Gearbox Design Feedback

[asid61]

The way your standoffs are supported, they're almost cantilevered off the main body of the gearbox for the left and right ones. You are also using 6 standoffs versus the traditional 4, any particular reason for that? Removing the leftmost and rightmost standoffs would simplify it a little.
I think you have 2-4 too many pockets, but proper build season planning can offset the machine time in the case of a drive gearbox.

[SerpentEagle]

Originally Posted by T^2

You're gonna have a hell of a time taking those CIMs off without disassembling the entire gearbox.

Standoffs do not need to be 1/2". You have too many of them, in any case; the ones on the far right and left are completely unnecessary.

Not really. The bottom two screws are externally accessible, and only the top two are combined with standoffs.

Im a bit confused with the standoffs. I've never had experience with these kinds of gearboxes. I see respected teams such as 254 use some pretty large standoffs, and some teams use smaller ones. Would there be any issues with rocking if the standoffs are too small?

And I agree the left and right standoffs are unnecessary, I've made changes accordingly.

[SerpentEagle]

Originally Posted by Ari423

From what I can see, the two screws holding in the CIMs are accessible from the outside. One screw looks to be the top standoff screw, and there is a hole (in line with top and bottom standoffs, below CIM output shaft) to unscrew the other screw. Then it should be as simple as popping off the CIM gear and sliding it out of the enclosure. I could be wrong, but I imagine this was SerpentEagle's intent when designing it.

This is a nice, compact gearbox. How much does it weigh? Also, did you think about the abundance of possible pinch points where someone could get a finger stuck? I imagine it shouldn't be that hard to cover with some clear plastic (which will also help keep out scruff) but maybe you have a better idea.

No your right, that was the intent.

According to solidworks it weights approx. 6.5 lbs, so ~7 lbs.

And no I didn't think about pinch points, good thing you brought it up. I'm thinking that a 3d printed shell with screw holes would work nicely.

[SerpentEagle]

Originally Posted by hectorcastillo

The design looks really cool! One thing that I thought of is you could add two or three #8 tapped holes in a circle around the front bearing and use some button head screws to hold your bearing in place instead of a retaining ring.

That's a really interesting idea. I ended up just reversing the bearing to eliminate the problem altogether.

[SerpentEagle]

Originally Posted by Richard Wallace

My team has been retaining things on hex shafts by means of 1/4-20 button head cap screws and standard washers at each end. Thunderhex shaft stock makes this method very easy, because its center hole is just right for the tap. We often drive the shaft using a 1/2 inch speed wrench while holding the tap stationary. Of course this method requires us to cut shafts very close the proper length to hold whatever components are riding on them -- we use a scribe to mark them and a small lathe to face them for that.

We do that too but just for backup in case the snap rings fail. Its definitely a neat technique.

[SerpentEagle]

Originally Posted by asid61

The way your standoffs are supported, they're almost cantilevered off the main body of the gearbox for the left and right ones. You are also using 6 standoffs versus the traditional 4, any particular reason for that? Removing the leftmost and rightmost standoffs would simplify it a little.
I think you have 2-4 too many pockets, but proper build season planning can offset the machine time in the case of a drive gearbox.

Yeah I agree. Next time I'll work on keeping things closer to the bulk of the body, or just put a ring around everything. I put these extra standoffs as support for the cims, but I realize that a whole another set of standoffs is unnecessary.

I personally don't think that pockets are a time problem for machining, as a water jet or CNC mill would zip right through them in a matter of minutes. But I will definitely work on simplifying the structure a bit more.

[SerpentEagle]

Thanks to all the helpful pointers you guys gave me, I have come up with a v2.

Link to model: https://grabcad.com/library/drivebox-2-1



-4 Standoffs instead of 6
-Front output shaft bearing is flipped to eliminate need of retaining the bearing
-Simpler structure?

I plan to mount this in an unorthodox way. The bottom two standoff bolts are combined as mounting bolts an the bottom CIM mounting holes on the front plate is tapped to seve as another set of mounting holes. Good idea or a dreadful mistake?

[Bryce Paputa]

Originally Posted by SerpentEagle

I plan to mount this in an unorthodox way. The bottom two standoff bolts are combined as mounting bolts an the bottom CIM mounting holes on the front plate is tapped to seve as another set of mounting holes. Good idea or a dreadful mistake?

This is very similar to what we did this year, and we had an issue or two where the small bolt loosened, fell out and got stuck in the chain. I would recommend making that bolt go all the way through the gearbox with a standoff so that even if it loosens up it won't be able to fall out, but that might make it harder to assemble.

[SerpentEagle]

Originally Posted by Bryce Paputa

This is very similar to what we did this year, and we had an issue or two where the small bolt loosened, fell out and got stuck in the chain. I would recommend making that bolt go all the way through the gearbox with a standoff so that even if it loosens up it won't be able to fall out, but that might make it harder to assemble.

Would loctite solve this problem? But yeah I could probably just run the bolt all the way through to the CIM.

[Chak]

Originally Posted by ARI423

From what I can see, the two screws holding in the CIMs are accessible from the outside. One screw looks to be the top standoff screw, and there is a hole (in line with top and bottom standoffs, below CIM output shaft) to unscrew the other screw. Then it should be as simple as popping off the CIM gear and sliding it out of the enclosure. I could be wrong, but I imagine this was SerpentEagle's intent when designing it.

Originally Posted by SerpentEagle

Would loctite solve this problem? But yeah I could probably just run the bolt all the way through to the CIM.

Wouldn't that ruin the accessibility of the CIM in the original design?
So Loctite would be the better choice.

[SerpentEagle]

Originally Posted by Chak

Wouldn't that ruin the accessibility of the CIM in the original design?
So Loctite would be the better choice.

Not really. There would be an access hole in the chassis and you would just loosen it up, but I would definitely prefer the screws to be separate for the CIM an mounting.

[BenGuy]

Just so you know Shashank - Superb is making this - I would have to spend the entire build season on the mill to make this... But a cool looking design for sure!

[SerpentEagle]

Originally Posted by BenGuy

Just so you know Shashank - Superb is making this - I would have to spend the entire build season on the mill to make this... But a cool looking design for sure!

Aw man! Looks like I'm gonna have to find someone else up for the challenge lol. Thanks.

[BenGuy]

Originally Posted by SerpentEagle

Aw man! Looks like I'm gonna have to find someone else up for the challenge lol. Thanks.

Yeah... because anyone else on the team would do this... Superb would have a hard time with this!!!

[Dunngeon]

Have you given any thought to how this would be machined?