windows build + cars

[joevenzon]

ok, so i think i see how hinge works. it's L/R coord's sign is a reverse of what the associated wheel has because the actual single conceptual hinge-point is so far behind its wheel that it's literally outside of the car on the other side.

with that in mind my plan is to make a pass at the hinges of all the cars i've done thus far, and set them as such. and then resume work on teh other cars.

Here's an awesome old post by reece that describes how the hinge should look with different suspension types (with pictures):

http://vdrift.net/Forum/viewtopic.php?p=7531#7531

It almost makes me wonder if the .car files should just define the suspension type, and then vdrift would automatically place the hinges in a location that made sense... maybe that's an idea for the future.

Anyway, I *think* the hinge point should be placed halfway between the "Side view IC" and "Front view IC" points on the "Instant Axis" line on the third diagram from reece's post.

With the refactored code, the anti-squat and anti-dive will be dependent on where the hinge is placed.

also, i happen to notice on my own usdm tc6's rear suspension that: as the springs compress it's wheel moves noticeably toward the rear of the car. with only 2 points involved in the suspension, i'm guessing this isn't modeled in the physics yet. is that correct? or is the 3rd point derived from the wheel position?

The way the hinge point works in VDrift (with the refactored code) is: as the springs compress the wheel moves around the curve defined by the perimeter of a (vertical) circle with its center at the hinge point. So you can get the behavior of the wheel moving to the rear of the car as the spring compresses by placing the hinge point forward of and above the wheel. Does this make sense?

edit, i'm noticing some strange things with some of these hinges. lots of hinges have an L/R position at 0. tc (& tc6 which i copied suspension) seem to have had their hinges originally right next to its own wheel. so virtually no suspension travel. in these cases should i try to tune each car so that the hinge is somewhere near/past the opposite side's wheel? a change like that will need to be tested a bit for each car () and might require extra changes to be made to the spring tension.

or should i just try to get the coords and signs swapped to just update each one?

The old vamos physics had hinge code that wasn't working right, so most of the cars have either: zeros, values that were by trial and error and give good results with the buggy vamos code but aren't realistic, or values that were placed realistically as if the vamos code worked like it was supposed to. So, feel free to move the hinges to places that make sense.

I also noticed wikipedia has some info about the "hinge" point, which in car lingo is (I think) the "Instant Center":

Instant center

A tire's force vector points from the contact patch of the tire through a point referred to as the "instant center". This imaginary point is the effective geometric point at which the suspension force vectors are transmitted to the chassis. Another way of looking at this is to imagine each suspension control arm mounted only at the frame. The axis that the arm rotates around creates an imaginary line running through the vehicle. Forces, as far as suspension geomentry are concerned, are transmitted either along this axis (usually front to rear) or through this axis at a right angle (usually right to left and intersects the ball joint). When you intersect the force lines of the upper and lower control arms, where they cross is the Instant Center. The Instant Centers when viewed from the front or side may not seem to have much of a relation to each other until you imagine the points in three dimensions. Sometimes the Instant Center is at ground level or at a distant point due to parallel control arms.

The instant center can also be thought of as having the effect of converting multilink suspension into a single control arm which pivots at the Instant Center. This is only true at a given suspension deflection, because an unequal length, multi-link system has an instant center that moves as the suspension is deflected.

(In VDrift we don't simulate the IC moving as the suspension is deflected, we just approximate with a single IC point.)

from http://en.wikipedia.org/wiki/Suspension_...ant_center