What Drivetrain?

[Jeffy]

Originally Posted by Teamcodeorange

3. Our drive base is very simple and easy to fix, just a piece of extrusion, bearing blocks, chain, and wheels. (Don't trust hex bearings.)

When you say extrusion, did you use something other than the normal 2X1 tubing?

Also whats up hex bearings?

[ablatner]

Originally Posted by Jeffy

When you say extrusion, did you use something other than the normal 2X1 tubing?

Also whats up hex bearings?

Not sure if this is what he was getting at, but I'll give it a shot. There have been a couple of issues with hex bearings this year. One of the main ones was simply supply. For a long period of time this season, hex bearings were completely sold out wherever you looked. There were also problems with the hex itself, which was often oversized or undersized.

1/2" hex bearings are sold out at VexPro and West Coast Products (although their store is down for maintenance). They used to be sold out at AndyMark, although it looks like they're back in stock with an order limit of 10.

[Teamcodeorange]

Originally Posted by Jeffy

When you say extrusion, did you use something other than the normal 2X1 tubing?

Also whats up hex bearings?

Yes, we use 1/8" 1 x 2 aluminum extrusion.

The hex bearings are a problem because they shouldn't exist, at least not for 4 dollars. It seems that the vex pro ones are just normal bearings broached to fit a 1/2" hex shaft. The problem with this is that the added force on the corners of the shaft crack the inner race and render the bearing useless. This happened to use every couple hours of driving in practice, and a 2 times in competition. If you use hex parts, do it with round bearings if at all possible. (you can machine down a 1/2" hex shape on 5/8th shaft)

[Adrian Clark]

Originally Posted by Teamcodeorange

Yes, we use 1/8" 1 x 2 aluminum extrusion.

The hex bearings are a problem because they shouldn't exist, at least not for 4 dollars. It seems that the vex pro ones are just normal bearings broached to fit a 1/2" hex shaft. The problem with this is that the added force on the corners of the shaft crack the inner race and render the bearing useless. This happened to use every couple hours of driving in practice, and a 2 times in competition. If you use hex parts, do it with round bearings if at all possible. (you can machine down a 1/2" hex shape on 5/8th shaft)

Has anyone else had this problem with hex bearings?

I'm curious because I know they're other teams that run WCD's with hex bearings and to my knowledge they don't have any problems.

How exactly were your bearings configured on your WCD? What was your bearing block setup like? How close together were your bearings? Did you do anything very different from the stereotypical WCD in your drivetrain?

-Adrian

[Gregor]

Originally Posted by Adrian Clark

Has anyone else had this problem with hex bearings?

I'm curious because I know they're other teams that run WCD's with hex bearings and to my knowledge they don't have any problems.

How exactly were your bearings configured on your WCD? What was your bearing block setup like? How close together were your bearings? Did you do anything very different from the stereotypical WCD in your drivetrain?

-Adrian

There was a lot of discussion about their issues this build season.

Here is an example of one thread:

http://www.chiefdelphi.com/forums/sh...d.php?t=111513

[Teamcodeorange]

Originally Posted by DampRobot

...

Originally Posted by Gregor

...

Originally Posted by Adrian Clark

...

I can only talk for the VEXpro bearings. I forgot to mention that the entire first batch we got was nowhere near concentric, the second batch was still not great but we didn't have the time to wait for more. The Andymark/WCP might not have the problem of cracking, but the VEXpro ones sure did. Next year we will definitely be using round bearings.

[Tom Line]

Originally Posted by Adrian Clark

Has anyone else had this problem with hex bearings?

I'm curious because I know they're other teams that run WCD's with hex bearings and to my knowledge they don't have any problems.

How exactly were your bearings configured on your WCD? What was your bearing block setup like? How close together were your bearings? Did you do anything very different from the stereotypical WCD in your drivetrain?

