KoP TB Mini- Transmission Seizing

[Type]

My team received our Rhino tracks we ordered yesterday, and we put the transmission that was in the kit of parts on. When we put the cims on today, we were having issues with both for awhile, but fixed one by greasing it up better. The other one is constantly seizing up, and after slowly taking the tracks apart to see where the problem is, it starts at the gearbox. Has anyone else had an issue with the gearbox seizing up, being very loud?

[dradel]

Check the gear that the cims spin against. Last year we had one that was slightly out of round and caused what seems to be the same problem you are having

[Donut]

Have someone disassemble and reassemble the gearbox, paying attention that all gears face the right way and everything is seated well. It's a precaution based on a few incorrect assemblies I've seen before. A few years ago we had one gearbox grinding because one of the gears was in reversed (flat side wrong way) and we just fixed a toughbox today that was binding (seemed like one of the bearings was not in flat).

[JohnFogarty]

I've had a problem where a student put a spacer that was supposed to be behind the CIM pinion gear and put it on top under the retention ring. That caused the gearbox to seize almost immediately.

Like others have said, get your assembly manual out for the gearbox and check EVERYTHING. It's likely been assembled wrong.

[pribusin]

We've had a similar issue where one gearbox was nice and quiet and the other one super noisy and ran much rougher. Turns out the gears on the CIMs were meshing too close with the large input gear. Apparently the CIMs are known for having sloppy tolerances (mounting holes can be slightly off-center) when it comes to the mounting holes and some are worse than others. Rotating the CIMs 180 degrees made our noisy gearbox run nice and quiet.

[Type]

Originally Posted by JohnFogarty

I've had a problem where a student put a spacer that was supposed to be behind the CIM pinion gear and put it on top under the retention ring. That caused the gearbox to seize almost immediately.

We took it apart once (so assembled the box twice) to regrease it since that fixed the issue with the other gearbox being loud, and even slower.

I'll try rotating the motor 180*, we already checked to make sure everything was assembled correctly.

[Al Skierkiewicz]

You will need to open the transmission to check. The CIM shaft key often is installed improperly and will fall out and find it's way into the running gear. Also check that the shafts and other parts are assembled in the correct order and everything is present that is intended.

[silverD]

These are all great suggestions. Not to hijack the thread, but we too are having a similar issue where one of the TB mini gearboxes is louder and not as smooth spinning as the other. The really odd part is that it is worse when driven in one direction versus the other and seems to bind/catch. We've reassembled it many times, reversed the cims, and swapped out internals. We are beginning to wonder if the molded plastic housing is the problem. We are running a 13 tooth cim gear with 14 tooth center spacing.
Thanks for any help in advance.
Nate

[BoilerMentor]

Originally Posted by silverD

These are all great suggestions. Not to hijack the thread, but we too are having a similar issue where one of the TB mini gearboxes is louder and not as smooth spinning as the other. The really odd part is that it is worse when driven in one direction versus the other and seems to bind/catch. We've reassembled it many times, reversed the cims, and swapped out internals. We are beginning to wonder if the molded plastic housing is the problem. We are running a 13 tooth cim gear with 14 tooth center spacing.
Thanks for any help in advance.
Nate

That's .025" further spaced than they should be, per a standard gear spacing calculation. I would be extremely hesitant to operate a gear box like this, because you're most certainly outside the range of appropriate gear mesh. You'll see a lot of back lash between the gears, noise, and potentially irregular gear wear or even failure.

Center distance = (N1 + N2) /2P
N1: Number of teeth on Gear 1
N2: Number of teeth on Gear 2
P: Diametral pitch

Generally we add an extra .002" spacing to account for misalignment

(13+50)/2*20 = 1.575" --> 1.577"
(14+50)/2*20 = 1.600" --> 1.602"

In our custom gearboxes, even with the extra .002", we've had situations where we see binding on one side and free movement on the other.

for reference: http://www.engineersedge.com/gear_formula.htm

[Thad House]

Originally Posted by BoilerMentor

That's .025" further spaced than they should be, per a standard gear spacing calculation. I would be extremely hesitant to operate a gear box like this, because you're most certainly outside the range of appropriate gear mesh. You'll see a lot of back lash between the gears, noise, and potentially irregular gear wear or even failure.

Center distance = (N1 + N2) /2P
N1: Number of teeth on Gear 1
N2: Number of teeth on Gear 2
P: Diametral pitch

Generally we add an extra .002" spacing to account for misalignment

(13+50)/2*20 = 1.575" --> 1.577"
(14+50)/2*20 = 1.600" --> 1.602"

In our custom gearboxes, even with the extra .002", we've had situations where we see binding on one side and free movement on the other.

for reference: http://www.engineersedge.com/gear_formula.htm

The 13T pinions are really cool. They actually have a 14T center spacing, and fit a normal 14T spacing without any issues.

However, I can see an issue with using them in AM gearboxes. People have noticed in the past that AM and Vex gears do not always mesh properly. That could be one cause of your binding. If you double check the assembly, and still see the issue, try the 14T AndyMark pinions that were included with the gearboxes and see if that solves the issues.

[silverD]

Thanks to both of you for your input. The 13T pinions are neat and we did use them successfully last year in TB nanos, but our robot never really needed to move very far or fast.
We have another gearbox coming and we can try the pinions from last year's bot too. We'll also try the stock pinions as well.
Thanks,
Nate

[BoilerMentor]

Originally Posted by Thad House

The 13T pinions are really cool. They actually have a 14T center spacing, and fit a normal 14T spacing without any issues.

However, I can see an issue with using them in AM gearboxes. People have noticed in the past that AM and Vex gears do not always mesh properly. That could be one cause of your binding. If you double check the assembly, and still see the issue, try the 14T AndyMark pinions that were included with the gearboxes and see if that solves the issues.

That's interesting and kind of cool. I was unaware, and I'm sure you can understand my concern at the statement without that information. 1747 is mixing gears from VP and AM in one place on the robot, but it doesn't seem to be an issue.

[Type]

So we determined tonight that it had nothing to do with the gears, but the plastic housing on the gearbox was bad. We replaced it with a housing we had from previous years, and it worked fine. We decided that what most likely happened was (because we could kinda see it from the outside) the cim was not sitting on there right. So one side of the cim would press into the main gear, of course creating the seizing problem.