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POST No. 2406963
Dynamixel XL430-W250 does not reach goal position
2018-09-12 01:27:45 radhika

When placed in position control mode and given a goal position, the motor moves towards the goal position but stops before reaching that position (+- 10 positions i.e. +- 0.88 degrees). Example: If i give the goal_position as 1000 , the motor stops at 995 (present_position); goal_position 1450, actual position 1446


I am using ROS dynamixel SDK to control the motors. What can be done to make the motors reach the position exactly?


dynamixel_state:
  -
    model_name: XL430-W250
    id: 1
    torque_enable: 1
    goal_current: 0
    goal_velocity: 415
    goal_position: 1000
    present_current: 0
    present_velocity: 0
    present_position: 995
    moving: 0

dynamixel_state:
  -
    model_name: XL430-W250
    id: 1
    torque_enable: 1
    goal_current: 0
    goal_velocity: 415
    goal_position: 1450
    present_current: 0
    present_velocity: 0
    present_position: 1446
    moving: 0

2018-09-12 01:27:45
Radhika Rajaram
2018-09-12 10:10:37 Will Son

Hello,


You can adjust the difference between Present Position and Goal Position with PID gain settings.

Increasing I gain will allow you to decrease the difference, but if there's a load on the output shaft(horn), there will be some differences even with adjusting PID gains.

These gaps could get bigger within a certain limit with bigger load.


Thank you.

2018-09-12 10:10:37
Will Son
2018-09-12 21:53:46 Roy Macdonald

Hi,
I am using these same servos with almost no load on them.
Using the following position PID settings I get almost always an accurate positioning.
P:4400
I: 100
D:800
also I pulled to zero the moving threshold.
hope this helps.
cheers

 

comment
2018-09-13 09:59:33 Will Son
Thank you for sharing your gain settings! :D
2018-09-13 09:59:33
Will Son
2018-09-12 21:53:46
Roy Macdonald
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