Collider seems to increase angular drag

Question

I have a game object with a rigidbody attached with an angular drag of 3.5. I am rotating the rigidbody using AddTorque( Vector3.up Time.fixedDeltaTime 200). This gives a nice rotation with the correct feel I'm looking for.

The problem is that when I add a collider to the GameObject the rotation becomes much slower. I have removed everything else from the scene for testing so it's definitely not hitting anything.

I've also tried adding a OnCollisionStay() but it is never called. Whatever is happening only seems to effect rotation not linear movement.

Any ideas?

Answer 1

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Answer by streeetwalker · Apr 03, 2020 at 07:47 PM

@Idual, there is nothing wrong. This happens because of how mass and torque forces work.

For the same reason an ice skater spins faster when they pull their arms in, without a collider the mass of the object is concentrated at the center of the object.

When you add a collider, you define the volume of the mass. It takes more torque to spin the same mass with a larger radius at the same speed.

In effect, you have spread the skaters arms outward and, given the constant torque force you've applied, the object rotates slower.

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Idual · May 05, 2020 at 03:48 PM 0

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This is something I had never noticed before. You are exactly right. The solution was to manually set the rigidbody center of gravity.

Collider seems to increase angular drag

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