EMTB gear drive design and build

Would 10mm motor shafts work with your gear drive design?
Also I would love to test these out when they are available.

Update! CNC aluminium parts manufacturing

I just received the first functional aluminium parts and I’m very please with how they turned out :grinning: The black anodised aluminium parts are beautiful; there are no visible machining marks, the black coating seams very opaque and durable and the Archer Boards logo details came out really clean.

Here are all the aluminium parts including the Truck Clamp, Motor Mount Plate, Gear Drive Casing and Hub Mount. I’m still waiting for the hardened steel M1 gear samples to arrive; they were shipped yesterday hopefully they turn up soon.

I’m going to use this functional protype for assessing the performance of the gear drives and stress testing them to see how durable they are.

This prototype has an experimental bearing arrangement that holds the drive gear in place, independently of the wheel hub axil nut. I was inspired to try this as I saw I guy shred his drive gear on a group ride recently because he didn’t have his wheel nut tight enough, and that resulted in some play in the gears meshing. All the gear drives I have seen rely on the wheel axil nut holding the wheel and attached hub mount and drive gear in place. This kind of bothers me because then the wheel bearings take the axial load from the helical gears, and this is not a load orientation that they are designed for. Maybe the axial force is low enough for it not to be an issue anyway, but an interesting idea to try out nevertheless.

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Not at the moment. I have only designed pinon gears for 8mm motor shafts. I did this because I didn’t wany to stock more part variants than necessary, and the smallest 17T gear diameter is a bit too small for a 10mm motor shaft as there wouldn’t be a lot of material left between the keyway and gear teeth. It would be possible to make the 20T and 23T pion gears compatible with 10mm motors shafts giving gear ratios of 4.5 and 3.9 respectively.

I’m really stoked that you are excited to try out my gear drives! After I have thoroughly tested this prototype and I feel confident with the design I will consider doing a Beta release, hopefully soon :grin:

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Update! Steel gear manufacturing

Just a minor update this time. I have received my first set of steel gears, I think they turned out great, the black oxide coating looks pretty cool. I can achieve 3 different gear ratios with these gears:

  • 17 tooth pinion : 90 tooth drive gear (5.29 ratio)
  • 20 tooth pinion : 90 tooth drive gear (4.5 ratio)
  • 23 tooth pinion : 90 tooth drive gear (3.91 ratio)

Next step is too do a full assembly test now that I have all the components. I don’t expect to come across any issues at this stage as I already verified the assembly using my 3D printed mock up. I will move onto properly testing the gear drives on my mountain board, and put them though some real abuse to test their performance, this should be fun :slight_smile:

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The spacer(s) you put outside the wheel on the axle belong between the hanger and clamp or between the wheel and clamp.

I’ve had a large spacer between hanger and clamp with no issues. The wheels are positioned at the very edge of the axle.

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I tried every combination of spacers i had available. I either had too much axle left, or not enough. I just made my own spacers in the end.

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I have 3ds hubs which I think are the same dimensions as superstars. Think it went hanger, large spacer, clamp, small spacer, wheel hub, bolt.

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I wasn’t comfortable putting the large spacer between the hanger and the clamp. Only left like 5mm of hanger inside the clamp and that seemed like nowhere near enough

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its actually enough dude although with the extra 4mm spacer inside it does leave more than 5mm. That’s how we did all our BN drive predators

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I haven’t finalised the truck clamp design for the Apex Air trucks yet, at the moment it would require a 10mm spacer between the wheel hub and truck axil bolt. I could increase the length of the spacers in between the wheel hub and gear drives, so that the 10mm spacer can be reduced down to a 5mm spacer. Is this what you guys are doing with the Predator boards?

We have been using Boardnamics drives for the last 14 boards we have sent but we have our own drive systems we are going to be releasing in the very near future (This is why Lee declined your very kind offer to help with testing your drive) The Boardnamics drives sit quite far onto the hanger as standard leaving a lot of axle sticking out of the wheel so we put a spacer in between the clamp and hanger to space it out. Its not the most elegant solution but it works and that’s what we ran with.

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Update! Gear drive assembly!

I didn’t run into any major issues; the assembly process was straight forward, and the drives seem to work pretty well. I haven’t been able to properly test the drives yet, as I am waiting for my new ESC to arrive, but I did ride down a hill to get a feel for what the gears sound like and the free role resistance :grinning:

The only things I would change at the moment are:

  • No adhesive on the gaskets; the self-adhesive cover gasket and truck clamp gasket were a pain to align compared to the motor mount gasket that has no adhesive.
  • My bearing interference fits were a bit too tight; I need to tighten up the manufacturing tolerances to resolve this issue. I had to use the fire and ice technique to fit them.
  • I might try and make the drive a bit lighter by cutting away any unnecessity material.
  • I’m going to decrease the amount of empty space around the pinon gear, so that less grease is required.

This idea worked really nicely :ok_hand: I got the tolerances just right, there is nice positive click when you push hub in or pull it out. It will also allow people easily fine tune the spacing between the hub mount and wheels by simply using different lengths of standard M4 spacers and bolts.

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Looks very clean, nice. :ok_hand:

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Thee look nice. very well finished.

What they weighing in at currently?

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Thanks man :smile:

Not sure, I forgot to weigh them before installing on my board :see_no_evil: the aluminium parts are pretty well optimized already, but the 90T gear feels heavy at the moment.

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Just for reference, here’s a great photo of the Kaly drive and how it uses what look like threaded spacers on the hub adapter plate to link wheel and gear motion

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Not seen those drives before, they look chonky, very cool! Similar principle to what I am doing with my wheel hub spacers.

This first prototype is relatively heavy at 1600g per pair (including everything), the production version will be around 1350g-1400g per pair, similar to Boardnamics’ M1 drive. I think they will be very hardwearing, can’t wait to thoroughly test them on my board. Here is a sneak peek of the production version with weight saving measures and other refinements:

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Update! Testing

I’ve put around 100 miles on the gear drives now and I’m happy with the performance :grinning: I’ve been riding exclusively offroad down mountain bike trails and on grass. I’m really enjoying the torquey 5.29:1 gear ratio, I feel like I can bast up any hill and the top speed is high enough for me :ok_hand:

Compared to by belt drive board with 6374 motors this setup is quite bit louder, I think it’s mainly because the FlipSky 6384 motors are loud AF! When free rolling the gear drive is not very noisy considering the metal-on-metal contact of the gears meshing. I think I could make them smoother and quieter by increasing the gear helix angle for the next iteration.

I’ve been actively trying to break the gear drives to find any week points that I can improve for the next iteration. I’ve been jumping and keeping the throttle on, doing loads of full send accelerations and hard breaking, and deliberately landing hard when jumping. The gear drive itself has held up well to this abuse, it’s super sturdy.

However, I have managed to break the truck clamp, as you can see it’s started to come loose from the hanger. I think this happened because the fit onto the hanger was too loose, I designed a 0.1mm clearance fit, and thus all the force goes through the 4 grub screws. I think I underestimated how much force goes through the truck clamp, those motors are heavy and that results in lots of torque on the truck clamp when the motor is bouncing around whilst riding on rough terrain and jumping.

I think I can resolve this issue by using a double row of set screws, using lager M6 set screws instead of M5, and having more of transition fit with the hanger rather than a clearance fit.

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Nice work so far.
Tightening up that tolerance to .01-.02mm max, will work wonders over the additional set screws. A slight press fit is even better.

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Thanks mate :slight_smile:
I think a slight press fit is a good idea!

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