Better 6-gear transmission spur/slip assembly?

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Re: Better 6-gear transmission spur/slip assembly?

Post by Swipe555 »

Brainstormed some ideas with a couple engineering buddies and came to the conclusion that there isn't much that can be done to these trannys without having to modify the case itself. Which I'm sure you guys already knew that. Did I mention that I tend to have a bad habit of overcomplicating things? haha

So here's what I'm planning to do when my new internals arive:
1: Install 3/8 x 5/8 x 5/32 bearings for the drive gears.
2: Attempt to locate bearings to replace the two tiny Teflon differential tube bushings. (though I don't think I'll be able to find bearings with the correct dimensions)
3: Sand both sides of the differential rings and glue them to the hubs.
4: Use a spur gear that holds more balls.
5: Carefully glue the thrust washers to the diff pinion gears.
6: I'm not sure if replacing the inner drive gears bearings with brass tubing would actually make a difference, but I'll give it a try.
7: Sand down the inside of the case to make sure none of the gears are rubbing against the case. I noticed evidence that the idler and drive gears occasionally rub against the case.
8: Probably replace the thrust bearing with a better design

Is there a limit to how many balls I should use in the spur gear? Has anyone noticed if using too many balls can impede one wheel's ability to turn fast than the other while turning?

Are avid bearings as good as many forums say they are? They seem way too inexpensive to believe, but it seems like ~97% of the forums I've found praise them repeatedly.

Are there any other ideas or proven mods that I haven't found or thought of?

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Re: Better 6-gear transmission spur/slip assembly?

Post by jwscab »

you can get a rps/losi or jammin diff tube that has bearings in it for the top shaft.

realistically speaking, you want the diff tight, and unless you are doing donuts, the differential action between wheels is really not that much when you think about it. That's why the teflon bushing is not as much of a liability as you might think.

more diff balls is a good idea. the brass ring idea is to reduce friction and misalignment by getting rid of a third bearing.

avid bearings at $1.00 each have a sweet price point. they are decent bearings that can last if you take care of them. better than bushings, better bearings would only be incrementally better. maybe not even enough to notice.

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Re: Better 6-gear transmission spur/slip assembly?

Post by Bottom Feeder »

As others have said, I'm not sure there is a whole lot you can do with a six-gear to improve it significantly enough to make it worth doing. The Stealth is just that much better in every way save for ease of diff adjustment, but how often is that done after the initial build and run-in?

Gluing the diff rings is cheap and easy but the end results and benefits would be hard to measure. And there's a very real possibility of causing the rings to not sit flush on the hubs anymore so you've now compromised how well the diff works.

Gluing the thrust washers to the gears would not be of any benefit since, unlike the diff, they are not responsible for providing any of the power transfer. Adding glue underneath the washers can compromise how it works just like gluing the diff rings. Also, I'm not sure how replacing it outright with a different design would be of any improvement. Different how?

Using a spur with more balls is also not necessarily a good idea. The standard eight balls is a good middle ground between clamping force and diff smoothness. Adding more balls spreads out the clamping load more, so the diff needs to be run tighter to keep it from slipping, which makes diff action stiffer. Using a 10- or 12-ball spur in an old RC10 converted to a monster truck (those were the days!) may have been a good idea since the diff would need to be run a little tighter to compensate for such a change in overall gear ratio with the big rear tires. The opposite would be true for something like an older 12th scale pan car that may have used only six balls.

Instead of creating clearance inside the case by removing material, best thing you can do is get some 3/16" shims of varying thicknesses and shim out all the play in the idlers and outdrives, making sure the shims are on the outside so the gears are pushed in as far as possible without causing bind.

Also, since there's always play in the topshaft on a built six-gear, before pressing the drive gear on the diff tube, put at least one 1/4" shim between the tube and the bearing. Take out the rest with a shim or two on the other end. This also creates a hair more clearance between the tube and the motor plate screws.

I've never done the mod that replaces the outdrive felt seals with bearings and eliminates the inner outdrive bearing using homemade brass spacers. That seems to be 'fixing' a problem that the trans doesn't really have and looks like it would only introduce more drag. I'm also not a fan of making metal idlers out of cut-down outdrives since that would seem to be noisy and eat the small topshaft drive gears in short order, even with lubrication. But others have apparently done both mods with reported good results, but who knows how their cars were used and what their expectations were.


