Swerve with a twist
 

So after a discussion with my mentor about swerve drive, we thought of a potentially new drive system that is swerve like but a bit different.

What we pictured was a swerve module where the wheel was extended out from the center of rotation.

(top view- The o represents an axle going through the computer screen).
_
| |
| |---o
|_|

When the wheel is powered, and the o axle is prevented from spinning (perhaps using a brake system), the robot would move in the direction the wheel is spinning.

When the wheel is powered and the o axle is allowed to freely rotate, the wheel would turn in a circle, and could end up pointing in a direction you want it to.

With both those combined, the robot could have holonomic drive capabilities.

The biggest problem I see with this is the weight distribution, as the force would be on the o axle, which would not be touching the ground (or maybe it could hmm...). I also dont see this as very practical for an FRC game, because swerve would probably be much faster at orienting itself.

But this drive system would make every swerve module require only one motor and one braking system, which in some industrial applications, could be better.

Anyway, does this already exist somewhere? If not, thoughts?

Re: Swerve with a twist
 

Could you please post a hand sketch showing top, front, and side views? I cannot form a confident mental image from that ASCII art.

Re: Swerve with a twist
 

Do you have a way of making sure the robot won't move forward while the wheel turns in a circle? After all the forward force is still there. Maybe you can turn 2 modules at a time, letting the other two modules brake the robot, but that's much slower than a traditional swerve.
How about the load on the cantilevered wheel axle?
Yeah, this is a cool idea.
If you're looking to use less motors though, there's always crab drive

Re: Swerve with a twist
 

If you are confident you have a proper understanding of what the OP is describing, would you be willing to draw and post the requested hand sketch?

Re: Swerve with a twist
 

I don't see how this is better than swerve drive. Is just sounds more complex.

Re: Swerve with a twist
 

Apologies for the darkness, but this is what I had in mind

Re: Swerve with a twist
 

Error 403

You can attach the sketch to your post. No need to upload it elsewhere.

Re: Swerve with a twist
 

^^^ no image


Also, here's a quick Inkscape job:

Re: Swerve with a twist
 

I guess I still don't understand how this works.

Re: Swerve with a twist
 

Somebody already posted a pic, so this would be a repeat post.

Re: Swerve with a twist
 

I feel like this would introduce a lot of variables which hamper reliability, which are not seen in a normal swerve. Your module pivot becomes a lot more sensitive to variations in terrain, weight distribution, and small variations between the modules, for example. The steering code would be no simpler, and in fact may take on new layers of complexity since your motors are performing double-duty. Some maneuvers, such as spinning while translating, would likely become more difficult to control.

It may seem simpler on paper, but I worry that you're in fact introducing things that will generate a whole lot more trouble for you. In my never-ending quest to learn how to effectively and quantitatively assess design simplicity (ironically, a very complex problem), I've become increasingly convinced that "minimize actuator count at all costs" is a crude and shortsighted way of approaching the problem.

Re: Swerve with a twist
 

Preventing the forward movement could have a lot to do with the load distribution on the modules. Braking does seem like a viable option however.

The load on the cantilever would be something to eliminate from this design, that's true.

Crab drive sacrifices individual module control for the loss in motors though.

Re: Swerve with a twist
 

Absolutely, this design solves little simplicity wise.

I primarily see its merits in an industrial setting. Repeatable holonomic actions could be performed, especially when engines are large and hard to fit into a compact design.

Re: Swerve with a twist
 

Are you suggesting something like what I've attached?

Attachment 19059

I developed this with a former team member for a project earlier, but haven't around to actually programming for it. Below is a photo of the completed system. Admittedly the wiring is a bit messy - we got around to cleaning that up and it looks a lot more functional now, but I don't have any photos of that at the moment. It's sitting in a box, unfortunately.

Attachment 19060

EDIT: I read through your post again and realize that this isn't quite what you're suggesting. Something like what GeeTwo is suggesting below me seems a lot closer to what you're suggesting.

Re: Swerve with a twist
 

If I understand correctly, you would essentially be making a gearbox which shifts between two outputs: One would power the wheel rotating against the floor, and the other output would control the orientation of the wheel. To make this work, you would still need a separate shifter control for each wheel to toggle between the states, so you would still need 2N controls where N is the number of wheels. You would also have an interesting time driving and steering simultaneously; you would have to switch back and forth for each steering maneuver. If you're simply after reducing the number of motors, it might make more sense to provide a (reversible) clutch from the drive shaft that can borrow a small fraction of the drive torque in order to steer. I still suspect that the extra complexity of the system would outweigh the reduction in motor count for most FRC purposes.