PhysX Vehicle Has Constant Force Applied

Development World Creation
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I have made a vehicle using the PhysX PxVehicleDriveTank.h file and there appears to be a constant forwards force applied to the vehicle. The effect gets worse the more wheels that I add.

In the attached video I have a vehicle with the max of 20 wheels and when I give it no reverse input it looks like it is breaking and when I give it no forwards input it doesn’t slow down.

Does anyone know where to look for this issue as I have looked through the code and can’t see what is causing it myself.

I have tried editing: wheel weights, engine damping, centre of mass, suspension forces, checked the physics asset for internal collisions and have not found the cause.

All I have worked out is it is something to do with the driveline/wheels as changing wheel weights makes the problem worse/better. But I don’t think this is the issue as even when better it still happens and It makes no physics sense, especially considering with higher wheel weights the vehicle will accelerate with no wheel torque applied.

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I have fixed my problem.

If anyone else comes across this, the issue stems from the Special input mode. In Special input you can use negative inputs on the engine to perform neutral steering. If you put negative inputs here for reversing the clutch on the vehicle will think that it is still moving forwards and will disengage the clutch to prevent stalling.

The other issue when moving forwards I have not completely fixed, but have made the symptom go away by increasing the Damping on the vehicles wheels.