AndyMark CIMple Box Stripped Out
 

So earlier today we were demoing our robot when it started making a nasty grind, and suddenly our CIMple box on our right side drivetrain locked up. This seems totally bizarre seeing as how both the CIM gear and the output gear are made of steel. Has anyone ever had a problem like this with a CIMple box? We're a little unsure whether it's going to wind up being a stripped cim or output gear, which basically will determine what we need to disassemble and replace. Has anyone had any similar experiences?

Re: AndyMark CIMple Box Stripped Out
 

Obvious (?) question...was the gearbox properly lubricated?

Re: AndyMark CIMple Box Stripped Out
 

When it was installed during build season, I'm fairly sure we did lubricate it.

Re: AndyMark CIMple Box Stripped Out
 

They do need periodic lubrication....

Other possible problems are loose screws, or the key falling out

Re: AndyMark CIMple Box Stripped Out
 

The sudden failure described suggests that squirrel is on the right track there.

Did you disassemble and inspect yet, and if so what did you find?

Re: AndyMark CIMple Box Stripped Out
 

If it locked up, it's unlikely that the teeth are stripped away.

Re: AndyMark CIMple Box Stripped Out
 

If you stripped a gearset you would be having the exact opposite of the problem you described. If it's locked up it's probably because a set screw or keyway has come loose inside the gearbox, as mentioned before.

Have you disassembled the gearbox yet? You'll get much more information from the gearbox itself than you will from a bunch of CD'ers trying diagnose your problem based off of one symptom.

Edit: In hindsight it was probably the external self-locking retaining ring popping off the CIM shaft and getting jammed between the gears. But if there was a grinding sound beforehand then you might have larger problems.

Re: AndyMark CIMple Box Stripped Out
 

We havent disassembled it yet, we've scheduled to fix it later this week back at the school. I'll post what it was once we confirm the problem.

Re: AndyMark CIMple Box Stripped Out
 

So your gearbox failed, and your first course of action was to post about it CD?

This is an interesting failure recovery plan. :)
Opening it up is probably a good next step.

-John

Re: AndyMark CIMple Box Stripped Out
 

We had this same thing happen to us just after the fall classic in 2011 with our back left drive gear box. Ended up that the teeth on the large gear had worn away and one of them had failed. Pretty sure the issue was the we didn't grease it enough during the season and we drove that robot pretty hard.

Re: AndyMark CIMple Box Stripped Out
 

For anyone still interested, the cause of the drivetrain malfunction was two completely stripped 12 tooth CIM motor gears. According to our lead pit mentor, we oiled it routinely throughout competition, but we must have let it slip this summer. Proper lubrication is certainly important to avoid things like this happening, we're just lucky it happened at the end of a demo, not at an offseason competition.

Re: AndyMark CIMple Box Stripped Out
 

Oiled or greased?

Re: AndyMark CIMple Box Stripped Out
 

I think many of us would like an explanation as to how exactly a stripped gear made your gearbox lock up.

Re: AndyMark CIMple Box Stripped Out
 

I'm not entirely sure, I wasn't in charge of that.

Re: AndyMark CIMple Box Stripped Out
 

Is oli the right lubricant? I would suggest a gear grease developed for high gear pressure.

Re: AndyMark CIMple Box Stripped Out
 

Sorry it took me a while to get back to you. It is possible the metal shavings got wedged between the gears, or the CIM gears which were stripped didn't mesh with the output gear. Also, when I said it locked up, I meant it provided heavy resistance and wouldn't turn over without seizing.

Greased with a high pressure lithium grease, as I have come to find out.

Re: AndyMark CIMple Box Stripped Out
 

Sorry it took me a while to get back to you. It is possible the metal shavings got wedged between the gears, or the CIM gears which were stripped didn't mesh with the output gear. Also, when I said it locked up, I meant it provided heavy resistance and wouldn't turn over without seizing.

Greased with a high pressure lithium grease, as I have come to find out.

Re: AndyMark CIMple Box Stripped Out
 

Photos would be great!

Re: AndyMark CIMple Box Stripped Out
 

The little tubes of grease that come with the CIMple boxes work great. We have a stash of them since we usually build transmissions and don't open the cimple boxes, but if you have some, those are great. We actually had the same issue this year at SBPLI, but we greased it a lot and it spun like a pro.

Re: AndyMark CIMple Box Stripped Out
 

We had the same problem. One must not have been lubed up as much as the others. We had it lock up and we came to find out that both sets of gears had about 90% of the teeth gone and their shavings mixed in with some grease at the bottom of the box. :ahh:

Re: AndyMark CIMple Box Stripped Out
 

We've found that you can't put too much grease in a CIMple box... literally! If there's too much in there, it'll work its way out in the first few minutes of running it - just turn everything up, wipe off what comes out, and you're good to go.

Re: AndyMark CIMple Box Stripped Out
 

Actually I posted an image of it before, heres the link:
http://postimage.org/image/l4hxqnftx/
Thanks for your interest

We're just lucky it didnt happen in competition :P

Re: AndyMark CIMple Box Stripped Out
 

Re: AndyMark CIMple Box Stripped Out
 

I dont have the specifics at hand, but I'll try my best.

Our robot was 119.9lbs w/o bumpers or battery.
I cant remember exactly what it was, but it would top out around 10fps.
1" aluminum box tubing 1/8th" thick.
With the bumpers, I believe it weighed around 130lbs.
We used the 6" kit wheels.

Re: AndyMark CIMple Box Stripped Out
 

Nothing seems out of the ordinary here. Weight/Gearing aren't out of wack (good speed for a heavy bot). A frame with that tubing can be crazy stiff if welded properly.

How crazy were your drivers during your competitions? Where there many instances of slamming the robot controls the opposite direction when the bot was at full speed?

Also, is there any possibility that the output shaft bearing popped out slightly (the one in the plastic, where the encoder goes)? Any sort of lateral stress on the CIMple box output shaft (over-tension on chain, massive shifts in control that are opposite the robot's momentum which 'snap' the chain into high tension) can lead to fatigue in the plastic over time that causes the bearing to unseat. This could cause the opposite bearing on the output shaft (the one in the metal) to seize, which could then cause the CIM gears to shred. It only takes 1-2 degrees of bearing misalignment for these bearings to become VERY inefficient; any more and they probably did seize.

Re: AndyMark CIMple Box Stripped Out
 

That does look like classic lack of lubrication. I know we have done it before ourselves.

Re: AndyMark CIMple Box Stripped Out
 

I measured the components of the CIMple gearbox including the 56T gear and output shaft. These parts are made to a loose fit tolerance. This in both the fit to the bearings and the fit to the 56T gear. Much looser than anything I have designed. It seems it would take quite a bit of misalignment for anything to bind.

Question - Is the 56T gear plated in your gearboxes?

Re: AndyMark CIMple Box Stripped Out
 

The image strongly implies not enough lube in the gearbox. You REALLY need to pack those things with grease and make sure they stay lubricated. Some teams use a clear spray-on lubricant that makes their gearbox look ungreased, but don't let that fool you - you need grease.

Re: AndyMark CIMple Box Stripped Out
 

I second the cyclical fatigue motion. Constant running would likely not shred the gears, but high stress cyclic loading would cause them to fatigue and eventually the teeth would fracture. Perhaps your drivers were cycling the controls back and forth when the gearbox seized up to get the robot moving and this resulted in the gears becoming stripped.

Just a thought.