwhile.  Starting here you can find a place in your area where to buy i.e. the StepRocker or the MotionCookie that will be released during the second half of 2013!

But that is not all and this videos and pdfs will add to the entertainment and learning effect of this tutorial. I want to write, that I have the authorization from Trinamic in writing to use the material for this kind of purpose! But as wonderful as the S-Ramp function is for the use of a stepper motor in some applications in our hobby, i.e. i have no limitation to the change in length of the sheet, even if 8.4 meters are required, the "position" or "step" orientated working mode of stepper motors make possible to take advantage of this operation mode to be as a sequence of steps and in consequence of having a known position of my drum at any time.

Good stepper motors usually make 200 steps for one 360 turn. Good stepper motor control i.e. move making 256 microsteps per each of the 200 full steps. Lets compute how many steps and therefor positions my winch to control the position of the boom by just providing the adequate amount of sheet.

200 * 256 = 51.200 microsteps for one 360 turn.

To support the full 8.4 meters of sheet length change I do need 21 turns are required to be supported!

51.200 * 21 = 1.075.200 steps or positions!

Lets translate this huge value into how big in millimeters each of this over 1 million microsteps changes the length of the sheet:

8400 mm / 1.075.200 = 0,0078125 mm!

As you can see, this is an extremely low value which absolutely can not even closely be controlled from a control stick on our transmitter!

Well, this just tells us that we have a huge reserve in precision to allow us to ignore much of it. But what it also opens the door for is to use this high resolution in combination with other sources to allow a better control. I do use a boom for the main and the fock sail, both rotate around a shaft, which is used to determine the angular position of the boom using a magnetic angular sensor with a resolution of 12 bits or 2 exponent 12 or 2^12 = 4096 positions that the angular sensor can report to the control software. Lets apply this information to the length resolution as follows:

4096 positions of the angular sensor apply to a 360 full turn. in case of the boom of a sail only 1/4 applies, as the boom will only turn 90 to either side and both sides are just equivalent.

So the 51.200 steps have to be matched to the just 1024 possible boom positions as this is the resolution of the angular sensor!

51200 / 1024 = 50 microsteps per maximum angular resolution per turn.  Expressed in millimeters:

0,0078125 mm * 50 = 0,390625 mm

This is the change in sheet length demand in average as the angular sensor can detect. The use? Well, imagine the boom of my main sail is in an 45 angle towards the center line of my hull. I do make a turn. The sail will change sides as the hull turns. The user keeps its control stick position for the main unchanged! As the boom moves towards the center position less sheet length is required and this is a source of possible trouble on a model sailship. We use the endless sheet method in the hull, as had we the sheet just on the drum of our winch, the sheet loosing its tension, would drop out of the drum! Well, here this is not a problem, as the software and the controller module would turn the drum to accommodate to the demand of sheet length due to a changing boom angle. This happens fully automated and benefits from the huge resolution of the components ensuring the sheet will never be able to drop out of a drum! Once the boom reaches the 45 angle position on the other side the software knows this is the maximum as desired by the user on the transmitter and would stop lengthening the sheet once the 45 position is reached! I am taking this examples and others to demonstrate that the awareness of the abilities of a stepper motor makes possible completely new approaches to standard solutions. The software will be completely parameter driven allowing to adapt the software to any existing geometry of another sailship. same applies to the controller hardware. Once i made it and it works I will publish all data to make it again.

But that is not the only great feature of this controller.

http://youtu.be/7eCLV7pALig


StallGuard is another one of those great features.  Imagine this stepper motor with a maximum torque of 3 Nm running into a mechanic failure of any kind the obstructs the free movement. This force can destroy the whole model! StallGuard, as shown in the video is used to detect when the movement reaches the end positions at both ends and when an obstacle prevents it from moving over the whole range.

Other features are lated to increase the efficiency of the power consumption of the stepper motor. It detects when the torque required for the function changes, i.e. when a gust hits the sail and adapts its power consumption to offer the required amount of torque and same if no torque is required, it lowers the amount of current flowing through the coils of the stepper motor. The IDE offers the tools to identify the right values of the involved parameters and to change them to the best possible values.

Finally I want to give you the link to a PDF document that gives a general introduction to the stepper motor topic!
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Re: Stepper motors
« Reply #18 on: June 22, 2013, 01:53:24 PM »


Well, my dear friends, in the process of developing the spreadsheet to compute the speed of the stepper motor by computing the revolutions per second or Hz I also wanted to compute it in rpm, revolutions per minute, I found that my stepper motor was not behaving as expected from applying the formulas out of the Firmware manual. Of course my first assumption was to have made an error passing the formulas to the spreadsheet. I could not confirm this!

