pic: GBX-114 swerve with PTO

[Mike Marandola]

Originally Posted by nathannfm

Assuming your contact patch is square an X with 45° wheels is the most effective (I know that a 1" wide, 4" dia wheel with Blue Nitrile is approximately square) because you are applying force along the longest line you can draw in that shape. If you measure your contact patch and find it is a rectangle you can calculate the most effective angle to put your wheels at when you make this maneuver. (Not sure how much difference that would make tho...)

Since the contact area and amount of force would be the same regardless of the wheel angle, there might not be any difference. This is not taking the tread pattern into consideration though. Which is why the X formation might be beneficial. I think the X pattern will both reduce the wheel's ability to rotate when pushed and utilize the effects of the tread "fingers".

Originally Posted by asid61

It would increase contact area

The contact area would remain the same.

Nathan, I know you said that 365 did testing on diagonal vs. normal tread. Did you guys happen to test the tread sliding sideways as well?

[asid61]

Originally Posted by Mike Marandola

Since the contact area and amount of force would be the same regardless of the wheel angle, there might not be any difference. This is not taking the tread pattern into consideration though. Which is why the X formation might be beneficial. I think the X pattern will both reduce the wheel's ability to rotate when pushed and utilize the effects of the tread "fingers".



The contact area would remain the same.

Nathan, I know you said that 365 did testing on diagonal vs. normal tread. Did you guys happen to test the tread sliding sideways as well?

Oh wait, you're right. I was thinking of another tread with diagonal tread in it...
Regardless, it shouldn't matter. An x-configuration would allow the motors to just sit in brake mode I think.

[nathannfm]

Originally Posted by asid61

I guess putting them in brake mode would do the trick.

Yea, I figured whenever you sent them to an X configuration you would want to be breaking.

Originally Posted by Mike Marandola

Nathan, I know you said that 365 did testing on diagonal vs. normal tread. Did you guys happen to test the tread sliding sideways as well?

Yes, I wrote up a procedure in that thread. Thats actually what started us doing the testing, we were getting pushed sideways more than we liked.

[Mike Marandola]

Originally Posted by nathannfm

Yes, I wrote up a procedure in that thread. Thats actually what started us doing the testing, we were getting pushed sideways more than we liked.

Awesome. I will check that out.

[asid61]

Originally Posted by nathannfm

Yea, I figured whenever you sent them to an X configuration you would want to be breaking.



Yes, I wrote up a procedure in that thread. Thats actually what started us doing the testing, we were getting pushed sideways more than we liked.

Pushed sideways while in an X? That woule be very hard to do if you set the turning motors in brake as well; they are geared down 1:26 with a secondary of 30:84.

[nathannfm]

Originally Posted by asid61

Pushed sideways while in an X? That woule be very hard to do if you set the turning motors in brake as well; they are geared down 1:26 with a secondary of 30:84.

Sorry, we did the tests last year on our 8 wheel WCD. With a swerve that has straight cut tread it should be just as hard to do as being pushed backwards. (I will have to think about how best to "break" with diagonal tread)

[asid61]

Originally Posted by nathannfm

Sorry, we did the tests last year on our 8 wheel WCD

Thank goodness. I was thinking, "Oh god, did my numbers come out totally wrong!?"
They did, as a matter of fact. This is only geared for 20fps, sadly. I messed up the numbers in the calculator (again). Fortunately, the speed is easy to increase, but hard to decrease.
EDIT: I added a 3-position cylinder to the CAD, but for some reason these cylinders from Bimba are around 6" tall. So you can technically put on one here, but I would probably learn to live with this version.

[nathannfm]

Originally Posted by asid61

Thank goodness. I was thinking, "Oh god, did my numbers come out totally wrong!?"
They did, as a matter of fact. This is only geared for 20fps, sadly. I messed up the numbers in the calculator (again). Fortunately, the speed is easy to increase, but hard to decrease.
EDIT: I added a 3-position cylinder to the CAD, but for some reason these cylinders from Bimba are around 6" tall. So you can technically put on one here, but I would probably learn to live with this version.

I'm confused, what's that have to do with being pushed while in X mode?

[asid61]

Originally Posted by nathannfm

I'm confused, what's that have to do with being pushed while in X mode?

If you get pushed from the side while in x mode, then because the contact patch with the floor (ideally) is a line or thin rectangle, the pusher will torque the wheel sideways a bit like a caster. It seems like it would take a ton of force to shove those wheels back into a straight position, but it is doable. I'm sure that the robot will lift before that though.

[nathannfm]

Originally Posted by asid61

If you get pushed from the side while in x mode, then because the contact patch with the floor (ideally) is a line or thin rectangle, the pusher will torque the wheel sideways a bit like a caster. It seems like it would take a ton of force to shove those wheels back into a straight position, but it is doable. I'm sure that the robot will lift before that though.

Theoretically it's a line, if your wheels and the floor were both hard and solid, ideally it's as large a rectangle as you can make it because with tread on carpet the physics class friction model goes out the window and surface area is quite important. But 45° wheels pushing from the side should be identical to pushing from the front. You are right though, it's quite hard to turn a (for us) 100:1 braked planetary gearbox. As for lifting, unless your bumpers are higher than your opponents there is no force that is going to lift your robot. Infact, if your bumpers are lower they will be pushing you into the floor a small bit, increasing your normal force and your friction.

[Bryce2471]

Out of curiosity, how are the side plates of your caster box attached to the turning gear that the robot is resting on?

[asid61]

Originally Posted by Bryce2471

Out of curiosity, how are the side plates of your caster box attached to the turning gear that the robot is resting on?

Ah, caster box. That's a good name for it.
The turning gear is a modified vexpro 84 tooth gear. A big hole is in the center for clearance, and about 1/8" is cut out of the face of the gear (deburring would have to be done carefully on the teeth). Of the 1/8", there is a small pocket that sticks up which the caster box side plates drop in to.
The pocket is wallled on three sides and has screws on the bottom to connect it properly. The fourth side of the pocket is the big hole in the center of the gear.