In my previous article I wrote I modified the servos to get the position feedback. I’m going to give you some information on how to do it.
Before you start, you should be aware that modifying your servos will break the warranty so if you do it, do it at your own risk. This operation requires a lot of patience and you must be thorough when you do it not to make short circuits which may burn irremediably your servos.
The full procedure is well described in the following links :
On my configuration, I connected two wires as shown in the first link. I think this hack is better than the second one because first of all, if you make your measurements on another card (which I do), you won’t have to find a way to get the cards ground together. Secondly, it makes a real measurement of the volt directly at the source of the potentiometer. And finally it may be better for electromagnetic immunity.
I also managed to use the seal to pass both cables (original cable + feedback). To do so, I just used a cutter to give the seal some more room to allow the bigger height caused by the new wires.In the picture you can see what it finally gives… It looks good ! If you see well, you may have noticed that there’s 6 wires ! Yes indeed, but there’s the red one which is not connected but let there for spare purposes and for esthetism too.
The cable composed of white, red and black wire is the 3002 cable from Phidgets. I connected the black one on the Ground signal (same signal as the black wire from the original cable) and the white one to the servo’s wiper. I soldered the wires as close as possible from the potentiometer to avoid losses and perturbations.
The final results are very satisficing and quite comparable to those obtained by this guy : http://www.youtube.com/watch?v=ygX7sQM2gq0.
Hope this will help people !
Here is another helpful publication : http://learn.adafruit.com/analog-feedback-servosMoreover, Adafruit is selling servos with embedded feedback position ! No more need to hack your servo to reach the holy grail !