VEX Pro vs. AM Bearings

[ToddF]

We don't have experience with the VEX bearings, but do have experience with AM hex bearings. This fall we converted our summer developed dead axle WCD to a live axle design, using hex axles. We ordered a bunch of hex bearings from AM for our bearing blocks. We found them to be frustratingly undersized. We are using standard 7075 1/2" hex extrusion for our axles and AM hex output shafts to direct drive the center wheels. We found that the AM bearings didn't even fit their own hex shafting. This led to hours of hand working the hex shafting to get everything to fit. Using a belt sander to resize the hexes resulted in scrapped axles from taking too much material off.

For our build season drive train, we ordered hex bearings from WCProducts. Whereas in the AM order, 2 of the 14 bearings fit our shafts, in the WCProducts order, 2 of 24 bearings are undersized. Most slide right on our shafts, and if they are snug, a few swipes over sandpaper to get the shaft faces planer (extruding leaves high spots in the faces) gives a good fit.

So, if you are having problems with AM bearings being too tight, or VEX bearings having too great of runout, try the WCProducts bearings. If we had not done so, we would probably abandon hex shafting as too labor intensive a system to be truly useful.

I should also point out that customer service for all these companies is great about replacing parts that don't measure up. But in the world of FIRST robotics, returning bad parts for good ones is not an acceptable option during build season. Getting good parts from a supplier the first time can make the difference between getting your robot built early, having time to practice with it, leading to a great season, and finishing your robot in your pit at your first regional.

[Paul Copioli]

Richard,

Remember that we increased the size of the hex in order to accommodate various larger hex stock. If used with the VEXpro shaft there could be as much as .001 gap between the flats of the hex shaft and flats of the bearing

The only true way to get runout indication is clamping the output and rotating the input.

We will perform this test on samples this Monday.

[Paul Copioli]

Originally Posted by jsasaki

Thanks for the reply Paul. Definitely will contact VEX asap. I just want to clear up with you that the VEX Pro bearings were in fact not concentric as you can see in this video at 0:27. I'm just hoping it was a small batch error but no matter what setup the bearings are in, it just wont work.

Yep, that is not normal. Call customer support today and give them your order number. We will send you new ones immediately ... After we inspect our inventory. When you get the new bearings there will be a shipping label, please ship the product back to us with the ram number we provide.

Paul

[Richard Wallace]

Originally Posted by Paul Copioli

Richard,

Remember that we increased the size of the hex in order to accommodate various larger hex stock. If used with the VEXpro shaft there could be as much as .001 gap between the flats of the hex shaft and flats of the bearing

The only true way to get runout indication is clamping the output and rotating the input.

We will perform this test on samples this Monday.

Paul, you are right.

I did the TIR check just for my own curiousity. Actually, the VEXPro 1/2" hex shaft I used was quite a tight slip fit for the bearings -- needed firm hand pressure to get them on. If there were as much as 0.001" clearance I would have been able to feel that. Anyway, the TIR that I saw is consistent with "good" ABEC 1 bearings, in my experience.

Nonethless, you are right about clamping for true runout tests.

[Paul Copioli]

Originally Posted by ToddF

We don't have experience with the VEX bearings, but do have experience with AM hex bearings. This fall we converted our summer developed dead axle WCD to a live axle design, using hex axles. We ordered a bunch of hex bearings from AM for our bearing blocks. We found them to be frustratingly undersized. We are using standard 7075 1/2" hex extrusion for our axles and AM hex output shafts to direct drive the center wheels. We found that the AM bearings didn't even fit their own hex shafting. This led to hours of hand working the hex shafting to get everything to fit. Using a belt sander to resize the hexes resulted in scrapped axles from taking too much material off.

For our build season drive train, we ordered hex bearings from WCProducts. Whereas in the AM order, 2 of the 14 bearings fit our shafts, in the WCProducts order, 2 of 24 bearings are undersized. Most slide right on our shafts, and if they are snug, a few swipes over sandpaper to get the shaft faces planer (extruding leaves high spots in the faces) gives a good fit.

