Tuning Analog multi-turn pot

Questions about using encoders with the Roboclaw product line
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Dmannstuff
Posts: 2
Joined: Fri Apr 29, 2016 2:51 pm
Tuning Analog multi-turn pot

Post by Dmannstuff »

I am having a similar issue. The analog photon my linear actuator is a multi-turn 10k. I am following the instructions for the resistor. In Pwm mode the actuator moves beautifully, the encoder counts in the correct direction and my span is roughly 50-1700. I have tried to calculate qpps multiple times. I have followed the instruction on the forum for calculating based on 360/deg of pot rotation * (max pos- min pos) * rpm/60. I do have some questions about this it is a worm drive with gear reduction and an acme screw. I have calculated based on the encoder rpm which was measured with a tachometer.
I have velocity Pid set to 0,0,0.
In position control I start with 2000,0,0.
The actuator moves but not fluidly and it does not reach the target position. It seems that I can get it dialed in to move in decently retracting but not extending. Thus far I have been testing on a bench without load. I believe my qpps is most likely the problem. Can you clarify the calculations based on a multiturn pot with gear reduction.

Thanks,

D
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Basicmicro Support
Posts: 1594
Joined: Thu Feb 26, 2015 9:45 pm
Re: Tuning Analog multi-turn pot

Post by Basicmicro Support »

I split your post into a new topic. It is not the same problem as the other user was having. He is using an older version of teh Robcoalw 2x5 with older firmware(because his old unit cant be updated in the field). He also wasnt using a multiturn pot. He is setting his tuning values from code and not using IonMotion. These are significant differences in problems/questions. Please do not hijack other posts in the future or you will be banned.

What was the QPPS you calculated? What were the starting values of the calculating? Then I can tell you if they seem reasonable. How many turns is the pot(while producing legitimate values? Have yoy confirmed the Roboclaw sees the pot values correctly(use IonMotion).

It soudds like you are using a linear actuator with a built in pot. If so one of the problems with those actuators is noise. I recommend you use the IonMotionQA release and update the Roboclaw firmware to that firmware(See the IonMotionQA announcement in the General Discussions forum). We added some new filtering to help elliviate such noise problems. Also I recommend you not run the pot signal wires parallel to the motor power wires. This is how most of these linear actuators are setup so you will need to cut the housing around the wires so you can pull the signal wires away from the motor wires. Its a horrible design descision the manufactorers made seeing how noise is particullary bad when you run wires parallel to each oth.

Also note linear actutators have very bad sticktion/slop. You will definitely need to add deadzone to your settings. anywhere from 5 to 50 may be needed depending how bad the slop is.
Dmannstuff
Posts: 2
Joined: Fri Apr 29, 2016 2:51 pm
Re: Tuning Analog multi-turn pot

Post by Dmannstuff »

Thank you. The software and firmware updates worked. Now everything tunes the way it should.

Also, thanks for the warm welcome to the forum. It seemed we were both having analog pot tuning problems. regardless of the means of tuning - iomotion, etc. It seemed like a decent shot that he may have had some suggestions.

Hopefully this is released to the masses soon. I've seen comments on several sites steering people away from using the roboclaw for linear actuators because it can't deal with absolute pot encoders. I can say after this update that the board performs absolute perfect.

dmannstuff
User avatar
Basicmicro Support
Posts: 1594
Joined: Thu Feb 26, 2015 9:45 pm
Re: Tuning Analog multi-turn pot

Post by Basicmicro Support »

Didnt mean to make you feel unwelcome but we have to deal with alot of thread spamming(you dont see it but we do) and hijackign a thread hurts the original thread starter more often than not. We much prefer users start a new thread if they are having a problem because as yours turned out to be it was very different from that other users problem(eg he had a very old non-updatable controller).

If you can point me to the forum(s) that has other users having problems with the Roboclaw and analog encoders I'd appriciate it.

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