Box2D Forums

Does the translation axis have units, or is it just a unitless axis along which motion occurs. "axis" in the API: void b2PrismaticJointDef::Initialize(b2Body *bodyA, b2Body *bodyB, const b2Vec2 &anchor, const b2Vec2 &axis)

I suppose the main question is - does the length of the axis have any bearing on behavior?
I ask this because I am updating automatic unit-conversion code to match what the documentation states.

In experimentation, I found that as the axis became too long, the simulation became unstable... it did have other problems because I forgot the polygon wrapping direction, but I do not think that should have had the catastrophic simulation effect I was experiencing.

The axis you set in the joint def is normalized when the joint is created so it shouldn't make any difference. Did you find a case where changing only the axis length in the joint def would cause the problem to appear?