What Drivetrain?

[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)

[EricH]

Originally Posted by MICHAELABICK

About them being the best, what do you qualify as WCD.

The "standard" definition of a WCD is a 6WD drop-center, cantilevered wheels, live-axle, center directly driven off of the gearbox (usually a 2-speed gearbox), outside wheels chain-driven off the center axle.

I don't necessarily agree that WCD is the best of the tank drives, partly because it does take some precision to make and thus might be rather difficult for some teams, but it is up there if a team can build it properly.

[cadandcookies]

What if your team switched drive trains through the season...

No, it didn't end well.

[Brandon Zalinsky]

Originally Posted by sentientfungus

What if your team switched drive trains through the season...

No, it didn't end well.

Last year, our team changed drivetrains at Championships. Try to avoid that.

[Niezrecki]

We use Six wheel drop center.

[Joseph Smith]

3539 used a 6w WCD this year. The past two years, we used 8 wheel standard tank drive, but this year we tried WCD to open up the inside of our frame for our ground intake and we were EXTREMELY happy with the results. Our drivetrain was easy to build, easy to maintain, rugged, light, and extremely nimble. We had a 1/8" drop on the center wheel, direct driven from our gearboxes. Custom 6" aluminum wheels with roughtop tread. We were geared for about 13 fps, so we were able to drive around most other robots on the field. We were very satisfied with the WCD style and will likely be visiting it in the future.

Here's a little video of our robot driving around at Troy. It was fun to watch this thing go
http://www.youtube.com/watch?v=gnDLFystS1Y

[ekapalka]

To the people selecting "other", could you explain? Thanks!
~

[Walter Deitzler]

Originally Posted by ekapalka

To the people selecting "other", could you explain? Thanks!
~

Our robot: http://www.chiefdelphi.com/forums/sh...=3397+Serenity

It runs two wheels in the front, a floating omni-wheel in the back. It does not really fit into any of the categories that were provided, I believe it is called a "kiwi" drive, which is not on the list.

If you want reason as to why we went with this design, all of the details are in the thread linked to earlier.

[Boe]

Originally Posted by LedLover96

Our robot: http://www.chiefdelphi.com/forums/sh...=3397+Serenity

It runs two wheels in the front, a floating omni-wheel in the back. It does not really fit into any of the categories that were provided, I believe it is called a "kiwi" drive, which is not on the list.

If you want reason as to why we went with this design, all of the details are in the thread linked to earlier.

A kiwi drive has 3 omni wheels all driven offset at 120 degree angles from each other the only team i know of that did one this year was 1425 but im sure there are others i havent seen. you can kind of see the drive in this video http://www.youtube.com/watch?v=jWGYa...ature=youtu.be

[Walter Deitzler]

Originally Posted by Boe

A kiwi drive has 3 omni wheels all driven offset at 120 degree angles from each other the only team i know of that did one this year was 1425 but im sure there are others i havent seen. you can kind of see the drive in this video http://www.youtube.com/watch?v=jWGYa...ature=youtu.be

We called our a "stingray" drive, due to the shape of the frame. I was just told by someone that it was kiwi, thanks for clearing that up.

[Ether]

Originally Posted by Boe

A kiwi drive has 3 omni wheels all driven offset at 120 degree angles from each other

The inverse kinematics for Kiwi are very simple and are shown here on one page.