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ODE joints

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Has anyone here using ODE had problems with rigid bodies connected by a joint becoming forced apart and staying apart - even though the forces on them have become small again? In my helicopter simulation, when I spin at a fast speed, the tail rotor is becoming seperated from the tail assembly, and then staying that way even after the speed has dropped. The main rotors also become out of axis alignment after a hard impact. If you had this problem and managed to solve it can you please let me know how? Thanks

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This is a common problem. There is a certain amount of numerical drift that can occur with rigid joints, and it is not surprising that extreme events such as high angular velocity and collisions would cause a larger drift than just typical motion with small forces. One approach to force a reduction in the drift after the extreme event is to place a spring between the two connected objects, in addition to the rigid constraint. The spring will pull the objects back together, reducing the drift. The spring cannot be too stiff, though, since this will potentially cause other problems.

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Guest Anonymous Poster
play with CFM and ERP until you get it right

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Thanks for your quick replies.

AP: This isn't an ERP/CFM problem, but thanks for a constructive suggestion :)

grhodes: Yep this sounds like a good idea. In ODE would I implement this using a fixed-joint with low ERP and high CFM? I don't see a speciality spring constraint anywhere in the documentation.

Thanks again

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