Custom printing of large timing belt pulleys?

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Hugh-Jassman
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Custom printing of large timing belt pulleys?

Post by Hugh-Jassman » Jan 15, 2018 1:42 pm

Found this video about printing 3D parts for a motor etc. But having no access to a printer I am hoping some one here can tell me where to have it done? And are there any plans for a large 7 to 10 inch belt pulley that will bolt onto a hub, already available? The hard part would be to make sure it will fit in the right distance from the hub. And it would need to be printed in four parts then bolted together, to get around the brake rotor mount.

Note how this bike has no rear brakes at all:
https://www.youtube.com/watch?v=IymLqEPUkvw

This does not seem to have what I would need: https://www.thingiverse.com/thing:16627

I assume that I can buy small factory made pulleys for the motor.
If I could have it fit this sprocket holder, every thing would be copacetic. http://www.mmbikeparts.com/Sprocket-Ada ... l-only.htm

Actualy I don't think that adapter will fit my hub. So the pulley will have to bolt onto the back side of the rotor mount.




The newest windows 10 has a 3D builder, but it does not already have the right shape. And I have no idea how to make it. Some one should make a file of a 3D timing belt pulley. So people could change the size to fit their need. But I think this 3D builder is only for playing with the 3D effect.
Last edited by Hugh-Jassman on Jan 15, 2018 2:17 pm, edited 1 time in total.

Addy
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Re: Custom printing of large timing belt pulleys?

Post by Addy » Jan 15, 2018 2:04 pm

I'm not sure exactly which kind of belt you plan to use, but I've made a parametric model for HTD5 belts by modifying the same parametric pulley you linked to: HTD5 Pulley

For my application I didn't need to print in multiple pieces, I used a delta printer with a circular build plate that was just barely large enough to print the ~20cm diameter pulley.

If you don't have access to a 3D printer, take a look at https://www.3dhubs.com/. With this you can find people in your area who are willing to print things for a fee.

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Hugh-Jassman
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Re: Custom printing of large timing belt pulleys?

Post by Hugh-Jassman » Jan 16, 2018 1:27 pm

I'm not sure what belt to use. looks like that one should work ok.

Is the plastic that is used soft?
And how much harder is it to make an edge on so the belt will not slide off?

what size is the center hole?

Addy
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Re: Custom printing of large timing belt pulleys?

Post by Addy » Jan 16, 2018 4:08 pm

I printed that pulley with PETG plastic which is pretty stiff. I actually did print it with an edge at first, you can choose that option in the openSCAD file. However, this was not a good way to keep the belt centered. The belt will still try to slide off and the pulley's lip will get damaged. Eventually I printed the pulley without any lip at all and by adjusting the angle of the motor mount or idler pulley the belt would stay centered on its own.

I don't remember the size of the center hole, but that can be adjusted in the openSCAD file as well.

whereswally606
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Re: Custom printing of large timing belt pulleys?

Post by whereswally606 » Jan 16, 2018 8:49 pm

So I spent a while reworking a pulley from a open scad DXF builder. I tried the code from thingiverse which produced the STL file direct but then I couldnt easily edit it in fusion 360. I have successfully created the STL for a 224 tooth htd5 15m pulley. It is in 8 pieces so I can print it on my Anet a8. I largely have ripped off Tom Stanton's design but the motor I have is 270kv where as his was 149kv so my larger pulley 128t on his and 224t on mine will average out at a similar 28mph top end. Anyways it shall eventually do on my dahon cadenza folding 26" single speed. Thus allowing me to ebike to my colleagues house to car pool everyday.
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Hugh-Jassman
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Re: Custom printing of large timing belt pulleys?

Post by Hugh-Jassman » Jan 17, 2018 1:45 pm

I need a lower gear from any motor, I have calculated that I need to be moving at about 13mph on my cycle truck, to be using 1300 watts on a 9% grade with 450lbs (total combined weight)....thats why I am worried about the plastic.

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Re: Custom printing of large timing belt pulleys?

Post by Addy » Jan 17, 2018 2:23 pm

I didn't run into issues with the pulley flexing, but the motor mount sure did. Originally I had a fully 3D printed motor mount which had all sorts of problems under heavy loads, like high acceleration or regen braking. The motor mount would bend inwards towards the rear wheel during acceleration. This would sometimes cause the belt to come off and in the worst case the motor mount got pulled into the spokes and it broke a few spokes off.

Eventually my friend made a hybrid motor mount, combining an aluminum plate with some 3D printed parts. This is much more rigid and hasn't had any major problems.

My pulley design uses zipties to attach to the wheel spokes. This works for me on flat roads, I haven't tested on any significant hills. I'm not sure how well this system will work for heavy loads, it only transmits the load through the spokes on one side of the wheel.

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