Meshing Gears

[Joshua May]

Originally Posted by FizMan

That's where the rounded teeth come in handy?

I believe that's where the rounding comes in handy. Also, at least in shifting while moving, the gears are moving so in the time that it takes to shift, there will be multiple times where the teeth do ot hit each other and should slide together. Now I'm not an expert on shifting gearboxes, I haven't even used one, I'm just familiar with some of the theory in them.

[FizMan]

I suppose it'd be a good idea to fashion multiple spares of the shifting gears in this case, eh? I mean, I suppose it's possible to damage them.

[Lisa Perez]

Originally Posted by FizMan

I suppose it'd be a good idea to fashion multiple spares of the shifting gears in this case, eh? I mean, I suppose it's possible to damage them.

Yeah.. We didn't really think of rounding.. That'd might've helped.

At any rate, does anyone know to what extent the rounding will help? Because if teeth still manage to hit each other on their sides, eating of the gears can still happen. And if one rounds too much, the teeth won't get enough grip on each other. What teams out there did round their gears and what was your experience doing this?

As for the spares.. We welded the gears onto the shafts.. Didn't really think of that, either

[Joshua May]

Originally Posted by Lisa Perez

Yeah.. We didn't really think of rounding.. That'd might've helped.

At any rate, does anyone know to what extent the rounding will help? Because if teeth still manage to hit each other on their sides, eating of the gears can still happen. And if one rounds too much, the teeth won't get enough grip on each other. What teams out there did round their gears and what was your experience doing this?

As for the spares.. We welded the gears onto the shafts.. Didn't really think of that, either

I got this information from the White Paper on 116's tranny. The white paper can be found here, it gives the amounts to round and everything. You'd really have to ask them about how it worked.

[sanddrag]

I would think using a dog type shifter is much better.

[FizMan]

Originally Posted by sanddrag

I would think using a dog type shifter is much better.

What about in transmissions like say, 33's 4 speed one? Does it make that much of a difference? Though I suppose, it wouldn't be that hard to modify it to use a dog instead.


Also, you think there'd be any problems with meshing helical-gears in this fashion without dogs and all? Just moving it to lock up with another helical gear?

[sanddrag]

Originally Posted by FizMan

Also, you think there'd be any problems with meshing helical-gears in this fashion without dogs and all? Just moving it to lock up with another helical gear?

Any rotating part ramming into another rotating (or stationary) part has inherent problems. It's the nature of the business. The better transmission is the one that copes with these problems best.

[FizMan]

What I meant was, are there any UNIQUE problems with meshing helical gears as opposed to umm "normal" teethed gears? (don't remember their name) And/Or are the same issues between the two not as much (or more of) a problem with Helicals?

[Kevin Sevcik]

This is more or less the exact tranny that Team 57 used this year. We had an issue with gears disintegrating, but that was poor design and wasn't the shifting gears. We beefed up that pair of gears and things were fine. We also had an issue with the shifter getting stuck, but that was an alignment problem and was fixed with the judicious application of a hammer.

On to some points brought up in this thread...

Yes, there will be times with the gears won't mesh perfectly when you shift. If you think about it, Dog shifters have this problem as well. Anyways, we had no issue shifting on the fly. Occasionally one side would engage before the other, but it was never very bad. The best thing you can do is shift the trannies with pneumatics. They'll naturally act as springs and keep pushing the gears together till they mesh.

I will say that the proposed method of "rounding" the gears isn't really productive. Especially if you that to both of the meshing gears. That won't really make the gears mesh better because you still have the same basic cross-sections trying to mesh. What you really need to do is dremel the sides of the gears down to points. That makes it much easier for the gears to mesh. You can also make it easier by setting the gears a little farther apart than would be strictly advised by pitch diameters. This increases backlash and makes the gears slightly weaker, but it makes meshing even easier.

Also, you can reduce the chance of breaking the gears by moving the shift as far up the gear train as possible. If you can shift gears on the low torque end of the tranny they don't have to be as strong so you can reduce the size.

Finally, I think this kind of transmission is a bit easier and more forgiving. Dog shifting trannies almost mandate a CNC shop to get the dogs right. A reasonable gear meshing tranny will just need a good drill press with an X-Y table without much slop, and possibly a lathe.

[Lisa Perez]

Originally Posted by Kevin Sevcik

Yes, there will be times with the gears won't mesh perfectly when you shift. If you think about it, Dog shifters have this problem as well. Anyways, we had no issue shifting on the fly. Occasionally one side would engage before the other, but it was never very bad. The best thing you can do is shift the trannies with pneumatics. They'll naturally act as springs and keep pushing the gears together till they mesh.

We did use pneumatics.. but that's part of the reason that the gears ate each other up

[Kevin Sevcik]

I think this is probably the advantage that our method of rounding gave us. the gears more or less had to mesh, so it wasn't really a problem. I think a little time and care with a dremel can make this kind of tranny work rather well.

[Travis Covington]

Although I will agree that meshing gears is an effective way to create a shifting gearbox, if reliability and consistency are a larger factor, then I would have to put my vote in for a shifting dog style tranny.

The benefits of the dogs are seen in a lot of real world applications, such as motorcycle transmissions and the like. Most motorcycles still use a clutch, where as most FIRST robots using a dog style tranny do not. The difference there is negligible, as most teams learn to back off on the joystick when they shift gears, but for the most part it is an insignificant factor for such low-torque applications. In alot of cases, motorcycles can be shifted without having to use the clutch.

While meshing gears works, there is the inherent wearing of the 'rouded' edge you folks are talking about that essentially helps ensure the gear is meshing. After long term use, these gear edges will see significant wear. The argument then follows, 'we won’t be using it THAT much on a FIRST robot, and so does the wear really matter?' I would probably say no. So overall, I say build what you are comfortable building. I know a lot of top teams use meshing gears, while other equally good top teams use dogs. I have not heard of many stories on either side where these transmissions fail in short term seasonal use.

Good luck either way...

Here is some motivation for you all... (Stock motorcycle tranny)