FLAT OUT

Hi chris,
Can you explain this a little more, I have put the narrow hexes on my CX but Id like to know/understand why this is done. How come we use narrow hexes but then put larger spacers against the bulkhead why not just use narrow hexes ??

grippgoat

iTrader: (8)

Yeah, that's kind of what I'm wondering, too. I know a bit about scrub radius from reading on real cars, but I really only understand its relation to steering effort and wheel bearing load. I don't even know what the scrub radius is like on an RC car. I imagine it's pretty high.

Some geometric ramblings...

The farther out your wheel is (bigger hex), the more it will lift up when turned in, and get pushed down when turned out, due to caster. This seems like it could affect weight transfer when the wheel is turned. i.e. it would press the inside front wheel back down to the track more with a larger hex. Whether that reduces front-end weight transfer, or just makes the front roll more, I'm not really sure. For the first time ever, I had some pretty bad chassis dragging, mostly in front, on wedsneday, but only in the main after grip came up, and only after I started really pushing corner entry hard. I wonder if the narrower hexes contributed to that, or if it was more from the additional chassis rake and increased rear droop I was running.

Also, the farther out your wheel is, the more it will move forward when turned in, and backward when turned out, altering the inside / outside wheelbase when turning. That effect seems like it would increase steering with a larger hex.

Paul Lemieux had an interesting analysis of wheel hexes in his "ask" thread, and I'm guessing they probably apply pretty universally. But then when you space the arm back out, it adds more variables.

-Mike

Benzaah

iTrader: (24)

Hey Guys. Does anyone know if this will fit in the New CX diff. U3704 Schumacher F3x8G Thrust Bearing w/SiNi Balls? Regards Benzaah.

grippgoat

iTrader: (8)

Is case anyone was wondering, putting a bit of CA in a ball cup, flicking it out, and letting it dry, does NOT seem to be a good solution for tightening it up again. I'm going back to teflon tape. Heh.

The CA inside the hinge pin hole in the C-Hub, an on the ends, does seem to have taken out a bit of the slop there, though. Thanks JayBee for that tip.

-Mike

jrxs-r

iTrader: (11)

Yes mate. It does fit. That is all I use in the Schuie diffs.

skypilot

iTrader: (14)

I'm finding what one driving says about one car doesn't always feel the same on another.

I run the Mi4 I run wide hex rear, narrow front, on the xray, I run wide front, narrow rear. don't ask why, cause I don't know, last race I went back to standard hexs on the xray all the way around and its more twichy with less steering. (which is good for me)

CA

You don't have to put the spacers back against the bulkhead, however the car will then be in my opinion too narrow. You will find you have a lot of steering and the car will try and fall over the front.

The narrow hex and the same overall track width will give you the best performance in almost all conditions.

YZFAndy

Another thing to remember with narrow hexs used with more spacers is that the camber link is also increase in length and shock incline is increased.

qcrc

iTrader: (11)

That's what I wanted to hear. It all makes sense to me now. It's not just the leverage out at the wheel hex that matters it's the way that the whole suspension works together.
Thanks Andy.

grippgoat

iTrader: (8)

I did my first runs on our new carpet today. We haven't gotten a groove going yet, but the grip is still pretty good. I'd guess it counts as medium grip at the moment. It was a practice day, and I got some setup help from Jeff Jenkins.

The car is working pretty well, better than my driving. But I feel like I could use a bit more on-throttle steering.

A bit less front droop is on my list of things to try. I'm running 5.5mm to the outer arm on blocks, front and rear, which is about 2.5-3mm of travel when I lift up on the suspension.

I'm running AE silver (14.x) front, and AE green rear (12lb), with 30wt oil. Front shocks in the middle, rear shocks are 1 up from laid down.
Short carbon arms front and rear.
Front 2mm spacers at the bulkhead, which I think is .5mm more than stock, on the plasic blocks.
Rears are on the alloy blocks, with 2mm at the back and 3mm at the front for 3* rear toe.
-2* camber rear, -1.5* front.
0* front toe.
Camber links are I think 1mm under plate in front and 0mm in the rear.
Narrow front hexes.

