Using PTO Hub in Transmission Gearboxes

[KohKohPuffs]

Last night I was designing a gearbox, but I couldn't get the ratios correctly with the current dog gears available. At one point, I did manage to find a good ratio, but it turned out later that parts were intersecting. This prompted me to find a decent way to somehow work around this without too much machine work. Since the PTO Hub from VexPro converts anything with a versakey to essentially a dog gear (or sprocket), I figured that this could allow me to have "dog gears" aside from the ones manufactured by Andymark or VexPro. For instance, I can have a 72T gear with a 1.125in bearing pocket, and use the PTO hub to get a decent low gear speed in a transmission gearboxes.

Here's a small proof of concept:
https://i.gyazo.com/2ebcf84f09fc311c4b7945814fd6cabd.png
Note that with this setup, the gear's bearing pocket had to be widened for the bearing that goes into the PTO hub. It might not be the best way to mount it (moving the gear to the other side saves space, but the distance between the two gears becomes too small for the gears on different shaft).

Anyways, this thread is here because I'm not sure if the PTO hub is designed for such applications and I would like to confirm that this could actually work, and also because with this people may be able to design gearboxes using better ratios (Not entirely sure, but hopefully :rolleyes: )

[asid61]

Neat idea! What's stopping you from putting the bearing in the gear instead of the PTO hub?

[KohKohPuffs]

Neat idea! What's stopping you from putting the bearing in the gear instead of the PTO hub?

A gear that rests on a shaft above the gearbox I'm thinking of would not be able to fit in the space between the DOG gears (can't really go outside of it because the CIM pinions wouldn't be able to reach it)

I kinda realized that this is a bit dumb; if you're going to make your own gearbox, then by that same process you might as well custom machine a gear to have the dog profile (unless somehow it's preferred to minimize machining time as much as possible)

[aJASONt_angles]

Cool Idea! I agree it might be heavy/unnecessary for a final gearbox but I think this would make an awesome prototyping tool.

[Chris is me]

I kinda realized that this is a bit dumb; if you're going to make your own gearbox, then by that same process you might as well custom machine a gear to have the dog profile (unless somehow it's preferred to minimize machining time as much as possible)

It's way easier to machine gearbox sideplates or gearbox shafts than it is to index and machine even a COTS gear with non-revolved features like dog teeth. They're both certainly possible, but it's just more effort to get the machining on the gear concentric than it is to mill out a gearbox plate from stock. I'd probably do something like this if I wanted to use a different dog gear; it's a good solution I think. I don't see why this wouldn't work.

[Joe G.]

It's way easier to machine gearbox sideplates or gearbox shafts than it is to index and machine even a COTS gear with non-revolved features like dog teeth. They're both certainly possible, but it's just more effort to get the machining on the gear concentric than it is to mill out a gearbox plate from stock. I'd probably do something like this if I wanted to use a different dog gear; it's a good solution I think. I don't see why this wouldn't work.

Yes, machining a dog profile into a steel sprocket on a manual mill was an experience filled with pain and regret. It's easy enough with the right resources, but custom gearboxes can easily be built without them through techniques like this.

[Cothron Theiss]

I wonder if you could actually print this hub? Not out of ABS or PLA, but something more substantial, like Ultem 9085 or even 1010 if you can get your hands on the blasted stuff. I know that if you shift at the appropriate times for whatever ratios you have, the forces on the god would be much smaller, but they'd still be significant. Maybe having a pretty slight first reduction so that the shifting occurs at a higher RPM with less torque?

It's probably not practical to print it, but it might be interesting.