Let's Make Robots!

Servo Position Feedback ?

So I just watched this video on youtube http://www.youtube.com/watch?v=V1-J0OWUygU

 anybody know how to do this? I failed to google any more information on the subject..

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Thanks for the information everybody. After reading your response I disassembled a servo I had laying around and BOY did I smash that servo... (over excited combined with eager)

BUT I found out how a digital servo is designed and I found it very easy to locate the potentiometer! A 5K Ohm if you wondered xD But I guess that size depends on each servo...

This is great! I never would've guess it to be that easy to do a readout of a servo position...

The main issue is that just because you tell a servo to go somewhere doesn't mean it will actually make it there. Absolute angle feedback can be used to determine how fast your servo is moving at any given time, it can tell you when the servo has reached its designated position (so you can issue the next command, for example), and it will effectively let you know if the servo is too weak to get there, or has encountered some sort of resistance/obstruction.
In many applications this level of servo monitoring is simply not necessary, but for robots that are expected to handle a variety of situation intelligently this kind of feedback is a must-have =)

well when you put it that way, it makes perfect sense!!  :)

 

 

I imagine it would be bad to do this on cheap hobby servos but good quality ones should handle it ok. It would have it's use in establishing the movements for the servos physically. Such as in the term reverse kinematics. Maybe you can find more information if you google that. Or just follow telefox's instructions. He'd never lead you astray ; )

so.....what would be the use of this if you know where it is by the fact that you set the postion of the servo in your code...?

And from my understanding, it's never a good idea to manualy rotate a servo...bad bad bad for the gears. Yes it's an example, but still bad bad bad.

I strongly suspect that the extra line arnoldwu uses is simply feeding the middle contact of the servo's internal potentiometer to an ADC input on the micro. Judging from the values he's stated (56-413 for 0-180°) he's using a 10bit ADC converter, so nothing too uncommon there.