btRaycastVehicle.cpp: forward impulse way too strong when sideImpulse==0 #3220
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After 8 months, I'm curious why this PR hasn't been integrated. If the Bullet project is no longer accepting PRs from outsiders, or if it's no longer accepting PRs to "BulletDynamics/Vehicle", that would be nice to know. |
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@erwincoumans What's the next step for this PR? |
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Contact me by e-mail if you want the diff for this bugfix. |
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This pull request fixes a recently discovered bug in
btRaycastVehicle. When a vehicle at rest starts moving, sometimes its forward impulse is much too large, causing it to immediately reach its steady-state speed.In my application (a particular vehicle configuration on a level surface) the impulse was 140x too large about 18% of the time. The bug was highly reproducible: it happened for some starting locations on the surface but not for others. I tracked it back to line 612 of btRaycastVehicle.cpp:
m_sideImpulse[wheel]was either-0(for bad starting locations) or roughly-2e-09(for good ones).For such a tiny side impulse to reduce the forward impulse by 140x makes no sense, physically. I suspect the test in line 612 was originally a hand optimization from at time when the loop was scaling
m_sideImpulse[wheel]only. Removing the test fixed the bug.