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Author Topic: Operating servos that rotate 180 degrees  (Read 500 times)

roycv

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Operating servos that rotate 180 degrees
« on: August 30, 2018, 12:47:55 AM »

Hi all, I am looking for help here.

I have bought servos advertised as 180 degree type expecting them to work on my (old) standard Tx. They just give 90 degree rotation.
On checking the spec of the servos more carefully I see that I have to have a Tx able to give a wider pulse of 500 - 2500 micro secs. (0.5 - 2.5 milli secs) instead of the standard one of 1 -2 milli secs.

Years ago I used to open up a servo and add resistors to the feedback pot to give a wider angle of travel.  My eyesight is not quite up to that now.  But happy to open up a Tx.

Is there something similar I can do in the transmitter?
regards
Roy


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derekwarner_decoy

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Re: Operating servos that rotate 180 degrees
« Reply #1 on: August 30, 2018, 04:15:30 AM »

Hullo Roy, not in the gizzards of the the onboard servo, nor the Tx, ..but the ACTion P96 servomorph [of Dave Milborn fame] installed in your vessel from Component Shop will possibly resolve your need

From Zero to ~~160 degrees of movement.....individual set point adjustable & with speed control........they are magnificent...... I have [3]...yes three of them 

[I will get them commissioned one day .......I am not using them in servo stretch mode, but to actually reduce each servo end point to point and most  importantly the servo slow function.....one each for Rudder, Stephenson's reversing gear linkage & Steam Regulator]

So if any nincompoop slammed   <*< any Tx stick in any direction, the P96 onboard takes over the function  O0 & gently gently does it :kiss:...it also saves the owner from trying to achieve a gently...gently by hand attempt in moving the Tx stick

Derek 

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwiM1emq5pPdAhXKFYgKHQZ0CXQQFjAAegQIChAB&url=https%3A%2F%2Fwww.componentshop.co.uk%2Fp96-servomorph.html&usg=AOvVaw1K-GSfER1L3OOtChAXcS7U
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Derek Warner

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Re: Operating servos that rotate 180 degrees
« Reply #2 on: August 30, 2018, 07:31:03 AM »

This unit also addresses 180 degree capability in servos with individually set end points and adjustable speed. My experience is that the servo horn will need re-fitting from the 1.5mSec centre position as 180 degrees is typically achieved with an asymmetric setting of eg +100, -80 degrees.   

http://www.forge-electronics.co.uk/index.php/boats/servo-controller
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john44

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Re: Operating servos that rotate 180 degrees
« Reply #3 on: August 30, 2018, 09:27:27 AM »

As Derek says action servo-morph, easy to set and reliable..


John
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BrianB6

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Re: Operating servos that rotate 180 degrees
« Reply #4 on: August 30, 2018, 10:11:56 AM »

As Derek says action servo-morph, easy to set and reliable..


John
But only about 160 degrees which may not be enough if you want a full 180
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roycv

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Re: Operating servos that rotate 180 degrees
« Reply #5 on: August 30, 2018, 10:54:21 AM »

Hi all, thank you for your responses, I was trying to avoid having a servo stretcher in each installation.  Have chased one down at 8.85 + p&p.  But will be experimenting with Tx.

Any Tx ideas would be welcome I am OK soldering and circuits generally as it was a bit to do with work.

I have veroboard and a hoard of ancient electronics from my experimental days and kit assembly.  Remember making a Micron Tx and Rx's from kits back in the 80's.
I was a bit surprised how dear they were.  I have a very nice speed controller (10 amp brushed) from Bang Good that was less than 4.  You have to change the leads as they are Rx battery type, but they are cheap enough.

Any ideas about playing with the AVC pot on old Hitec Tx's?  I use these as they have a convenient 3rd. channel that is on the top and just goes where my thumb is.
kind regardsRoy


 I know I can get cheap 2.4 Ghtz rc but I use a servo adjuster type channel for tweeking a flying jib on a couple of yachts.



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cos918

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Re: Operating servos that rotate 180 degrees
« Reply #6 on: August 30, 2018, 01:59:30 PM »

Hi
Two resistors in line on the other pot wires will do it . With any servo you need to were the manufactor has put the mechaniacl stop. Some will alow more that 180 deg with out mods some wont

John
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roycv

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Re: Operating servos that rotate 180 degrees
« Reply #7 on: August 30, 2018, 04:55:42 PM »

Hi Cos, yes that works well and I have been doing that for many years, well 30 or so, but when I was making a Micron Tx all the extras were in the Tx.  Mixer etc.

I have just taken a Hitec 3 ch. 40Mhtz FM Tx apart and the answer may well lie with the AVC adjustment (volume control) but it is rather integral with the motherboard and I decided not to touch it. 

I did put a servo lead in to act as a parallel charging socket.  Rather than a low current non-intel  charge point I can use an intelligent 4 - 10 cell charger I have.
The reason for all this is that I can use standard servos which have a high torque as sail arm servos and in smaller yachts.
I have gone down the servo expander trail this time as I want something quickly and I found a UK source at a good price, I will report how I get on.
Kind regards to all who have contributed.
Roy
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Hellmut1956

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Re: Operating servos that rotate 180 degrees
« Reply #8 on: August 31, 2018, 08:22:44 PM »

If you use i.e. an Arduino UNO board from China you have the cheapest way to adapt the functionality of servos if not limited by hardware in the servos. You can get an Arduino UNO board from China extremely cheap including shipping costs! The Arduino would digitize the PWM signals from all channels of your RC receiver and generate for each of the channels individually the PWM output to the servos. You can find information about how to write the code.


