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Issue 590: btRaycastVehicle ignores brake force if accelrating
2 people starred this issue and may be notified of changes. Back to list
Status:  Moved
Owner:  ----
Closed:  Mar 2014


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Reported by Niclas.H...@gmail.com, Jan 14, 2012
What steps will reproduce the problem?
1. use btRaycastVehicle
2. apply an engineForce (e.g. wheelInfo.m_engineForce = 100f;)
3. apply a much higher brake force (e.g. wheelInfo.m_brake = 100000f;)

What is the expected output? What do you see instead?
I expect to slow down the vehicle if accelerating and braking at the same time (Or if the vehicle stands still, it shouldn't even accelerate), because the friction of the wheels is much higher than the force that turns them.
Instead the brake value is ignored if an engine force is set, thus the vehicle accelerates. This is especially a problem if one simulates a drive train that continuously updates the engine force based on the rotation speed of the wheels. As there is no friction when accelerating, the engine never slows down.

What version of the product are you using? On what operating system?
Tested with jMonkeyEngine 3 and native bullet bindings, see forum thread there [2]. Issue still valid on SVN trunk, see [1].

Please provide any additional information below.
I already checked the btRaycastVehicle class and found the check in line 609 [1]. The brake value should be included into the rolling friction of the wheel, instead of ingoring it.

[1] https://code.google.com/p/bullet/source/browse/trunk/src/BulletDynamics/Vehicle/btRaycastVehicle.cpp#609
[2] http://jmonkeyengine.org/groups/physics/forum/topic/vehiclecontrol-braking-while-accelerating/?_wpnonce=bd1b7b7110#post-159280

Feb 28, 2012
Project Member #1 erwin.coumans
Can you please provide a patch with all the changes you like to make related to btRaycastVehicle (based on the up-to-date Bullet svn trunk version) ?

Thanks a lot,
Erwin

Mar 30, 2014
Project Member #2 erwin.coumans
See https://github.com/bulletphysics/bullet3/issues/128
Status: Moved
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