Help with swerve drive.

[Benj895]

This year we decided to try and make a swerve drive train. It won't go on this year's robot, but we want to get it ready for next year. I've looked online and I have a basic idea on how to make it, but don't know the materials I need to do so. I am trying to achieve these constraints:

• Low cost
• Efficient (What's the best way to the chain the wheels together?)
• Light (What are the lightest materials that will work?)

If anyone has any information that may help in any way, I would greatly appreciate it.

[bkahl]

I would recommend these:

http://www.andymark.com/product-p/am-3009.htm

For the price, I just don't think they can be beat.

We found some ways to improve them too (thrust bearings, snap rings, etc.)

They're in no way a complete custom module, but for beginners at swerve, this low cost, simple COTS solution helps to get used to the system.

[Ether]

Originally Posted by Benj895

Efficient (What's the best way to the chain the wheels together?

If you chain the wheels together, it's not really a swerve.

[asid61]

Originally Posted by bkahl

I would recommend these:

http://www.andymark.com/product-p/am-3009.htm

For the price, I just don't think they can be beat.

We found some ways to improve them too (thrust bearings, snap rings, etc.)

They're in no way a complete custom module, but for beginners at swerve, this low cost, simple COTS solution helps to get used to the system.

+1. I want to work on some mods to that in the offseason too. It's extremely hard to beat that price, even if you make one from stock metal in-house, due to COTS parts prices.

[GeeTwo]

Originally Posted by Benj895

• Efficient (What's the best way to the chain the wheels together?)

Originally Posted by Ether

If you chain the wheels together, it's not really a swerve.

Agreed. Assuming that you're planning to point all of the wheels in the same direction with one chain, and drive them all at the same speed with a second chain, that's what's usually called crab drive on CD.

The big problem with this form of drive is that you don't have a good way for the robot to rotate (e.g. so as to face a game piece or goal). I've never seen a post which provides a name for a crab drive with a robot that rotates atop it posted, but in my own thoughts, I've dubbed it a dizzy drive.

[fr05ty27355]

Actually, crab drive can work just fine with turning as long as you set it up in either a square or wide configuration. If you chain together the steering of each module, then they will all turn together. For the actual driving, you simply have two different motors, one running each side of the drive train. This way you can turn just as if you had a normal 4 wheel drive setup.

This is the same idea, but here they split the steering into two sections.

[asid61]

Originally Posted by fr05ty27355

Actually, crab drive can work just fine with turning as long as you set it up in either a square or wide configuration. If you chain together the steering of each module, then they will all turn together. For the actual driving, you simply have two different motors, one running each side of the drive train. This way you can turn just as if you had a normal 4 wheel drive setup.

This is the same idea, but here they split the steering into two sections.

The main issue is that some maneuvers that are possible with full coaxial swerve drives are not possible with crab drives, such as rotating about the center of the robot while moving. The wheels need to move at different speeds at different angles to avoid scrubbing. If one is okay with the scrubbing or has a solution I'm not aware of, then it's fine.
If it's for a practice bot, going crab is easier but if you have the time and programming full swerve would be beneficial long-term. You can adapt a swerve to crab, I would think.

[GeeTwo]

Originally Posted by asid61

You can adapt a swerve to crab, I would think.

You can certainly down-program a swerve chassis to a crab performance.

[runneals]

If you're gonna build your own, take a look at ours and the thread that developed from it: here.

Our alumni mentor also further refined our design to work with the VEX Versachasis (which can be found here)

Bomb Squad has some nice ones that they are trained to use to the fullest.

We partially used swerve in 2012, and it hasn't returned to the robot since (and I don't think it will return anytime soon).

[asid61]

Originally Posted by runneals

If you're gonna build your own, take a look at ours and the thread that developed from it: here.

Our alumni mentor also further refined our design to work with the VEX Versachasis (which can be found here)

Bomb Squad has some nice ones that they are trained to use to the fullest.

We partially used swerve in 2012, and it hasn't returned to the robot since (and I don't think it will return anytime soon).

Your swerve was a really good one IIRC. Why did you elict not to use it again?

[Benj895]

Originally Posted by GeeTwo

Assuming that you're planning to point all of the wheels in the same direction with one chain, and drive them all at the same speed with a second chain, that's what's usually called crab drive on CD.

What I don't get is all the names being thrown around. I've heard swerve, swivel, ocelot and crab. Is there any difference? If so, what?