pic: Input Stage Wear



This is one of the input stage gears from our WCP 3-CIM SS gearboxes after our first district (with a new gear for reference). As you can see, there’s a fair bit of wear on the teeth. We noticed that our CIMs had been pushed from inboard to outboard several times over the competition, which we think was likely the cause of the damage. We secured the CIMs with hose clamps (holding them in the inboard position) for the next two events, without further damage.

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.

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.

Or just ship the things with hose clamps included :wink:

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.

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. .

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.

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!

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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.

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.

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. :wink:

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.

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?

I unfortunately don’t have any pictures of this. However, it looked like it was a gradual wear of the thread on the gearbox plate. The threaded holes (when they failed beyond the point at which they could hold the gearbox to our frame) were oval shaped generally in the horizontal direction. (with typical orientation of mounting) In fact, after drilling out the holes for a 1/4-20 tap, the holes were still not perfectly circular, that’s how much damage had occurred. We noticed this issue right before eliminations at Fall Fiesta.

We haven’t contacted WCP, but plan to do so, along with all of the other issues we have experienced with the SS gearboxes, namely with the CIM mounting.

Something with these gearboxes and oblong shaped holes :rolleyes:

Edit: The gearbox on the other side had the same issue shortly after, and has not been repaired yet. When it is disassembled, I will be sure to post a picture, however cannot comment on the failure of it yet as I haven’t seen it, it’d be reasonable to assume it is the same failure method however.

As a general rule, talking to the company directly is going to get you further in having your problem fixed/helping the company fix the problem( if there is one) then simply complaining about it on ChiefDelphi.

WCP works very hard to bring good valve and good quality products to the marketplace, and it doesn’t seem right to talk about your problems without a bit more specific detail about each use case and failure mode. Not giving enough detail in the circumstances, could cause teams to get a bad impression of the gearboxes when it was really you pushing the boundaries with how you used them.

If you have enough time to write a post on CD you have enough time to send an email to WCP.

The gearbox mounting holes are an issue RC has already indicated will be fixed for next season, along with the bearing retention (which was not an issue we had) My intent was not to complain, except to demonstrate the issues we have had with these gearboxes.

You’re right, there was not one problem with this gearbox, there were at least two that WCP has accepted, and indicated will be fixed for following seasons.

What is it that we were doing to push these “boundaries” which you failed to demonstrate us pushing in our implementation of this gearbox in a West Coast Style Drive train with 8 wheels? - For the record, that is our drive setup.

I will concede not being clear about the setup, and will explain it. We had an 8 wheel drive with 8" (~7.85") Pneumatic wheels. The gearboxes directly drove the “rear” two wheels. The rest of the wheels were belted together using 15mm HTD belt on 42T pulleys. The wheels immediately in front of the gearbox were driven with a belt from the gearbox itself, (the pulley was placed on the inside of the gearbox ie. between the two plates)

The post I made was simply to alert teams about the problem we had, and if any teams had similar experiences to make posts in the time during which I was able to gather more information about the failure and pictures, rather than making a somewhat incomplete post about the details of our issues.

It’s pretty easy to criticize a team for improper implementation of something from an anonymous account without detailing how the implementation was pushing boundaries of the product.

I will happily send you pictures and video (if you like), of our setup along with answers to any questions you may have of our implementation so you can demonstrate how we have pushed the boundaries of this gearbox, we’re eager to learn! :slight_smile:

For the record, expect a supplementary post with pictures of the failure on our other gearbox, and that a report to WCP has infact been in the process of being prepared, and has not yet been sent as we are still getting pictures of the failure and find it mindless to send a company a primitive report with not enough information about the issue, and would rather send something they can use to fix these issues.

You must not regularly check these sorts of posts much. In my 10 years on CD, I have found the vast majority of these “hey, here’s what i’m seeing with my XYZ product. Can anyone help me out.” posts are VERY productive. Most, if not all, FRC suppliers have a strong CD presence. It allows suppliers and the community to have discussion and resolve problems quickly. Very little “complaining” happened on this thread and that’s par for the CD course for this type of post. CD has lost some of it value for me the past few years, but it still working well for posts like this.

It’s not just WCP gearboxes. Our vex 3cim ball shifter had a similar failure last weekend. See the attached photo of the 1st stage gear.
Google Photos

I’ll buy that it’s a motor mounting issue. We may not have had the cims bolted tightly, especially as we were fighting screw lengths and the cimcoder on one. This hasn’t helped my engineering distrust of aluminum gears though.