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First leg test

A project log for Quadruped Robot

A quadruped robot using cheap servos closed-loop control and force-sensing resistors for ground force feedback. Uses Teensy and PCT.

YannisYannis 07/20/2018 at 16:063 Comments

After facing a few setbacks related to proper dimensioning in 3d printed components, I finally managed to assemble the alternative leg design today and perform a simple test using a servo tester, to verify motion behavior. The video is below:

This initial test shows satisfactory motion, although the cheap servos have a different PWM range that the servo tester supports (!) so the full range of motion can't be realized with this setup. I'll be conducting proper testing in the days to come, so stay tuned.

Discussions

de∫hipu wrote 07/20/2018 at 21:11 point

That looks like it's working much better! Forget about full range of servos, especially with the cheap ones. The only thing that is "standard" is 90°. Servos have larger range (usually almost 180°) just because it was easier mechanically to build them that way, but even the same model from the same manufacturer will vary in range and center point. You *will* need a procedure for centering and trimming them if you want any accuracy.

Note that the range and duty/position mapping will also change with the frequency. I use 5V servos with 4.2-3.7V, so I give them higher frequency than the standard 50Hz to compensate, and that moves the center away from the traditional 1500ms.

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Yannis wrote 07/21/2018 at 14:24 point

Oh yeah those cheap servos are fun to work with! I ended up using the full range of around 100µs to 2000µs to achieve almost 180º motion! I'll surely calibrate for individual servos thanks for the advice.

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davedarko wrote 07/20/2018 at 17:26 point

yay cool, this is more like what I have thought would make a better design :) 

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