Re: pic: Single Speed Gearbox Iterations
 

Here is our prototype from earlier in the summer:

Re: pic: Single Speed Gearbox Iterations
 

What I like;
-Combing the upper standoffs with the CIM bolts! So many advantages here.
-Overall profile looks clean and logical.
-Pocketing is a solid start, that's the hardest thing to do right... and everyone has a different opinion of what looks good.
-Combining the lower standoffs with your frame mounting.
-Using the same plate for both plates.

Re: pic: Single Speed Gearbox Iterations
 

The benefit could be a better running gear mesh. I believe a 12 tooth gear has an undercut at 20 pitch and 14.5 degree pressure angle, while I think a 14 tooth is out of the range requiring the undercut geometry. That said, for typical FRC applications, I'd still go with 12 tooth gears, since they fit through the hole, as others stated. And yes, I too highly recommend a close-fitting .75" hole to locate the motor.

Re: pic: Single Speed Gearbox Iterations
 

Would a better running mesh mean more a more efficient or quieter stage in the gearbox? And would there a mathematical method of calculating at what point there is an undercut?

Re: pic: Single Speed Gearbox Iterations
 

I'd have to confirm this, but an undercut shouldn't be any less efficient. It just needs the tooth to be reduced in size near the base to prevent impact of teeth; the involute surface should still be maintained.

It really is a substantial strength decrease; but as shown by numerous robots running them they are still strong enough.

Re: pic: Single Speed Gearbox Iterations
 

Thanks, I never realized the strength decrease but it makes a lot sense thinking about it now.

Re: pic: Single Speed Gearbox Iterations
 

In the first stage of a gearbox the force would be lower than it would be in later stages so the effect is minimized, identical gears in later stages might not fare as well. This is why the gear teeth in the fisher price gearbox get larger with each successive stage.

Re: pic: Single Speed Gearbox Iterations
 

I'm not sure what you're getting at with this post, this matches what I said about increasing toothsize as you go further in the stages.

EDIT: Reread, you're referring to the undercut gears not the plastic gears. Your Point is valid.

Re: pic: Single Speed Gearbox Iterations
 

Suggestion,

A couple of pressed in stainless steel guide pins would make this baby slide right in/out and align to the mating shaft and frame. Using guide pins can reduce the number of bolts to the frame and provide a accurate fit.

See how a car transmission bolts to a engine. Usually a couple of pins on the bell housing that mate to blind holes on the engine. The pins help to align the shafts and just a couple of bolts to hold the transmission on.

Roy

Re: pic: Single Speed Gearbox Iterations
 

You're spot on with our thinking, but note that the plates are mostly the same because the CIM-side plate uses a 7/8" OD (FR6) bearing on the output shaft rather than the 1.125" (FR8) bearing on the output plate side. Otherwise, there are no differences between the plates, although we had considered tapping the screw hole in the CIM-side plate to elimnate the nuts.

The "design" is really more or less a copy of what we've observed in the Cheesy Poofs' gearbox designs. We wanted to start simple with a single speed gearbox, then move forward at a comfortable pace to determine what works best for us.

Re: pic: Single Speed Gearbox Iterations
 

Both the 12-tooth and the 14-tooth pinions will be undercut, but the 12-tooth more severely so. From page 141 (PDF link):
The formula for the number of teeth (z) required to eliminate undercut is:
z = 2 / sin^2(a)

where a is the pressure angle. Interestingly, this isn't dependent on pitch.

Re: pic: Single Speed Gearbox Iterations
 

It is independent from the pitch since all gears of the same pressure angle and tooth count are geometrically similar. All 14.5 degree pressure angle gears with 24 teeth are the same profile, just at different scales.

Re: pic: Single Speed Gearbox Iterations
 

Hey guys I really appreciate all of the discussion and its helping out a LOT. There is a bunch of things that I've seen, like the CIM .75 shaft guide extrusion, that have really helped me out with more detailed design.

On that note, wouldn't it be possible to have a press fit of x OD and .75 ID to fit over the CIM that would allow the possibility to help guide into larger sized holes? I feel as if the trade off would only help getting a much larger reduction in a smaller packaging and ultimately a smaller finished assembly. If anyone opposes to the fact or sees it as being not beneficial then please let me know!

Re: pic: Single Speed Gearbox Iterations
 

This is totally possible, but if you want a larger reduction in a smaller package, that's exactly what a 12T pinion would do for you!

Re: pic: Single Speed Gearbox Iterations
 

Ah ok! I suppose I just had my logic a bit backwards when writing the post. Also, proved it with a little bit of math too haha.