So, if you are having problems with AM bearings being too tight, or VEX bearings having too great of runout, try the WCProducts bearings. If we had not done so, we would probably abandon hex shafting as too labor intensive a system to be truly useful.

Todd,

I am sorry about your troubles with the hex bearings. You will have the same troubles with VEXpro hex bearings as we decided to make them the same nominal size as the AM bearings. WC Products decided to make their bearings larger to accommodate the standard hex shaft.

We chose to solve the problem differently. Standard hex shaft as a really large tolerance of almost +.005". Practically most shafts come in at +.003". We decided the shaft was the problem so made a custom hex shaft that is sized appropriately to fit in both the AM hex bearing and the VEXpro bearing both in 3/8" and 1/2".

I can't really speak for WC Products or AM, but we made a conscience decision to make out bearings the same nominal size as the FRC industry standard.

Paul

[ToddF]

Thanks for the info, Paul. We'll take a close look at your stuff for next summer. I somehow missed your vex pro product line until the start of this build season, but I like what I see.

We are attempting to move into the mode of students and mentors working during the summer on drive train development, using as much COTS parts as possible. During the fall we work on skills training for new members, and getting everyone intimately familiar with the hardware. We also pre-purchase all the COTS stuff we think we may need, to avoid the build season rush. Then when build season hits, we tweak our previously developed drive train to work with the game and execute as quickly as possible. This year, we will have a running drive train in less than 50% of the time it took last year, even with the smaller size limitations.

We are trying to raise our level of competitiveness by taking FIRST robotics from a build/competition season activity to a develop/train/build/compete activity that engages students year round.

[jsasaki]

Originally Posted by Cory

I would be interested in more details.

Did the VEX bearing stick before you pressed it in your bore? If not, it's possible (if not probable) that your bore could be too tight, or you pressed it in and indented the shield, or somehow damaged the race/ball interface.

Did you try an AndyMark bearing in the same bores that you displayed the runout in your first shot? Did you independently chuck the shaft and hub in a lathe/drill press/something else that spins to verify that each component spins true? Without all 3 of those actions, there's no way of isolating the problem to your bearing.

The bearings fit on the VEX .5" hex shaft snug. On a cnc'd one piece bearing block the shaft would not go all the way through. I've tried most of the bearings and both VEX Pro and AM hex shafts.

[jsasaki]

Originally Posted by ToddF

We don't have experience with the VEX bearings, but do have experience with AM hex bearings. This fall we converted our summer developed dead axle WCD to a live axle design, using hex axles. We ordered a bunch of hex bearings from AM for our bearing blocks. We found them to be frustratingly undersized. We are using standard 7075 1/2" hex extrusion for our axles and AM hex output shafts to direct drive the center wheels. We found that the AM bearings didn't even fit their own hex shafting. This led to hours of hand working the hex shafting to get everything to fit. Using a belt sander to resize the hexes resulted in scrapped axles from taking too much material off.

For our build season drive train, we ordered hex bearings from WCProducts. Whereas in the AM order, 2 of the 14 bearings fit our shafts, in the WCProducts order, 2 of 24 bearings are undersized. Most slide right on our shafts, and if they are snug, a few swipes over sandpaper to get the shaft faces planer (extruding leaves high spots in the faces) gives a good fit.

So, if you are having problems with AM bearings being too tight, or VEX bearings having too great of runout, try the WCProducts bearings. If we had not done so, we would probably abandon hex shafting as too labor intensive a system to be truly useful.

I should also point out that customer service for all these companies is great about replacing parts that don't measure up. But in the world of FIRST robotics, returning bad parts for good ones is not an acceptable option during build season. Getting good parts from a supplier the first time can make the difference between getting your robot built early, having time to practice with it, leading to a great season, and finishing your robot in your pit at your first regional.

We will check around for all of out products but the AM shaft does states on their website with the .5" hex shaft "This dimension is slightly larger than the bore for the 500 Hex Hub and 1/2" Hex Bearing. In order to make this material fit into the hub or bearing, we suggest that the user slightly modify the hex stock. We have found that the best way to do this is to use a belt sander and carefully sand off a small amount of each side of the hex stock until the stock fits into the Hex Hub or Hex Bearing."

small tolerances are manageable but this was just not working out for us.

