John Stranahan

iTrader: (27)

This is what I found from a year of hard and frequent use outdoors with regard to the 1/10 pan diff. Anything you do to the rings is useless as the balls, on breakin, immediately cut a new surface (groove) to run in. If you spring for the $20 for the carbide balls, those and two to 3 sets of rings will last the whole year. The rings can be reveresed. I am running the original carbide balls. The diff is always smooth. Steel ball bearings will always have a little more roughness as they are not as hard to cut a smooth groove in the ring. Use green rubber seals to extend your bearing life.

The thrust bearing is a non issue. Radial ball bearings are designed to and will tolerate axial loads. The main damaging forces on these bearings used as a thrust bearing is dirt entry and brinnelling damage from crashes to the side. Certainly a non sealed thrust bearing would be worse in this regard as it would not have good seals. Brinneling would be the same if it was a ball bearing. A tapered roller bearing would be ideal for thrust but it would be heavy and large.

Run it just like Boomers Diagram. You need the Aluminum cone. You need 3 or so Belleville washers. As you stack these washers the spring tension is reduced much like stacking coil springs. There is no effective difference between the Associated TC diff which uses a stiff little coil spring or the Losi system which uses about 10 stacked Belleville washers. Both systems have good consistent spring tension.

Here is some Tech from Boca Bearings on radial ball bearings which is what we use in the diagram. We do not use full complement V-Type bearings.

"Load:Single row radial ball bearings with ball separated by a cage can support radial loads, axial loads and tilting movements.

All full complement V-type ball bearing can support only radial loads and some low axial loads.

Speed:Maximum permissible speeds for ball bearings are mainly related to the bearing design and size, cage type, bearing internal clearance, the method and type of lubrication, manufacturing accuracy, sealing methods and loads."

InspGadgt

True they can support an axial load as it says but that axial load is more likely the loading a wheel puts on the bearing as a car corners. The diff bearing is under a lot more load then this. Even if it does handle the load the slightest little bit of dirt in the bearing ruins it. Time and time again I see guys rebuild and rebuild their diff trying to find out why it feels crunchy and they always seem to forget the bearing in the hub which when dirty or worn attributes to probably 90% or more of the cause of a poor diff. Sealed or not I always had problems with dirt getting into this bearing and just ruining it. With the Slapmaster thrust bearing that is no longer an issue.

I agree that whatever you do to the diff rings changes once the groove is cut into the ring. I feel though that from build to breakin the diff feels more consistant with a polished ring though then it does with a roughed or raw ring. Polished the diff starts off smooth so there's no need to wait until it breaks in. Back when pan cars were the only on-road class there were some very interesting diff ring diff ball options out there that today seems like everyone has given up on and just run cheep components. My favorite was a diff ring and diff ball set you could buy that were matched in hardness. With those I could get a super smooth diff with polished rings and there was very little grooving if any from the diff balls.

Boomer

Don't get me wrong, there are some bearings which have extended races that can handle loads at a right angle to the bearing (the way we're using them) but that's not what they were designed for - and any load which requires the balls to re-cut their own new race is probably bad (to some degree) for the bearing!

We just got decent bearings (for like $3/pair or something) and changed them every week or so - didn't cost much and our diffs were pretty much always as smooth as a baby's bum!

And now. . .back to Jon's fire!!!

fla racer57

iTrader: (1)

http://www.youtube.com/watch?v=uO0Xy...elated&search=

John Stranahan

iTrader: (27)

Thanks for the video. Fast track. A lot of attrition.

Just a note, I break in the Diff on the bench by running for 30 seconds holding one wheel. It is ready to go and does not change once its on the track. No polishing or sanding needed. Carbide balls are very nice.

Boomer I am not sure what groove you are talking about, but the annular bearing channel is shaped to take axial loads. No new groove should be cut by the balls. The contact area is not decreased only the angle of contact is changed. I found the math on this but it was not very clear. Grease is nice to prevent ball to ring contact. A seal is very nice. The $1 dollar bearings with shields instead of seals don't last long at all.

The diff rings do get a groove because they are not a bearing in the typical sense where metal to metal contact is to be avoided by using the proper lube. The diff rings rely on metal to metal contact which makes the groove for the friction required to drive the axle forward. The balls drive the diff rings.

