pic: The worst of the stripped VexPro gears



As promised, the two extremely destroyed gears from our VexPro gearboxes. HUGE thanks to Cory and the guys from 254 for helping us out with some new 24T gears.

You still have teeth left!

It seems to be a common problem with cantilevered pinons on the final reduction of drive gearboxes like the one on the Vex Pro 3rd stage. I wouldn’t blame it on the gear. I still would like to see some changes to the Vex 3rd Stage though.

Few games in FIRST have this much wear and tear on robots, nor require large diameter wheels. Vexpro has designed a great product to fit the usual requirements of robustness for the average game. This game puts the components to their maximum stress and in my opinion is a testament to how good vexpro’s product is.

Though this is not really Vex’s technical issue:

I’d like to see Vex acknowledge it publicly.
I’d love to see Vex turn this into a teaching moment by showing with math how to determine the gear load limit.
I’d like to understand if Vex has more 20/24 gears.

Okay so the students are potentially building gear grinders. Why do they have no source for the spares?

If Vex misses this teaching moment it would be no more frustrating than other such opportunities in FRC where those moments have been missed. However I’d like to see incremental improvement.

As I mentioned in the first thread on this topic: This is the best demonstration of why to traction-limit drive gearboxes.

In over 3 years and over 100 VP gears and 9 VP gearboxes, we have lost teeth on exactly one gear: the small gear on our 2014 choo-choo mechanism. It was totally our fault, we had way too much tension on the system (at least 500lbs), but it made it all the way through the season before it failed in an off-season event.

Obviously I can’t speak for every VP gear that’s made, but it might be worth at least considering that you may have a problem with your specific implementations, and not with the gears themselves.

Once I get the pictures, I can show you what happened to our 3 cim ss Vex pro gearboxes. For the 8 inch wheels, we used the 60:14 gear kit. This was to keep everything in just two stages.

During the Hartford District event one of the 14t gears in our drivetrain completely broke. All that is left are 3 teeth and two halves of the gear.
then during Champs, both sides broke in the same match. Luckily, it was our last match of the day and had plenty of time to fix it. We replaced the 14t gears with steel variants (a mix of Andymark and VP) and so far so good.

Then you remember that this game is rougher than aerial assault.

This was our first year we used v-belt rather than chain or timing belts with idlers to control slip. Very happy with the results. Sometimes slip is good…

Cbale2000 posted about it, so I guess it’s my turn.

Personally, I’d like to see us really understand the failure, because maybe as a community we can help VexPro understand the issue and solve what, at this point, is not a uncommon problem. This presents an opportunity to show VexPro what we need what the bounds of our use case are.

As a supplier, at some level, the needs of the customer and the use case for the component need to be considered. I’m not suggesting that didn’t happen, but I am suggesting that multiple, multiple failures indicate there’s a problem, likely worthy of a fix.

I’m all for teams taking accountability when they use COTS components improperly, but using a gearbox designed to be a part of an FRC drive train in an FRC drive train isn’t something to apologize for or be shy about in terms of customer service situations.

If what a number of folks are saying is true, why isn’t there a specification for strength provided, like the shaft torque spec on the AM PG series gearmotors? I know the idea that a product needs to stand up to every possible use case is silly, but none of the reported failures have been that far outside the realm of what I would consider typical use for a gear box in FRC.

I’m still of the opinion that angular misalignment has to be related to these failures. It drastically reduces the apparent face width of the gear and as a result can initiate failures. Coupled with such a brittle material there’s no reasonable expectation that the gear would survive. The question then becomes, what is the source of the misalignment.

As a bonus, here’s a handy reference:

http://www.faculty.fairfield.edu/wdornfeld/ME312/ToothLoads04.pdf

Did anyone destroy steel gears in the final stage of the VexPro ball shifters?

Just curious.