2 Falcon Ball Shifting Gearbox

[lucuszha]

Been playing around with a gearbox for Falcons for a bit, and would love feedback/constructive criticism on it.

Disclaimer: I am not a cadder (I do electrical normally) and this is my first time attempting a shifting gearbox.

Specs:

STEP File: Gearbox V7.stp (31.2 MB)

[ProPain37]

You’re over constraining the main shaft with 3 bearings. Get rid of the middle plate and just extend it to the outside. Use spacers between the gears, sprockets, and bearings.

[lucuszha]

I thought about removing the middle plate, but from what the ball shifting shaft looks like, it has to be supported by bearings at both ends at specific points, necessitating the middle plate. If you have solutions, they would be much appreciated!

[ProPain37]

I’m pretty sure it doesn’t have to be supported at both ends. I may be wrong but from what I understand, you can extend the hex portion of the balls shifter shaft to your desired length

[ClayTownR]

@lucuszha

it has to be supported by bearings at both ends at specific points, necessitating the middle plate. If you have solutions, they would be much appreciated!

The ball shifter shafts are retained in the shifter body with both a press fit and a spring pin. If you remove both you can replace them with a custom-length hex shaft; however, this does require some difficult finagling. While I wouldn’t call it perfect, I made an admittedly flawed stab at a gearbox which did this some time ago. If you use a custom-length shifter shaft, there is no reason why you can’t put a bearing wherever you please.

A couple other bits of feedback, for you to peruse at your pleasure:

• Note that the Falcons (and NEOs, for that matter) have enough power and good enough performance at low RPMs that shifting is not as useful as it was, say 2 years ago. Most people have gotten away with just 1- or 2-stage single speed gearboxes.
• Take another look at your pocketing scheme. You’ve got most of the critical load paths, but it looks like there’s a long unsupported bit on the gear guard on the back plates.
• Thunderhex is a pretty bulky solution for standoffs. If you poke around a bit on McMaster-Carr, you can find some very nice low-profile standoffs.
• Watch out for motor mounting screw access. Right now, it’s impossible to replace the motors without disassembling the gearbox, because the mounting screws are hidden under a gear. Consider rotating your motors to improve accessibility.
• The support for the pneumatic cylinder plate is a bit overkill. It’s under relatively little load, so just 2 standoffs will do.
• I’ll echo what lucuszha said and say that once you remove the need for a middle bearing, it becomes very hard to justify a middle plate. Consider dropping that plate and lengthening a few shafts.
• You have a lot of weight tied up in that idler stage in the middle. You might want to play around with the reductions more and see if you can find a way to trim that down.
• 1/4" overall center drop is quite generous. Unless you expect a terrain game, you can take that down to 1/8" overall.
• Look again at how your shafts are constrained. It looks like 2 of the 3 shafts are able to move around axially and would eventually fall out.
• Any particular reason why the wheel is held in with a shaft collar, or why the output shaft is overlong?

[lucuszha]

Thank You! About some of our questions

• The main reason I anted to do a shifting gearbox was the current draw (again, electrical here). In high gear at a reasonably geared gearbox, the current draw per motor is around 80 to 90 amps, which is okay for a little while, but for a long period of time like you would see in a pushing match, the high current draw would trip a lot of breakers. Plus, the fact that Falcons and Neos have such a small thermal mass makes me nervous about drawing a lot of current period.

• I tried for a long time to get rid of the second stage in the gearbox while maintaining a good gear ratio, and I couldn’t find a gear ratio that would work. If you have solutions it would be much appreciated

• I thought it was an 1/8 inch center drop. Weird.

• Generally, we just use e-clips on our shafts to prevent them from falling out.

• Shaft Collars are just how we’ve gone for as long as I can remember, and the output shaft is just long cause I made it too long and was too lazy to shorten it.