Cliff's notes: Really, just assemble the six-gear carefully and precisely and run it as designed, or just buy a Stealth and enjoy a smoother, stronger, and less complicated modern design with the benefit of a slipper.

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Re: Better 6-gear transmission spur/slip assembly?

Post by Apt Rib »

Hi, folks,

Long time reader and first time poster - I hope to come back and thank a few members for their contributions at some point but wanted to jump into this. My friend has an Edinger with a 6-gear that we have been trying to optimize. We have a rebuild planned and I hope to post some pictures at some point. Here are some of key points around our setup:

- Full ball bearings, including the outboard mod (we do have one bushing that still needs to be changed). During our rebuild, we plan to use only the inner races for the "deeper" bearings in the outdrives.
- 48 pitch pinion and spur (I'll get the exact gearing but it approximates the recommended ratio for brushless). We use the Kimbrough 18-hole gears and fill them with bearings.
- We use the following bearing balls (grade 25, I believe) from McMaster-Carr: 9528K11
- We have no machining experience but we have also been trying to come up with a G10 version of the transmission brace that is about 1mm longer than stock to help with antisquat. I can explain our thinking for this if you are interested.

We also have cross referenced the RC10 Classic, RC10 CE and RC10 Graphite manuals which probably have the best AE-sourced detail on building the trans. Using the RC10 Classic manual for instance, we believe that the actual internal gear ratio for the 6-gear is 1.83:1, not 1.85 or 1.87 as is often stated. Past that, the Halsey and the "copper tubing" article posted on rc10talk as well as some old RCCA articles (I can probably find the specific issues if you need) might be helpful as well.

Brian

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Re: Better 6-gear transmission spur/slip assembly?

Post by Bottom Feeder »

Correct. Outdrives (and idlers, not that it matters) have 22 teeth, topshaft has 12 = ratio of 1.83333333->

Even the Thorp 48 pitch conversion keeps the same ratio. Outdrives have 33 teeth, topshaft has 18 = 1.833333333->

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Re: Better 6-gear transmission spur/slip assembly?

Post by harvey »

[quote="Apt Rib

- Full ball bearings, including the outboard mod (we do have one bushing that still needs to be changed). During our rebuild, we plan to use only the inner races for the "deeper" bearings in the outdrives.


Brian[/quote]

I worked over a 6 gear last summer that I had assembled with inner bearing races for the out drive bearings also, along with 3/8 x 5/8 outer bearings.

Previously I had assembled both bearings on the shaft without the out drive, then cut the shaft until it sat just below the second bearing race. I wanted the button head to really secure the inner races. What I found upon close scrutiny was that the flanged bearing was not tight in the out drive, and rocked against the c clip. This was on a thorpe 48p set, so this poor tolerance may not be present on the AE parts. I felt it needed further experimenting.

What I did this time around was to omit the inner races. Next, as before I cut the shaft (on the spine plate) so as to be flush with the flanged bearing, then just a bit more so the button head would secure the inner race firmly. It was necessary to cut the internal threads a bit deeper with a blind tap, and also cut the button head bolt very short (green loctite). Next I had to secure the outer race to the out drive. To do this I used an oilite bushing 3/16 x 5/16 plain drilled out (size was 1/4" by memory) to clear the button head bolt, which had to have its button reduced in diameter as well for clearance. A shim was placed between the bearing and the bushing to take up play. Finally, a 1/4" rear axle shim was used to secure the flange of the bearing against the C clip. I sanded the thickness of this shim until the C clip had to be forced into it's groove, ensuring a secure fit. It was a lot of work, but it resulted in a rock solid assembly, and the brass shims are not necessary. In theory the brass shims should ensure perfect alignment between the two bearings, but this assumes a perfectly square tube can be cut, and would ideally include a method of pressing the 3/8" bearing against the shim, like with a wave washer and c clip installed in the 3/8" bearing bore.

I hope you could follow all that, maybe it would have been faster to tear down the tranny and take a picture!

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Re: Better 6-gear transmission spur/slip assembly?

