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

[Colin Small]

Originally Posted by Joey Milia

Yeah, bit curious why you left the first stage gears when you've used them everywhere else. It seems to be the reverse of optimal.

Could you post the tooth counts of each stage and any math you've done to confirm you'll have enough power capacity with the belts.

Also need to think lot harder about that inverse pneumatic. I know this is a rough CAD but what you have could potentially kill the cylinder, way to flimsy.

Otherwise I like how it's turned out.

EDIT: by belts not lining up I think he means if you're not carful how you join the pulleys together one of the two belts might not fit into the teeth correctly.

EDIT2: pneumatic is less flimsy if you have another one the other side. Still could be stronger.

The spacing worked better to have a single large gear for the first stage. It's thinner than pulleys and I'm not concerned with the width of the gearbox.

TBH I haven't done any math for the strength of the belts. Again, I didn't intend this to be a production gearbox and more an experiment/proof of concept/CAD practice. I'll post the tooth totals though. I think it's 18-50, 18-30, and then either 20-50 or 30-40.

What about the paramedics are flimsy? I can always add a support on the back of them.

Edit: I realize that the pictures pneumatic is orientated wrong. The fittings should be either vertical up or horizontal to the outside of the gearbox.

[Joey Milia]

Originally Posted by Colin Small

What about the paramedics are flimsy? I can always add a support on the back of them.

Edit: I realize that the pictures pneumatic is orientated wrong. The fittings should be either vertical up or horizontal to the outside of the gearbox.

It's less the pneumatic itself and more of the connection with the shifting shaft. This is helped a lot by having a second pneumatic on the other side, but thats not ideal. With only one pneumatic theres a huge moment on plate connecting the pneumatic to the shaft. That will want to bend both the plate and the pneumatic shaft and generally push everything out of alignment. It's very important that that connection and whole assembly be very stiff. Once again though, if there are two pneumatics then that moment is balanced and it's less of a problem.

The pneumatic layout on the GRT gearbox this year was designed for just one pneumatic and designed to deal with this moment. There are two on there because we were having a bit of trouble shifting in a few extreme conditions so added the second for safety, there is improvement to be made to get back to one.

[Colin Small]

Originally Posted by Joey Milia

It's less the pneumatic itself and more of the connection with the shifting shaft. This is helped a lot by having a second pneumatic on the other side, but thats not ideal. With only one pneumatic theres a huge moment on plate connecting the pneumatic to the shaft. That will want to bend both the plate and the pneumatic shaft and generally push everything out of alignment. It's very important that that connection and whole assembly be very stiff. Once again though, if there are two pneumatics then that moment is balanced and it's less of a problem.

The pneumatic layout on the GRT gearbox this year was designed for just one pneumatic and designed to deal with this moment. There are two on there because we were having a bit of trouble shifting in a few extreme conditions so added the second for safety, there is improvement to be made to get back to one.

Just curious, what'd you guys do to get it to work smoothly (for the most part) win one pneumatic?

[KohKohPuffs]

Originally Posted by Colin Small

Just curious, what'd you guys do to get it to work smoothly (for the most part) win one pneumatic?

Oh wow, interesting design!

Apparently three days ago I went on and designed a similar gearbox: inverted, two-piston shifting using a dog, except that the thing runs on gears entirely. Here's a picture:


Regarding how to reduce the number of pistons to one, I'm not so entirely sure, but to reduce the bending force to the shifting plate, the piston cannot be offset from the shaft. However, by doing so, you have to consider that the wheel is also going on the output shaft, and if the piston sticks out too much, it will hit. Also, the other issue that would come up would be connecting the piston to the shifting rod. Tried that once, and I hated it. You could add a third plate for spacing like what 254 did with their gearbox this year. Then piston-wheel collisions wouldn't happen anymore.

Just some things that I thought of, having designed 3+ of these inverted gearbox. Hope this helps!

[Colin Small]

Originally Posted by KohKohPuffs

Also, the other issue that would come up would be connecting the piston to the shifting rod. Tried that once, and I hated it. You could add a third plate for spacing like what 254 did with their gearbox this year. Then piston-wheel collisions wouldn't happen anymore.

Just some things that I thought of, having designed 3+ of these inverted gearbox. Hope this helps!

Not quite sure what you mean by a third plate or piston-wheel collisions. The cylinders are contained inside the gearbox so they won't be hitting any wheels.

Anyways, I like your design! I want to try doing the ribbing between mounting/clearance holes but it's never worked out well for me.

[Joey Milia]

Originally Posted by Colin Small

Just curious, what'd you guys do to get it to work smoothly (for the most part) win one pneumatic?

For it to work smoothy the goal is to have the moment supported by something other than the pneumatic shaft and shifting shaft. The strength of the connecting plate isn't a huge concern, it can be made stiff, the joints are the problems. There are a few different ways to do this. The option chosen for the gearbox this year involved flipping the pneumatic, having the plate mounted to the back of the pneumatic and have the whole cylinder move inside a plastic bushing that took the load. This can be seen pretty clearly with more examination of the posted gearbox picture.