Motor Joint Wobble

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robertSacamano
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Joined: Tue Jun 18, 2019 3:08 am

Motor Joint Wobble

Post by robertSacamano » Tue Jun 18, 2019 3:16 am

I've been working a project that involves top-down arm control through motor joints. I've been having trouble getting the arms to be stable though, there is a lot of wobbling when either the hand is too massive, or if I weld other bodies onto it (to simulate grasping). Setup diagram below

[Shoulder] - Motor Joint - [Elbow] - Motor Joint - [Hand]

When the hand is a small object (circle radius ~3) this works fine when I set a target angle and distance for each joint, but with larger rectangular shapes it quickly becomes unstable. Please let me know if anyone has encountered and solved this problem. Thanks!

iforce2d
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Joined: Sat Dec 22, 2012 7:20 pm

Re: Motor Joint Wobble

Post by iforce2d » Sun Jun 30, 2019 2:01 pm

You can usually only expect a good outcome from a sequence of connected bodies if they get progressively lighter. So for example the shoulder might be 10kg, the elbow 6kg and the hand 2kg. A joint constraint lets each body tell the other one how it can move, and the heavier one has more influence, or 'voting power' in the decision.

https://www.iforce2d.net/b2dtut/joints-overview

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