So next was to use the GAP instruction, "get Axis Parameters" and could also not find the mistake, as I just was looking onto the usual variables! Trying to demonstrate with such videos how the stepper motor behaved as we apply the parameters and wishing to make this spreadsheet available to you, was as shaming me as you can imagine!

So studying the formulas again in detail I went into more detail and did concentrate on 2 variables I usually never touch, those being the "ramp divisor", parameter 153 and the "pulse divisor", parameter 154 and yes, they did not have the values expected! As the manual states to change the values carefully and just changing the values in increments of "1" I did so until the values of given in the example of "1" for each of them was reached while having the stepper motor stepping. Thanks lord, than the motor behaved as the formulas said, or better said, the motor was always behaving in accordance to the formulas, but just with the values given!

So thanks to those of you that at least glimpse into the tutorial once in a while I learned from the experience a lesson! Never assume the values are what you expect, but make sure upfront they are! This will impact this tutorial and the spreadsheet!

Lets introduce the formulas:

Microstep Frequency

Represents the rate per second the stepper motor does its microsteps!

s[Hz] = (CLK [Hz] * velocity) / (2pulse_div * 2048 *32  s: Microstep-frequency

Fullstep Frequency

Represents the rate per second the stepper motor does its full steps! Full steps are the steps a stepper motor does by design and is specified for every stepper motor!

s[Hz] = s[Hz] / 2srs  s: fullstep-frequency


Velocity

Is the value that can be set with values between -2047 and +2047 with the parameter 2: "next speed" in the GUI in "Direct Mode"


I will use the following data set to present a behavior of the stepper motor in a video:

Example:

CLK     16 MHz = 16.000.000 Hz

Velocity           = 419

a                    = 10   the acceleration used as parameter 5 "maximum acceleration".
                               Which can have values between 0 and 2047 and I do use 10 first so you can watch as the stepper motor accelerates!

pulse_div         = 1

ramp_div         =  1

srs                = 8     This is the microstep resolution exponent to the base of 2, means here 2E8 = 256 microsteps per full step

The result of this parameters entered into the spreadsheet that will be made available to you is:

Turns:  1,0 Hz   One turn per second
RPM:   60

As a consequence of the lesson learned the sequence of steps done in the GUI is as follows

1. "6 - SAP"     "4 - max. positioning speed"     "0 - Motor 0"      Value: 2046

This sets the maximum speed while travelling between 2 positions to 2047, leaving all options available in the future.

2. "6 - SAP"     "4 - max. acceleration"     "0 - Motor 0"      Value: 10

This sets the acceleration rate to a very low value so you can see as the stepper motor accelerates

3. "6 - SAP"     "4 - max. current"     "0 - Motor 0"      Value: 255

As the stepper controller is set to a maximum current of 2,8 A and the stepper motor can withstand 3 A, I set this value to the maximum possible of the values between 0 and 255. Playing with this value allows to see, when the current limitation which expresses what torque can be achieved by the stepper motor impacts its ability to operate. You will have frequently the opportunity to see in the videos how the motor stops to deliver its service by stopping to move and just vibrate!

4.  "6 - SAP"     "7 - standby current"     "0 - Motor 0"      Value: 10

When a stepper motor is not operated, when the coils do not have current flowing through them, you can rotate the shaft with your fingers. The amount of current flowing through the coils defines what torque is available to resist external torque applied to the stepper motor, be it by trying to rotate the shaft with your fingers, or be it, when the stepper motor is being used as a winch in a model sailboat to hold the sheet to the main boom i.e. to withstand the power of the wind into the sails. The Trinamic controller has a function called coolstep which allows to have the hardware notice when the torque stress applied tends to rotate the shaft, to increase the current flowing through the coils. The effect is that you can reduce the power consumption of the stepper motor considerably and so have the batteries to last longer! I have not yet played and experimented with this function, as I will experiment with it later.

By choosing a low value I can try to rotate the shaft with my fingers to demonstrate it.

5. "6 - SAP"     "138 - ramp mode"     "0 - Motor 0"      Value: 1

This parameter can have the values "0", "1" or "2" and represents a fantastic function of this controller.

"0": With this value assigned to this parameter when the stepper motor is instructed to move from a start position, the actual position to a new position, the target position, both positions expressed as integer numbers, those are just numbers with no fractions, i.e. 1 or 2 or 3 are integer numbers, "1,5" is not an integer number, it will accelerate using the defined acceleration and follow a trapezoidal speed curve.

"1": With this value assigned to this parameter the stepper motor will accelerate following an S-shaped acceleration and deceleration speed profile as introduced to you before. I have provided the link to a video from trinamic that shows how a glass, half filled with water will accelerate and decelerate without the water in the glass moving!

