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  • Axle
    replied
    Related to this topic, RT-HO is now selling a T-jet belt drive setup ("whisper jet") with a plastic pinion pulley.

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  • RichD
    replied
    The OS3 TFX appears to have been very carefully thought out. Some years back Wizzard was going to do an updated pancake chassis, but the Wizzjet is more or less a T-Jet clone. With all of the earlier T-Jet types the only way to lower the chassis is to use very small diameter wheels and tires and that is likely to upset the people that like cars with a scale appearance. The TFX sits a lot lower to the track, if you want to use a body that has been trimmed to sit low on a T-Jet you will need to add spacers on a TFX chassis.
    Getting back to the issue of all plastic gears, so far so good with the TFX. If you need to pull and reinstall a plastic gear it probably can be swaged just like you would with brass gears.

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  • Grandcheapskate
    replied
    I just thought I would bump this topic back to the top. As you may know, OS3 recently introduced the TFX chassis with all plastic gears. This is the chassis which was under development I referred to back in post #33. I know Jerry is very meticulous in everything he does so I am confident he has done the necessary work to insure the gears will hold up. Now that the chassis is in production and "out in the wild" we will see how it all works out. So far I have heard nothing but good things about the chassis and production value.

    Here's hoping the chassis is a clear winner.

    Joe

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  • Grandcheapskate
    replied
    Early in this thread it was discussed (and theorized) why plastic gears are workable at certain points in an HO chassis. Plastic gears in AFX chassis are limited to the idler gear, cluster gear and the crown gear. Only the crown gear is a press fit and that works because there is enough material to "grab" onto the axle.

    Same with the pinion gear on an inline chassis - there is enough shaft exposed to "grab" onto. And on JL/AW chassis, the shaft connecting the driven and pinion gear is splined as Bill shows in his photos earlier.

    On no HO pancake chassis will you find a plastic armature gear.

    It will be interesting to see how the plastic gears hold up as I hopefully get updates on the testing of those gears.

    Joe
    Last edited by Grandcheapskate; 12-30-2020, 07:53 PM.

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  • smalltime
    replied
    Originally posted by HO RacePro View Post

    Is bronze better than brass for T-Jet gears? Interesting question. Which would will wear faster? Dunno. Which is easiest to machine to close tolerances? Dunno that either.

    The CNC guy probably knows best. I'd be interested to hear how he justifies making T-Jet gears out of expensive bronze when brass is so cheap and machinable. I'm always willing to learn.

    Ed Bianchi
    It has been years since I talked to Rick, of RTHO fame, so some of this may have changed since then.

    When I asked about materials, he said the reason he used a bronze type alloy was when he machined the 9 tooth pinions, they would split when pressing them on the cluster shaft when making them from free machining brass.

    He may have changed the pocces since then, IDK.

    As far as teflon goes, Ed is probably right about the softness thingy. But maybe coatings? I know that teflon coats aluminum very well, so maybe brass also?

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  • NicoRosberg.
    replied
    Originally posted by HO RacePro View Post
    I said 1/32nd or 1/24th aftermarket crown gears.
    You clearly edited the post, that is not what you said.

    Now you have changed it, why do you think the bigger scale crown gears need metal hubs, when HO ones do not?
    Last edited by NicoRosberg.; 12-26-2020, 02:21 AM.

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  • model murdering
    replied

    Agreed, the whole world is plastic. One of my earlier points was that the engineers use tricks to extend the cross section, and or dog the gear to the shaft; so that it permits the use of plastic components while maintaining a safe margin of reliability.

    Rather than re-inventing the wheel, I spent some extra time with the currently available plastic offerings, and assembled a nicely free wheeling AW chassis from spares.

    Otto Whirled uses a gnarly 6 spline arrangement on either end of the cluster shaft, to secure the driven gear and the pinion.








    I simply moved a good pinion to the armature. Even with cleaned acetone, the press fit is "gooshy" as you would expect on a smooth shaft. The gear cross section is .060". Typically the mesh is all over the road.

    Certainly it's doable in the short term, putting your name on thousands is quite another matter. I purposely built her loose. The Mini has been completely "Krylon" after a coupla hundred laps on 24 volts. No drips, no runs, no errors. Plastic creeps, so do lubricants. Heating and cooling cycles exacerbate these traits. If it survives a stock set up for any duration, I have a Yellowjacket 3 ohm crank by Srigs to test the outer limits.

    Tossing armature pinions isnt a new phenomenon. Thats why we occasionally see them soldered in hi-po aplications

    ***********




    Last edited by model murdering; 12-25-2020, 08:07 PM.

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  • SouthShoreRacing
    replied
    I must of read your post before you edited it. In any case the majority of HO crown gears and pinion gears are some form of plastic. It is not uncommon to run these in temperatures up to 150 F with no issues. Beyond that I have run as hot as 200 F and not melted, but I prefer to stay under 150 I’ve never seen a pancake arm get that hot unless it soon goes up in smoke.

