No position feedback for DC linear actuator L16-50-35-12-P connected to DC1000/DC1001

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Theo
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No position feedback for DC linear actuator L16-50-35-12-P connected to DC1000/DC1001

Postby Theo » Sat Jul 28, 2018 2:13 am

Dear all,
sorry in advance if I am asking something obvious, this is the first time I am trying to use phidgets components :).

When I branch the L16-50-35-12-P to DC1000 to VINT and open the Position controller from the phidget control panel, the Motor Position field keeps a constant value of 0. By setting a dummy "2.0" target position, the actuator will extend after a while, but the motor position field remains at 0 and I have no PID loop logic going on. (I manually desengage the motor to avoid running into its max lenght).

When I open the Voltage Ratio from the phidget control panel, I see that the Data/Voltage input ratio corresponds to the correct position of the actuator.

Corresponding screenshot: https://pasteboard.co/Hwwck18.png


So is there an issue of the Motor Controller object not able to get this value? Or do I have to configure something?

Via Python, I am also getting errors trying to perform MotorController.GetPosition() in the python sample code. Trying to set a target position will not work well neither as no PID loop is happening.

Library information: Phidget22 version 1.0.0
OS: Windows 7 64 bits/Windows 10 64 bits (tested on both without success)

Thanks in advance for your help.
Best regards
Theo

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mparadis
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Re: No position feedback for DC linear actuator L16-50-35-12-P connected to DC1000/DC1001

Postby mparadis » Mon Jul 30, 2018 7:42 am

The MotorPositionController object is intended for motors with encoders as their feedback mechanism, so it's looking for an encoder position. If you want to use the linear actuator's potentiometer as feedback, you'll have to read it in with VoltageRatioInput like you have been doing, and write a control loop using that.

I wrote an article a while back showing how you can write a simple PID loop for a linear actuator. The code is written for Phidget21 so you won't be able to directly copy and paste, but the logic is all there: https://www.phidgets.com/?view=articles&article=LinearActuatorPidControl


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