VEXPro - After the season

[Donut]

We used the 8" VexPro Mecanum wheels this season with 1/2" round keyed VersaHubs and were pleased with them. Our robot only competed in 1 regional event but we never had to use any of our spare wheels or rollers. Our students loved not having to spend hours assembling them like last season and I loved the multi-pound weight savings we got in our drivetrain by switching.

And for reference, they just barely fit on the Andymark Nanotube output shafts for direct drive (I don't think we had to get the longer shafts, but that was a while ago).

[topgun]

We had several of the VersaPlanetary gearboxes on our robot and we liked the easy configuration between shaft output types and the multiple motor inputs.

The biggest issue we had with a couple of them was we stripped the hexagon socket set screw that tightened onto the motor shaft. I haven't determined if this was the students using worn hex keys, incorrect size hex keys, or what. If we tried to take the set screw off, the internal hexagon socket became damaged so that we couldn't remove the set screw. Maybe a different quality set screw would eliminate this problem.

[Richard Wallace]

Originally Posted by topgun

The biggest issue we had with a couple of them was we stripped the hexagon socket set screw that tightened onto the motor shaft. I haven't determined if this was the students using worn hex keys, incorrect size hex keys, or what. If we tried to take the set screw off, the internal hexagon socket became damaged so that we couldn't remove the set screw. Maybe a different quality set screw would eliminate this problem.

We used several VP gearboxes this year. On some (but not all) we found that an M2.5 hex key fit better than a 3/32", which is the size indicated in Step 3 on p. 8 of the VP User Guide. Probably a higher quality set screw would help fix this variation.

[AllenGregoryIV]

Originally Posted by Richard Wallace

We used several VP gearboxes this year. On some (but not all) we found that an M2.5 hex key fit better than a 3/32", which is the size indicated in Step 3 on p. 8 of the VP User Guide. Probably a higher quality set screw would help fix this variation.

We have been using the M2.5 for most of ours and they have't stripped at all. I'm probably going to find a source for better set screws in the future and just replace them all.

I've also found some other variations in the gearboxes. I think we have bought around 12 of them and on occasion they don't have the alignment peg thing at all in one or two of the stages. We also had one of the snap rings come off and drop our shooter wheel to the floor. It was a quick fix but it did happen once. Like I said before they amazing and I wouldn't trade them for the world but they do have the occasional small problem.

[JesseK]

Preliminary Data:

Single Speed 12:64 Gearboxes with 30:50 VEXPro Gear post reduction
The didn't go together smoothly -- the 3/8" bearing wouldn't accept one side of the output shaft and the 1/2" hex bearing was too snug a fit for the other end of the shaft (started stripping the annodization off the hex corners). Used AM bearings in both cases to solve it. On the two VEXPro gears after the gear box, the annodization is wearing off fairly quickly -- possibly due to imperfect alignment, but the wear is even across the teeth. Will probably use the double reduction gearboxes next year, even though I liked the versatility of choosing custom gear ratios. Or we might use Gates or AM belts. Who knows. We really like all of the mounting options of this gearbox though.

22T Hex-bore Sprockets
We are using these in our drive train, geared for 12 ft/s. It's a typical 4WD WCD, with these sprockets transmitting power from front to rear in a 1:1 ratio. We've been hit hard twice, and both times had one of these sprockets eat itself a few seconds later while driving. It'd be nice if someone also offered a steel version that was hex broached. The first time we thought it was because the wheel block slid on the impact; the second time we verified that the block didn't move (so the chains were in proper tension the whole time).

Hex Shafts
We got the hex shaft stock, then sized them for our WCD drive train. Found that the shaft isn't perfectly straight nor an exact consistent diameter even over short runs, meaning that it doesn't "just work" with the hex broached VEXPro items. Sanding down the corners helped. Could have been a shipping / temperature thing. We have had the same issues with every hex shaft stock we've purchased. Imperfections were on about 50% of the shaft length, so about half of our shafts still have their nice annodized corners.

VersaPlanetary (Single Stage)
Used with BB-550 and AM-9015. Aggravated with the assembly. We're swapping a 550 out for a 775 to get a better PID responds on our tilt, so we'll see how the assembly works there. We also stripped a 9015 collet when a disc jammed early in the season, rendering the piece useless. We had a spare from the other transmission we got, which was a plus. I do like the interchangeable gears.

Versahubs
It's nice that the bolt pattern remains the same. It's kinda funny -- we have this hub and an AM hub on the shooter wheel since that was the best spacing configuration . Very nice for quick prototyping overall. We enlarged the holes for a #10 bolt since those are the smallest bolts we have in enough variety of sizes to do the prototypes.

