VEXPro - After the season

Can I ask a question–

Why is everyone using hexagonal shafts? What’s wrong with a simple 1/8" keyway?

They’re cheaper, easy to DIY, fit standard bearings, hubs etc.

In a perfect world* hex makes things much easier to assemble and disassemble, decreases total parts count and in some applications, is stronger/more resilient than a similar application.

Having used keyed components in the past, one of my biggest fears with keys is always losing the keyway during rushed assembly or disassembly of the system. It got to the point where the team I was on began loctiting keys into shafts with the hope that they wouldn’t be lost in a pinch.

Beyond the lost key issue, there’s also the fact that having a key/keyway in a part creates a major stress riser. I’ve seen a handful of 7075 1/2" keyed sprockets fail in the same system, all of which (from what I can remember) failed/began failing at the keyway. I’m not saying that all keys/keyways are bad, they’re just not my thing.

*A perfect world being one where all hexes are the same size and hex bearings rain from the sky forever.

Hex shafts make assembly a lot easier. No need to deal with finicky keys. Hex is just as cheap as key shaft. It’s still very easy to do in shop, as long as you have a lathe(many teams do). It’s true that hex shaft does not fit standard bearings, but many times you can round the ends of the shaft. We have bought boraches for 3/8" and 1/2" hex, so we can hex anything we want.


For the first time in years with FRC teams (starting 1996), a team I am part of built a robot using NO KEYS at all. Everything is 3/8" or 1/2" hex. (Well, the CIM pinions are still keyed.)

I also really like the 1/2 tube shaft. It makes quick-change dead axle wheel set-up very easy. Our wheels this year are AM 4" performance with 32T #25 sprockets. We cut-and-faced our axles 2.5" long, then set up the sprocket axial alignment using ABS spacers parted to the correct length on one side of each wheel, with a shaft collar on the other side. A 1/4" bolt through the middle holds the wheel-sprocket-axle assembly in place between our slotted frame rails, and a simple two-hole tensioner adjusts the C-C distance to suit the chain length. Wheel changes are really fast and can be done without removing bumpers. It’s the little details that excite me. :]

Wow, I want hex shaft CIMs :rolleyes:

I forgot about the 1/2" tube shaft. Yes, that is extremely useful - with practice we can change out any drive wheel in about a minute.

Amen. I wish to heaven above that the major FRC suppliers (AndyMark, VEX, WCProducts) would get together and agree on some standards for their hex products that would allow them to fit together properly and interchangeably. Hand fitting parts went out in the late 1800’s, people. Hex shafting has the potential to be such a boon, and once everything is sorted and hand fitted, it’s great. But, that sorting and fitting process is incredibly frustrating. We really try hard not to swear in front of the kids, but when it takes two days to put together something that should take two hours, there is a lot of under the breath muttering going on.

I understand the desire to have standardized sizes but we must remember that these parts need to be cheep enough for us to purchase.

The tighter the tolerance the more the cost will go up, exponentialy.

The VEXpro 3/8" and 1/2" hex shafting was meant to do just that. They are designed as undersized shafting such that they fit into the hex bearings without the hand modifying.

The problem lies with the hex bearings themselves. We are working on this problem and we will reach out to AndyMark and WCP to standardize on the hex bearing size and tolerances since there is no standard for this in the bearing world today.

I am investigating the claim that the VEXpro 3’ hex stock was oversized, because this is the first time I have received that complaint about the hex being oversized.

Our QC department has checked hundreds of the hex shaft and they all come within tolerance. We checked all of our hex gears on this shaft and they all “just work”.

If there are cases where the shaft didn’t work with one of our gears, sprockets, or hubs, please contact me and we can work it out with you. A lot of additional time, tooling, and development effort went in to making a custom hex shaft that holds the undersized hex tolerance so that it just worked without hand sanding and filing. As a side note, my team used tons fo the 1/2" shaft and we did not have to hand file any of the shafts to work with the VEXpro gears, hubs, and sprockets.

