OK. . .I can get more specific. . .I'm just gonna use what we have on our SAE Baja buggy right now
-10HP B&S engine (spec engine required by rules. . .it's a design series not a power series. . .everyone has to run the same stock engine)
-our buggy has a 76" WB and a 62.5" track width (outside of tire to outside of tire) both front and rear
-we are running dual unequal length A-arm front and semi-trailing arm rear
-it's a manual R&P steering (the buggies are in the 350-500 lb. range so the steering effort isn't bad. . .it feels the same as a car driving around town) from desertkarts.com (the centerload one if you are looking)
-our joints our 1/2" rod ends
. . .the wheels seem to be able to turn pretty far. . .we can turn them so far that there is only about 1/2-1" of clearance between the tire tread and the A-arms, I know we need some more weight on the front end because it pushes when you really crank on the wheel, and I know that we need a differential because it's a PITA to push that thing around the pits or anywhere else (not under it's own power). . .we have considered turning brakes and 4 wheel steering but I would like to address design concepts and not just put a band-aid on something that has to do with our design.
It sounds like you have enough steering angle but are lacking traction. Easiest fix would be to locate more of the accessory weight of the car toward the front. A turning brake wont work for you unless you have a diff in the rear or you plumb it to the front brakes. The other thing you could do is make new wishbones that would shift the weight of the intire car forward. This however could negativly effect your steering and axle geometry.
Yeah. . .shifting the weight around would help a LOT!!!
The car is so light that there isn't really any weight to shift around without adding ballast and we were already one of the heaviest cars!!!
That's why for this particular buggy I'm thinking about scrapping this chassis and building a new one with the driver farther forward since it's rear engine. We're also gonna swap engine and transmission position so that it's closer to a mid-engine than rear and the weight will be better balanced. . .but it won't necessarily put more weight over the front tires. . . might have to cut some of the larger diameter tubing off in the rear and replace it with some smaller stuff so that we can ballast the front. . .
Jo. excuse the quick hijack, Dump I have been thinking about fitting cutting brakes to the front axle (I have a spool in the rear) I have thought long & hard & can see no major reasons not to give it a try. Your feedback would be appreciated.
I don't see why it wouldn't work. . .I don't think that cutting brakes would work as well on the front as the would on the rear but they would still work. . .stomp on the inside wheels cutting brake and it should stop moving forcing the other front wheel to pivot around that point as the rear end pushes the vehicle. . .
. . .I don't think front cutting brakes would give as tight a radius as a rear cutting brake and it would take a little getting used to if you were already accustomed to a rear cutting brake. . .I think that you would apply it sooner with a front cutting brake than you would with a rear cutting brake. . .
For the SAE mini-buggy that we built it would be easier for us to throw front cutting brakes on because we are running a midboard single rear brake caliper instead of two outboard calipers at the wheel. . .
Are you gonna install a second set of calipers for the rotors. . .
. . .just curious on how you plan on setting it up. . .I've used turning brakes on tractors growing up on a farm, but I never paid any attention to how they were set-up and I was never into rock crawling so I haven't seen how they do it on their rigs either. . .should have looked closer at some of the rock buggies at Goldendale's race this past weekend!
Each front brake passes through a remote res. master cylinder (or a proprietory cutting brake assembly). When foot brake is used fluid just passes through the cutting brakes, when cutting brakes are used inlet port (from footbrake) is cut off therefore only 1 brake is engaged. This system utilises the existing calipers so does not increase unsprung weight.
If you are pushing the tires through corners just in the pits, take a look at your Ackerman. You may have inadvertantly designed anti-ackerman into your system wherein the outer tire turns farther than the inner. Good for stability at high speeds, but not so good when making tight corners with little lateral G's. Check onboard vids of F1 cars for examples of anti-ackerman. Shoot for 100% ackerman per the equation and it should help your steering without the complexities of turning brakes.
It could be a number of things. Incorrect Ackerman, Too much Caster, Incorrect Scrub Radius, Light Front end, Wrong tread pattern in tires.
Sounds like your Ackerman is incorrect, this will make your car push. Ackerman basically creates "toe-out" when turning
A "band-aid" for this is to set the car up with more toe-out.