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Digital Servos?

In another thread, DJ said that to prevent the "jump" on power-up of servos, we could use digital servos, and that in the new year EZ-Robots would be offering a line of digital servos with full motion range (apparently a limit on those available today).

I have a couple of questions about these.

I know digital servos can provide position feedback. Can they also provide feedback on resistance to movement? What I am looking to do is have the claws on my Roli close until they "feel" something is gripped tightly, but not too tight. Currently, I have to close based on the size and resistance to being squeezed of the object I am picking up, and if I size it wrong, the servo buzzes to complain that it is under stress. Since I am picking up cat toys, this isn't a huge deal as they can all be squished without breaking, but I would like more flexibility.

If I am right, that feedback will be available, does EZ-Robot plan on selling micro, or just full size?

Alan

AI Support Bot
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Synthiam
PRO
Canada
#1  
Hey @thetechguru,

The micro servo we currently offer is actually a digital servo. Digital servos don't provide feedback to the controller unfortunately they just have higher resolution, holding torque, and are usually programmable to take different timing signals. Chainable servos provide feedback as they have a data line, but the only digital servos that can provide positional feedback are those with an extra potentiometer wire broken out.

A couple things I could suggest are:

You could solder a wire to the potentiometer wiper inside the servo and break it out to an ADC port on the ez-b (with a voltage divider configuration) and you could write a script to compare the value you are sending to the servo versus where it actually stops (monitored by the ADC port).

You could also breakout the ground line of the servo and monitor it with an ez-b ADC port and watch to see if there are any current spikes. This is less exact but a method that I have seen work.
#2  
Thanks! I'll look into those options. Since it is working OK with what I am trying to pick up now, I probably won't do this for a while (have a lot of other programming I want to get done first) but I will add it to my list.

Alan
PRO
Synthiam
#3  
Keep in mind that I said more than "digital servos" - please quote my response ton prevent future confusion. I also said you won't get the full range of motion with digital servos.
#4  
DJ, if you re-read my initial post, I did paraphrase you, but here is the exact quote:

Quote:

We will be offering full range Digital servos made specifically for ezrobot in our store in the new year.


Alan