Micro Suspension and Handling Theory

[patcollins]

Well I guess this should go in the Micro Science section.

For those who dont know me my name is Pat Collins. I have raced RC Cars for over half my life. I also have background in fullsize race car suspensions and chassis setups. A few years back I wrote several articles for XTreme RC Magazine, a few of which included suspension tuning but I am totally new to micros and want to share/learn more about these wonderful little cars and their amazingly simple yet effective suspensions. So lets talk about how the micro suspension works, remedys, adjustments etc.

My primary reason for starting this is I raced yesterday and had pretty good results 2nd and its only the 2nd time I raced my micro but I had the infamous rear end hop going around a fast tight corner. It was quite controlable but still wasn't optimal. If I got rid of this I think my lap times would be much more consistant, or atleast I could place more blame on traffic :)

I have researched this topic and found conflicting points of view. HPI says its because the rear suspension is too firm for the high grip tires (carpet with meduim foams on rear and firm foams on front). I also find people saying its because the suspension is too soft, I adhere to this theory myself.

I got HPI's tuned spring set and it comes with some really thick silicon damper grease and on their sheet it says smear some of this on the rear shock shaft and it will remedy this. But if you look at the rear shock it doesnt effect the lateral movement at all so it really doesnt do anything as I observed. I have come to the conclusion that I need to dampen the lateral movement of the rear pod but the stock micro doesnt have provisions for this. In a pan car when this happens you either tighten up the damper disk or put heavier fluid on the damper tubes.

Has anyone out there played around with a way to independantly adjust lateral stiffness and damping without going to some complex aftermarket chassis or suspension?

I was looking at the Penguin chassis and it looks like to me that its lateral stiffness and longitudinal stiffness are independant of each other, is this true?

Oh yea its great to be on this board, I have been reading for days. nice to meet y'all.

[Pipeous]

Hey Pat, I think you will find most people here have gone to a pan chassis with adjustable suspensions. vcs shocks or gpm dual rears. oil filled types.
I found it more common for roll overs rather than chatter running one of the many pans. There are many brands out there and all have their good points.
Keep reading, the wealth of info on this board is truly amazing and pretty tried and true methods.

Welcome to yourmicro

[hpidriver]

I think the EXO2 is the only chassis on which you can actually tune lateral and longitudual independently. But it's pretty expensive.

[patcollins]

Well for the stock class we aren't allowed to do any changes other than a ball diff.

Im going to get a wider body to run my wheels at their maximum setting, try lowering the CG as much as possible, and try loosening my ball diff as the suggestion of someone on another board.

[BLiND]

the proper diff setting is so loose that when you spin the diff side wheel, it will diff the other side, rather than spinning the belt.

dont worry if it slips, the front end will pull it if the rear slips a little.

[patcollins]

That could explain alot, my diff was almost as tight as it would go, still felt silky smooth thouth.

[BLiND]

thats probably where your side bite chatter was coming from ;)

[hpidriver]

I don't know if you all use the rear ball diff, but I personally use the gear diff in the rear with my Rapid 300. I don't have to worry about slip and with the right grease, it's very smooth. It seems to fit my driving style better.

[BLiND]

yea on my super stock class car (4 cells + rabid 300, otherwise box stock) I run the gear diffs and they work great, granted you have to build them perfectly!

very slight amount of clear associated or MIP dif lube on the gears, and a bearing in the diff side wheel with a washer over it and then the locknut, lock it all the way down and the diff will free spin for a couple seconds when you give one wheel a firm spin, and the diff wont slip because of its design.

[ALapDown]

Originally posted by BLiND
yea on my super stock class car (4 cells + rabid 300, otherwise box stock) I run the gear diffs and they work great, granted you have to build them perfectly!

very slight amount of clear associated or MIP dif lube on the gears, and a bearing in the diff side wheel with a washer over it and then the locknut, lock it all the way down and the diff will free spin for a couple seconds when you give one wheel a firm spin, and the diff wont slip because of its design.
You should see...uh...feel some of the front gear diffs that the Rialto guys are building. They can get the FRONT diff to spin with a flip of one wheel!