Post by harvey »

Bottom Feeder wrote:
Using a spur with more balls is also not necessarily a good idea. The standard eight balls is a good middle ground between clamping force and diff smoothness. Adding more balls spreads out the clamping load more, so the diff needs to be run tighter to keep it from slipping, which makes diff action stiffer. Using a 10- or 12-ball spur in an old RC10 converted to a monster truck (those were the days!) may have been a good idea since the diff would need to be run a little tighter to compensate for such a change in overall gear ratio with the big rear tires. The opposite would be true for something like an older 12th scale pan car that may have used only six balls.
.
I'd like to explore diff theory a bit as this view is different than that I've held. I'm always glad to learn something new!

I wonder if the ball count theory above takes into account the friction each ball generates against the rings to resist slipping. Lets use imaginary, simple numbers.

Diff A uses 5 balls and needs to be torqued to 50 oz/in to generate enough ball friction to eliminate slipping. Each ball therefore needs 10 oz/in to not slip.

Diff B uses 10 balls and is also torqued to 50 oz/in. Each ball is now only under 5 oz/in of torque, but with twice the balls I'd postulate that this diff wouldn't slip.

The above assumes a linear relationship between torque and ball friction. Is this a sound assumption? Does it sound reasonable when

Diff C uses 50 balls and is torqued to 50 oz/in. Now the balls are only torqued to 1 oz/in each. I'd bet this diff also wouldn't slip. Sounds like a lot of friction for diff action! I'll bet the balls and rings would last forever. But would some quality of the ball-on-ring surface area not generate more resistance to slipping, despite of the reduced torque? My gut tells me that it would, which sounds like a non linear relationship between torque and friction is implied (or imagined!). Meaning as the torque increases, the friction against slipping increases more. I could be wrong here, but I don't know enough physics to say either way. Would anyone better educated than a bike mechanic care to weigh in?

The diff balls are harder than the rings, so with infinitely hard balls and softer rings the friction to resist slipping would result in wear to the rings, actual displacement of ring material that results in a groove. In a real diff, this groove can be observed in a properly functioning diff over time. Friction generates wear, always, and if the diff were frictionless it would not function. Ae says their silicone diff lube generates friction, resulting in a smoother diff. Meaning each ball needs less torque to generate sufficient friction, which optimizes operation (smoothness) as a result of lower necessary torque. When we run a diff until its lube breaks down/flings off/ gets contaminated we need to tighten it just so it won't slip ( I know, we should have rebuilt sooner!).

I don't think 8 balls is a magic number, as the stealth uses 12 balls, now 14 in newer higher torque models. I'd guess the 6 gear diff is sort of sucky because all the action has to be transmitted through 2 gear meshes per wheel, compared to none in a stealth. A 6 gear diff feels great in your hand, but less so in the car.

Synopsis: I'm stubborn and I think more balls are better! I'll concede misunderstanding but tell me why!

P.S. Bottom Feeder, I've enjoyed you insight into our hobby over the years and don't intend to argue or attack your statement but rather seek deeper understanding of these killer toys we all like so much.

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Re: Better 6-gear transmission spur/slip assembly?

Post by Apt Rib »

Bottom Feeder, Harvey - thanks for weighing in. Although there are numerous threads on 6-gears, this one seems to be shaping up as a new look at best practices for building a 6-gear with today's parts.

I certainly appreciate the two vintage articles as being the best of their time and I have tried to use bits from each to arrive at what I use now. To summarize for anyone who is not familiar, the Halsey article had key details such as shaping the teeth and elongating one of the holes in the spine plate - if I'm not mistaken, the re-release parts address many of these issues. The other article focuses on simplifying the outdrive assembly and taking the third bearing out of the outdrive to reduce bind and drag.

Harvey, I will let you know if the AE outdrives have tighter tolerances (I hope they do, because I don't have the ability or the courage to cut the shafts that the bearings sit on). I plan to use the buttonhead screws to secure the outdrives, and I agree that the brass tubing is not necessary since that mod seems to rely on the tubing to secure the outdrives against the outboard bearings. Our 6-gear is built with both bearings in the outdrives at the moment and I recall it not having any play. I hope that because the inner race is the same depth as the outer race, that nothing will change by just using the inner races of the inner bearings. I hadn't thought of shimming anything - it's a great suggestion and I'd like to experiment with that - I know lots of serious racers really perfect that, so I would love to see pictures of your setup (as well as input from anyone else that seriously pursued optimizing the 6-gear in the past). My thinking up until now was that the wiggle of the original helped to overcome its faults in tolerance but I realize this might not be true, especially with the better gear profiles and tolerances of the reissue parts.

