A Swerve Drive Question

[lndnny]

I've been doing research on the swerve drive design for some time now and can't seem to find an absolute answer to this question:

Can a four wheel swerve drive with omni-wheels rotate while translating?

I've read threads saying that swerve drives can only translate, but the SimSwerve whitepaper seems to disprove that. Thanks for your time.

Dan
Team 808

[AdamHeard]

Originally Posted by lndnny

Can a four wheel swerve drive with omni-wheels rotate while translating?

what do you mean by that line?

[Noah Kleinberg]

I haven't had any experience with swerve drives myself, but I believe that they can.

If you rotated the wheels so that diagonal wheels are parallel (like a holonomic drive), then it should be able to rotate and translate simultaneously.

P.S. A holonomic drive can rotate and translate at the same time, right?

[sanddrag]

why would you have a swerve (rotating wheel modules) drive with omni wheels?

[Jeff Waegelin]

Originally Posted by Noah Kleinberg

P.S. A holonomic drive can rotate and translate at the same time, right?

Correct. My team built one this past season, and, with the proper programming, it can rotate and translate simultaneously.

In response to the original post, you could theoretically design a swerve drivetrain that could do both... however, you'd probably have to make the wheels turn at a 45 degree angle to the corners, making it essentially a holonomic drive. However, why would you want to? In my mind, the biggest reason for choosing holonomic over swerve is the simplicity of construction. Going holonomic means no rotating wheel modules, which cuts down on weight and build time. You also gain the ability to rotate and translate at the same time. The programming, however, is considerably more difficult if you want your robot to drive in a straight line (we've still never quite perfected that). All those omniwheels also mean that your robot gets pushed around easily. Adding the extra programming and omniwheels to swerve just doesn't make sense to me. You lose power, and add a lot of complexity. One or the other is hard enough; don't drive yourself crazy trying to do both.

[Dave Scheck]

Originally Posted by sanddrag

why would you have a swerve (rotating wheel modules) drive with omni wheels?

After rereading your question, I think you're asking about a rotating module with an omni wheel mounted to it. The answer below answers the question of why would you mix crab and omni.

In 2004, we had crab on the front and fixed omnis in the back. You can see it in this picture. The treaded wheels are able to rotate and the omnis are fixed.

We learned from past experience (2002, 2003) that with 4 treaded wheels, zero-point turning was hard on the battery. In 2003 we ended up with a skid pad that was dropped pneumatically to turn quickly in place. In 2004, the omnis did the job. They allowed for quick turning, as well as crabbing with a little software magic.

[lndnny]

Originally Posted by sanddrag
why would you have a swerve (rotating wheel modules) drive with omni wheels?

I figured that rotating and moving would involve wheels at awkward angles to each other. The omni wheels would prevent scrubbing (bouncing).

Originally Posted by Noah Kleinberg
If you rotated the wheels so that diagonal wheels are parallel (like a holonomic drive), then it should be able to rotate and translate simultaneously.

I had figured you could just do that, but wondered if there was another way to do it. With a holonomic drive, isn't it best to have the wheels in a perfect square (or diamond)? The wheel modules in a design I've been working on are farther apart. I've been working on a swerve bot for the learning experience and as a cool demonstration robot .

Sorry I don't know how to do the quotes

Thanks
Dan
Team 808

[sanddrag]

What is your reason to put omni wheels on a crab/swerve drive? Is it so you can have 100% of your power going toward your direction of travel as opposed to 70% and still be able to rotate while translating? That's the only reasoning I can think of.

[Noah Kleinberg]

Originally Posted by lndnny

I had figured you could just do that, but wondered if there was another way to do it. With a holonomic drive, isn't it best to have the wheels in a perfect square (or diamond)? The wheel modules in a design I've been working on are farther apart.

They don't have to be in a perfect square, and not being in a square shouldn't make it much less efficient, but it might be harder to program it. See this thread for more: http://www.chiefdelphi.com/forums/sh...ad.php?t=38839.

[Stephen Kowski]

Originally Posted by lndnny

I've been doing research on the swerve drive design for some time now and can't seem to find an absolute answer to this question:

Can a four wheel swerve drive with omni-wheels rotate while translating?

I've read threads saying that swerve drives can only translate, but the SimSwerve whitepaper seems to disprove that. Thanks for your time.

well depends on how you have it set up if you can only translate. is it a synchronous drive swerve, or are the modules independent? if they are independent (a la 67) you can translate and rotate at the same time, but if it is setup like 71 you will only translate, stop, turn (like a 4wd skid), and translate again....

if you have the independent modules i would consult Ian's document that he presented at the 2006 championship where he described the kinematic equation for similar systems: http://www.chiefdelphi.com/media/papers/1836

[lndnny]

Originally Posted by Stephen Kowski
well depends on how you have it set up if you can only translate. is it a synchronous drive swerve, or are the modules independent? if they are independent (a la 67) you can translate and rotate at the same time, but if it is setup like 71 you will only translate, stop, turn (like a 4wd skid), and translate again....

Thank You, yes four independent modules
That seems to answer my question.

Dan
Team 808