To each his own method, but on all the other RC cars that I have owned the 30 second breakin recommended in a manufacturers manual works fine as it does in the 1/10 pan car. They pretty much all include the carbide balls now. There are different types of thust bearings present, but all seem to fail at about the same rate. I agree that failure of this bearing is a common source of gritty diff action.

Here is a link to the Slapmaster Bearing. Losi used a similar design for a while, but it was well shielded from dirt entry. Failed about as fast as the Associated flat washer thrust bearing. What seals this puppy.
John

JevUK

If I was designing a pan car, I would have the thrust race down inside the hub near the spur gear, and have the outer bearing go in after it, that way the thrust race would be 100% sealed from dirt and water.

elvo

Except that the belleville washer system needs to have the washers replaced every now and then. losi has since the XXX changed over to a sturdy coil spring - much more durable!

The old belleville washers used to flatten out and lose their spring action, making the diff very hard to adjust. Then again, they are 3x6mm, much smaller than the ones used in pan cars.

For off-road usage, I still think the AE diff spring is just a tad too small/weak. All the adjustments are done in the last 1/8 of a turn and the region where it's half bottomed-out....

JevUK

Here is my design

The bushings would probably have to be bronze though.

strodedawg

iTrader: (85)

hello,
i am looking to purchase a roadcource 1/10th pan car. it will be used both for asphalt running and carpet running, mostly carpet though. what options as far as chassis are there? I also like the 1/12th scale look, do they sell bodies to fit the larger scale?
thanks for the help
jim

John Stranahan

iTrader: (27)

Strodedawg-There are several narrow (200mm) pan cars available. All would be quite capable indoor on carpet. A CRC Pantoura or Darkforce I-force would be a good starting point. I have links to some of them on the first post of this thread along with links to bodies that will fit.
Wide pan cars are also available but not too numerous. Doug Powell makes a kit to widen you narrow car. The corrally C10x is available overseas. See the first post for links.

JevUK-Your design safeguards the thrust bearing nicely, but the axle is going to be more prone to snap in two right where it narrows in a crash. Even the full diameter axle is prone to breaking on occasion where the pin that secures the inner diff flange weakens it. I don't like the bushing much.

I see where losi did change to the little stiff coil spring with the type R JRXS.
John

strodedawg

iTrader: (85)

thanks,
should be ordering in a week or two

Boomer

John - I just figured out where the communication disconnect is!

You're talking about the diff balls, the ones in the spur gear, sandwiched between the rings which actually make the Diff into a true thrust bearing.

I've been talking about the bearing which the cone and belvilles essentially tear apart - the flanged bearing outboard of the diff where we make the adjustments. It's a normal ball bearing which has the outer race held by the flange and the inner race pushed in by the cone washer. This is our adjuster - but because we're taking a normal ball bearing and thrusting the inner and outer races in different directions, we're ripping it apart!

Boomer

Jev - a: I wouldn't want bushings. There will be spin against those bushings (as the car goes around a corner, for instance) and bushings do two bad things. First they provide MORE resistance than a bearing does, and second as they wear out, they get sloppy.

b: Your design would be a pain to assemble, maintain, or adjust. Imaging trying to set the bearing and then spring assy that deep. . . ack!

c: The achilles heel in it is that with the conventional design, there is a bearing at the inboard side of the hub as well as the thrust bearing (conventional) at the outboard which provides stability to the hub. If you eliminate the outer bearing, the hub will want to wobble, which would be bad!

The conventional setup actually does have the bearing set inside the hub - about 3/8" - so if you did want to protect it, just slap some black tape over it, shrink it a bit, and run! I've done that (did it with the thrust bearing experiments) and it worked okay (came off once in a while. . .) but didn't really accomplish much for me.

V12

iTrader: (1)

John now you can find the pictures in the pan car thread.

TEM

It's been a long while since I run my pan cars. Could you guys please give me some suggestions on gearing.... Foam tires on carpet or asphalt (both available). I want to know the starting roll outs for mild mods 10-12 turn motors using both 4 cell and 6 cells. And rollout for HOTTER mods; 7-9 turns... Thanks!