sliding joint for steering rack in 3dsmax.

[super gnu]

Im working on an animation of a vehicle with exposed suspension.. ive managed to rig the suspension, including axles, dampers and steering, using a load of dummies, and a combination of linking, parameter wiring and orientation constraints with a couple of lookat constraints in there too where unavoidable.

.. its all working quite nicely considering ive not really done much mechanical animation.

However now ive come to the steering rack. i need a linkage connecting the wheel hub to a sliding bar, which must remain constrained so it slides on a single axis.

i thought i might be able to do it with lookat constraints and linking with one axis enabled. however it (kinda obviously) didnt work... either not matching the motion properly, or giving the dreaded dependency loop.

here is an animatic showing my current result.

https://youtu.be/mgE_BWCNrLQ


as far as i understand it, i need to use ik or expressions for this kind of setup, but ive got zero experience with either. there was a tutorial on youtube using expressions but it was basically algebra and maths is "not my forte"

i tried following some vague suggestions using linked geometry as a chain of bones, and the HI solver, but ive no idea what im doing, and the best i got was worse than the lookat version.

anyone got a method i can follow which doesnt involve tons of maths? i need something robust which will allow the vehicle to be rolled over etc without nodelock issues.

[super gnu]

so i followed this tutorial:

http://www.scriptspot.com/3ds-max/tu...ing-rod-system

which was very straightforward since the maths was basically copy/paste...

however, it wont work in my case.

it only applies to a 2d crank movement, and in my case with both steering and suspension travel affecting pushrod position, the movement is 3d.

(in the real world of course, the suspension moving up and down would not cause the steering rack to move, it would affect the wheel instead, but in my simplified case im happy if the rack moves a little with suspension movement.)

[fixeighted]

Hmm...just off the top of my head, after looking at the vid, could you not simply add a null which is linked to the central vertex of that geometry piece at the relevant point, then wire that to the other piece?
Maybe that's just too simple but I'll have a look tomorrow anyway

[super gnu]

i didnt actually try attaching to a face/vertex... it might work! given the lookat on the pushrod references a helper attached to the steering rack, attaching the rack to a helper linked to the pushrod gives a circular reference.. the best ive achieved so far is linking a helper to the wheel hub, to which the pushrod is linked, limiting it to move only in one axis, then linking the rack to that... but a) this gives the inaccurate movement u see, and b, ive since realised i cannot move the rig, hence the vehicle, since the helper cannot move in other axes. so i need to avoid using the "inherit movement" locks.

ill figure something out!

[super gnu]

yes! this tutorial is what i was looking for:

https://www.youtube.com/watch?v=fPesFcs53Cs



dunno why, ive seen several people saying that if you drive the sliding element by the rotation of the cam, and not vice versa, in a crank/slider system like this, you cannot use IK, and must use expressions....

ive just followed this tutorial and splineIK seems to work perfectly. ill find out if it has any issues later on i guess!


seems robust though, and allows free movement and rotation of the whole setup.

heres an updated test:

https://youtu.be/ut0bFI_LHp8

[fixeighted]

Glad you found a solution...seems to work nicely.

Anecdotally, one of the first commercial projects I completed, maybe 25 years ago, was a V10 engine that was firing and the explosions were visible.
I knew nothing about cars, or engines, or the internal combustion thing...it was a complete headache in terms of animating the thing
and there was no Youtube to help out...LOL I used a lot of tricks to make it work but I brute forced it to do my bidding in the end
It must have stayed on the company's showreel for a good 10 years afterwards, so I called it a win