Servo with output??

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Lliam20789

New Member
Does anyone know who to change a servo motor by adding an output so that the position is readable?

This would be helpful to determine when the servo reaches its destination, if it is under extreme load, and also in programs were the same variable is used to drive different motors at different times.

Anyone got an easy, cheep answer? (I'm hoping...)
Thanks,
Lliam

 
 
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BeanieBots

Moderator
There are a few options depending on the make of servo you have.
All servos have an internal potentiometer which is used to give position feedback. On SOME makes, you can simply make a connection and feed it into an analog input on the PICAXE. Unfortunately, many servos use the potentiometer as part of an oscillator and so the signal is not a simple analog voltage. You could test it on yours with a 'scope and then determine if using pulsin would be a viable option for your specific servo brand.
If you don't want to hack into the servo itself, another way is to fit a resistor with schottky diode fitted in parallel in series with the servo 0v line. The diode is required to prevent high current from developing more than 0.4v volt drop in the line. The resistor value should be chosen to produce a voltage of around 0.2v at maximum normal torque. The voltage will give a reasonable reading with readadc10.
If the servo has stalled, the value read back will let you know. OK, not ideal for determining if position has been reached but as long as the current is below that which is known to move the servo under normal loads, it can be used as a reasonable assumption.

Edited by - beaniebots on 04/04/2007 22:33:15
 
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leftyretro

New Member
How about just mechanically attaching a pot to the servo output wheel or linkage and powering one lead to 5vdc the other to ground and the wiper would be a analog voltage feedback to the micro's ADC measuring actual travel position. Just a cost of a pot and no internal mod needed to the servo.
 
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