Revoslot Spur Gear Failure

[HO RacePro]

A few days ago my Revoslot car suffered a complete failure of its anglewinder spur gear...

IMG_3144.jpeg

The gear appears to have completely separated from its hub.

In looking for a replacement part I discovered Revoslot offers spur gears in two materials. 132slotcar does not carry them, but I found the replacement parts at LEB Hobbies. One, in Nylon, appears to be the original replacement part and sells for US$5.99. The other, in aluminum, goes for US$9.99.

The description for the aluminum part lists it as "Ergal" -- something I had never heard of. A quick internet search taught me that Ergal is another name for the alloy 7075 aluminum. It also mentioned that, "This aluminum alloy is typically used when exceptional mechanical robustness and lightness are required."

So I ordered the Ergal part, two of them in fact. I'm hoping to get better service life out of the aluminum gear, but that is not a given. Grades of Nylon used for gears typically are self-lubricating. Aluminum is not. While I doubt the aluminum gears will fail like the Nylon gear did, they may wear quickly since there is no good way to keep them lubricated. TBD.

Just in passing, I'll mention that a well-respected fellow racer told me that the tooth form of the original equipment Revoslot spur gear is not ideal, and is a major reason Revoslot cars tend to be noisy. Apparently the peak of the tooth form is too high and tends to bottom in the pinion gear. He has found that removing the excessive height of the spur gear teeth improves the gear mesh and reduces noise. He has also used the old trick of heating the gear while running it to further improve the gear mesh.

Since I have yet to receive the aluminum gears I don't know how well they'll mesh with the pinion gear. I may try smearing valve-lapping compound on the gears to see if I can quickly wear-in the replacement gear for a good, quiet mesh. I think valve-lapping compound works better than toothpaste, as it is specifically designed to abrade metal.

Ed Bianchi

[SouthShoreRacing]

We have a group that has been racing Revo cars every other Thursday evening. Nobody has suffered a gear failure that I am aware. A couple of guys have had guide flags break. There have been some loose motor wires where they are pressed into the guide flag and loose motor pedestals on new cars, but that has been it.

[RichD]

SMR has used Revoslot cars as IROCs, they do not race them against cars with plastic chassis. The cars have accumulated a fair amount of mileage with no gear failures that I am aware of. When I raced high performance 1/24th cars I never had problems with plastic spur gears. Slot.it has sold Ergal spur gears for a long time, I never bothered to run those in, but I do use a little Lubriplate on them.

[AptosC6]

Ergal are aluminum which has been alloyed with trace amounts of copper. It makes the aluminum a bit tougher.
You should have no trouble with a brass pinion against an alloy gear but run break in using grease and keep it oiled.

[chrisguyw]

Ergal are aluminum which has been alloyed with trace amounts of copper. It makes the aluminum a bit tougher.
You should have no trouble with a brass pinion against an alloy gear but run break in using grease and keep it oiled.

While Ergal often has trace elements of copper, its main alloying elements are (by percentages)....Zinc, then Magnesium, then Copper.

Cheers
Chris Walker

[HO RacePro]

Today I received and installed the Ergal aluminum spur gear in my injured Revoslot...

The gear appears to be high quality and meshes nicely. Installing it was puzzlesome until I realized that the motor mount is held in place by screws located in slotted holes. Those screws are accessed from underneath the chassis. Once I saw those, installation became simple. I used the old plastic-film-between-the-gears trick to set the mesh and the proper location of the motor mount screws in their slots.

The car is running fine now. A few thousand laps should be enough to wear in the gears. I won't be using abrasives.

As suspected, the original plastic spur gear had broken completely free of its hub. I salvaged the set screw.

Ed Bianchi

[Scaleracing]

What a strange post. Of course I stock RevoSlot gears and also supply LEB.

They are always in stock here both the standard:

https://www.132slotcar.us/product_in...ducts_id=38337

And the ergal version


https://www.132slotcar.us/product_in...ducts_id=39519

Maybe Ed is confused as they are sold under BRM part numbers, as made by BRM and also used on the BRM Mini Cars

[HO RacePro]

I'm sorry Al, but I was not able to find the Revoslot gears on your website, and the fact they are listed under BRM is probably the reason. I did try.

The reason I bought the parts from LEB Hobbies is, after I failed to find them on your site, they came up first in a Google search for "Revoslot Gears". They are listed on the LEB website as Revoslot parts, and it only took me 4 clicks to find them:

- Slotcar Spare Parts
- Revoslot Spare Parts
- Gears & Pinions
- BRM/RevoSlot S-419A Anglewinder 33t Spur Gear Ergal 12.4mm dia

Which is as logical a progression as you could want.

I'd recommend cross-referencing the BRM parts so they also show up as Revoslot replacement parts.

Sorry this has cost you business, but if it threw me it has probably frustrated other folks too.

Ed Bianchi

Edit by Alan,

They are listed in both sections on my Site Ed. Plus if ever you have difficulty we answer the phone

PS unlike Paul Simon Sang you can call me Alan, I am not an Al, never have been and never will be.

[dangermouse]

"Sorry this has cost you business, but if it threw me it has probably frustrated other folks too."
I think it is all good Ed

Alan supplies the BRM/Revoslot spare parts to LEB Hobbies

[stez1970]

Once again, I have many REVO slot cars and am involved in a REVO race program with 18 other drivers at Modelville Hobby in Ashland. We have no REVO spur gear issues.

