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[Hellmut1956]

Dear admins


I would like to share my knowledge as I develop a winch for a sailboat model based on a stepper motor. Looking into your sections I do see brushless and brushed motors sections, but not for steppers. Stepper motors have some interesting abilities which make them interesting for model boat builders. I do use those i.e. as a winch, but also, using steppers from old CD-, floppy drives or printers, which you find for free out there, to make things move slow and controlling its position. Where should I publish such threads?


Best regards Hellmut

[Rottweiler]

Hi Helmut,
I suggest you put your article under this section,and the moderators will move it if neccessary?
Mick F

[Hellmut1956]

I have been blocked by other activities and additionally, I killed my PC due to being electrostatically loaded. My old laptop is unable to run W10 and is so slow I feel like I can follow the processing of each byte. Since the time I had the intention to write about stepper, motors technology has advanced and the products of the company Trinamic I had used now are the defacto standard in 3D printers on small boards, stepper motor driver boards, called SilentStepStick followed by the name of the stepper motor driver used. Today most common are the TMC2208 and TMC209. I have decided to use the SilentStepStickTMC5160hv which now seems to have changed the device name to TMC5161. Contacting members of forums about 3D printing with my questions that reflect that I have been dealing with stepper motors and Trinamic driver ICs I was attacked on a personal basis, typical behavior of forum members that feel superior to everybody else. But reviewing my understanding of topics related to the driving of stepper motors I did find an error in my understanding. The error happened to me due to the fact that I did my experiments operating stepper motors that had no load to take. So I am happy I can now share with you my understanding of stepper motors and about parameters that influence their operation.


My first experiments trying to operate a stepper motor NEMA34 with 3.6 VDC nominal voltage and 2.8 A nominal current, were done using a stepper motor controller board that used the IC pair of L298/L297. I did apply 12 VDC and I did operate the stepper motor with full steps. The motor had a step of 1.8° or 200 full steps for a 360 turn. All my stepper motor did was vibrating. After a while, I started to question my ability to deal with stepper motors.


This changed when at a trade show in Munich Trinamic gave me as a present a stepRocker stepper motor driver board. So I downloaded and installed their development tool, the Trinamic IDE, and fed the board with 12 VDC for the stepper motors. I found out that my stepper motor just started to do steps when I did use the setting of 16 micro-steps per full step. The IC pair L297/L298 did support only 4 micro-steps per full step. So getting my stepper motor to do steps with those old stepper motor driver ICs was prone to fail. It was impossible to have my stepper motor even doing a single step.


The Trinamic IDE was ideal to experiment with all those parameters with which I could play in the process of understanding stepper motors. The IDE is for free. Trinamic has a full set of parameters that influence the operation of the stepper motor implemented not only in their TMCxxxx driver ICs but also in combination with code they execute on an ARM Cortex M3 controller. In those distant days, I did purchase the LPCXpresso1769 board. Quite a few of the current 32-bit 3D printer controller boards use this old LPC1769 controller from NXP. I have a channel on YouTube, Hellmut Kohlsdorf, where you can see videos I uploaded. Especially valuable for me in those days was to find out how fast stepper motor could do its steps. The video is relatively long due to the fact that I had not expected the stepper motor could do its steps at such a high frequency resulting in a huge velocity I did achieve feeding this stepper motor that had a nominal voltage of 3.6 VDC with 12 VDC. Each 360° turn is 200 full steps, each split into 256 micro-steps or 51200 micro-steps for every 360° turn.


https://youtu.be/nopezWBlDL0


Here a very strongly simplified description of stepper motors:


There are different types of stepper motors. Unipolar, Bipolar and Bypolar Hybrid. The unipolar stepper motors are very simple to control using a controller and so it was the predominant style of stepper motors used and they can be very cheap. We see this kind of stepper motors when we cannibalize old printers. Bipolar and Bipolar Hybrid stepper motors are identical in the way they are controlled, the hybrid ones can realize higher torque performance. I will write exclusively about bipolar stepper motors meaning both kinds of bipolar stepper motors.


Stepper motor like other motors does have coils through which the applied voltage and current results in a certain amount of current flowing through the coils. The torque a stepper motor can deliver depends exclusively on the amount of current that flows through the coils. Stepper motors with 8 cables coming out of them can feed the coils connected in series or parallel, each way has its pros and cons. But mostly you will have stepper motors that show 4 cables that are feeding every pair 1 coil. There are also ones that have 6 cables, as this offers access to coils connected in series between those coils. It is simple to identify the pairs of cables that are connecting to a single-coil. Those have a resistance resulting from the copper cables that make the coils. 2 cables that are connected to different coils will show infinite resistance.