    Leave a comment:


  • HO RacePro
    replied
    I said 1/32nd or 1/24th aftermarket crown gears... I've never seen an HO crown gear with a metal hub.

    But crown gears do not experience elevated temperatures like armature pinion gears do. Nylon starts to soften significantly around 60C (140F). By 100C (212F) its mechanical properties are shot.

    Ed Bianchi

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  • SouthShoreRacing
    replied
    I’m not aware of any plastic HO crown gear that has a brass or aluminum hub. Who makes them?

    I think RT-HO justifies using the material he does because it produces a product that is pretty much the standard for Fray style cars.

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  • NicoRosberg.
    replied
    I have 100s of crown gears from 20 or so HO concerns, all of them are all-plastic.

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  • HO RacePro
    replied
    Look at just about any 1/32nd or 1/24th aftermarket plastic slotcar crown gear and you will see they have a brass or aluminum hub. Why? See my post #34, above.

    We've been all over the question of plastic T-Jet armature pinion gears. Sixty years on it can be assumed that it has been tried. Probably more than once.

    Engineers and designers are always trying to wring a penny out of production costs. The fact plastic armature pinion gears aren't standard means it didn't work. Probably a combination of small contact area and heat driving plastic creep, leading to loss of press-fit stress and failure.

    As for Teflon -- I've never seen it used for gears. Too soft. Won't hold tolerances. Will deform too easily.

    The best plastic I know of for gears is Nylatron -- an industrial grade of Nylon specifically designed for gears, bushings and other such applications, especially applications that have to run dry. It has its own lubricant alloyed into the tough, strong, wear-resistant Nylon. And yes, it is commonly used for slotcar gears as well as industrial gears.

    Bronze is very commonly used for industrial gears, but it spends its entire life immersed in a bath of gear oil. You won't find it used dry because without the lube it will wear out quickly. And bronze is expensive.

    Is bronze better than brass for T-Jet gears? Interesting question. Which would will wear faster? Dunno. Which is easiest to machine to close tolerances? Dunno that either.

    The CNC guy probably knows best. I'd be interested to hear how he justifies making T-Jet gears out of expensive bronze when brass is so cheap and machinable. I'm always willing to learn.

    Ed Bianchi
    Last edited by HO RacePro; 12-25-2020, 12:13 PM.

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  • SouthShoreRacing
    replied
    Originally posted by HO RacePro View Post
    The problem with plastic gears may be long-term retention. Plastics tend to creep -- slowly deform to relax the stresses on them. That is why plastic parts are usually designed to snap together rather be press-fit. Snaps only take momentary stress while press-fits have to maintain their stresses for the life of the assembly.

    The use of metal gears instead of plastic is one reason why T-Jets that were assembled almost 60 years ago still run.

    Ed Bianchi
    A/FX and magnatraction came with plastic gears and are still running today. Modern inline chassis from WUZZARD, Viper, and BSRT all come with press fit pinions and crown gears and the majority of racers use them with no problem. Many racers use smooth axles and the majority use smooth armature shafts. These cars have a lot more torque than a t-jet so I don’t see why gears of the same material would not work on T-Jets.

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  • smalltime
    replied
    Originally posted by Axle View Post

    So the CNC T-jet gears from RT-HO and FLR. Are the teeth on those gears fully CNC cut, or do they just use a CNC baloney slicer, to use Ed's term.

    I had always assumed they were fully CNC cut teeth, but I suppose one could use a CNC machine to slice and drill a gear extrusion and still rightfully call them CNC cut. But they would not be as cool.

    Now that I think about it, $6-$8 per gear, at T-jet cottage industry volumes, is pretty good if they are actually milling every tooth from bar stock.
    RT gears are fully CNC cut gears. The machine cuts the outside and the inside in the same settup. So the concentricity is as good as you can get it. This is the most important dimension on these types of gears.

    Also, the material is not brass, as the originals were. It;'s a type of bronze that is used in the machine tool industry because i has its own lubrication kind of built in, as it were.

    It also is very good at long term wear.

    Yes, they're expensive, but they are almost always a perfect mesh, they don't wear out, and they are slipperyer than stock gears.

    As far as plastic gears go, I would be interested in a machined teflon gear set. I think it would be the ultimate. you would probably need to use steel or brass inserts for the press fit applications, but you would not need to lubricate the geartrain. For that matter, while we're at it, why not an entire chassis, and gear plate from teflon?

    Now you're talkin'

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  • NicoRosberg.
    replied
    Originally posted by Grandcheapskate View Post
    Just an FYI. I spoke with someone who is testing a T-Jet style chassis using all plastic gears, including the armature gear. So far, testing has shown none of the press fit gears are slipping and/or causing any issues. So maybe an all plastic gear set is feasible and quite workable.
    Excellent. Keep us posted.

    Always love a convention being tested.

    Merry Christmas to all.

    Leave a comment:

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