Sequential Gearbox

by NateTG, published

Sequential Gearbox by NateTG May 14, 2013
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Constant mesh sequential gearbox using Emmet's gear bearings. I need to work out how to make it printable...

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Sequential Gearbox by NateTG is licensed under the Creative Commons - Attribution license.

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Finally got around to printing the synchro mesh prototype. The clearances are all wrong, and I need to rework it.

Wow. What a friggin brilliant concept, well done!

Synchronous shifting seems like a tough problem that would be awesome to solve. A thought that just crossed my mind is to use a cylindrical (probably slightly tapered, so I guess conical) friction fit to drive the output shaft, which would have some sort of expanding/contracting end portion to engage/disengage each gear.

Assuming a friction drive would work decently (which I'm not sure of) the best way I can think of to actuate the expansion would be to use concentric shafts and have the inner shaft move axially in/out a bit to expand/contract the engagement mechanism. The end of the inner shaft that actuates the expansion/contraction of the outer shaft would need a freely rotating portion (relative to the rest of the inner shaft) so that when engaged in the expanded configuration the entire inner shaft wouldn't start rotating and you could still control it's axial in/out movement without introducing a ton of friction to the system all at once.

Man it's difficult to convey this stuff in writing... I hope that made some kind of sense.

You don't have to restrict yourself to a single type of clutch:
In a conventional modern automotive transmission, there are basically two clutches per gear, a friction clutch (the synchro mesh) which is used just to get the pieces in synch, and a dog clutch that is used to do the actual power transmission.

The tricky parts are, really setting things up so that the clutches can both engage independently, and packing it all into the available space.

I find myself with an idea, but it's the sort of thing that will require some fiddling to get right.

Initially I was trying to think a of a way to add the dog clutch, but didn't have any decent ideas. Hope your idea works out, that would be quite a feat. Best of luck :)

I just added a concept model for the way that a synchro mesh might work. Friction at the top and bottom, and dogs in the middle.


Not certain that I understand - is the basic idea that the inner shaft moves axially a certain distance to engage the friction fit, at which point it starts spinning at the same rate as the gear, then moves axially again just a bit more to engage the dog clutch?

Yeah, that's about the size of it. Though the teeth on the shaft really want tapered/beveled ends so that they'll mesh better and so on.

Gotcha. That's pretty elegant to use the cutouts in the outer shaft to both enable expansion and to engage the teeth of the inner shaft :)

This has my brain juices flowing again and I may try to model something based on this concept. If I'm able to come up with anything decent I'll be sure to let you know.

If only we had dissolvable support material working well. That's a cool idea; how do you envision the input / output / gear shifting to work?

The other day, I realized that if the outer rings are printed as halves, the rest of the components can be printed separately and then assembled. Time for more openSCAD tinkering.

An easy way to work input or output would be to put a belt on the outside, but my original thought was a round shaft with a hex head, and the head just engages with whatever layer of the gearbox. (The stepped center bore is pretty apparent in the section view.)

The input and output would work in a similar fashion, though one would probably just be fixed to one end, with the other doing the shifting. I've been thinking about how to work in a synchro mesh, but for right now it's just a crash box.

With suitable gear sizing, a cap arrangement a bit like this:
Could also allow for a reverse gear on the end of the gearbox.

Differential Planetary Gearset
by emmett