pic: OmniSwerve chassis Bottom View and Concept Discussion

[Gdeaver]

It's summer. No pressure. No time constraints. Why waste your time on this project. Isn't there something your team needs to work on to improve it's skill set? Something that could actually be used in the future?

[Scott Kozutsky]

Originally Posted by Gdeaver

It's summer. No pressure. No time constraints. Why waste your time on this project. Isn't there something your team needs to work on to improve it's skill set? Something that could actually be used in the future?

This was entirely my own project and an excellent opportunity to brush up on CAD. I figured Chief Delphi posters in general would also enjoy this kind of thought exercise but apparently not.

[Aren Siekmeier]

The sqrt(2) speed increase is certainly a different way to think about things. I imagine it wouldn't coast terribly far on the rollers, and it's not powered through any obstacle in that direction. And sounds like you've considered how it would mess with the driver to be in a constant uncontrollable powerslide.

Put in a traction wheel and you've got a decent crab drive. Two more turning motors for unicorn.

[nuclearnerd]

Originally Posted by Scott Kozutsky

This was entirely my own project and an excellent opportunity to brush up on CAD. I figured Chief Delphi posters in general would also enjoy this kind of thought exercise but apparently not.

On the contrary, I think this is really cool! The way you have thought past everyone's initial "why" to discover some really novel performance details shows that you have the creativity, and deep thinking a robotics team needs.

I spent some time last year thinking about a wheeled version of a cyclorotor for similar ridiculous reasons

[GeeTwo]

Originally Posted by Scott Kozutsky

This was entirely my own project and an excellent opportunity to brush up on CAD. I figured Chief Delphi posters in general would also enjoy this kind of thought exercise but apparently not.

I also enjoyed the thought exercise of looking at the drive and working out the probable advantages/disadvantages of its distinctive constraints, even if no one could come up with enough advantages to want to build it.

I wish we had a few team members "waste time" this summer developing CAD skills.

[Cothron Theiss]

Originally Posted by Scott Kozutsky

This was entirely my own project and an excellent opportunity to brush up on CAD. I figured Chief Delphi posters in general would also enjoy this kind of thought exercise but apparently not.

There's never any reason to not mess around with CAD for practice, so it's awesome that you've done this. I'm hoping to post several oddball/silly designs over the next month, as soon as I get off my butt and get to CAD-ing. But great job on getting the ball rolling with off-season designs.

As for the design itself, it might be really interesting to lock the back two wheels in the forward direction, and then replace the forward omni wheel with some sort of traction wheel with VERY high amounts of scrub (or even a small tread module). Theoretically, if the forward steering module has enough friction against the carpet, powering the motor on the front steering module would actually turn the entire chassis in relation to the front wheel. With the front wheel pointed in a different direction from the back wheels, it might steer similar to a front wheel drive car, but without the need for a differential since the back Omni's can be powered at different speeds.

[Scott Kozutsky]

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[Moskowapplepi]

I am curious how well this would work in practice as well as how the triangle design came to be.

[EmileH]

Originally Posted by Moskowapplepi

I am curious how well this would work in practice as well as how the triangle design came to be.

Relevant thread/threads.

[Scott Kozutsky]

Originally Posted by Moskowapplepi

I am curious how well this would work in practice as well as how the triangle design came to be.

The triangle design is a byproduct of maximizing motors and minimizing other complexity. Minimum amount of wheels to be fully supported is 3 and maximum reasonable amount of CIMs is 6. It also ensures all the wheels are in contact with the ground. 4 CIM 4WD would end up weighing about the same, be more mechanically complex and less powerful.

[Hitchhiker 42]

With the max speed thing, here was the way I though you could possibly do it:

Have one wheel face one way, another face 90* from it, and the third point right in between. If you power the two at 90* to each other, you'd get sqrt(2) the speed.

[asid61]

Originally Posted by Hitchhiker 42

With the max speed thing, here was the way I though you could possibly do it:

Have one wheel face one way, another face 90* from it, and the third point right in between. If you power the two at 90* to each other, you'd get sqrt(2) the speed.

The velocity vectors don't add like that I think. You would get sqrt(2) + 1 times the torque of the single cim pointing in the right direction, but the max speed is still only the speed of that cim.

[GeeTwo]

Originally Posted by asid61

The velocity vectors don't add like that I think. You would get sqrt(2) + 1 times the torque of the single cim pointing in the right direction, but the max speed is still only the speed of that cim.

The velocity vectors can add up so that the speed of the robot is greater than the speed that any individual wheel is driven. The issue is that with the number of rollers providing resistance to this motion, I find it unlikely that those two motors could achieve a significantly greater speed than one in which all three motors are providing drive force in the desired direction. The only way to know for sure is to build it.

[asid61]

Originally Posted by GeeTwo

The velocity vectors can add up so that the speed of the robot is greater than the speed that any individual wheel is driven. The issue is that with the number of rollers providing resistance to this motion, I find it unlikely that those two motors could achieve a significantly greater speed than one in which all three motors are providing drive force in the desired direction. The only way to know for sure is to build it.

Well, if you take the two non-pointing-in-the-right-direction motors and give them each an angle theta away from the main wheel...
If you assume velocity vectors add, then the output speed is (cos(theta)+1)*v0, right? If that's the case, as theta goes to 0* (AKA point all whee;s in the same direction) one would end up with just 2 times the target speed- but all the wheels are just pointing in the same direction like a tank drive. That doesn't make sense to me, is there another way to add it?

[Aren Siekmeier]

Force vectors add. Velocity vectors do not. Rather they are constrained by slip conditions and the relative motion of bodies.

It's sort of a continuously variable transmission.

Say you are constrained to go in a direction 0 (by a wall or omnis opposing each other, etc.), but an omni wheel is pointed in a direction theta relative to your heading, and spinning at speed w about its axis. The overall translation velocity vector v is identically the velocity of the center of the wheel relative to the ground, which can be broken into the rotation of the wheel (w), and the rotation of the rollers (s), assuming no slippage. Then v must project onto the wheel speed w, as w=v*cos(theta). The roller speed is s=v*sin(theta) and has no limit. The overall speed is v = w/cos(theta), resulting in a higher speed.

To do this, you could have a four wheel drive with steerable omnis in each corner. Start with them directed forward, (theta=0), and spin the wheels at speed w. Then v = w / cos(0) = w. Then turn the left and right wheels toward the middle by an angle theta. Now v = w / cos(theta) will give an increase in top speed.

However, the force available in the forward direction drops. Each wheel supplies F in its own direction. When theta = 0 then the total force is 4*F, all straight forward with no sideways component. When theta is increased, the sideways components cancel, but at each wheel, the sideways component must add with the forward component to get F in the direction theta. So the forward component from each wheel is F*cos(theta), and the overall force available is 4F*cos(theta).

In this way, steering the wheels toward the middle by an angle theta acts as another stage of reduction, increasing the speed and decreasing the force by a factor of cos(theta), assuming no wheel slippage.

Vector diagram to help