Stepper motor driver ICs use a technique called PWM. That is known to us naval modelers from the signal pin of a receiver channel. Pulse width modulation means that the signal flowing through that pin has a duty cycle, that is when the polarity is plus and the reminder length of a wave the polarity is zero. So stepper motor driver ICs use PWM to limit the current supplied to the coils of a stepper motor to that value specified on its plate, the nominal value. So applying a voltage higher than the nominal value requires the driver IC to reduce its duty cycle from 100% when the nominal voltage is applied to 25% when the applied voltage is 4x the nominal voltage.


Now comes a very important topic. When the voltage applied to a coil changes, the coil will generate a voltage of inverse polarity to the applied voltage. So when a stepper motor makes a step or micro-step the amount by which the applied voltage changes than every time an induced voltage is generated. But besides the amount by which the applied voltage to a coil changes, the frequency at which it changes is responsible for the amount of induced voltage generated.


This is why a stepper motor has its highest torque when it is holding its current position. This means there is no change in the applied voltage and the induced voltage is zero. The simple equation shows this:


Veffective = Vapplied + (-Vinduced)


Lets put values in the equation:


6 VDC = 12 VDC + (-6 VDC)


Now, as the current that flows through the coil is responsible for the torque of the stepper motor, at a certain speed at which the stepper motor makes its steps, the induced voltage will halve the effective voltage. This means that then the stepper motor has only 50% of the torque when holding a position. So when the speed at which the stepper motor makes its steps reaches a value wherein absolute numbers the induced voltage is very close to the applied voltage, the current would practically stop flowing and therefore the stepper motor loses all its torque.


So what stepper motor do we choose when 2 stepper motors have the same torque capability? Yes, the one with the lowest nominal voltage value which means the higher capacity to allow for more current to flow. In the FAQ section of the Trinamic website for motors, there is a section as to why we operate stepper motors at a higher voltage than the nominal value and that 20x is a value often found. It was when I published this section of the FAQ all those aggressive and the ones attacking me personally disappeared. There is much more to say and a lot of pictures that can be used to present topics related to stepper motors.


I have recently purchased a Creality Ender 5 Plus 3 D printer and for upgrading, I purchased the most powerful controller board offered for 3D printers and SilentStepSticksTMC5160hv. The controller boards for 3 D printers and the SilentStepSticks board with the Trinamic stepper motor driver ICs are really cheap. So as soon as I can reopen my electronic workbench I will reinitiate the experiments with the stepper motors as I plan to use them as winches on my sailboat model.

[Martin (Admin)]

Wow!   Great information Hellmut!   

[Hellmut1956]

Hi Martin, Thx for the information that you liked my quick overview of what a stepper motor is. Allow me to continue. Stepper motors suffer from a widespread misunderstanding of it and due to the often year-long experience using stepper motors, it is difficult to accept the information I am providing. I am providing this information because as a naval modeler I am using stepper motors to control the length of the sheets to control the position of sail because I believe it opens opportunities to solve challenges I have set for myself and that cannot be achieved using a conventional winch. I use the stepper motor as a winch by taking advantage of its specific features. Stepper motors implicitly know their position if no step error is encountered.


Stepper motors do have the highest torque when holding their position. But this also means that while holding their position the highest amount of current flows through the coils of a stepper motor. Being aware of this I thought about ways to save energy so that the battery pack I am planning to use, 12 LiFePO4 connected in series where required, and those batteries were the ones storing the largest amount of energy and they could fit into the hull of my model. I decided to use electrical brakes that required energy when releasing. So during those phases operating my sailboat I did assume the stepper motors would not be doing steps, just holding their position. The brakes I found did require at least 24 VDC to release and so the 12 battery cells connected in series when empty so far that they had to be recharged still offered the 24 VDC. Fully loaded the pack would supply nearly 40 VDC.


But as it is when your knowledge improves and I did achieve this by doing experiments first using the stepRocker and later a board from Trinamic that tolerates 40 VDC, the motionCookie, I learned that I would not need the electric brakes. The motionCookie board I did use was never released by Trinamic. The stuff about stepper motors parameters I could take benefit of using the Trinamic stepper motor drivers I learned is what I would like to share. After nearly a decade since I started to play with stepper motors and Trinamic stepper motor drivers, a lot has changed due to advances in science and in functionality taken advantage of by newer Trinamic stepper motor drivers.


