Bump Steer!

[SteepJeep]

Hello everyone,

I just recently built a custom crawler with the steering servo attached directly to the chassis. I'm having problems with excessive amounts of bump steer. Can anyone tell me how to remedy this without having to attach the servo to the axle?
Thanks,
-Aaron-

[Digger]

It would help if we knew what type of suspension setup you're running and how the servo is connected to the axle...

[obijuan]

observe, think, adjust.

[SteepJeep]

Here are some pics.

[davway]

i think the main problem is that the servo is attached to the chassis instead of the axle.
maybe just try it on the axle and see if that solves the problem. if it doesnt, look somewhere else.

[obijuan]

one problem. servo saver. second problem theres a long screw being used on the pass knuckle for the two link ends. either shorten that screw or get aluminum knuckles. that will clear up alot.

[K_B]

Take a look at this one. He apparently has zero bumpsteer with his setup. As far as I can tell, his draglink is longer and it uses a Z-bend.

Military Geländewagen Build

Also, rather than the z-bend thing, you might wanna try a spacer between the draglink and tierod to get the draglink more parallel to the tierod, that might do the trick. The downside is that you lose some steering leverage and put extra stress on the knuckle arm.

[slugzracing]

Originally Posted by K_B

Take a look at this one. He apparently has zero bumpsteer with his setup. As far as I can tell, his draglink is longer and it uses a Z-bend.

Military Geländewagen Build

Also, rather than the z-bend thing, you might wanna try a spacer between the draglink and tierod to get the draglink more parallel to the tierod, that might do the trick. The downside is that you lose some steering leverage and put extra stress on the knuckle arm.

All a z link does is improve the range of motion for the ball ends at either end of the link. The distance between the servo horn and the knuckle is the same regardless of the shape of the link that connects the two. You did hit on something very good and that is to lower the drag link to make it more parallel to the axle as most builds this is the problem. For steepjeep the angle of his drag link looks fine but the steering servo is mounted just about dead center over the axle. The farther you can get your steering servo out to one side of the vehicle the better to reduce tire movement during articulation.

Steep, can you post a side shot of your rig? It looks like the links are kind of steep going out to the axle thus causing them to pull the axle in much faster when it drops from ride height. This looks like more of an issue than the steering to me

[K_B]

Originally Posted by slugzracing

All a z link does is improve the range of motion for the ball ends at either end of the link. The distance between the servo horn and the knuckle is the same regardless of the shape of the link that connects the two.

That certainly clears things up and means I'm on the right track at least. I kept looking at Ryan's build and when Ryan said "with the Z-bend I get no bumpsteer" I was trying to figure out how. But now it makes sense; his servo is over much further than Steep's so the draglink is longer which is what really reduces the bumpsteer along with keeping the draglink and tierod parrallel. Right?

[SteepJeep]

I have been tinkering around with this chassis and i'm not very satisfied. I definately need to decrease the break-over angle of the suspension links. I also need to make both the upper and lower suspension links the same length or damn close to it. I feel that the COG for this rig is fine, even with the motor mounted high up. Like Slugz mentioned, all of my problems, (besides the bumpsteer, which I know how to fix now ) are related to my suspension geometry. I will definately be in the garage this weekend. Here is a side shot of my rig in it's current set-up. Its all about to change. Thanks for your help fellas,
Aaron