Need info on general steering geometry

[Coelacanth]

Thanks... The shock tower will go anyway. It interfere with the body. So I'll make a new part...

AYKBOBCAT, I just resolved a pretty significant toe-out bump-steer issue with my custom Optima. The tie-rods (if possible) are supposed to be more or less parallel with the front control arms--but that's in a typical A-arm setup. I think the Bobcat/Buffalo (my buddy has the latter) uses swing-arms, but I figured the principle might more or less apply. I happen to have his Buffalo here, I'm supposed to solder on a bunch of EC3 connectors on all our cars, and figured I'd put my theory--that worked so well on Barney--to the test on his Buffalo. You'll be amazed at the difference.

Basically, you reverse the ball-ends on the steering knuckles so they're underneath instead of on top. Then, you reverse the ball-ends on the servo saver similarly, so they're on top instead of underneath. This changes the angle of the tie-rods quite significantly. You will also need to either use the top hole of the servo horn (as shown with this Buffalo) or mod it somehow so it won't interfere with the tie-rods when steering left/right.

The result--almost no bump-steer. Kinda makes you wonder who engineered these things, eh?

[AYKBOBCAT]

Ooooooooooooohhhhh.... Will definitely try that tonight... Thanks man...

[AYKBOBCAT]

Ok I tried Coelacanth's idea and I combined it with another set of parts I had... It's the ball post that usually goes in the front but those are much longer. Noe clue who made those... By putting them at the back of the shock instead of the front the turnubuckles are nearly parallel to the suspension arms. So basically perfect. I took the steering knucles off and the shaft now stays perfectly vertical. There is still a little bit of "bumb steer" but that because of the steering turnbuckles... This thing needs a bellcrank I think...

[Charlie don't surf]

Bump steer is a funny thing, its all about non matching link arcs causing pushing and pulling on moveable parts like steering components. Try extending the height of the bellcrank studs to more closely match the arm angle, see what happens.

[Coelacanth]

Looks pretty good, AYKBOBCAT. I did some more suspension tuning with my bud's Buffalo--these cars have a great deal of steering slop. A lot of it is caused by those hinky-dink balls & ball ends, and also the servo saver, which I found was too forgiving.

I swapped out the front monoshock for a Kyosho Gold front shock with 30-weight oil and re-used the Buffalo's spring & spring cup. I then installed about a 2mm plastic spacer underneath the lock-nut on the servo saver rod, which forced the spring down a bit and increased the tension so it wouldn't be so sloppy. I also replaced the 2 dinky ball-studs on the tops of the knuckles with spare 4.8mm ball-studs & ball cups. Now the front suspension is really smooth and has a lot less wobble and play when steering.

I'm considering removing those little 2mm tie-rods in favor of some titanium turnbuckles & 4.8mm ball ends but I have to make sure this won't weaken the knuckles by reaming out the holes to make them slightly bigger to accept 3mm-threaded alloy ball-studs. 2mm rods are just too weak IMHO. Heck, that's what the Marui Galaxy uses.

[AYKBOBCAT]

One thing that really help fixing the sloppiness also is to relocate the links behind the shocks instead of in the front like I did. Makes a big difference. I also use aftermarket king pins which helps.

[Coelacanth]

One other issue I found with this car is the rear wheels can't be easily upgraded to modern wheels because of their use of that weird lock-bushing and offset. Even the few spare wheels I had that would mount to that lock-bushing would go inward way too far and rub the suspension. I believe Mr. ED talked about rear axle extenders, that would definitely be an essential mod item, but I can't find any anywhere. Anyone happen to have a pair, send me a PM. I'd love to get rid of his worn out tires & wheels and put on something more up-to-date. The fronts are an easy swap, you just need to find wheels that accept bearings with 4mm I.D. holes.

[AYKBOBCAT]

Oh yes... I have been looking for wheels to switch to 2.2 tires also. I found this picture on time tunnel but I don't like this solution...

[Coelacanth]

Well, mounting modern wheels backwards is certainly one idea, but it looks like crap, I agree!

[AYKBOBCAT]

I agree

Let me know if you find a set of wheels that works. I think there is 12mm between the side of the rim and the whole. There must be some Tamiya wheels that works. If I remember, someone here was using Tamiya buggy wheels (holliday buggy) on the bobcat. But I'm not sure they are 2.2

[AYKBOBCAT]

Ok I fixed my geometry problem. The last touch I did was to rise the sevo saver. For now I did that by putting 2 tamiya bushing under the servo saver assembly. It gives nearly the same angle to the turnbucles as the angle of the suspension arms... No more bump steer...


Now I need wheels

I am thinking of those in the front

http://www.ebay.ca/itm/Racing-Borrego-Wheel-Team-Durango-Dex210-Front-Black-BBDFB-/320808608669?pt=Radio_Control_Parts_Accessories&hash=item4ab1aee39d

According to the Durnago Manual they use 5x10mm bearings. I guess I can find 4x10 bearings.

De Racing makes these wheels for several buggies. Hopefully I can find one that has rear wheels that match.

I tried a set of tamiya wheels (TL-01 buggy) in the rear. I had to double the pressure bushing on the axle but it worked. I used a plastic hex in the wheel to fill the hole and I tighted the wheel on. Just looks ugly. I think better wheels with more offset would be better.

[Mr. ED]

Bloodclod used a set of OFNA/Hongnor CRT.5 rear wheels on his frog. Those use 12mm hexes, and have a large offset, so maybe you can use the old presson hexes of kyosho instead of that round press-on of ayk?
Otherwise you can use the rear axles of the super blackfoot maybe: they look like they are super wide and allow to mount standard corsspin hexes further out.


for the bearings: http://www.avidrc.com/product/8/metric-bearings/226/4x11x4-Revolution-694-RSZ-metric-bearings.html

[Coelacanth]

I agree

Let me know if you find a set of wheels that works. I think there is 12mm between the side of the rim and the whole. There must be some Tamiya wheels that works. If I remember, someone here was using Tamiya buggy wheels (holliday buggy) on the bobcat. But I'm not sure they are 2.2

Check out my updates on this topic in the Wanted section:

http://www.rc10talk.com/viewtopic.php?f=56&t=24445

Basically, if you install some clamp-on 12mm hexes and find wheels with a positive offset (the wheel tubs extending outward from the center instead of inward), you can do this upgrade very easily. I tried this on my friend's Buffalo and the rear wheels I installed--narrow crawler 2.2" beadlock wheels with Losi IFMAR tires--and it installed perfectly. For front wheels, I'm thinking the Traxxas 2.15" front wheels would be perfect, but the places I want to buy them from are all sold out at this time (and I won't buy from Tower because they'll charge me $20 or more for Priority shipping).