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Fixed Joints are Detaching and Moving

asked 2021-01-21 19:29:03 -0500

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Hello, I'm working on a project with having a quadcopter model execute a flip and land on a ceiling surface.

A big problem we are running into is that any sizeable impact on the legs causes them to move and become detached from the model even though they are connected through a fixed joint.

This can be partially remedied by increasing the step iterations in the range of 750 but the problem only happens less often and we want the legs to be fully rigid to the model. At this point I'm thinking it might have something to do with the very low inertia of the legs but I've run out of ideas on what else could be going on or how to fix it

Any help would be appreciated!

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image description

C:\fakepath\ C:\fakepath\model.sdf

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answered 2021-01-23 21:33:33 -0500

BHabas gravatar image

Increasing the mass and the ERP value definitely helped a little bit but it never went away totally. I found out you can apply multiple collision and visual geometries to a single link so I just remodeled the legs that way and it's working perfectly now. C:\fakepath\model.sdf

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answered 2021-01-22 12:11:49 -0500

I think you're right, I've seen this before with low masses (not inertia specifically). Try setting the mass to be 0.001 and see if that helps. I would not increase the step iterations that high, as you say that won't really fix anything. You might however need to mess with the simulation step size (0.001 should be low enough, and I believe is the deafult). Another parameter you can mess with is ERP, default is 0.2 but 0.8 might work. See the ODE manual for more info.

In my experience inertia doesn't matter for this bug, but mass does.

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Asked: 2021-01-21 19:29:03 -0500

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Last updated: Jan 23