With regards to straightness, the 3/8" shaft definitely has some bow. partially, this is due to shipping methods, but mostly it is due to the process by which the shaft is made and the length to diameter ratio of the shaft.

It is possible to get much straighter shaft if the length is around 12" per part. If there is interest in the shorter length for a tighter straightness tolerance, then I will have my team investigate the possibilities.


I was very impressed with the VexPro products we used. One of the things I appreciated most was the pricing. They started the whole thing… they lowered the price on the Victors/Jags and everyone had to follow. With quality, price and support, their site became one of my first choices when looking for parts.

What we used:

  1. Versaplanetary gearboxes - Awesome product. Love being able to design the mount interface quickly with the idea that we interchange gear ratios and motors at any time. Slight issue aligning a AM9015 motor on one gearbox but it was resolved.

  2. Gears - Very high quality, lightweight and strong 7075 AL, perfect. Used lots of these on our intake and shooter. Drilled and broached several of the 3/8" hex gears for a 1/2" keyed shaft on our shooter wheel.

  3. Hex Shaft, Bearings, Collars - It was very hard to find 7075 3/8" hex shaft at the start of the season, they had it. We used a ton of 1/2" hex shaft, with no problems. We ordered 40 VexPro bearings - not so good. The shaft fit fine but was off-center and wobbled. We ended up using them on our practice robot anyway after the global shortage of hex bearings. This and the AM bearings being too small had me questioning the whole hex thing… I’m sure it will all be worked out next year. Used several collars, very nice and lightweight.

  4. Pneumatics - While not VexPro products… I really appreciated the one-stop shopping and not having to spend hours figuring out the SMC and Festo catalogs.

Below is my VexPro product Wish List / Improvements for next year:

  1. 8mm keyed CIM to 1/2" Hex adapter from 7075 AL - we made several of these ourselves using the 1/2 hex shaft. Would buy them if they were available… the $10 AM product is steel and too expensive.

  2. Hex washers - we used these a lot of places, had our supplier laser out 0.050, 0.063, 0.090, and 0.125 thickness. VexPro has 0.125 delrin which is great… but need other thicknesses.

  3. More gears! - 11 and 14T CIM motor gears from 7075 AL would be nice. Also 45T 1/2" hex and more 3/8" selections.

  4. 1/4" flanged bearings and collars - we ended up with a bunch of these on our robot. There aren’t a lot of choices… the McMaster ones we used are pretty awful.

  5. Planetary gearbox shaft length - small thing but… we had to cut off the shafts and drill/tap the end hole on all the gearboxes we used. My first thought was that we could take them apart and put a snap ring groove on the lathe, but that was not happening, they don’t come apart. Would be nice to have a couple choices in shaft length or perhaps a few snap ring grooves to use instead of the end screw.

  6. Pneumatics - Single solenoid valve… would have bought several of these if available. Some air tanks would be nice as well.

  7. GT2 pulleys - 9mm 1/2" hex AL and/or plastic pulleys would be sweet. Out with the chain… belts are here to stay.

  8. Wavy washers for 3/8" and 1/2" Hex - Not a big deal to buy from McMaster but goes along with the drive train theme and one-stop shopping is nice.

  9. Faster website - it’s designed well and nice but a tad slow.

All-in-all I think VexPro hit a home run for FRC with these products and with time will only get better.

An update from my post-the issues we were having with the motor mountings of the versaplanetaries coming undone seems to have been an isolated, onetime thing (probably due to my own lack of skill in tightening motors :smiley: ). However, we have recently been experiencing issues with a BAG Motor through a 1:1 having it’s set screw come loose…we’re gonna try replacing it to see what happens, but hopefully this doesn’t remain an issue…

versaboxen: i love them. great planetary gearboxes. totally worth the money.

hex shaft, sprockets and other related hardware: haven’t had a problem. like the tooth count on the sprockets only thing i don’t like is the black shaft hides sharpie marks…

verawheels: i don’t know what my team did wrong but our versa wheels lasted about an hour of practice driving and 10 matches before they were balded and had to be replaced. picture

Could you describe your drivetrain and driving conditions?