-Adrian

Yes. We destroyed probably a half dozen bearings in a non-loaded low speed application. We ended up not using that particular mechanism on the robot. However, the incidents of failure left us with a very low opinion of the current generation of hex-bearings.

Our application was single shaft non-cantilevered (supported by bearings at both ends). The bearings blew out sideways after the races cracked.

[DampRobot]

Originally Posted by Tom Line

Yes. We destroyed probably a half dozen bearings in a non-loaded low speed application. We ended up not using that particular mechanism on the robot. However, the incidents of failure left us with a very low opinion of the current generation of hex-bearings.

Our application was single shaft non-cantilevered (supported by bearings at both ends). The bearings blew out sideways after the races cracked.

That's amazing... I've never seen anything like it. We used hex bearings, and even Vex Pro hex bearings, on very high axial load, high torque and cantilevered shafts without any problems. Perhaps there was a bad set?

[Adrian Clark]

Originally Posted by Tom Line

Yes. We destroyed probably a half dozen bearings in a non-loaded low speed application. We ended up not using that particular mechanism on the robot. However, the incidents of failure left us with a very low opinion of the current generation of hex-bearings.

Our application was single shaft non-cantilevered (supported by bearings at both ends). The bearings blew out sideways after the races cracked.

Interesting. Were these were vexpro bearings?

[apples000]

The VexPro hex bearings are complete garbage. All the other parts from vex pro are well made, and designed with attention to detail, but the hex bearings are awful. We have an older robot for demonstrations that has a transmission that uses a hex bearing (not on a cantilevered shaft). For 6 years and thousands of cycles in competition and at demonstrations, the original hex bearing worked. Then, we took apart the mechanism for cleaning, and we decided to try out the vex pro hex bearing. After 3 cycles of the arm, the bearing failed completely.

[Teamcodeorange]

Originally Posted by Tom Line

Yes. We destroyed probably a half dozen bearings in a non-loaded low speed application. We ended up not using that particular mechanism on the robot. However, the incidents of failure left us with a very low opinion of the current generation of hex-bearings.

Our application was single shaft non-cantilevered (supported by bearings at both ends). The bearings blew out sideways after the races cracked.

Same as us. Bad bearings, don't do that.

[AdamHeard]

Originally Posted by Teamcodeorange

Yes, we use 1/8" 1 x 2 aluminum extrusion.

The hex bearings are a problem because they shouldn't exist, at least not for 4 dollars. It seems that the vex pro ones are just normal bearings broached to fit a 1/2" hex shaft. The problem with this is that the added force on the corners of the shaft crack the inner race and render the bearing useless. This happened to use every couple hours of driving in practice, and a 2 times in competition. If you use hex parts, do it with round bearings if at all possible. (you can machine down a 1/2" hex shape on 5/8th shaft)

Interesting. We have a lot of time on both our practice bots, and 4 events on comp. All on 1/2" hex bearings from AM; no failure or issue whatsoever.

[DampRobot]

I've never seen a hex bearing that came "out of the tube" with significant runout issues or race damage. We've bough bearings from AM, WCP and VP. That said, poor (read: >~.008 too tight) press fits, mishandling, or excessive loads can damage the bearings. Especially damaging is when you press on the inner race while pushing the outer race into a too tight press fit.

I've never seen using 1/2" hex broached bearings per se as a problem, but there are a couple of hypothetical workarounds. First, you could turn down the 1/2" hex to 1/2" round to fit in a bearing (this would only really work if the round bit was at the ends, so it wouldn't work right for a traditional WCD). Also, you can press a 1/2" hex broached 1/2" ID 3/4" OD brass bushing into the inside of a 3/4" ID ball bearing. We've done somthing similar with 3/8" hex in a 1/2" bearing. A little excessive, but it would let you use 1/2" hex unmodified in a bearing that didn't have the inner race broached. Others have mentioned fine foxes as well.

To answer the origional question, we did 4WD skid stear. It was solid but not excellent.