Re: Ball posession: Roller (ball magnet) or vacuum?
 

What I was wondering was, if you were to use a ball magnet/roller would the roller have to spin at the same speed as the wheels? What's the math behind it?

Re: Ball posession: Roller (ball magnet) or vacuum?
 

Roller needs to spin so that it's surface is turning at least twice as fast (relative to the robot) as the robot is driving, so it can hold the ball as the robot drives backwards.

The actual rotating speed (rpm) depends on the diameters of the roller and the wheels.

Re: Ball posession: Roller (ball magnet) or vacuum?
 

How well does that work? We are currently using one window to a pvc roller with 35 teeth on the window and a 12 tooth on the pvc. It is a bit too slow for us to really grab the ball well.

Re: Ball posession: Roller (ball magnet) or vacuum?
 

As of right now it is fairly effective but we are still maximizing the effectiveness.
The model that you see in the picture there is a 36:16 reduction from the denso motors with 2.5" diameter Vex wheels. We found that while driving backwards at full speed we cannot hold the ball as well as we desire, so we have changed the ratio to 48:10, to give us about 400 rpm. This may change again before our regional (week 5) but after a bit of testing we will know for sure.

Re: Ball posession: Roller (ball magnet) or vacuum?
 

for the florida regional, we had a shop vac that was powered by a fisher price motor. but when we get to palmetto, we are planning on testing our ball magnet to see if that works any better

Re: Ball posession: Roller (ball magnet) or vacuum?
 

We used long rollers with latex flaps at BAE, which did not work well at all. We changed to vacuums for our week 2 regional at WPI and we were unparalleled in our ball possession. However, the ball had to be centered as we drove into it in order for us to gain possession. We were able to go around anybody once we got possession, using our swerve drive at full speed. Now we may be changing to something that's even better :D . I'll hesitate to call it a roller but it's along those lines...

Re: Ball posession: Roller (ball magnet) or vacuum?
 

I'd look at the lack of rigitidy (softness) in addition to gripiness and speed of rollers.
I also saw a lot of FP and gearboxes for the rollers.
We used a CIM with a 2:1 reduction and adjust the maximum output via programming. We used 60% in SD, but for some reason had to step it up to 80% in AZ to achieve the same result.
Go figure.:confused:

Re: Ball posession: Roller (ball magnet) or vacuum?
 

Check out 1501's ball handling abilities. We are using a two wheeled system and it's performance far exceeded our own expectations.

http://www.vimeo.com/10396844

Re: Ball posession: Roller (ball magnet) or vacuum?
 

It looks like you have three wheels :-)

Seriously though, did you mean that only 2 of the 3 wheels are driven? Are they omni or mecanum?


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Re: Ball posession: Roller (ball magnet) or vacuum?
 

Two wheeled ball magnet.

Re: Ball posession: Roller (ball magnet) or vacuum?
 

We have a three wheeled Kiwi drive system for the robot and a two wheeled Dribbler System for holding the balls while we move around the field.

Re: Ball posession: Roller (ball magnet) or vacuum?
 

Right. I got so caught up watching the fascinating video that I lost the context.

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Re: Ball posession: Roller (ball magnet) or vacuum?
 

I'm not familiar with Kiwi drive. Does that use omni wheels?


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Re: Ball posession: Roller (ball magnet) or vacuum?
 

Yes it does. Kiwi is a three wheeled drive utilizing omni wheels. We used the A-M Nano gearboxes direct driving the omni wheels.

Re: Ball posession: Roller (ball magnet) or vacuum?
 

Did you guys home-brew your own kiwi drive algorithm, or is there a good-quality tested library routine available somewhere?


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