All right after about one day's worth of trail and error stuff I having a working solution to the wheel problem. There are limitations such as the wheel cannot reverse direction (so you can't through the car into reverse with this method) but at least it finally works for traveling along splines:

1. Create a Null Object (distance) and add user data to it called TotalDistance data type float, interface float, unit real, min 0, max some very large number (I used 50,000) step 1.

2. Create another Null Object (movement) and place the wheel inside it. Give this wheel an Align to Spline expression and an XPresso expression.

3. Set up the XPresso expression like this: Drag the movement null object in and give it both "position" and "previous position" output nodes. Connect these both to the input nodes on a Distance node.

4. Drag in the distance null object and give it the user data output node. Connect this node (should be called TotalDistance) to one input node in a Math:Add node. Connect the output node from the distance node (in step 3) to the second input node in the Math:Add node.

5. Drag in another copy of the distance null object. Give it user data input and output nodes. Connect the Math:Add node (in step 4) to the input node of the second distance null object. Connect the output node of the second distance null object to the input node of a formula node.

6. In the formula node use the following formula: (x/(2*pi*r))*360
where r is the radius of your wheel.

7. Connect the output from the formula node to a Degree node (making sure to change the degree node to "Degree to Radians" in the Node Properites)

8. Finally drag in the wheel object and create a Roation input node (making sure to use the correct axis for your wheel). Connect the output node of the Degree node (in step 7) to the Rotation input node.


Phew I hope I wrote all that correctly. Thanks to everyone who offered input. Again I'm sorry I can't post a scene but I am still working with the demo version of R8. Hopefully I can remember all this or find this post again when I get my copy of R8.

Thanks again for all the input.

XPresso and wheels	Anonymous	11-03-02 13:34
Re: XPresso and wheels	mdme_sadie	11-03-02 13:45
radians and degress	Anonymous	11-03-02 14:38
Still same problem	Anonymous	11-03-02 15:11
maybe getting closer...	Anonymous	11-03-02 17:28
Re: XPresso and wheels	Gunter	11-03-02 16:31
Success!	Anonymous	11-03-02 18:13
Re: Success!	mrblifil	11-04-02 13:41