Re: VexPro Bearings
 

I'm an advocate of getting the students to understand the reasoning behind selecting those bearings, and not just go with what vexpro uses. If that makes me a jerk or a bad person l, oh well. My life doesn't revolve around this forum.

I feel that it is odd for them not to post that information, especially since I know how much vexpro cares about making sure the students learn and understand engineering principles.

Re: VexPro Bearings
 

*blows ref whistle* Okay, okay. Now let's all take a deep breath and take a break for an hour or three. I've PM'd Aren Hill, and steeler emailed Vex and they've said they're working on information for this thread. I think we've all vented enough to express our opinions at this point, so let's wait for some data.

Re: VexPro Bearings
 

Kevin B.,

We actually have never been asked to put up the specifications on our web site. My team is working on getting the specifications for all of the bearings since most of them are standard ABEC 1 (or ISO 492 Normal Class for the Metric Bearings) bearings.

The total ratings (mostly the load ratings) have zero applicability in FRC for many reasons (I will make another more detailed post about this later), however the speed rating is important.

So, the Thunderhex bearing limiting speed is 31,000 RPM

The standard 3/8 and 1/2 hex bearing theoretical limiting speed is also 31,000 RPM.

However, the nature of hex bores make them oversized a bit in order to practically install the shaft. So there will be clearance between your shaft and the hex bearing (this is true with ALL hex bearings no matter who makes them or what they tell you). This clearance causes extra load at high speeds.

The reason you can only find AM and VEX (and at one point WCP) who make the 1/2" hex is because it is extremely custom for our application. Most bearing volume usage is for industrial, high precision applications and the Hex tolerance is unacceptable for that use case. For most FRC applications that don't involve high speed shooting, the hex has served us well.

Now, I absolutely despise hex bearings for many reasons. I almost despise them as much as mecanum wheels but that is a story for another day.


We wanted something more from a hex compatible bearing that could give us the flexibility of the hex bearing and the precision of a regular ball bearing.

For this reason, we decided to create the Thunderhex bearing. Bearing manufacturers are really good at making round things round with very little total indicated runout. As a matter of fact, no one does that better than bearing companies. However, they are not very good at making hex holes in bearings. We inspect 100% of our hex bearings to make sure they meet our drawings. The factory scraps about 20% of the hex bearings they manufacture for us before anything gets shipped because they do not meet our specs. The Thunderhex bearing scrap rate is below 0.1%. The reason is simple: Thunderhex bearings are just round bearings with a special inside diameter of 13.75mm.

So my recommendation is use Thunderhex shaft with Thunderhex bearings and you will never have an issue. By the way, for high speed applications we recommend a slight press fit between the bearing and the shaft in order to keep the system balanced at high speed.

The basic issue for high speed applications with Hex bearings is that the clearance to make the hex shaft install properly causes eccentric loads on the bearing which causes premature wear and higher loads on motors, which is the most probable reason you saw a speed difference.

So let me be clear, the VEXpro bearings all use standard industrial balls and bearing raceways and can attain the speeds of their industrial counterparts.

One last thing: my team does not use hex bearings anywhere. We use Thunderhex exclusively and Thunderhex shaft in most places. It has made life so much easier.

I hope this helps.

Paul

Re: VexPro Bearings
 

Thanks Paul!

Re: VexPro Bearings
 

This would be why I was questioning if steller was switching from hex bearings to plain round bearings. I knew hex bearings were not equivalent to round in some ways, though I didn't know the specifics.
And so much this. My team was claiming we were out of thunderhex bearings, so they swapped in some "normal" hex bearings. I informed them that the hex bore bearings were only for use as a last resort, and week 2 was not last resort time. Thunder hex just makes life easier. The real problem is that Versaplanetary outputs only come in true hex, not thunder hex. So i have to turn them down for any high speed applications.

Re: VexPro Bearings
 

Thank you Paul for the technical input. I also appreciate the prompt response from your team. It would be great to see the bearing spec ratings on the VexPro website, similar to how other suppliers provide a rating and similar to how you provide full disclosure on your other products (ie 775Pro).

This gives us confidence this year to continue using the product without modification to our design. We just started using thunder hex this year for intake rollers, drive train and shooter. The high RPM application was our only concern.

You mentioned getting the fit right is important when you turn down hex stock to use thunder hex bearings (13.775mm round). When using the thunder hex stock are there any tips and tricks to get the right diametrical clearance, understanding the oversizing from the manufacturer? When working on the lathe and a 3 jaw chuck we had to try a few times and experiment to get the fit a "slight press fit". As soon as the tool started removing material from the part was too much to get a press fit. We also tried a live center to keep it straight. It took a couple times and some scrap material to finally get it right. When we were able to turn down the shaft to achieve the correct fit the cuts were still inconsistent. This may have to do with the lack of eccentricity of the part vice thunder hex stock, I'm not sure how to get it perfect. It is unfortunate that the thunder hex stock still requires precision machining to get the "slight press fit". This burned a lot of our manufacturing time this year.

Is this something VexPro is looking to change in the future?

Thanks again for your help!

Re: VexPro Bearings
 

Did you try using some emery cloth instead of a cutting tool to take off the necessary material?

We've done that for all of our thunderhex this year and it just takes a few seconds. You could even chuck the thunderhex in a drill press, mill or hand drill and take off the necessary material with emery cloth, no lathe required.

-Mike

Re: VexPro Bearings
 

This. Since you are only taking off a couple 0.0001's of an inch you won't be able to hold that tolerance cutting unless you have a really nice lathe. We sand the thunderhex stock on the lathe with emory cloth until the axle turns a certain shade of silver and get very consistent results.

Re: VexPro Bearings
 

Have not tried Emory cloth to get the shaft to the right diameter. Seems like that might work better. Will give that a shot for the next few. The drive axles are made from steel hex so our only real option was to use a lathe and cutting tool to get the 13.75mm.

Re: VexPro Bearings
 

Emery cloth, the original finished to fit option for machinists of old. "Oh, it doesn't fit?" "Just work down the high spots a tad"

Re: VexPro Bearings
 

The Emory cloth is absolutely the way to go. Basically, we take off the anodizing on the round part of the thunderhex and it is a nice slip fit.

However, right now since the thunderhex is slightly oversized it is the perfect size for a press fit. We use our small arbor press to get the shaft in the bearings.

With that said, the Thunderhex used with thunderhex bearings is supposed to be a nice slip fit. The bearings are completely within our expected tolerance but the thunderhex stock is a few 10 thousandths large. This is large enough to make it a slight press fit. It is so close that when it is about 30-35 degrees here in Texas the shafts are a slip fit!

In any case, once we run out of the current inventory we will make sure the next batch is within our size requirements at 75deg F.

Paul

Re: VexPro Bearings
 

So... you're saying I just need to toss my shaft in the snow for a few minutes and it'll fit. Hmm, I wonder where I'll find that around here :p

Re: VexPro Bearings
 

Interesting, I'll have to remember this. Ain't thermodynamics great?