pic: OmniSwerve chassis Bottom View and Concept Discussion

[Scott Kozutsky]

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[Scott Kozutsky]

Sorry, double posted the pictures.

[ctt956]

Good concept IMO. This would probably also be advantageous if a motor/gearbox/drive module failed, as it seems like it could be pulled along by just one wheel. All of the gears should probably be protected better so debris doesn't get in them.

[The other Gabe]

this is ridiculous, a complete waste of time, and probably not particularly effective. I love it!

[Chak]

The theoretical max speed is 1.414 times what the bot is geared to (because you can add the velocity vectors of X and Y travel after a fast turn, ideal hypotenuse is 2^0.5)

It would be a very interesting math problem to calculate the theoretical max speed. I don't think it's 1.414, because that either assumes the motor can get up to max speed immediately after a fast turn, or it assumes that omniwheels have no friction laterally. Instead, as the robot turns, it decelerates in one direction and accelerates in the other. With the omniwheels, the net acceleration will probably increase the speed. But to what maximum?

[Scott Kozutsky]

Originally Posted by Chak

It would be a very interesting math problem to calculate the theoretical max speed. I don't think it's 1.414, because that either assumes the motor can get up to max speed immediately after a fast turn, or it assumes that omniwheels have no friction laterally. Instead, as the robot turns, it decelerates in one direction and accelerates in the other. With the omniwheels, the net acceleration will probably increase the speed. But to what maximum?

"hypothetical" might be a better term for that. This unit is geared pretty low (free speed at 14.9 fps) so the acceleration on 6 CIMs should be pretty good. The lateral resistance of omni wheels is kind of an unknown at this point.

[Chris is me]

I'm really having trouble seeing what this gains over a normal kiwi drive setup.

If you have six motors on it, you're going to have plenty of torque in any direction of travel even if all wheels aren't pointing in the same direction. You'll be able to do advanced maneuvers (simultaneous rotation + translation) with a kiwi drive, but not with this drive.

[Scott Kozutsky]

Originally Posted by Chris is me

I'm really having trouble seeing what this gains over a normal kiwi drive setup.

If you have six motors on it, you're going to have plenty of torque in any direction of travel even if all wheels aren't pointing in the same direction. You'll be able to do advanced maneuvers (simultaneous rotation + translation) with a kiwi drive, but not with this drive.

You'd have one and a half times as much power in any direction ,assuming a power if 1 unit per wheel you'd get 2*cos(30)+1*cos(90)=1.73 to 1*cos(0)+2*cos(60)=2 for kiwi and 3*1=3 for omniswerve. If you have the motors mounted you might as well use them.

You are able to do advanced maneuvers with this because you can just tank turn at any time, there's no scrub from the omni wheels so even with the sub optimal platform it would still work.

[Chak]

Originally Posted by Chris is me

I'm really having trouble seeing what this gains over a normal kiwi drive setup.

If you have six motors on it, you're going to have plenty of torque in any direction of travel even if all wheels aren't pointing in the same direction. You'll be able to do advanced maneuvers (simultaneous rotation + translation) with a kiwi drive, but not with this drive.

Originally Posted by Scott Kozutsky

You'd have one and a half times as much power in any direction ,assuming a power if 1 unit per wheel you'd get 2*cos(30)+1*cos(90)=1.73 to 1*cos(0)+2*cos(60)=2 for kiwi and 3*1=3 for omniswerve. If you have the motors mounted you might as well use them.

You are able to do advanced maneuvers with this because you can just tank turn at any time, there's no scrub from the omni wheels so even with the sub optimal platform it would still work.

I think we can all agree that this design is not meant to be realistic anyways.

[Dan_Karol]

Maybe i'm missing something, but how does it turn?

If all pods are ganged together then you have no control over what your heading is or you have no ability to strafe.

[GeeTwo]

TL;DR Trying to wrap my brain around what this does and why you'd want to do it.

If all the wheels steer in unison, you have crab drive - with the inherent [crab] inability to rotate the chassis (not good for a triangular chassis in most conceivable games) and the additional [omni] weakness of being highly vulnerable to cross-drive forces. I don't see any way to get anything faster than geared speed in this scenario, either.

If only the wheel near the steering motor is steered, I can imagine a scenario where you can get up some extra speed, though I haven't done the math to convince myself it's viable. If this is the case, why are the two non-steered wheels built up so they appear to be swerve modules?

Or is something else going on (e.g. one of the wheels steers counter to the other two, or something even more arcane)?

Edit:

Originally Posted by asid61

How are you getting above max speed?

Originally Posted by Scott Kozutsky

drive straight to max speed, turn left at 90 degrees and accelerate in that direction to max speed. Because of the omni wheels, you actually (ideally) don't lose your forward momentum after turning and, as such, move in both directions at your maximum geared speed, hypotenuse of that vector triangle is 1.414 times the side length.

Maximum speed is achieved when the drag/frictional forces are equal to the drive forces, and the drive forces are applied. Once you turn the drive in another direction, you'll begin to slow in the direction you are moving. You may be able to achieve a bit better maximum velocity, but after accounting for the longer distance traveled, I don't see how you can achieve a higher net speed.

Edit2: That is, at maximum speed, saying you don't lose forward momentum, even ideally, is not valid. Maximum speed is inherently the result of significant loss of forward momentum due to friction.

[Scott Kozutsky]

Originally Posted by Dan_Karol

Maybe i'm missing something, but how does it turn?

If all pods are ganged together then you have no control over what your heading is or you have no ability to strafe.

The way I have it is they all point in the same direction. You can tank turn in any orientation by simply driving one side forward and one side back. Only the pivots are chained together not the actual drive.

The reason you can't turn in conventional crab is because the drive is all chained together and because the wheel scrub from trying to tank turn is too significant.

here's a crude vector diagram of my 3 wheeled swerve rotating.
http://imgur.com/0HMYj0g

If they were traction wheels the steering would be awful (non existent) because the wheels would oppose the lateral forces exerted on them. With omni wheels this does not happen so it should be able to turn quite nicely.

[Aren Siekmeier]

Originally Posted by Scott Kozutsky

Pure silliness

Hahahahahahahahaha.

I love the three wheels though. Also, your packaging on a non-coax module is not bad.

[asid61]

How are you getting above max speed? You might get more power in a direction (like with a kiwi), but not more max speed.
The major advantage I can see to this is being able to run a crab drive without worrying about turning scrub, but at that point one might as well run mecanum or pure swerve. I think this would be usable for a team with low programming resources that wants to get into swerve (say during the build season) but wants a good backup plan for if it doesn't work out. Crab is significantly easier to program than full swerve.

[Scott Kozutsky]

Originally Posted by asid61

How are you getting above max speed? You might get more power in a direction (like with a kiwi), but not more max speed.
The major advantage I can see to this is being able to run a crab drive without worrying about turning scrub, but at that point one might as well run mecanum or pure swerve. I think this would be usable for a team with low programming resources that wants to get into swerve (say during the build season) but wants a good backup plan for if it doesn't work out. Crab is significantly easier to program than full swerve.

drive straight to max speed, turn left at 90 degrees and accelerate in that direction to max speed. Because of the omni wheels, you actually (ideally) don't lose your forward momentum after turning and, as such, move in both directions at your maximum geared speed, hypotenuse of that vector triangle is 1.414 times the side length.

There are also the standard "butterfly" advantages of this over traction wheels. See 33 in 2014 for similar reason, why would they go for omnis over traction in a standard tank. This concept is silly but IMO does merit actual consideration, even as just a thought experiment; it has some significant advantages.