RC Servo linear actuator cannot maintain stable position

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RC Servo linear actuator cannot maintain stable position

Postby amelia » Fri Apr 20, 2018 2:46 am


I realized that my brand new Phidget RC linear actuator cannot maintain a stable position when the target position is around 71%.

This is my configuration:
P/N 3540_0: RC Linear Actuator L12-100-100-06-R
P/N 1066_1: Phidget Advanced Servo 1-motor
Library information: Phidget22 version 1.0.0
OS: Windows 7 64 bits

I am using the Phidget Control Panel. In the "RC Servo Motor Controller" window I use the motor calibration parameters provided by Phidgets:

https://www.phidgets.com/productfiles/3 ... asheet.pdf

Which are:
Min pulse width: 1000 micro seconds
Max pulse width: 2000 micro seconds
Position at min: 0
Position at max: 100

When I move the target position to a value between 70 and 72, the actuator moves to that position but instead of stopping there, it keeps extending and retracting around the target position with an amplitude of about 1 mm. This behaviour is independent of the selected acceleration, velocity or SpeedRampingStat flag value.

The actuator works fine for other target positions (outside the 70%-72% range).

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Re: RC Servo linear actuator cannot maintain stable position

Postby mparadis » Mon Apr 23, 2018 9:55 am

Sounds like there's some weird math happening in the servo motor's internal control loop. I tried to replicate your results using those numbers on my own servo but didn't see any oscillations. Have you tried changing the position at min/max to see if it affects where the oscillation occurs? For example if you changed it to 0/1000 I would expect you will see oscillation at position 700-720. What happens if you change it to 0/101?

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