[BLiND]

they're probably sanding the gears....I haven't tried that yet but a lot of people do that to 10th scales ring gears at camarillo, TC3's that can free spin without the pinion gear for over 10 seconds, etc...lol!

[ALapDown]

Originally posted by BLiND
they're probably sanding the gears....I haven't tried that yet but a lot of people do that to 10th scales ring gears at camarillo, TC3's that can free spin without the pinion gear for over 10 seconds, etc...lol!
I polish/sand the sides of the crown gears, flat/back side of the crown gears and polish the silver washers. It does get smooth, but these guys get their diff to spin free with a flip of one tire while holding the belt. Not a long suration spin, but several revolutions. TC3's need a lot of work to spin free, but for yours you better sonsider 10 seconds as a STARTING point. Mine was more than that and most guys at So Cal would embarrass me with how free theirs were!

[BLiND]

that's pretty cool, I'd love to have my front diff like that, as it is right now mine feels smooth but will only spin for maybe 1.5-2 revolutions....compared to the rear diff that spins like butter.

I'm not too serious with my TC3 yet, I like driving it with the brushless so that when I go pickup my micro it feels slow and I can drive a better line with it :)

[ALapDown]

my front diff is super smooth, just not as free. My rear diff isn't as free as yours...but I use all the ...ahem...stock parts!:p

Good thought on the TC3. You should always have it when you race the Micro to learn the line, especially at So Cal. Practice with a Micro there is more like testing to see if you're in the ballpark.:(

[patcollins]

If their front diffs are that smooth do they even have any grease in them?

[MystRacing]

They most likely are using a friction reducer or dry libricant. My TC3 would free wheel for 20 seconds. After all the sanding and shimming tricks. I used a friction reducer. The stuff is super slick and doesn't leave a sticky film like normal grease. Some people use spray lubricant for saw blades (I think it's teflon based), I use the friction reducer because I'm sponsored by Crescenzi Racing and they sell it. Actually did a lot of R&D on the stuff for the GT. I have never even assembled a stock micro diff so I don't know how it would work.

I might be getting a Micro for stock class. My current car is a EXO (Original Epic/Motek). I overdrive the front a little by trueing the front foams slightly larger than the rears. Only about .01". Don't know if it makes any difference just wanted to make sure the rear wasn't pushing the front. I run the front diff tighter than the rear to pull the car through the corner and just let it drag the rear. I'm off on a tangent here.

I ran a BRP SC18 before the micro days and the only solution we could find for the wheel hop was letting the rear diff slip. I've been running the rear diff pretty loose on my micro as well to eliminate wheel hop with a 300 sized motor. I'm confident loosening the diff will solve the problem, but the lateral movement issue has me intrigued. I was wondering if a rear sway bar might eliminate the wheel hop by keeping the rear pod more level with the rest of the car. I might mess around with that at this weekends race and see what the results are.

[patcollins]

I think a lateral damper is atleast part of the solution. After next Saturday I will let you know.

[jswinkos]

pat, you coming this saturday? Charlie said we will run even though the schedule didn't say.

[ALapDown]

Originally posted by patcollins
If their front diffs are that smooth do they even have any grease in them?
Hey Pat,

My guess is they use some type of oil, not a grease. I saw some residue at the ends of the diff assembly, so I don't think (though don't know for fact) that they aren't using a dry lube.

[patcollins]

Ski, no Im in WV right now. I will be back next week though. I'll be running two classes then :)

[jswinkos]

Cool, javier will be back also then maybe we will have 5 in the mod class for once.

[patcollins]

I played around with my ball diff this weekend and wasnt happy with adjusting it loose. It was either tight or too loose. I went to the hardware store and found some #2 split lock washers and made myself a psudeo diff adjustment spring. After my duratrax evader thrust bearing I put a #2 flat washer, a #2 split lock washer, a #2 flat washer, a #2 split lock washer, and finally a #2 flat washer. Now I have some range of diff adjustment just like with a 1/10th scale ball diff. Its a good thing the shaft is so long. This mod gives me a fairly linear adjustment of the ball diff from the point the lock washers begin to collapse to the point where they are completely collapsed. I also replaced the chrome steel diff balls with some silicon nitride ceramic balls that I had laying around.

