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vrljc
02-03-2003, 01:18 PM
I have a tire object that moves based upon its rotation (set up with a simple expression). However I am limited by the way I have it set up, that is the tire will only move along the z-axis when it rotates along the pitch orientation. Is there an expression set-up (or any other set up) that i can use so that I can point the tire in any heading direction and rotate the tire with the pitch and the tire will move accordingly? I guess I am wanting to be able to actually steer the object in any direction and still have the tire rotate accordingly.

And BTW, the tire is a stand alone object and is NOT part of a car or bike or anything.

-vrljc
MrWyatt
02-03-2003, 01:35 PM
have you tried to set the coord system to local ?
Eugeny
02-03-2003, 01:54 PM
Damn i need this expression too ...
I found that one of Polk plugins collection can make it really great (don't remember his name - try Flay search ) ...
vrljc
02-03-2003, 01:55 PM
i have but unfortunately that doesn't work because by using expressions, u have to base the action of the object based upon the action of another, or from within itself. In my case, my pitch rotation drives my z-axis values. If i set the coordinates to local, the tire will be moving along the z-axis AND the x-axis as well. According to Lightwave, if I were to head rotate the tire 45 degrees, then move the tire to point (1,1) using the local cooridinates, the tire in fact has NOT moved the distance of 1 meter, because the tire has actually moved along the hypotenuse of a 45, 45, 90 triangle. It instead has moved the distance of

D=z-axis divided by the sin(45)

I tried this approach as well in Lightwave with a nice expression of:

Expression: (360/PI)*A/B
A: tire.pos(Time).z
B: sin(rad(tire.rot(Time).h))
C: (blank)
D: (blank)

And this did not work, it did work when the coordinates were set to local, and the heading of the tire was 45 degrees, but if the heading is anything OTHER than 45 degrees, then the rotation of the pitch of the tire does not work.

I guess I need some way to find the distance of the motion path? Any help on that anyone?

-vrljc
ajk48n
02-03-2003, 06:01 PM
I've come across the same problem. My rotation was based on the translation, though. I haven't figured out how to solve it with expressions yet, but this link

http://www.gignews.com/kappmarch02.htm

has a different approach. The tutorial is for Maya however.
vrljc
02-03-2003, 06:54 PM
how did u do it with translations at least? maybe i don;t need an expression.....
ajk48n
02-03-2003, 07:17 PM
What I did, was have a box for a car, and parented the wheels to the car. Rotation of the wheels = (2*PI*Radius of the wheel*Translation value of the car in the direction you want it to go)*(a number around 10-30, you have to experiment to get the right result). If that doesn't work, try dividing by the 10-30 number. It's weird sometimes. After all that, group everything again, and you can then rotate the group, and the tires will still rotate the direction the car moves.
vrljc
02-03-2003, 07:44 PM
and if your car makes a complete 180 u turn, will the tires still rotate forward, or will they start rotating back to 0 degrees?
ajk48n
02-03-2003, 10:12 PM
I haven't tried it rotated 180, but in theory it should work since the null is getting rotated, and doesn't transfer rotation values downstrem.
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