pic: WIP 3 CIM 2 Speed All Belt Cim Above Tube Gearbox

[Colin Small]

Originally Posted by asid61

Not quite all belt- the first stage is gears.
In any case, this is a very interesting concept. I really like your compact execution of the idea.
The one thing that I'm worried about: why 9mm wide 3mm pitch GT3 over 15mm wide 5mm pitch? Even using 2 parallel 9mm belts (which may face issues with not lining up), this looks like it may not be strong enough.
I thought this type of gearbox would be unworkably large, but the first stage gear takes up most of the reduction so it works out.
The flipped cylinder arrangement looks a lot like 192's gearbox this year.
What are the reduction ratios?

SDP doesn't make belts smaller then 40 tech so using 5mm GT3 would mean spacing everything out too much

What do you mean by the belts not lining up?

And yeah, I took a bit of inspiration from 192

I had the reductions written down somewhere but I think it's something like 10:1 and 20:1.

[asid61]

Originally Posted by Colin Small

SDP doesn't make belts smaller then 40 tech so using 5mm GT3 would mean spacing everything out too much

What do you mean by the belts not lining up?

And yeah, I took a bit of inspiration from 192

I had the reductions written down somewhere but I think it's something like 10:1 and 20:1.

For your second stage pulleys, they are constrained in rotation by the hex bore. Let's say you accidentally broach one so that the tip of the hex lines up with a groove, and the one next to it such that the flat of the hex lines up with a groove.
At this point the two pulleys do not perfectly match up in their rotations. This wouldn't be a problem, only for their mating pulleys you have the same problem- the teeth may not match up.
This means that you could face some major indexing issues that would screw up the meshes on at least 1 pulley at a time.
The way to fix that would be to use a jig to align the pulleys before broaching/machining.

[Colin Small]

Originally Posted by asid61

For your second stage pulleys, they are constrained in rotation by the hex bore. Let's say you accidentally broach one so that the tip of the hex lines up with a groove, and the one next to it such that the flat of the hex lines up with a groove.
At this point the two pulleys do not perfectly match up in their rotations. This wouldn't be a problem, only for their mating pulleys you have the same problem- the teeth may not match up.
This means that you could face some major indexing issues that would screw up the meshes on at least 1 pulley at a time.
The way to fix that would be to use a jig to align the pulleys before broaching/machining.

Ah, I see.

Considering that there'll be three holes for joining the two sets of large pulleys, I don't see a problem with those. If I do end up having this made I'll probably use a jig for the driving pulleys.

[asid61]

Originally Posted by Colin Small

Ah, I see.

Considering that there'll be three holes for joining the two sets of large pulleys, I don't see a problem with those. If I do end up having this made I'll probably use a jig for the driving pulleys.

The same problem still exists.
This has killed me before, so I'm always careful about overconstraining now lol.

To avoid this problem, you could try using timing belt pulley stock instead of just pulleys. That would be a guaranteed fit. As it is, you are machining them anyway.

[Colin Small]

Originally Posted by asid61

The same problem still exists.
This has killed me before, so I'm always careful about overconstraining now lol.

To avoid this problem, you could try using timing belt pulley stock instead of just pulleys. That would be a guaranteed fit. As it is, you are machining them anyway.

We were actually thinking of that when I presented the design to the rest of the team. It would also let us run custom width belts if they're not too expensive.