How to design a gear drive

ESK8 Mechanics
1

Hi everyone, I’m finishing my first build but I need some help with the geardrive. I’m not a mechanical engineer so this is getting quite challenging.

I’m doing a 12s4p 190kv motor build and retrofitting an old mountainboard.

My idea was to laser cut the gears and motor mounts from a sheet of 8mm aluminium. And then 3d print an enclosure too keep everything away from road debris and the lubricant inside.

My problem is how to design the gears. Is there any tool I can use? I’ve design the motor mounts in fusion 360, but I don’t know where to start with gears.

I searched online and found https://geargenerator.com/#200,200,100,6,1,0,902.1000000000228,2,1,11,2.75,4,27,-90,0,0,48,12,4,27,-60,0,0,2,292 but if I try to import into fusion the measurement aren’t correct, the gears end up bigger than stated in the website.

(I got the 11:48 from the esk8 calculator, I would like to increase 48 to a bigger number but the size of the gear would be too big?? maximum is about 120mm~130mm with current wheels)

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2

You need a CAM software to get correct gear mesh, there are few options I think but I forget names :thinking:

3

Looks like the suggested way to do it in fusion by most people is to start off with an existing model from mcmaster carr or elsewhere and then tweak it from there https://forums.autodesk.com/t5/fusion-360-design-validate/designing-spur-gears-in-fusion-360/td-p/4336688 . for Pulleys I found a OpenSCAD file that has parameters you can adjust to generate new models that is useful for trying different number of teeth… found some googling for openscad gears too https://www.thingiverse.com/akaziuna/collections/openscad-gear-scripts openscad is free you can adjust parameters in model definitions then hit F5 to regenerate the model then F6 to generate an STL and export.

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4

Aluminum isn’t the best material choice for gears

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5

Why? I believe bikes use aluminium sprockets sometimes. I can use other materials…

6

You want a hard material with low friction coeff and low deformation + high impact resistance IMHO

I think steel based gears are better?

7

Can be done, it’ll a bit more expensive but manageable.

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8

The spur gear generator works like a charm, how can it be I never found it before.

I just need to understand the concepts and I’ll be good to go. Some studying tonight. If some gear wizard comes by and is willing to review my design please say so, I’ll be very happy to show. (I reckon I’ll post anyway just in case)

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9

You might be best with a combo of steel and plastic gears. A metal pinion gear and POM spur gear is what’s used most commonly in other gear drives

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10

Do you know why? That increases the cost a bit sice I need the shop to setup the machine for two different materials.

11

It usually cuts down significantly on noise, plastic + metal gears are (iirc) one of the quietest combinations.

You also have significantly less wear on your wheel gear since it is much larger. Because of this it doesn’t require as hard of a material, and is cheaper when produced at a larger scale.

Also, I’m more than willing to look over your design. I haven’t made any gear driven esk8’s, but I am quite experienced in gearbox design.

12

Get Fusion 360 and download spur gear examples from Grabcad or Maedler catalog which you can use as a starting point. Isn’t as complicated as it seems. Just need to get the tooth profile right, but there are a ton of examples which you can simply google. As pointed out earlier, get an off-the-shelf steel (stainless steel) motor gear and use POM as material for the wheel gear.

13

This is due to have “x” many less rotations on the large gear due to the small gear rotating 3-5 times per one rotation of the larger gear

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14

So this is what I created using fusion script.

I’m a bit doubtful about the shape of the teeth in the wheel side, they seem kinda pointy.

gears%20v2

step file here: https://drive.google.com/open?id=1b9MCSgAbDDHtzydaEZEWpb9NcB7fSTJO

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15

I searched my area and couldn’t find a POM machining shop.

Anyone knows one in Portugal? Or maybe a Chinese website like they have for pcb’s.

I could also buy the POM as a block and look for a milling place locally. Any suggestions for POM sourcing?

16

Search for POM, Acetal Resin and Delrin

I buy mine here

https://www.eplastics.com/shapes/acetal-delrin/rod

Not in Portugal, but the site will give you additional product names to search.

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17

What tooth width did you go for in the end

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18

8mm, but I’m yet to order the parts so it could be changed based on feedback.

19

Do you guys reckon a 3d printed PLA gear can hold for a testing? Validating the design before milling the POM is useful.

20

Depends on what you mean by testing. For test fit its fine, but you are not going to be able to testride it. Especially not with only 8mm width. I had 15mm width and shredded through gears within a couple hundred meters.