Live Robot Hack Session
DJ Sures

PWM Servo Position Feedback (read servo position)

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I'll be hacking a PWM servo to have positional feedback for ARC using an EZ-B v4. You can also perform the same functionality with an Arduino or IoTiny on EZ-Builder. I'm merely using a EZ-B v4 because I'd like to play with my EZ-Robot JD Humanoid during the hack as well :).

You can read the servo positions of a pwm servo using this hack. Adding an extra wire to the PWM servos by reading the potentiometer position allows you to know the position of the servo at all times by the ADC input of an EZB.

I will be using these two robot skills....

  1. Reading positions with the 8 onboard EZ-Robot EZB v4 controller:

  2. Reading additional ADC positions from an arduino over I2C to the main controller:


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This will be a good one to watch for me. A very useful hack that I've always want to do.


So cool, I could have never figured out how to do this by myself...such a great hack to improve servo functionality!! :D


This is awesome. Synthiam needs to have this Addedtoo their Hdd servos. As far as I know no one else makes them. Just a thought. I know I would replace all of mine.


Cool nice hack DJ.  Maybe do a puppet video next week with 2 JD's one with feedback and one without so JD 2 replicates moves of JD 1.

#5   — Edited

@Nink - that's a brilliant idea!! Okay, I'll do that. Thanks for the suggestion.


Question. Can servos be controlled by a pot connected to the ADC instead of a whole servo. I assume its just using the pot from the servo. That way you could build a slave system with cheap pots to puppeteer your robot without having to use servos for every joint. Will the plug in allow the the use of just pots?

#7   — Edited

Will's always asking the good questions!  If the answer is "yes", then I wonder what value pot is best to use.  To the best of my knowledge (which is limited) I think most servos use around a 5k pot inside, which would seem like the best choice.  The middle leg of the pot I think would go to the ADC line and the other legs of the pot would go to the pos and neg respectively.


Are you thinking of a controller board like this one?

Otherwise you could also use very cheap servos on the "driver" robot, as they do not need to carry any load, I would guess you could use any type of servo...

Probably you could even scale down you robot and fit it with micro servos. As long as the scaling stays correct, the angles will stay the same! :)


Something even more fantastical than that.. but the concept is the same. Yes you can get cheap servos for

Look forward to Friday’s hack. DJ has an idea for expanding ports. The more the better for what I’m thinking.


Looking forward to see whats on your mind...maybe you want to build a rig for yourself? I thought about this a while ago, but binned the idea because I figured that it might be too hard to build with all those cables and straps!! :)