That’s remarkable wear on those wheels. Is there any chance your practice field is on cement rather than carpet?

Sean, we were probably a good match there because we have similar setups :yikes:

2729 used the 8 wheeled (Versawheels) Drive in a Day chassis with the 5.33:1 single speed transmissions each driven with 2 CIMs. We basically followed the recommended setup process and had something together in no time. It took us a little while to get the recommended encoders, it would be nice if they were sold with the gearboxes as an option.

There was some maintenance we had to follow-up with down the line. We replaced the wheel alignment shaft collars with PVC spacers after seeing them start to shift. It is also on our check list to take a look at the CIM motors to make sure they are tight to the transmissions before we found a solution to the problem.

Sharpie does make a silver pen, which works well in this situation. They also have a line of paint pens.

All of my wat is this?

  • Sunny G.

I don’t know how realistic this is, but PLEASE. I don’t even care if they’re slightly more expensive (though I know others might), this would have simplified our drive train so much.

I love belts, but chain is just so much easier for my team to do (not that we can’t-- we did it this year with quite a bit of success, it was just a pain along the way).

I feel so odd for getting as excited as I am over this concept.

4wd 4cim 10fps all wheels were versawheels. drive conditions were, about an hour on carpet similar to FIRST field carpet and 10 matches…

Our experience with the Vexpro products:

Ball shifter gearboxes
Pros: Compact, light, and in our experience they shift more quickly than dog clutch shifters. They were also easier to mount than the AM Shifters we used last year.
Cons: The output shaft came out! Please fix this. We had to pin our shafts (through a hardened steel shaft housing, mind you) to prevent this from happening. It would be great if IFI could implement a mechanical connection between the steel housing and the hex shaft that would be removable so we could swap out shafts of different lengths. One of our steel shaft housings also had a hairline fracture on it, but this seems to be an anomaly. The encoder gear press fit is not very good, and eventually it was so slippy in the shaft that we couldn’t use it without supergluing it in. Finally, it would be nice if we could have different spreads that outputted at appropriate speeds. The way they are now, the output speed is only appropriate for direct-driving very small wheels, without a third stage.

Mini-CIMs are awesome. BAG motors work pretty well (we didn’t have failures with ours like some other teams did), but I wish they were a bit more powerful, perhaps on par with a 550. Side note: if you stall a BAG motor for a really long time, as we did in Madera, it’ll burn out and smell as bad as anything you’ve ever smelled in your life. Sort of a sickly sweet fruity vomit smell.

Pros: Very easy to adapt motors of all types, even CIMs and Mini-CIMs if you need to. Swapping out gear ratios is very easy, as is swapping output shafts. We’re never going back to BaneBots planetaries.
Cons: It’s so hard to get 550s concentric! I know there’s some play in the face plate mounting holes, but it doesn’t work amazingly well. It shouldn’t be that hard for IFI to include a plastic or aluminum centering ring with the gearboxes, like some teams have made themselves. Also, it would be nice to be able to put a CIM or Mini-CIM on a planetary without butchering it.

Gears, Bearings, and Shaft Collars
Flipping fantastic.

Pros: They work well, when they work.
Cons: They’re so bent, all the time. Out of five 3/8" shafts we received today, only two were within a straightness tolerance that we could use. This is fairly representative of all the shafts we bought during build season.
The 1/2" shafts are better, but not too much better – one of three shafts we received today was bowed noticeably. We would happily buy 18" long shafts (12" might be too short for many purposes) if they were straighter.

Can you also supply single-ended solenoid valves, please? Everything else is great, and easy to purchase.

(Disclaimer: we didn’t use these on our robot; only bought 1 with hubs for testing, so take this with a grain of salt. I also can’t speak to durability over a season.)
Pros: Very cheap, easy to put together, and grips very well…
Cons: In one direction. When pushed from the side, the wheel slides without much resistance. Given that when we play defense, we often block with the side of our robot, this is an issue. Perhaps this could be helped by offsetting the W pattern like so:

Of course, this would probably make the wheel more expensive.