pic: Input Stage Wear

[Oblarg]

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[hectorcastillo]

Can you explain inboard/outboard?

[Oblarg]

Originally Posted by hectorcastillo

Can you explain inboard/outboard?

The WCP gearboxes allow four CIM pinion sizes, from 11-tooth to 14-tooth. The 11t and 12t are one pitch diameter, and the 13t and 14t are another. In order to accommodate this, the gearboxes can be mounted in one of two orientations: "inboard" for the smaller pinions, or "outboard" for the larger (this is accomplished by having a overlapping holes for one of the two bolts that holds the CIM in place).

Unfortunately, it seems the rather rough nature of this year's game produced sufficient forces on the motors that they managed to move from inboard to outboard (there's not much metal preventing this from happening between the mostly-overlapping mounting holes). Once that happens, the gear spacing is no longer correct and grinding/wear is unsurprising.

To prevent this at future events, we wrapped the groups of 3 CIMs on each gearbox in hose clamps, which worked like a charm.

[akoscielski3]

This is not the first time I've seen this this year. I have helped many teams this year who were having "mysterious" wear on their CIM output gears and the driven gear from the CIM motors. It is definitely from the CIM motor mounting on the Gearboxes. For these gearboxes the mounting holes are slotted so teams can use different sized gears on the CIM motors. The motors are forced away from the gears and the gears destroy themselves.

I Hope WCP changes the design so this doesn't happen anymore.

The best way to change this would be to make different sets of holes for the different gear sizes. I haven't looked at the design but hopefully the design allows for these other holes.

[Oblarg]

Originally Posted by akoscielski3

I Hope WCP changes the design so this doesn't happen anymore.

Or just ship the things with hose clamps included

[R.C.]

We'll be adding a fix to this next year, we didn't notice this problem in our 3 years of testing (2011-2013 robots) but had a few teams email us about this issue.

[hectorcastillo]

Cool, thanks. I was wondering if this was related to a problem we had with one of our gears. It broke just before we were about to go into a semi-finals match on Newton, but I'm pretty sure it was because we droped ~140lbs on our back wheels every time we crossed the CDF, and it eventually blew out one of our bearings which misaligned the shaft, taking two teeth off of a 3rd stage gear. But we have VEXpro 3 CIM ball shifter gearboxes which just have one set of mounting holes, so it doesn't appear to be related. .

[wilsonmw04]

We found something similar to that on the 2 cim version. For some reason the CIMs would slide though the slot and disengage from the input shaft. Luckily this causes the gearbox to make a noise you can detect. We were able to correct this without too much damage. We are not sure if this a design flaw or a product of the extreme abuse this year's game had on the bot.

[PayneTrain]

Originally Posted by R.C.

We'll be adding a fix to this next year, we didn't notice this problem in our 3 years of testing (2011-2013 robots) but had a few teams email us about this issue.

I'm going to assume that you never tested it in an environment like Stronghold, with a lot of repeated impacts and sudden changes in the z-axis.

We had a couple WCP SS gearboxes from an old project that we were able to beat the crap of right at kickoff. Everything in the gearbox had a habit of not being where we initially put it after running it over the rockwall a few times. Bent a couple plates and killed a couple gears before we figured out how to brace them properly to handle the rigors of this game. Once we got it right, 80 matches later and the only thing we ever did on the drive was monitor chain tensioning!

[Johncvt]

We had the same issue in our first district tournament in Centerline. What we did to fix it was to take a few small set screws or pieces of steel rod, ground one side flat and then used that to fill the outer half of the slotted hole in the gearbox plate. Then, we also Loctited the CIM screws. We never had a problem after that in our next district, regional and worlds. And we played a lot of tough matches where the drivetrain did get worked over pretty well.

This is indeed a design flaw that needs to be fixed. We also made 3D printed pieces for the gearboxes to also give them so additional protection from being hit.

[JesseK]

Our WCP/DS/2CIM were fine until WCMPs, at which point a CIM came loose and I believe we put it back into the wrong 'slot' position. There wasn't noticeable wear, but we did notice the noise after a couple of matches and fixed it.

On that note - if the game is rough enough and there are enough matches, the taped #10-32 bolts will work themselves loose eventually. Best to Loctite it from the start.

All-around, these gearboxes have stood up to the roughest game they've seen, even with the aluminum 14T pinion on the 2nd reduction.

[Sohaib]

Originally Posted by akoscielski3

This is not the first time I've seen this this year. I have helped many teams this year who were having "mysterious" wear on their CIM output gears and the driven gear from the CIM motors. It is definitely from the CIM motor mounting on the Gearboxes. For these gearboxes the mounting holes are slotted so teams can use different sized gears on the CIM motors. The motors are forced away from the gears and the gears destroy themselves.

I Hope WCP changes the design so this doesn't happen anymore.

The best way to change this would be to make different sets of holes for the different gear sizes. I haven't looked at the design but hopefully the design allows for these other holes.

Can confirm had the same issue on our gearbox and showed Aaron.

This issue really plagued us during games. On the flip side, blowing apart a gearbox and reassembling it at a competition is a really good team bonding opportunity, we had the luxury of doing it three times.

[nathannfm]

Can also confirm. I helped a team diagnose this issue. The symptom was that it would bind up when going one direction.

As others have said would suggest a CIM mounting style similar to this
http://www.chiefdelphi.com/media/photos/39544
Where there are 2 holes for each distinct gearing option. Also, since the clearance hole for the bore is not actually a locating feature any more could you make it big enough to slip the 14T pinion through. This way it can be pre-installed on the CIM before assembly. One last request would be to separate the CIM mounting bolts from the standoff mounting bolts. That would make it much easier to take the CIMs off without the entire thing falling apart.

[Sohaib]

I'd like to add, that during our off season, we had issues with the two 10-32 bolts used to attach the bearing block to the gearbox (through the tubing) Namely, the thread stripping, and us having to tap it to a larger bolt right before elims, resulting in us missing a game.

[Andrew_L]

Originally Posted by Sohaib

I'd like to add, that during our off season, we had issues with the two 10-32 bolts used to attach the bearing block to the gearbox (through the tubing) Namely, the thread stripping, and us having to tap it to a larger bolt right before elims, resulting in us missing a game.

Could you elaborate more on this? Specifically what the failure mode was, when and how it happened, and whether or not you contacted WCP regarding the issue?