Racing Rovers - Downforce Issues

[NQMT]

Hey all,

Small question. I have made a rover that can achieve 60m/s under its own wheelpower, but I add downforce for improved cornering. Problem is, if it's too far forward, the car is too touchy, and if it's too far back, it stays straight as an arrow and is horrific in the corners.

Is the CoL meant to be in the same spot as the CoM, sort of like for planes? Or is it based on where the wheels are positioned?

(before anyone asks, Kerbin-only rover. 60m/s on Mun would be absurd.)

Thanks in advance, everyone.

Kyrian

Edited November 30, 2013 by Kyrian

[Taki117]

60m/s under it's own wheel power is impressive, before you try anything though, be sure you are using Linear Docking controls and have SAS on. I would remap either the Rover forward button or the RCS down button (Or use an Ion engine) but your RCS should be balanced around your CoM. If you are not adverse to mods you can get RCS Build Aid that will show you the effects of using RCS while you are still building your rover (Or whatever else you have that uses RCS)

[peadar1987]

There's a reason F1 cars are so finicky to set up, too much front downforce, you get oversteer, and the thing is crazily twitchy (although if you handle it right it will brake and corner faster), too much rear downforce, and you get understeer, basically the front wheels aren't stuck to the road well enough to turn the thing. Still, 60 m/s isnae bad for a KSP rover!

[NQMT]

It's not stock. Taverio's Pizza and Aerospace wheels.

It has RCS but that's only to simulate KERS. I always use Docking Mode and there are no control surfaces.

Also, for Taki117, I'm trying to figure out where to put the Centre of Lift, not the CoM.

[Nao]

Think of lift as added mass. You want to have the sum force of mass and downforce to act somewhere in the middle between two wheel axis. But the actual placement depends heavily the actual design, i would start by placing the lift center at the middle between two wheel axis and work from there to get more or less responsive steering at speed.

What also can influence responsiveness is speed sensitive steering that is set in part.cfg of wheels themselves. IDK if pizzas mod modify it to suit greater speeds that the wheels achieve thou.

edit: after a quick dab into Pizza's mod and a moment of though later:

Looks like for basic racecar designs having center of lift roughly in the middle is good. And if you go for the RWD design like real F1 cars have, having center of mass at the back is also good for traction (acceleration).

Also if you wand to add some stability for high speed, you could add some negative Toe-in on front wheels. Adding some Camber can reduce the steering effect, and also from my limited testing adding Caster can also help somewheat (it also helps lowering CoM).

Edited November 30, 2013 by Nao

[NQMT]

That's really helpful, I'll consider all of that next time I'm on. Thanks, Nao!