"2": With this value assigned to this parameter  a continuously rotating stepper motor will accelerate or decelerate with a constant acceleration value equivalent to the maximum value set for acceleration, which is what we see in the trapezoidal speed profile picture given above!

Choosing a value of "1" will allow to increase the acceleration rate later without impacting the motor operation and allowing for higher speeds to be reached. With the low value of "10" assigned to acceleration rate here this will not be visible until I do change the acceleration rate value!

5. "6 - SAP"     "140 - microstep resolution"     "0 - Motor 0"      Value: 8

6. "6 - SAP"     "153 - ramp divisor"     "0 - Motor 0"      Value: 1

This is to make sure the value is "1" and the rotation speed of the stepper motor is as calculated in the spreadsheet.

7. "6 - SAP"     "154 - pulse divisor"     "0 - Motor 0"      Value: 1

This is to make sure the value is "1" and the rotation speed of the stepper motor is as calculated in the spreadsheet.

8. "6 - SAP"     "160 - step interpolation enable"     "0 - Motor 0"      Value: 0

This parameter can have the values of either "0" or "1", "0" meaning the step interpolation function is disabled! This is another interesting function of the controller that allows to reach very high speed of the stepper motor, effectively multiplying the speed by 16! it is only available when the microstep resolution value is set to "4", meaning 16 microsteps per full step! When the motor is stepping with this microstep resolution setting and enabling this function will increase the stepping speed by a factor of 16. I plan to show this in the first video by starting with 256  microsteps per full step as written above and the keep changing the value of the microstep resolution from "8" to "7" to "6" to "5" and to "4" and further down until the stepper motor either stops operating or down to "0" to show full step operation!

Depending on the value I will assign to the velocity parameter, which I will select last, as this makes the stepper motor start rotating. I will start choosing a speed value of "419" which will make the stepper motor rotate once 360 per second and which can nicely bee appreciated in the video.

To those friends that see the operation of a stepper motor in this tutorial as being far too complex and far too sophisticated I want to point out that the purpose of this tutorial is to help you to understand a stepper motor and so i am introducing you to all the parameters that influence its operation. Once you plan to use a stepper motor for any specific function you will use default parameters, verify that those make the stepper motor do what you actually want and that it operates silently, as I guess you wish! Should it not operate or operate making noise or vibrating I hope you learn from this tutorial how to fix it and have the stepper motor operate smoothly, silently and with the torque requirements you have at the desired speed!

 
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Re: Stepper motors
« Reply #19 on: June 24, 2013, 03:51:34 PM »

absolutely fascinating,but way and above,much too technical for me I am afraid!
You should publish a book!
Mick F
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Re: Stepper motors
« Reply #20 on: June 24, 2013, 08:47:58 PM »

absolutely fascinating,but way and above,much too technical for me I am afraid!
You should publish a book!
Mick F

Must admit.......I was totally lost after the first paragraph, sorry.
 
think I'll stick to my Buhlers, lol  %%   %%   %%   %%   %%   %% 
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essex2visuvesi

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Re: Stepper motors
« Reply #21 on: June 24, 2013, 09:08:18 PM »

absolutely fascinating,but way and above,much too technical for me I am afraid!
You should publish a book!
Mick F



Must admit.......I was totally lost after the first paragraph, sorry.
 
think I'll stick to my Buhlers, lol  %%   %%   %%   %%   %%   %% 


Me too..... but it does make a bit more sense after the 4th or 5th read and a long sit down :)
Just remember that computer you are using now probably did the same thing to you when you first got it.
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Re: Stepper motors
« Reply #22 on: June 24, 2013, 09:46:48 PM »

I found a nice simple controller project from https://store.cunningturtle.com/product/ct-60
looks pretty good:
http://www.youtube.com/watch?v=BBwjsPy687E
A start anyway.
 
 
 
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Re: Stepper motors
« Reply #23 on: June 24, 2013, 09:58:30 PM »


Must admit.......I was totally lost after the first paragraph, sorry.
 
think I'll stick to my Buhlers, lol  %%   %%   %%   %%   %%   %%

Cant agree more with you Neil........To Be perfectly honest with you I fully understand what has been said about them as I used to be in the RAF as an electrical tech but some of it has gone straight over my head............I think a lot of mayhemers have had the same problem and think all they need to know is will they work or not...........I may be totally wrong in what I have said but it is what I Personally think...............

Please don't take offence at what I have said and I am NOT AT ALL critisising the nature of the reasearch that has gone into this Thread.

Dave
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Re: Stepper motors
« Reply #24 on: June 24, 2013, 10:03:36 PM »



Me too..... but it does make a bit more sense after the 4th or 5th read and a long sit down :)
Just remember that computer you are using now probably did the same thing to you when you first got it.

It still does  O0 O0 %% %%
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