[microfuzz]

Hi Pat,

Could you perhaps show a picture of this mod? I am having a little difficulties picturing it and I'd like to do it too :)

It will also give me an indication on the parts you used, my english is not sufficient to see what you mean by split lock washer :) (not to mention the availability of some items here in Europe...)

Thanks!!
Fuzz

[patcollins]

Sure, give me a couple days though very busy at home and work.

[Supertweak]

I race a number of classes at Spooky's raceway in Plesant Grove Utah. We have a rediculously wicked Pro-Stock Class that has forced us to really refine our cars to a stupid level. I was reading the forum replys about diff adjustment and types and thought I should share some of our experience.

The stock front diff can be made to freewheel 5-10 turns with a little TLC. First the gears need to be cleaned and de-burred. Then the tensioning spring needs to be cut slightly to reduce drag on the teeny intermediate gears. Be careful not to cut it too much, just enough that the gears are held in place, but not forced into the diff housing. Then re-assemble the diff without the two plastic covers that go over the diff assemblies. We run the diff coverless, and without the o-rings, rather using a drop of CA glue on the end of the diff rod (?) to hold it in place. I found that the absolute best lubricant you can use for either your front or rear diff is graphite.. QUIT LAUGHING! It allows much more free movement of the gears without any friction to speak of. If you run this setup, you are absolutely messing it up if you dont get 3-5 freewheel turns out of it just by flipping it.

The stock rear diff can be made to sing too. Use an extra rear carrige bearing in place of the bushing in the right side wheel hub. On all of my bearings I take the shield off, and blow all of the lubricant out with electronic parts cleaner. Clean and de-burr the gears, lubricate with a small amount of fine graphite and you should have yourself a nearly perfect rear diff with a little run in time.

This setup with the rear diff virtually eliminates wheel hop, any hopping around that continues can be eliminated by giving the rear end of the car more lateral flex by cutting up the body a bit to allow more movement.

Anyway I hope this helps. It has taken us almost 2 years of racing to figure some of this stuff out.

Happy Racing

[RadiShack]

Usually when I get rear wheel hops,I make a custom or bigger wing on the rear of the body...IM NOT KIDDING!!!

[Mobil1]

Pat,

I differ with ya'll. I dont think the diff can effectivly in a tight, high speed turns where wheel hop is a factor do its job unless its REALLY loose, but by making a diff too loose, it slips and it becomes a liability under acceleration.

I think wheel hop is caused by lack of weight in these cars. It sounds a bit simplistic, but let me explain. When you get wheel hop, essentially your car is drifting around the track (the rear end atleast). The rear end has little traction and litteraly flies up in the air waiting for the force of gravity to take it back down. Aerodynamics might be the key, but realistically the coef. of drag these bodies produce is minimal compared to the necessary weight needed to keep the rear end down. Take for example in the Le Mans series. In the P900 class, Audi runs the rear engine with more emphasis on aerodynamics in the front (big air dam), while Panoz's front engine has a more stream line front end with a blunt rear end for more downforce. There is less weight in the rear of the Panoz, so they compensate by adding aerodynamic downforce.

One theory I've been working on is raising the center of mass to raise the body roll and increase traction. Since HPI's car is not indipendently suspended, doing this effects the front more then it should, but bare with me. If you try putting your ESC or possibly reciever on top of the rear deck, you will have a higher center of mass toward the back and the body will roll more. In roll you are applying more force to the outside tyre (in a turn) rather than trying to artificially apply equal force to both tyres by not having irs. Now this is a temporary fix, I think. The ideal solution would be irs, which allows for transitional transfer of weight better then a solid axle.

I apologize for my confusing description... i could do much better if I had a car in front of me and I could show you the dynamics.