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POST No. 2407584
PID gains parameters for final position accuracy on xl430-w250 with no load
2019-09-09 21:03:10 Larcay

Is there some good tested PID gains for obtaining maximum accuracy on the final position for Dynamixel xl430-w250?


My application needs the final position of the actuator to be close as possible from the command position. I though using the PWM control mode since there is no significant load and no dynamic force applied but the resolution is not good.


PS: I do not have much practice with PID and control.


Thanks in advance.

2019-09-09 21:03:10
Larcay
2019-09-17 10:41:10 Will Son

Hi,


I'm sorry for the late reply due to Thanksgiving holiday.

The PWM mode doesn't reflect PID gains as user will have to control the motor directly with the given PWM value.

If you want to use PID gain with XL430-W250, you can use other operating modes.


In order to decrease the gap between Goal Position and final Present Position, you can increase P gain.

However, increasing P gain too much will cause an overshoot and fluctuation.

D gain will help to decrease the side effect of P gain.

Please refer to PID information from wikipedia below.

https://en.wikipedia.org/wiki/PID_controller 


Thank you.


2019-09-17 10:41:10
willson
2019-09-19 03:01:18 Italo

But can PWM mode reach a 12_bit_resolution/revolution like Position Control mode?

2019-09-19 03:01:18
Larcay
2019-09-19 08:54:26 Will Son

Yes, regardless of the control mode, Present Position will be kept updated.

In case of PWM mode, Present Position will use 4 byte continuous range(-2,147,483,648 ~ 2,147,483,647)

Thank you.

2019-09-19 08:54:26
willson
2019-09-20 03:16:23 Italo

And what about Goal Position versus Goal PWM resolution? The datasheet shows that Goal PWM can only vary within a range of 0 ~ 885,  instead of 0 ~ 4095 (12 bits/rev).


Am I missing something?


2019-09-20 03:16:23
Larcay
2019-09-23 11:54:33 Will Son

The range of PWM is different from Position range.

Unlike the traditional RC servo's PWM,  you cannot use DYNAMIXEL PWM mode as a joint.

Please refer to below exerpt from eManual.

PWM Control Mode is similar to the Wheel Mode of Dynamixel AX and RX series. 

2019-09-23 11:54:33
willson
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