pic: Basketball Drive

[BotDesigner]

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[Bernstern]

This looks awesome! We might have to try something like this ourselves ...

Would moving diagonally be an issue though, with the scrub force on the wheels you are using to drive the balls? Omniwheels might be better to use to drive the balls.

[JohnFogarty]

I agree, omni wheels theoretically would be a better wheel to drive the balls with.

[Chak]

It might be simpler and easier to replace the red basketball supports with a ball transfer like this. It could also help with the tiny scrub forces from the bearings.

[Lil' Lavery]

Leaving some room for the motor leads may help.

[SoftwareBug2.0]

Originally Posted by BotDesigner

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I built something very similar (four balls and no wheels) in 2005. Unfortunately I'm not sure if any pictures or video survive.

This is feasible. Don't expect this to be something useful in a FIRST game though. If you build it I will be interested to see if this ends up with the same sorts of issues as the one I built.

[pilleya]

Originally Posted by Lil' Lavery

Leaving some room for the motor leads may help.

It is great that you have attempted to make it as compact as possible. In regards to the leads, you should be ok as the curvature of the adjacent CIM case should allow adequate space( unlike BAG's the leads come out rear). But you will need to check this.

[Kevin Sevcik]

Originally Posted by JohnFogarty

I agree, omni wheels theoretically would be a better wheel to drive the balls with.

I disagree. The balls should never be moving perpendicular to one of those wheels, which is what an omni would help with. Drive just one wheel and the basketball will spin around the other wheel.

I think the problem would be that your traction is based on how much you're compressing ball, since there's no weight transfer from the robot. Plus compressing the ball is likely to make it pop out of where you're capturing it. I'd suggest moving the wheels up to get more weight transfer, but then you would need omnis, and you'd run out of room for the balls unless you used bigger wheels...

[JesseK]

Originally Posted by Kevin Sevcik

I disagree. The balls should never be moving perpendicular to one of those wheels, which is what an omni would help with. Drive just one wheel and the basketball will spin around the other wheel.

I think the problem would be that your traction is based on how much you're compressing ball, since there's no weight transfer from the robot. Plus compressing the ball is likely to make it pop out of where you're capturing it. I'd suggest moving the wheels up to get more weight transfer, but then you would need omnis, and you'd run out of room for the balls unless you used bigger wheels...

Interesting points. Perhaps tires instead of hard wheels?

[Lireal]

Originally Posted by Kevin Sevcik

I disagree. The balls should never be moving perpendicular to one of those wheels, which is what an omni would help with. Drive just one wheel and the basketball will spin around the other wheel.

The issue is when you would move diagonally. Wheels on both sides of the ball would have to spin, and the axis the ball is turning around would be no longer be perpendicular to either of the wheels.

Here is a quick sketch of where I would think the axis would be when moving diagonally: https://docs.google.com/drawings/d/1...it?usp=sharing

[Lireal]

Originally Posted by SoftwareBug2.0

This is feasible. Don't expect this to be something useful in a FIRST game though. If you build it I will be interested to see if this ends up with the same sorts of issues as the one I built.

What were the issues that you had?

[hotwheel326]

I would only see this useful in a wide open game or flat floored like overdrive or aerial assist. But it is a very cool concept that I would like to see passed around from what other people can do.

[Maxwell777]

Reminds me of this guy's rideable ball balancing robot, that sat on top of a bowling ball

https://www.youtube.com/watch?v=vx-jCQpHRTo

[SoftwareBug2.0]

Originally Posted by Lireal

What were the issues that you had?

The major problem was that when you impart a force to make the balls turn you're also giving a force that wants to make some of the balls come out. So you couldn't immediately go full power without risking unseating some of the balls. You could just go partial throttle to start though and you'd be ok, but that basically meant that you wouldn't want to ever get in a pushing match either.

These balls are larger and heavier than the ones that I used while having an identical amount of power so it's possible it might not be quite so bad. Another difference is that in this system the spring is the balls. I don't know if that's good or bad though. I don't know that this system is radically better as far as keeping the balls in.

To me it's almost uncanny how similar it looks: We used a 1x1 tube frame with two different levels that was mostly 90 degrees except for the pieces at 45 degrees over the top of the ball. Also, this doesn't matter functionally, but seeing this image really surprised me because one of the types of balls we tested was bright yellow. We also ran with 4 CIMs, one per side, but we used belts and pulleys rather than large wheels to distribute the power.

The second issue that we had was that it wasn't super controllable. There are plenty of robots that don't like to drive quite straight - most of them will just sort of wander off into a big cicrle though. This one liked to be going straight and then it would decide that one of the sides was going to just start going slower at unpredictable times. So you could be walking down a hallway with it and things are going smoothely and then the robot decides that it's going 30 degrees to the left of where it had been a second ago. I'd be interested to know if that was due to a flaw in our robot or if that's sort of inherent to this type of drive.

The third issue was how it stacked up to the alternatives for that year's game. It used four CIMs, which was as many as were allowed, but 2005 was also the first year with the AndyMark C-base drive chassis and gearboxes that could take all four of those CIMs. It wasn't the first year with powerful tank drives, but it was the year that it became easy and common. And this was before mandatory bumpers and for a game that was played in a largely open field. The name of the game was go someplace fast don't be movable once you're there - exactly the opposite of what this kind of drive gives you.

[Team3844]

It looks like each ball is in contact with 2 wheels. that would make every ball turn at the same rpm since they are all tied together which would just make the bot rotate in circles.