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POST No. 2406661
PID Backlash in MX-106
2018-01-09 18:08:14 aaddymehndi94

We are building a 1 meter humanoid with MX-106. We have tried tuning the PID in Protocol 1 along with punch, as well as in protocol 2.0 . We are struggling with removing around 1-2 degrees of movement around the goal position even with only 5-10% torques. We have seen better control on cheap chinese servos since they are hard coded for maintaining position and not for compliance. Could you please help us with our current situation as we feel we are probably not using the features on your motors correctly.


Sirena Technologies,

India

2018-01-09 18:08:14
Aadarsh Mehndiratta
2018-01-10 13:32:50 Will Son

Hello,

In order to help you, please specify your current setting(such as operating mode, protocol version, PWM/Current Limits, PID gains) of MX-106

and how much of actual torque is applied when operating the joint.

Thank you.

comment
2018-01-10 20:09:10 Aadarsh Mehndiratta
Firmware Version 41, Model number 321, Joint Mode, Position Control, Protocol 2.0, Current Limit 2047(default), PWM Limit 885(default), actual torque applied ~ 10kgcm

Deflection observed in present position ~ +-(3) degrees

We have tried ranging the P values throughout the range in r+ manager 2.0, This only reduces the deflection to 1.5-2 degrees. Changing I and D values manually have shown no improvement. We would like to know an approximate value for PID that we should test it on for such conditions.
2018-01-10 20:09:10
Aadarsh Mehndiratta
2018-01-10 13:32:50
Will Son
2018-01-11 09:56:14 Will Son

The mechanical backlash of the normal MX-106 is 20 arcmin(about 0.33degree).

If reduction gears are worn out, the gap could get bigger.

In order to acquire better position traction near the goal position, please try bigger Position P gain(such as 1,600) and I gain(such as 800).

However, these values should be adjusted based on your system as lager values could cause unwanted vibration.

2018-01-11 09:56:14
Will Son
2018-02-01 19:42:22 Saurabh Bansal

Hello Team, We are facing similar issue with XM-430 motors.

So did you got this problem fixed???

Or what alternative solution we can have for this problem??
 

Regards,

Saurabh

2018-02-01 19:42:22
Saurabh Bansal
2018-02-01 20:30:27 Saurabh Bansal

Hello Team Robotis,


I  tried to check the values of P, I, D gains of XM-430 motor from register addresses as 84(P gain), 82(I gain), 80(D gain).

And there default respective values are for P(800), I(0), D(0).


So can you please confirm me if by default it uses only Proportion, and not Intergration and differentiation.

And also please let me know how I should tune it for proper functioning.


Saurabh

2018-02-01 20:30:27
Saurabh Bansal
2018-02-14 16:54:10 Will Son

Hello,


With the default setting, Position Control mode will only use P gain for PID control as you expected.

For tuning each gain value, there is no right answer for the gain value since each application requires different setting.

I'd recommend to adjust P and I gains for reducing margin between desired position and actual position.

BTW, how did you measure the distance/angle error?

2018-02-14 16:54:10
Will Son
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