[HO RacePro]

At my last IHSR race day I ran my RevoSlot Toyota Supra, now equipped with the S-419 aluminum spur gear. It didn't do well at all and made a horrible racket -- by far the loudest car on the track.

So afterwards I decided to try going back to a plastic spur gear. I ordered two.

Yesterday I installed one, and was appalled to find it was way out of round. The gear mesh went from loose to tight and back to loose again in one rotation.

I suppose I should have tried the other gear, but instead I chose to use a trick I'd first heard of in the 1960's -- heating the teeth of the spur gear with a flame while running. The idea is to get the plastic teeth to deform under load and become a better fit to the pinion gear.

I removed body and the adjacent wheel for this. The aluminum chassis of the car made this trick a bit less risky. Not so likely to damage the chassis as it would be with plastic.

I first tried heating the end of the brass pinion gear with a 100-watt soldering iron. That didn't work, so I switched to the flame from a propane lighter. I listened for the change in gear noise. It took more heat than I expected to get an improvement, and not as much improvement as I hoped. But under a loupe I could see that the plastic had moved. So I reassembled the car and put it on my track, running in robot mode under reduced power. That for a couple of thousand laps.

This morning I tried running the car at racing speeds. My best laps were about 4.6 seconds. I was still not happy with how the car sounded so I tried something I'd never done before. I ran the car on my bench while dressing the spur gear teeth with an emery board, both the face of the teeth and the sides. I was careful not to over-do it. It did seem to improve the gear mesh.

Back on the track there was a remarkable improvement. My best lap times dropped from about 4.6 seconds to about 4.1! A half-second per lap! I had achieved a bit more than a 10% reduction in my lap times!

Shaving a tenth of a second off my lap times I consider a good day's work. Half a second is extreme.

The take-away... The RevoSlot spur gears are still problematic. That spur gear was clearly defective. Bad luck? I don't expect bad luck when it comes to gears. Certainly not twice in two tries. Fortunately those plastic gears can be improved. A lot. That's good. But they still have big quality issues.

Ed Bianchi

[HO RacePro]

Looking back to my original post of July 13th, I rediscovered this text:

"Just in passing, I'll mention that a well-respected fellow racer told me that the tooth form of the original equipment Revoslot spur gear is not ideal, and is a major reason Revoslot cars tend to be noisy. Apparently the peak of the tooth form is too high and tends to bottom in the pinion gear. He has found that removing the excessive height of the spur gear teeth improves the gear mesh and reduces noise. He has also used the old trick of heating the gear while running it to further improve the gear mesh."

So I have confirmed what "a well-respected fellow racer" told me two months ago. Reworking the original equipment spur gear tooth form is necessary for best performance.

It would be interesting to try a set of aftermarket replacement gears. Slot.It's comes to mind. Probably would not be allowed in IHSR competition. Sucks that.

Ed Bianchi

[SouthShoreRacing]

If the gear was way out of round, why not return it for a replacement? I have a Viper and a Supra that I've raced for the past few months with no issues. I did blueprint the chassis by making sure the stands for the axles were aligned, adjust gear mesh, and I did run the gears in for about 5 mins. with Simachrome. I then applied a little bit of molly grease to the gears and then are smooth and quiet. Still haven't heard about or seen any gear issues from the group I have been racing with. Guess we've just been lucky.

[HO RacePro]

The design of the RevoSlot spur gear has a lot to do with its issues. As someone who used to design injection-molded plastic parts for a living, I can see obvious weaknesses in its design.

RevoSlot Spur Gear.jpeg

The three oblong cutouts in the face of the gear jump out as problematic. Even an amateur could see that the thin bridges supporting many of the gear teeth could flex under load, and if overstressed could break.

But there is a less obvious issue. The molten plastic is shot into the injection mold through the three round ports you can see in the photo. That means as the mold fills the plastic flows into the bridges from two directions, and has to weld in the middle of each bridge. Even if the plastic is hot enough to weld properly each of those welds represents a location of molded-in stress, which weakens the plastic and also tends to make it warp.

The situation is not helped by two of those injection ports being obviously off-center.

Finally it should be understood that the plastic is reinforced -- most likely with tiny, almost microscopic glass fibers. The glass fibers in the molten plastic tend to align with the direction of flow when the injection mold is filled. And that makes the plastic, as it shrinks as it cools, shrink more crosswise to the direction of flow. The glass fibers also do not bridge the welds, again tending to make the welds weak.

To produce a better gear I would eliminate the oblong cutouts and make the center of the gear a solid disk with one injection port in the middle. That way the plastic would smoothly flow radially from the injection port all the way out to the gear teeth, without any welds. I would punch out the center of that disk prior to assembling the aluminum hub. Proper design of the center of the disk would make it easy to punch out without damaging the rest of the gear. I'd have a circumferential rib on one face of the hub that I could mechanically stake to clinch the plastic component.

Once upon a time a company would have paid me good money to help them with the design issues of this part. Done it for free here.

Ed Bianchi

[Speedynh]

nice analysis, Ed. i took a couple plastic materials science courses back in the late '70's for work when we were having trouble with a potted hi-Voltage CCA, so i understand a little about injection molding.