[jspatz1]

We are experiencing this wobble in our shaft/bearing/wheel assemblies also, and it is pretty severe. With some experimentation we are confident the problem is with the hex hubs, and is not confined to just the bearings, although they may be contributing. We believe the hex broach is not square/perpendicular, and also possibly not concentric.

To test this we put two plate sprockets, each mounted on their own hex hub, side by side on a spinning hex shaft. Both shafts wobble, sometimes in sync with each other, sometimes opposite of each other. When one is removed and rotated to a different position relative to the other, the wobble with respect to each other changes. This would happen if the hex broach in one or both were not perpendicular.

As a second test we take a wheel assembly with hex hubs and spin it on a bearing-mounted shaft. It wobbles. We note and mark the location of the high points of the wobble. We then put the same wheel on a different shaft and different bearings, and the wobble is identical. This would be the case if the wobble was in the wheel/hub assembly. This same wheel spins true when it is fitted with round bearings, so the wobble is in the hubs, not the wheel.

We also see the hex shafting is not straight. A shaft segment laid on a surface plate will rock in some orientations, and not others.

It is difficult to assess the contribution of each of these factors (bearings. hubs, shaft) but we believe the squareness/concentricity of the hex hubs is the primary problem.

Teams experiencing this problem may want to duplicate these tests and look further at the source of the wobble. In our case it is not just the bearings.

[Tristan Lall]

Originally Posted by jspatz1

We are experiencing this wobble in our shaft/bearing/wheel assemblies also, and it is pretty severe. With some experimentation we are confident the problem is with the hex hubs, and is not confined to just the bearings, although they may be contributing. We believe the hex broach is not square/perpendicular, and also possibly not concentric.

Which models of hex hubs, bearings and shafts are you using?

[jspatz1]

Originally Posted by Tristan Lall

Which models of hex hubs, bearings and shafts are you using?

The VexPro hex shaft stock, hex hubs, and bearings.

[Paul Copioli]

We are experiencing this wobble in our shaft/bearing/wheel assemblies also, and it is pretty severe. With some experimentation we are confident the problem is with the hex hubs, and is not confined to just the bearings, although they may be contributing. We believe the hex broach is not square/perpendicular, and also possibly not concentric.

If you are experiencing these issues with any of your components please contact customer support and we will replace them

With that said, we have tested all the hubs that we have in inventory and we do not see this issue. In addition, we have not seen this issue with the shafts that you describe.

In any case, return the items you think are not to the appropriate dimensions and we will replace them.

[jspatz1]

Originally Posted by Paul Copioli

If you are experiencing these issues with any of your components please contact customer support and we will replace them

With that said, we have tested all the hubs that we have in inventory and we do not see this issue. In addition, we have not seen this issue with the shafts that you describe.

In any case, return the items you think are not to the appropriate dimensions and we will replace them.

Yes, we will contact customer support and I am confident it will be fully resolved. Just unfortunate that we observed it on a Friday evening. I just wanted to share the observation so others can check their situation and check other factors than the bearing. It can be difficult to diagnose the source of the problem in a turning assembly.

[Grim Tuesday]

We have experienced this issue with our shifters as well. We think it might not be the bearings -- the shaft is slightly bent and the hole holding it is slightly too big. See video below:


http://youtu.be/sdGAuatJCqw

[Paul Copioli]

Originally Posted by Grim Tuesday

We have experienced this issue with our shifters as well. We think it might not be the bearings -- the shaft is slightly bent and the hole holding it is slightly too big. See video below:


http://youtu.be/sdGAuatJCqw

You guys have your bearing in backwards. The flange is supposed to be on the inside. We also noticed a problem where the standoff pockets are too deep. You will be receiving washers to fix this problem. The bearing is moving because it is not seated in the plate properly due to the reversed installation.

Please contact customer support to get more details.

Paul