My thinking on using all 18 bearings was that it would hold the ring flatter than just having the outside ring filled with bearings, which I thought had the potential to flex or warp the diff rings. I believe that both rings of bearings sit on the steel diff rings rather than the aluminum hub, so hopefully we will see wear paths on the rings that reflect that. Obviously a wear path on the diff hub would be bad, but I believe I checked that as being unlikely before putting the diff together. In any case, I'll post my results here.

One new question I have is about grease, specifically whether the AE Factory racers used it in their 6-gears before the Stealth was released. I know that in the thread below it was mentioned that Cliff used diff lube in some of the Stealths although I believe that most people follow the standard "no lube" instructions, which I believe were also from Cliff. One possible reason for the AE hesitance on recommending grease is that petroleum-based grease will degrade plastics over time - it was probably best at the time to not muddy the waters with conflicting information. I plan on using Finish Line grease, which lubricates well and is safe for both plastic and metal. I originally considered this to preserve the plastic blue retainer for the thrust bearing, but I began to think that the same grease would work equally well between the plastic and metal gears. I thought there was a similar statement about AE factory racers greasing the 6-gear, but I may have been confusing it with the Stealth thread. Here's that thread by the way, where I see Bottom Feeder was a contributor:

http://www.rc10talk.com/viewtopic.php?f=88&t=34024&start=870

Does anyone have any AE anecdotes or other experience using grease in the 6-gear?

Brian

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Re: Better 6-gear transmission spur/slip assembly?

Post by DaveM »

Hi,

If you were running full metal gears in the 6 gear you would need to lubricate the gears.

By using Delrin/plastic idlers, this does away with the need to lubricate them.

You can see the Stealth is the same, using a plastic idler against a metal top shaft, no need for grease.

One thing I found when building a 6 gear, was the four bolt holes for securing the cases to the motor

plate.

They can be out of alignment, so I held the cases together and re-drilled the 4 holes, so the bolts can

pass through the cases and not pull it out of alignment.

I think you are right about the tolerances, I believe the out drive bearing conversion, is simply to keep

the out drives in alignment with the idlers, thus making the idlers last.

With the mods I have run my 6 gear Oval racer on the street on rubber tires, using a 6.5 turn Brushless

system, with no problems.

I am using the ASC6614 black idlers, but I would think the re-release idlers should be as good.

Here is a pic, I won't be using the circlip.

:)
Attachments
6 Gear Mods 001 (Medium).JPG

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Re: Better 6-gear transmission spur/slip assembly?

Post by jwscab »

The outdrive bearing mod is good for a couple reasons. One, the bearing is larger and stronger. Two, you spread the contact bearing points making angular misalignment much less initially and over time.

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Re: Better 6-gear transmission spur/slip assembly?

Post by n20capri »

How about a 3D printed top shaft out of stainless to accept a stealth slipper??? Not sure how long it will last but my stainless dogbones are holding up. I tried drilling some 3d printed stainless parts and it's wicked hard.

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Re: Better 6-gear transmission spur/slip assembly?

Post by yellowdatsun »

n20capri wrote:How about a 3D printed top shaft out of stainless to accept a stealth slipper??? Not sure how long it will last but my stainless dogbones are holding up. I tried drilling some 3d printed stainless parts and it's wicked hard.

Because you'd still need a place for the diff.

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Re: Better 6-gear transmission spur/slip assembly?

Post by n20capri »

yellowdatsun wrote:
n20capri wrote:How about a 3D printed top shaft out of stainless to accept a stealth slipper??? Not sure how long it will last but my stainless dogbones are holding up. I tried drilling some 3d printed stainless parts and it's wicked hard.

Because you'd still need a place for the diff.
Yeah I forgot the spur setup WAS the diff...

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Re: Better 6-gear transmission spur/slip assembly?

Post by Mark Westerfield »

You don't need brass spacers to replace the bearing on the bottom outdrive gear, just dismantle the existing ball bearing and just use the inside and outside races.

I use white lithium grease or wax (chapstick) for lubing gears.

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Re: Better 6-gear transmission spur/slip assembly?

Post by DaveM »

Hi,

The brass spacer is not replacing a bearing, it is a shim to stop the out-drive moving outwards.

Here is a pic with the spacer fitted and all the needed parts.

:)
Attachments
Out-drive mod 002 (Medium).JPG

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