EMTB gear drive design and build

Thats actually not a problem I think, because the case will stiffen everythink up a ton. :smiley: And those baseplates look quite meaty themselfes.

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If you did the stress analysis, I’d bet the meat equidistant from those 4 mounting holes has the least impact on strength. A little additional thickness elsewhere would easily reinforce the moment arm of the motors weight.

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I mostly agree with your thoughts on waterproofing - it’s probably not something to stress over. I spent a lot of time waterproofing my first two boards in practically every way you can - was mostly a waste of time, & I go thru puddles and ride in rain. Like, I’m happy it’s done, but I’m not going to be as concerned in the future.

With regards to ingress from screw holes tho - butyl tape completely takes care of this. Very small blob of butyl tape on your screw, no water is getting past. It also somewhat acts as loctite does for mechanical retention.

That said, a small bead of butyl tape around the perimeter of the gear drive may work as well as a gasket would for those who want to be sure things are water tight. Scrape off the excess that gets pushed out on first assembly & aesthetically you’d never know it’s there.

But in the end… if he has the means to easily make the gaskets, more power to him. I think from an outside perspective from somebody who isn’t part of our community it may be a minor selling point & a more refined looking product.

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Destroyed? It only looked like a banana, i’d still ride it it.
The ‘weight of the motor’ force your describing actually mainly runs through the truck clamp, example-

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great project! will like to see if your gear drive is reliable in the future, btw l have wait almost 2 years for the
boardnamics dual gear drive and l bought one yesterday lol

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Update! 3D printed mock up and design finalisation

Hey guys I ‘ve spent the last couple of weeks taking everyone’s feedback on board as best I could, and I have made tweaks to the design. I’ve also been 3D printing all the parts and physically testing the assembly, I’m glad I did! Because I identified some issues that would have gone unnoticed in CAD. What did people do before 3D printers, testing designs must have been a real pain!





Some of the most notable changes to the design are:

Increased the thickness of the motor mount plate. I designed the gear drive to be a thin as possible without sacrificing the gear width, however what I didn’t consider is that the motor shaft would be too short (22mm), resulting in you not only having to cut the shaft down to size but also the keyway. In this design revision the motor shaft is 26mm long and the pinon gear utilises the full length of keyway making it stronger and removing the need to cut down the keyway as well as the motor shaft. This does have an advantage, as the drive should be stiffer now and resolves a concern @ShutterShock had:

I’ve also come up with a new wheel mounting method, I didn’t like the way that the extended bolts just slotted into the gear drive hub mount before, and @sleepless has his concerns as well:

This new method uses custom round nuts as a replacement for the for the wheel hub hex nuts, and then the round nuts slot into the hub mount of the gear drive and everything is retained with the truck axil nut. I think this is a more elegant method and there shouldn’t be issues with the bolts wearing through the hub mount like with the previous design iteration.

@jack.luis I have come up with a method using thrust bearings in that would make it impossible for the pinion gear to come loose from the motor shaft due to helical gear axial force; his method would also negate the use of Loctite retaining compound. However, it adds too much cost to drive and thus not really affordable for most eskate builders, so I might develop this idea separately as pro version of the drive.

I made other minor changes such as making the motor mount gasket wider, adjusting tolerances etc… but I won’t bore everyone with the details.

The 3D printed mock works quite well, ABS is pretty strong, but I will wait until the I have the first metal functional protype before properly testing the drives. I did have some issues cutting the neoprene rubber gaskets using my girlfriend’s Cricut Maker, it’s basically too stretchy for the drag knife to cut through it effectively. I’m going to try laser cutting the gaskets or having some die cuts made, this is pretty much the only manufacturing detail left unsolved now.

The next step is to fully lock down the design, get the first protype manufactured and test it to see how it performs on a mountain board.

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Looking really good, nice work so far. I like your hub interface method, seems like it will work pretty well.

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Can you elaborate on this for innovation’s sake?

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That’s a really cool idea. :smiley: could be even more simplified by just using the cylinder head of the bolts that hold the wheel together I think.

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So bolts go in from the back of the wheel hubs? Hmm that’s an interesting idea. The bolt heads would have to be floating in pockets in the drive hub mount, otherwise you’d never be able to assemble. Could work. Still don’t love floating though - you’ll get wear unless material hardness is similar.

^ FYI, you’re going to get dirt and dust that works its way through the hub spokes into the gap between your truck mount and the hub mount. It might not make it into the drive past the bearing, but it’ll accumulate there. Maybe nothing to change, but something to be aware off.

What’s the point of going custom round? This actually seems worse. If/when they spin, they’re coming off with the hub when you try to change a tire. I like the embedded nut approach though. You could go square if you don’t like hex. You could also find other ways to embed steel threads into an aluminum/composite hub mount - flanged nuts (installed from the boardside) or rivet nuts, for example.

On your hanger mount, please consider adding more mounting holes. Add them with 2 or 3 different, offset patterns, so your combined minimum angle of adjustment is very small. This will allow people to fine tune the ground clearance of their motors regardless of deck tip angle.

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Sorry I don’t want to give too much away at the moment. It’s not that innovative to be honest, Lacroix Boards already have a method of retaining the pinions in the Falcon gear drive using a circlip and spacer built into the pinion design itself.

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Thanks for all the feedback mate, this is very helpful :grinning:

I can imagine that happening, but there is rotary shaft seal in that crack between the hub mount and truck clamp, so dirt/water won’t get as far as the bearing and into the gear box itself.

I went with custom round because, I was concerned that if I used hex stand offs for example there could be alignment issues with the corresponding hex shaped holes in the gear drive hub mount. Whereas the round holes and nuts combo will be easy to align and slot in when you push the wheel on; the tolerances are tight to reduce movement and wear, but the holes have slight chamfer to help you guide the round nuts in. I don’t think the round nuts will be pain when changing a tire, as one end is slotted so you just tighten them down with screwdriver; admittedly it would probably be advisable to use some Loctite as the original hub nuts are nyloc to prevent them coming undone.

Dude! That’s a good idea! I will definitely add in a set of offset holes to affectively double the adjustment resolution from 18° increments to 9° degrees.

I like this idea! If I could source bolts with extra-long heads then they could slot into the gear drive hub mount and I could use standard nyloc nuts on the other side of the wheel hub.

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Just use some M4 spacers. :smiley: Or really any spacer that fits onto your bolts. For a quick mockup you could even use a stack of washers.

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patrick-star-spongebob-squarepants

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Could be minimal if the correct tolerances are used. In that case the holes should outlive the drive. Also a bit of widening shouldn’t matter that much, but thats depends to be seen.

giphy

what’s the secret for getting hardened and ground gears for this cheap? Is it just volume? Even the stock gears of this kind I’ve seen online made by KHK tend to be about $200US for just a bull gear and pinion.

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Ordering in volume is pretty much the only way to get the price down, ordering a one off it always going to be expensive.

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Yeah, from what I’ve seen this tends to be the case. Its really unfortunate there’s no other way of getting stuff like this for more justifiable prices. It’s times like these i wish i had a friend with the equipment to do high precision gear cutting, hardening, and grinding, but alas people like that aren’t all that common lol.

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