1) What would adding more shims at the bulkhead in the front do?
2) What would going back to the wide hex in front do?
3) My rear diff is pretty loose. I can slip it if I hold one wheel and the spur, and spin the other wheel. Would tightening that up make the rear come around more on power?

I could also stand to lose just a wee hair of corner-entry steering.

Any other suggestions for things to try?

-Mike

skypilot

iTrader: (14)

one tip, the wider you go on the spacers against the bulkhead, the closer your front drive pins get to the edge of the outdrives. if you hit a board they WILL pull out. I did that twice today. its gonna be a bear to find, but I do know that if you use yokomo MR4tc steering knuckles it will move the blades back in. not sure which other makes might fit.

btw, I was going to use my Mi4lp at nats in 21.5 but i think i will buy a CX just for this race so it will be all fresh and tight. Probably sell it after the race. start saving up. and before you ask, cause for ME, IMO, the shouie is a better small motor car then the xray. or should I say my xray is a better big motor car then the shouie on carpet, I don't have to fight traction rolling.

grippgoat

iTrader: (8)

I'll keep an eye on that. I haven't had any problems so far, even snapping a c-hub today. I didn't even notice it was busted for at least a full run.

Used Mi4CX with a dialed H30 setup? My finances should be in order after my next payday on the 15th. PM me when you've got a price in mind. I priced out the spool, diff, and axle parts from Schumi UK, but it was like $170, and at that point it it just didn't seem worth it.

I've only ever had the nasty traction roll issues with the old layout, before we stopped spraying. And even then, I was starting to get it under control. I didn't have issues at NORA, and I'm hoping our new carpet breaks in like that.

How often do you replace the spring washers in the diff? And how often do you replace the diff balls? I've been having some consistency issues with it. When I clean / reassemble it, it seems too stiff when I tighten it enough so that it doesn't slip, and it feels a bit chunky. I'm not sure if it's flat springs, worn rings, worn balls, the way I'm building it (too much grease?), picking up too much grit from the old carpet, or some combination. I'm still on the original balls, rings, and springs, and I haven't been sanding the rings at all. :/ I just got the new balls and springs I ordered, but for some reason I decided not to get new rings. I guess if it doesn't feel good, I'll know it's the rings, or me.

EDIT: I just double checked track width on my setup board... I'm at 190mm at the back of the rear wheels, and about 188mm front, so I can't space things much more.

What's the recommended technique for trimming axles? I need to knock the fronts down if I'm gonna keep using the narrow hexes. Should I just hit it with a cut off wheel, or go at it with a grinding bit of some sort?

-Mike

skypilot

iTrader: (14)

on the diff, I have never replaced the washers, although i guess they would get weak over time. many racers will tell you the shuie diff is the best ever, but for some reason my diffs when new feel like there is some sort of drag, almost like the rings are rubbing on the diff gear. I find using assoc diff lube the red label cures this, however if i just leave the diff with shuie grease alone it starts to feel better over time, with a 17.5 my diffs last forever, with mod, only a few runs before they get crunchy, most of the time its the thrust bearing, I would buy new rings or at least flip them over if you haven't already, diff ring prep is the key to a awesome diff.

on the NW thread under set up tips theres a post with great info on diff building. either that or pay JB to build one for you.

for the axles, I've never trimmed mine, but if you were going to do it, i would say just use a cut off wheel but do it with everything together. after it was brought up recently, I've been looking for something to just put over the end that would sit flush, like a cut down antenna tube cap, or a piece of shrink wrap or a purple nut thats been rethreaded, something like that, but I haven't decided on just what, most of it so far just looks "hokie"

MattW

For anyone struggling with diffs, I really would recommend watching Chris's diff building video - this is the reason that they made them!! You can find them on the Schumacher YouTube channel, which is linked from Schumacher's home page.

The diffs really are very good. For modified running, it really is possible to keep running them for a number of race days. Mine in the car has currently done 4 race days, and if i wanted to, i'm confident it could do at least 2 more.

Double D Donuts

iTrader: (15)

Has anyone tried the litemodz CVDs yet? I'm looking to get rid of the nasty chatter from the front end.