How to reproduce:

1. Open attached project
2. Open scene test.unity
3. Select Cube 1
4. Set the X vector of the Target Velocity of the Configurable Joint to any number.
- A number that's 1 or larger should be fine in order to see movement
- Notice how nothing happens and the cube does not move
5. Set the PositionDamper of XDrive to a number that is greater than 0
- The number should also be no smaller than 0.05 (approximately)
- Note how the cube starts moving
- Setting the number to less than ~0.05 causes the cube to only move slightly and stop
- Rapidly changing between two numbers (for instance 0.02 and 0.03) causes the cube to accelerate

- By Design: The drive is a proportional derivative drive, which applies a force as follows: force = spring * (targetPosition - position) + damping * (targetVelocity - velocity). So if Position Damper is zero, damping is zero, therefore the force is zero and the cube will not move.