Even cheaper it is with an ESP8266 based board like this one! But it is a bit more challenging it as you need to add the support for the board in the Arduino IDE, the programming tool for all this boards.


Just to emphasize: Programming the digitizing of the PWM channels is very simple: You use a clock within the microcontroller. You start the clock when the signal changes from low-high and you stop it when the signal changes from high-low. Save the value of the counter, this is a digital information of the length of a signal. You track what is the length when you pull control and dimmers maximal to get the shortest signal length and corresponding you get the maximum length. Then all you do is to generate a PWM signal on your board to control the servo by adjusting the min and max length to what you need to have your servos extended or reduced movement angle!
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Best regards Hellmut

malcolmfrary

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Re: Operating servos that rotate 180 degrees
« Reply #9 on: September 01, 2018, 10:50:32 AM »

Servos use a 270 degree pot as a sensor.  the 90 degree movement generally puts the required travel somewhere in the middle with plenty of room at each end.  Extending the travel does run the risk of causing the travel to go past the track end inside the pot, or into the mechanical end stop.  Both are unlikely, but a change of transmitter between, say, a Futaba and anybody elses might manage it. 
For a 180 degree task, I would use a low turn winch with an arm rather than a drum and a travel adjuster to go down from 720 (2 turns) to 180 (half a turn).  In a sail boat, of course, just using it as a drum might work well.
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roycv

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Re: Operating servos that rotate 180 degrees
« Reply #10 on: September 01, 2018, 02:11:08 PM »

Hello Malcolm, I did think of using a sail winch and reducing my AVC down to a minimum and may do so in a larger yacht.  This one is not quite big enough for the usual sail servo winch.

I do not want to go down a new technology route (for me) with Arduino but a good idea.
Regards to all
 Roy


 
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Hellmut1956

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Re: Operating servos that rotate 180 degrees
« Reply #11 on: September 01, 2018, 02:30:23 PM »

Good decision! I did the mistake to get into electronics for my model and now I spend nearly 100% learning, experimenting and this 2 activities in a loop! Still worth. Technology interesting to apply to in RC controlled boats is exploding thanks to the Internet of things, short IoT and AI, artificial intelligence! Most people have a wrong understanding of AI, but the technologies of Deep learning, Machine Learning and Neuronal Networks are not too difficult to understand. In my case they are an interesting possibility to implement in my project of a sheet control system for my sail boat called Carina and presented in my thread in the forum for building from scratch.
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Best regards Hellmut

roycv

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Re: Operating servos that rotate 180 degrees
« Reply #12 on: September 01, 2018, 02:54:21 PM »

Hello Helmutt, you made me smile! I remember being trained to fault find and repair computers in 1965 we had to also learn basic programming skills.  I nearly got hooked on programming as it was machine language then.  I did what I had to then stopped, life was too short, it took over trying to find shortcuts to reduce the number of instructions used.

My son got involved in parallel processing 20 odd years ago and I proposed an autonymous yacht with a processor on board monitoring speed wind direction and sail adjustment.  You would just have to set a course with the rudder, and the yacht would set the sails, not a pefect situation as you would have impossible courses.  We never found the right sensors.
regards Roy
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Hellmut1956

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Re: Operating servos that rotate 180 degrees
« Reply #13 on: September 01, 2018, 05:02:40 PM »

Dear roycv, I am on my way to collect 62 years on this planet. By what you write I guess you have collected some more then me. As you have been into the topic, here a link that presents the basics of my sheet control system. Here the link to my report of building my Carina from scratch!


If you happen to look a bit in depth to the presentation of the fine control of the sheet, this is where I guess AI has potential to address it. The most important think when programming an AI based solution is to get enough data for training of the AI engine. Having sensors, magnetic angle sensor and the length of the sheet by the position of the stepper motor. This position determines the length of the sheet. This allows me to create many data sets required to train.


The core of all this is based on digitizing data from servo angular position from what the operator wants, captured by digitizing the active period of the PWM and relating angular position that reports the actual true angular position of the sail and the "current step position" of the stepper motor.
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Best regards Hellmut

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malcolmfrary

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Re: Operating servos that rotate 180 degrees
« Reply #15 on: September 01, 2018, 08:55:40 PM »

The ebay servo might well suffer from the same problem that the original had - the need for a reprogrammed transmitter to give the required pulse width.


Quote
This one is not quite big enough for the usual sail servo winch.

The new winches  (new a few years ago) have a body the same size as a standard servo, and are about the same price as a standard size, high torque servo.  Installation is simpler, and you don't need room for the swing of the arm.
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roycv

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Re: Operating servos that rotate 180 degrees
« Reply #16 on: September 04, 2018, 03:35:59 PM »

Hi all the Flytron device arrived this morning it is the same size as the socket part of a servo plug! 
It is called a servo expander circuit.  8.85 + p&p 2.50

 http://www.flytron.com/

Tested it on a few servos and it extends the rotation to about 160 degrees which is great for a yacht sail arm winch. 
So with a cheap metal gear Tower Pro MG 965 servo, sold as 180 degree type, I bought 3 for less than 10.00  I have a small and quite powerful sail arm winch. Finger crushing at servo edge.
I will explore later the transmitter option but the expander circuit does keep the system standard and not needing a specific Tx. for the job.
Thanks for the input guys I think that unless you buy a dedicated yacht winch, you will have to use an expander or stretcher circuit to get the extra rotation. This changes the standard 1 - 2 milli second pulse width to 0.5 - 2.5 milli seconds.
I bought servos listed as 180 degree rotation not knowing you need the change to a wider pulse width to get this rotation.
 
I do not know if computer Tx's already have the facility but most times I use just 3 channels.
regards Roy

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