The biggest breakthrough in the use of stepper motors is due to their use in 3D printers. 3D printers for the consumer market, my Creality Ender 5 Plus 3D printer is one of those. Stepper motors are often defined in categories that reflect their size:





This table list some of the popular stepper motor sizes and NEMA 17 is the size of choice in 3D printers. Makers of 3D printers do use NEMA 17 stepper motors without a plate that informs about its parameters like nominal voltage and current, as well as the holding torque. When you go and look for NEMA 17 stepper motors i.e. at Amazon or eBay often that data is also not supplied. You need to know what you are looking for to be able to find it. In my sailboat, I am using NEMA 42 stepper motors. The reason why this is so is that the consumer users should not know about this so they do not notice that the NEMA 17 stepper motors used in 3D printers are the cheapest bipolar stepper motors you can get and as a consequence, they have the weakest values for their torque. So the way to look for NEMA 17 stepper motors look for those whose length is 2x to 4x the standard length and then try to identify their nominal values. Longer stepper motors can offer more torque as they have more coils connected in series. Such a longer stepper motor can be replacing the ones in the 3D printer where they are used to move the printing head in X, Y, and Z directions. The ones used to move the filament can be left unchanged as here their weight is key to support movement without vibrations due to the kinetic energy of the moving parts.


So having presented the above let us move to another parameter, the applied voltage. I have purchased a Meanwell 600W 48 VDC so that I can benefit from those aspects that benefit from supplying just the stepper motor driver cards with 48 VDC for motor supply. The benefit of using 48 VDC as opposed to the traditional 12 VDC or 24 VDC, 4x to 2x more voltage is as I did explain in my previous contribution, is that the effective voltage is the sum of the applied voltage, in my case 48 VDC and the induced voltage that is of inverse polarity. So as the frequency at which the stepper motor makes its steps increases so does the absolute value of the induced voltage. So, as long as the resulting voltage is well above the nominal voltage value the PWM used by the Trinamic stepper motor driver can ensure the nominal current is achieved and so the holding position torque can be kept. The Trinamic stepper motor driver can monitor the torque load of a stepper motor as the slightly changed angle of the rotor in the stepper motor makes it possible to identify the size of the load.


Again this capability, besides effects that 3D printer users know light operating without causing noise and that I show in my experiment on my YouTube channel "Hellmut Kohlsdorf" how this depends on the frequency at which the stepper motor is doing its steps, has multiple uses that are of interest when you plan to use a stepper motor in a naval model for heavier work. On the website of Trinamic, you can get the information in detail and in videos. You do not have to choose a stepper motor capable to supply peak torque requirements! The current that flows through the coil and its amount is responsible for the torque generated also is responsible for heating the stepper motor. So the Trinamic stepper motor drivers in combination with the software they supply can change the length of the duty cycle of the PWM that controls the amount of current to a value of up to approximately 120% and so that stepper motor will supply that much more torque for a limited time. The time length limitation is due to the additional heating the stepper motor will show when more than the nominal current value flows through its coils. A weaker stepper motor can be chosen for an application. But at least equally valuable is this same technique when the stepper motor has a smaller load and requires less torque. The driver IC can reduce the amount of current so that the stepper motor gets less hot and consumes less energy as only the required amount of torque required is generated. This means the stepper motor used as a winch in my sailboat model will consume less energy and so the batteries will last longer.


Now, due to the use of stepper motors in 3D printers, the controller board processes the instructions using the same language, G-Code, that CNC milling machines use. Additionally, the 3D printer consumer market has led to the creation of the so-called SilentStepSticks, which are Open Source-based boards, which are in tough competition and so their prices are really low.


Obviously, my intention about how to benefit my naval model projects is not inline with neither the 3D printer market nor the CNC market. So what I will investigate and do experiments once my electronic lab, a part of my workshop, is ready enough to start to use it again. I will investigate if and if yes, how I can benefit myself in my projects. G-Code is a human-readable text file and simple G-Code instructions allow me to make extensive use to control stepper motors in my sailboat model using the also available cheap but powerful controller boards used in 3D printers. The operating system widely used there is called Marlin and the version used is Marlin 2.0.7.2 as of today.


But typical for me and one of the reasons why my work to improve my workshop is taking so much time is that I got the appetite to build myself a CNC milling machine.


So, enough for now. But if anybody is interested I am here to help and inform same as I am here to learn.