I have a four wheel vehicle that I am trying to animate moving along the ground. I have been able to convert horizontal linear motion into rotational motion for the wheels, and it works fine as long as I move the vehicle in a straight line.
The problem comes when I put the vehicle on a path, in this case a circle. As the vehicle moves away from the starting point and approached the 90 degree point, the rotation of the wheels slows, then on the far side of the circle, it runs in reverse until it gets to the 270 degree point, then slowly reverts back to forward motion.
Is there anyone who knows the secret magical incantation to make this work?
I have taken the original model (currently a bit over 10 MB) and reduced it by removing a bunch of detail, etc to create a much smaller blend file which I present here in case anyone wants to look at it.
track-test.blend (1.58 MB)
Here is a screen capture.
The large greenish horizontal bone in the picture is the root bone and the greenish bone aligned with the gear is the crank bone which has a transform constraint to the root bone. The yellowish bone has an IK constraint to a bone extended from the crank bone to move the lever. There are two bones (one for each axle) which are constrained to the crank bone.
The file has four key frames to move the handcar along the path.
The camera has a track-to constraint to follow the handcar moving around the circular track.
I built the original model according to plans which are measured with imperial units and the file is in imperial units mode. The wheels are 10 inch radius, so 2 * pi (3.14159) * r = 62.8318 inch circumference = 1 yd 2.2 feet = 1.595928 blender units.
The gear to pinion ratio is 4:1 so the circumference of the wheels drives the gear 90 degrees which in turn drives the axle and wheels 360 degrees, so it all works out mathematically.