Problem: IK behaves differently when using different simulation time steps

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acercyc
Posts: 1
Joined: 06 Oct 2017, 04:15

Problem: IK behaves differently when using different simulation time steps

Post by acercyc »

Hi,
I am using the "7 DoF manipulator.ttm model" with the IK mechanism.
I encountered a serious problem when I changed the simulation time step from 50ms to 10ms.

With the 50ms time step, everything is fine. But with 10ms, the model arm always overreaches when moving upwards (only upwards).

You can see the problem in this video:
https://www.youtube.com/watch?v=Y0m27U4 ... e=youtu.be

From this video, you can see when I move the IK target downwards, it is fine.
The IK mechanism guilds the IK tip to the target smoothly.
However, for upward movements, it consistently overreachs the target.

I don't understand why simulation time step can cause this problem.
I know it is possible to improve upward movement by changing PID controller parameters.
But that means I need to change PID parameters every time I change the simulation time step.

What's the reason that causes this problem when using small simulation time step value?

You can download the scene file I used in this demonstration.
https://goo.gl/SLuDuF

Best,
Acer

coppelia
Site Admin
Posts: 10339
Joined: 14 Dec 2012, 00:25

Re: Problem: IK behaves differently when using different simulation time steps

Post by coppelia »

Hello Acer,

when you start the simulation, you have several warning messages that you simply ignored. For instance: It appears that there is at least one static respondable shape built on top of a dynamic tree structure. This is never recommended since it might lead to some strange and unrealistic behaviour...
Isn't this something you are experiencing?

You have attached a vacuumGripper to your robot that is causing that problem. If you remove it, the problem will disappear. Or you will have to attache your gripper correctly to the robot. Make sure to carefully read this page.

Cheers

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