Generally a mixed bag. May have more to say after Chesapeake & Champs.

[Jared Russell]

As a meta comment to all FRC suppliers this year I will say that one of my bigger frustrations has been with all things hex.

Finding straight, well-toleranced hex shaft that has a decent fit on runout- and wobble-free hex bearings/gears/sprockets has been a real pain. We had to mix and match hex products from VexPro, AndyMark, West Coast Products, and McMaster (and re-broach/clean up some pieces ourselves) to make assemblies that we could slide together while still being mostly runout/wobble free.

[Akash Rastogi]

Originally Posted by Jared341

As a meta comment to all FRC suppliers this year I will say that one of my bigger frustrations has been with all things hex.

Finding straight, well-toleranced hex shaft that has an decent fit on runout- and wobble-free hex bearings/gears/sprockets has been a real pain. We had to mix and match hex products from VexPro, AndyMark, West Coast Products, and McMaster (and re-broach/clean up some pieces ourselves) to make assemblies that we could slide together while still being mostly runout/wobble free.

Quoted for truth.

[thefro526]

Originally Posted by Jared341

As a meta comment to all FRC suppliers this year I will say that one of my bigger frustrations has been with all things hex.

Finding straight, well-toleranced hex shaft that has an decent fit on runout- and wobble-free hex bearings/gears/sprockets has been a real pain. We had to mix and match hex products from VexPro, AndyMark, West Coast Products, and McMaster (and re-broach/clean up some pieces ourselves) to make assemblies that we could slide together while still being mostly runout/wobble free.

Just to elaborate on Jared's Post really quickly.

From what we've found (along with many others), aluminum hex bar tends to run a few thousandths oversize, usually somewhere in the .501-.503 range - a quick sanding with an Emory cloth or similar usually fixes this problem so it's not that big of a deal. Interestingly enough, 2024 Hex bar from McM does not seem to have this issue though as it runs a consistent .499-.500 over it's entire 3' length or so with very little run out. (at least the handful of pieces we've gotten)

Hex broached parts on the other hand are a completely different ball game. From what we've seen, WCP's parts run the tightest hexes at .501-.503, VexPro's hexes run on the larger end at .505-.507, and AM's stuff seems to be right in between the two. For some stuff, the difference in the broaches isn't a big deal, but if you're chasing backlash, that extra 5 thou in a gear's bore can get really annoying....

[Cory]

Originally Posted by JesseK

22T Hex-bore Sprockets
We are using these in our drive train, geared for 12 ft/s. It's a typical 4WD WCD, with these sprockets transmitting power from front to rear in a 1:1 ratio. We've been hit hard twice, and both times had one of these sprockets eat itself a few seconds later while driving. It'd be nice if someone also offered a steel version that was hex broached. The first time we thought it was because the wheel block slid on the impact; the second time we verified that the block didn't move (so the chains were in proper tension the whole time).

I'm pretty confident this is something caused by your design, not a defect or inadequate material. We have used 7075 22T sprockets for 7 years (of our own design, or from AM) with no failures whatsoever. 7075 is stronger than many steels, including some commonly used in sprockets.

Originally Posted by JesseK

Hex Shafts
We got the hex shaft stock, then sized them for our WCD drive train. Found that the shaft isn't perfectly straight nor an exact consistent diameter even over short runs, meaning that it doesn't "just work" with the hex broached VEXPro items. Sanding down the corners helped. Could have been a shipping / temperature thing. We have had the same issues with every hex shaft stock we've purchased. Imperfections were on about 50% of the shaft length, so about half of our shafts still have their nice annodized corners.

We have had the straightness problem with the majority of our hex shaft. We're almost 100% certain it is because it is shipped in a flat package that is extremely non rigid. A switch to round cardboard tube (like McMaster ships all shaft/rod/tube in) would likely eliminate this problem. We have not had issues with VEXPro gears sliding onto straight shaft though.

[FrankJ]

Planetary gearboxes are great.
Love the versa wheel hub system along gears & sprockets.
We ran 6" mechanums on a relatively light robot (100lb without battery/bumpers). Lost a roller on the comp bot & 2 rollers on practice bot. (Did I say I love being able to buy spare rollers? Change out is fast. I not really sure of the failure mode.
Love the fast shipping & customer service.

[fox46]

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.

[thefro526]

Originally Posted by fox46

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.

[MichaelBick]

Originally Posted by fox46

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.

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.

[Richard Wallace]

Originally Posted by MICHAELABICK

... We have bought boraches for 3/8" and 1/2" hex, so we can hex anything we want.

^This.

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.

[Gregor]

Originally Posted by Richard Wallace

^This.

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.

Wow, I want hex shaft CIMs