Couldn't find the old thread on this one, so here we go.
I seem to remember from the previous discussion that the main reason most were going for rack and pinion over a kart-style system was bump steer considerations.
I figure that if I can come up with a front geometry with the lower inboard a-arm points very close to the car centerline (think F1-style single keel here, but simpler and probably metal), and mount my kart steering arm such that the tie-rods are in the same plane as the lower-arms (or pretty close), I could get some very acceptable bump steer values.
I guess what's really bothering me about such a design is what happens to the bump steer/ackermann/steering linearity once you turn the wheel.
We've usually designed our steering to minimize bump steer to the outside wheel for some small steering angle. Our logic here is that a small change in toe will not have a significant effect in straight line performance, but a change in toe to the more heavily loaded outer tire in a high speed wide-radius turn would probably put the driver off. If anything, I'd think that a kart system could be designed such that you could decrease bump steer to the outside wheel. Do any other teams take a similar approach to ours for bump steer (i.e. design for some steering angle instead of straight ahead condition)? Has anyone looked into bump steer for kart steering systems?
The major point that I think would be problematic would be steering linearity though. We see about an inch and a half of rack travel in either direction, so let's say with a 3inch arm on the kart steering system and each inner tie-rod point offset an inch to either side, we're looking at the inner tie-rod points moving longitudinally about an inch over all the wheel steering angle we want. What potential effects do you think would happen as a result of this. I'm pretty sure any ackermann effects would probably be very non-linear, but could it be possible to tune to vary the ackermann in the direction you want? Like ackermann steer in wide-radius high speed turns to minimize drag, and maybe more parallel in tighter turns to put some heat in the tires and increase your yaw moment.
Mostly just thinking out loud, but I would like to know your take on this. Especially how everyone goes about determining where they want no bump steer.
Matt Gignac
McGill Racing Team