Car Rigging (2)

[dr-skoda]

Hi
I am trying to do animation of fast driving car .
Does anybody know how to make rig for a car with suspension, turning wheels and
slides ?

[joojaa]

yes, i also know you dont want a rig that works like real car. oo complicated, and too little controll for the animator-

[dr-skoda]

So .
Could You give me more info ????

[jdj]

Hi

I have done one. As Joojaa says it is quite complicated to do an mechanically correct suspension - especially the front wheel spindle if you have what is called a "McPherson spring strut". But if you drop that notion and go for something that looks good instead, it can be done without a ton of math and API programming.

Basically you have to create a good hierarchy whom you aim constrain in a good way. For instance one side of the front suspension:

subframe
|-> lower link arm
||->spindle U/D
|||-> spindle L/R

Create a locator at the center of the wheel in x/z direction and at the y-position of the lower control arm. Aim constrain the lower link arm to this one. If you then move the locator up/down you get a good lower link arm movement.

Then create a new locator and position at the top of the spring strut. Aim constrain the spindle U/D to this one and you have a fairly good motion of the spindle for an up/down movement.

However this is the one where all the API and maths come: since usually the "action line" (i.e. the line through the upper spring strut bearing and the lower balljoint) is not parallell with the spring strut itself, the movement of the spring strut in the sideways direction is not good.

If you want, it is quite possible to solve the movement equation and do an new API node - "aimOffsetConstraint" or something. I was thinking along that line when I did my spring strut, but in the end it is far easier to cheat. It always is

The cheat I made is like this:
I put an SDK on the upper spring strut locator in the sideways direction (x?) and linked it to the up/down position of the control arm locator. Create a new locator and point snap to the upper spring strut locator. Take a few sample points while moving the wheel locator up/down. In each position, you can point snap the spring strut locator to the copy - since that stays in position.

If you made it this far the left / right movement of the spindle is just another locator and an aimConstraint. If you really want there are ways to make the wheels turn accurattly if your car is path animated too with the "pointOnCurveInfo" node and some tinkering with mechanics

That is the difficult part.

Springs are just some utility nodes (multiplyDivide, distance) connected to one axis of the scale attribute of an helix nurbs curve.

scaleX = lenth_current / length_restPosition

Then extrude a circle along this curve.

etc. etc.

Think it over and play around with this and you will see the light.

Good luck
/ Daniel

[joojaa]

QUOTE
I have done one. As Joojaa says it is quite complicated to do an mechanically correct suspension - especially the front wheel spindle if you have what is called a "McPherson spring strut".

Yeah thing is the macPherson isnt the only supension thing they use (but ist common) so bepending on the car your depicting this may wary, but yeah se mechanical eingeneers have been doing cars seriously for allmosta a Century now so you can prettymuch do a full university doctors degree just on car supenssion design (yeah i know first cars start to spring up in 1800

[jdj]

QUOTE(jdj @ 12/07/05, 05:15 PM)
subframe
|-> lower link arm
||->spindle U/D
|||-> spindle L/R
[snapback]221789[/snapback]

Just remembered - you do not need spindle U/D and L/R, one is enough. Put the up-vector to point at the locator that controls the left/right movement and you are set to go.

QUOTE(Joojaa @ 12/07/05, 05:31 PM)
Yeah thing is the macPherson isnt the only supension thing they use (but ist common)
[snapback]221791[/snapback]

Yes of course - but it is the one I made - just to see if I could.

QUOTE(Joojaa @ 12/07/05, 05:31 PM)
(again a 100 years worth of research has a tendency to produce a lot of data)
[snapback]221791[/snapback]

Let some engineers loose on a problem for a while and you will end up with a huge pile of data - one of my professors in mechanics had his phd in... belts. (yes yes - I know it is a serious topic and that belts are somtimes better than gear transmission but anyway. Belts!)

Cheers!
/ Daniel

[d7man2000]

this setup is very complicated. I don't follow, is there a setup to download

[jdj]

Hi

Spend some time with it and you will work it out. Get some pictures on the internet to clear things out.

A McPhearson front suspension is basically a triangle, lets call it A-B-C where the lower control arm is A-B and the shock/spring is B-C.

The control arm is basically a hinge-joint (1 degree of rotational freedom - rotates around one axis) and is usually attached to the car's subframe (i.e. a piece of the car that usually supports the the steering gear and sometimes also the engine) in point A. On the control arm's other end you have a ball joint (3 degreees of rotational freedom - i.e. all axes) called the lower balljoint - B.

The lower ball joint is then attached to the spindle. That is the piece which holds the hub and the wheel. The spindle is rigidly attached to the shock/spring. The shock/spring is then attached to the car again in point C where you have a rotational bearing. This bearing needs to be there since the spring rotates together with the spindle whe the wheels turn. However for your purposes I believe that it is not of any importance.

The whole weight of the car is supported by the spring. The lower control arm's "only" role is to ensure that the wheel stays in position.

The basic setup for what I describe above is very simple: control the angle of the lower control arm ( A-B ) with an aim constraint pointing at a locator. Then control the shock/spring ( B-C ) with another aim constraint pointing at a locator which is located at the top bearing.

Then this basic setup can be further refined.

Cheers
/ Daniel