What Drivetrain?

[MichaelBick]

Originally Posted by ablatner

Erm, west coast drives are a form (in my opinion the best form) of tank drive.

About them being the best, what do you qualify as WCD. They aren't the best for every team though. If I mainly used sheet I wouldn't be cantilevering wheels.

[Teamcodeorange]

We used a 6WD West Coast Drive this year for several reasons:

Note: we have a square robot (27.5" x 27.5")

1. The field had no raised obstacles, so no need for mechanisms like in 2010 or 2012 to traverse the field.

2. It gives you the widest wheelbase/track possible for the size. (I suppose wheelbase is debatable because of the dropped center.)

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.)

4. It gave us more room for electronics and other mechanisms because of how little space the entire drive system takes up.

5. The drive base is very maneuverable, the added ability to shift allows us to go around or under the pyramid quickly, in addition to being able to push through defenders.

I am sure there are other reasons, these are just the ones I can remember off of the top of my head.

[EricH]

Actually... Switching drivetrains is something you could get away with, IF you've planned correctly. For example, if you've got the extra hole(s) drilled already, it'd be relatively simple to go from 8WD to 6WD, or vice versa, or 4WD to 6WD, or 4WD to mecanum (with a pair of transmissions added). Planning correctly means that you built the robot to be able to switch--though it does not necessarily mean modularity.

330 did that back in 2005--the competition robot had an extra set of transmission slots so we could swap to mecanum from 6WD if we thought it was a good idea. The testbed--a Kitbot--ran mecanum. We didn't have the weight that year to switch. To this day, 330 has yet to run mecanum on a competition robot.

[IndySam]

Originally Posted by EricH

Actually... Switching drivetrains is something you could get away with, IF you've planned correctly. For example, if you've got the extra hole(s) drilled already, it'd be relatively simple to go from 8WD to 6WD, or vice versa, or 4WD to 6WD, or 4WD to mecanum (with a pair of transmissions added). Planning correctly means that you built the robot to be able to switch--though it does not necessarily mean modularity.

330 did that back in 2005--the competition robot had an extra set of transmission slots so we could swap to mecanum from 6WD if we thought it was a good idea. The testbed--a Kitbot--ran mecanum. We didn't have the weight that year to switch. To this day, 330 has yet to run mecanum on a competition robot.

The one year we did mecanum (logomotion) we machined our frame with holes to easily be able to add dropped center wheels if the mecanum didn't work. We were happy with it's performance because the ease of strafing to hang tubes and that games rules limiting defense.

This year we made major drivetrain changes at our second regional and we were inspected and driving by 2:00 on Thursday. It can be done if you plan properly and practice the change, a second robot is invaluable for this.

[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.