CGTalk - Motorcycle suspension rig

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Xoliul

01-11-2008, 04:58 PM

Hi guys. I hope to get some help here with my problem. Been testing and trying to make a fully working rig for a motorcycle. The rear suspension (swingarm type with springs) was pretty easy, no problems there. But I've been trying for hours to get a system for the front suspension (telescopic fork) that works just like in real life. Creating piston behaviour is easy, but the problem is the pistons can't rotate at all (except when you turn the handlebars), so for example, when I push the frame down, the front wheel has to move back to accomodate the fork leg movement. I'm using 3D Studio Max 9 by the way.
I really hope somebody can help me out here, maybe build a little test rig to show the principles of what I have to do ? Also, if the principle of a telescopic fork is a bit strange, here's some info on wikipedia: http://en.wikipedia.org/wiki/Motorcycle_fork

mcernusca

01-13-2008, 01:41 AM

I'm not sure how you created the piston rig, but to make sure we are on the same page:

I would use a spline that goes down the center of the fork and position constrain another shape or object to it. Now when you move this object it will only move up along that line. You also have access to how far up along the spline percentage wise you are so you can start moving the body.

Now you say you want when you push down on the bike, the front wheel reacts and moves in as the piston contracts.

I'm not sure how you want to animate this, but I'll assume you are running ray intersect tests on the wheels to stick the bike to the ground. So when the bike moves down towards the road, the wheels stay in place vertically but because the wheels are parented or constrained to an object that moves along a set path, they also move in towards the body of the bike.

I'm not sure this will help you any, but I hope it gets you thinking in the right direction.
I don't have a practical example file for you but I could try and put one together.

edit:

I just looked at your portfolio, really great modelling and lighting skills. Looking forward to seeing this bike now :)

PEN

01-13-2008, 10:26 PM

The front wheel needs to be linked to the fork then you need to drive the fork up and down in some manner. Not sure what you are thinking here but one way would be to cast a ray through the fork to the ground. Now with a fork having a rake on it the math will be a little more complex then just a stright hit test with the ray and setting the length of the fork. You are going to have to do a little trig to know where to move it to based on the rake of the fork.

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01-13-2008, 10:26 PM

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