Meshing Gears

[FizMan]

I'm pretty sure there's a thread aboot this somewhere, but me being on a break at work, don't have time to sift through the site.

Anyhow, lots of talk aboot dogs in transmissions letting you 'shift-on-the-fly'. What are the problems when it comes to meshing two gears directly?

______
 |  |
=== |
 | ===
 |  |
______
 
shift to:
______ 
 |  |
======
 |  |
 |  |
______

I hope you get the picture; it's a top-down shot of a simple system pushing one gear to align with a second. (the === are the gears, the | are the axles, and the _____ is the housing)

And is shifting like this not possible on the fly? Didn't that team with the 4 speed automatic transmission do it on the fly? (forgot the team name)

If there's already a thread like this, you can point me in the direction of it too if you'd rather (don't want to waste your time writing a post if the information is there)

Thanks for your help.

[Joshua May]

It's possible, many tranny's are shift-on-the-fly, and the team you're thinking of is Team 33.

I haven't built one of these gearboxes yet, so I don't know the problems, but I'm pretty sure that at least team 116 used a lathe to "round-out" the edges of the gears so that they would mesh better, you just have to make sure that everything is aligned correctly. If you don't get the image of the "rounded gears", they would look something like this from a view facing the gear.

 _____
/     \
|     |
|     |
|     |
|     |
|     |
\_____/

[Lisa Perez]

We TRIED to have a 2-speed transmission ('tried' being the key word ) but one of the main problems that we encountered was that when we shifted, sometimes the two gears would not mesh or "catch on to the other". Thus the shift did not work, and the shifted gear would come in conflict with the other.

There is always that possibility that one gear will not catch on to the other while being shifted (even if the two shafts rotate at the same speed). We ended up with an eaten up gear and we had to change back to a shift-less transmission. But hey, that one worked

[FizMan]

So would a system of meshing the gears like that (rounding them as well) work alright for a transmission where the robot has to stop first, then shift? Any problems with that? What if the gears happen to have their teeth aligned so when you try to push the gear in, one of the teeth hit each other directly on the side? That's where the rounded teeth come in handy?

[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?

[team222badbrad]

Thanks for the comments.

The gears were not spaced apart. However we did grease/oil them. We greased them about once a regional.
The transmissions were sealed pretty well from leakage. They were not full of oil but if FIRST saw a little oil on the carpet the wouldnt like it... And yes our robot was uprighted several times and we never found any oil spots on the carpet

The non-engaged ball bearings didnt seem to cause much friction at all. The only time the ball bearings could accually enter the slots in the gears is when one hole is |- | upside down like this, so gravity can pull it out.
Even then |O| both the slots and the holes would have to do so at the same time. As soon as that would occur the ball bearings would just be forced back up in the shaft. I have easily pushed the robot along the floor when the robot is in neutral.

The transmissions are still working great! So far the robot's transmissions have been through 2 regionals, nationals, and 3 minis. We have only had to oil them and check set screws! Never even had to change a CIM motor!

The only drivetrain related problem we had this year was a shattered 4 wheel drive sprocket. Not a big deal considering we still made it up to the top platform with 3 wheel drive and it was just a practice round...

Next year we are going to make it even better!

www.tigertrons.com/2004/transmission222 Link includes Powerpoint,white paper, and Chiefdelphi Links.

[camtunkpa]

Just to fill in some gaps here and there:

1) Our design didn't use the balls in the shaft to create a ball bearing like assembly when the gears were not engaged.

2) Though simple in concept, these transmissions take a while to build for the first time (get prototyping!!!!).

3) Spring load your shifting device!!!! One thing I've seen with the designs is that everyone uses air or some sort of device to engage gears.....Air is good, but at the same time air along with a spring load is less harsh and more accurate at engaging the gears and will tend to solve SOME of the syncro. grindage. The spring load allows for error in shifting with no damage to your machine.

Happy Shifting!

[helly180]

Do you know where to get schematics for transmissions?

Originally Posted by FizMan

I'm pretty sure there's a thread aboot this somewhere, but me being on a break at work, don't have time to sift through the site.

Anyhow, lots of talk aboot dogs in transmissions letting you 'shift-on-the-fly'. What are the problems when it comes to meshing two gears directly?

______
 |  |
=== |
 | ===
 |  |
______
 
shift to:
______ 
 |  |
======
 |  |
 |  |
______

I hope you get the picture; it's a top-down shot of a simple system pushing one gear to align with a second. (the === are the gears, the | are the axles, and the _____ is the housing)

And is shifting like this not possible on the fly? Didn't that team with the 4 speed automatic transmission do it on the fly? (forgot the team name)

If there's already a thread like this, you can point me in the direction of it too if you'd rather (don't want to waste your time writing a post if the information is there)

Thanks for your help.