Re: Ball Magnet
 

The roller is mostly above the ball, it spins in the direction that drives the ball "into" the robot. We don't yet have the spec ball nor spec carpet, so we dont' know how well it will work...but the idea is to have the ball actually spinning the whole time, and as you drive the robot around the ball is always spinning on the carpet towards the bot.

As for the dimensions on our prototype...if the roller were at the very front of the FRAME PERIMETER then the ball would ingress just over three inches. We need to experiment with roller size and location to see what works.

I did notice that the ball was marked up from sitting still with the roller spinning on it, so there is more work to be done to see if this is really feasible.

Also the roller should be made only wide enough that one ball can contact it. If two balls can both be POSSESSED by the robot at once, bad penalty things happen.

Re: Ball Magnet
 

Wow how did I not see this thread before. We're also prototyping something similar (using our 09 and 08 rollers) but I'm adding tiny tiny ball casters

Re: Ball Magnet
 

It's very important that you have a surface with enough friction that it can actually apply force to the ball. Otherwise the roller/wheels don't do anything. And as Jones571 said, the contact point is also important.

Re: Ball Magnet
 

We've been working on this some more, tonight's video:

http://www.youtube.com/watch?v=BNjdnmkAEUs

(wow, the first video has over 7500 views)

Re: Ball Magnet
 

We stumbled upon the weirdly amazing effectiveness of backspinning the ball entirely by accident at our second team meeting. We'd just finished building a goal and some bumps and were discussing how to kick the ball. We've had good success with spinning "shooters" in the past, so the idea was to try a roller. (Zeki, one of our grade 12 students who has been on the team for four years is coming up with all sorts of really cool ideas this year. One, for a non-functional decoration... we're hoping to be able to fit into the weight and size limits.)

We took our old "Aim High" bot, laid it on it's back, spun up the IFI traction wheel and touched the ball to it. The wheel was spinning the wrong way to "kick" the ball... and the ball started to backspin and was held in place.

It didn't work particularly well, but I think its the first time we've ever figured out an essential component of the game that early. I think 1726 must have posted the ball magnet video about the same time, because we saw their video very shortly afterwards... and account for a few of those thousands of views.

So, of course, we figured if backspin is good... more is better. So we rigged up a test chassis using 6" AM wheels spinning at a couple thousand RPM and disovered that we could actually melt the outer lining of a soccer ball at those speeds. So we tried it with last year's intake mechanism, as 1726 had, and it worked much better... but we lost a couple days of build doggedly researching the "more is better" idea, and wondering why it didn't work.

Now we've got a 2" diameter aluminum roller directly driven by a 25:1 banebots running off last year's FP motor (about 600 rpm-ish) as our "final mock-up" and it's running okay. We've got a couple 26:1 P60 gearboxes from banebots on order for use with this year's FP's for competition. We used "magic tape" the black plastic wrap that sticks beautifully to itself, as a traction surface, but will probably go back to the rough top tread when it arrives, riveting it to the roller in a helical pattern in the hopes that it might help control lateral ball movement. We could probaly do with a little bit more speed, but can order a "faster" P60 and change it out in Seattle if we need to.

I can't believe how well this seems to work... mind you, EVERYTHING always seems to work well on the practice field.

Jason

P.S. We are trying this with an HS500 DTI ball, which apparently has a very similar finish to the HS300 ball on a carpet that, while not official spec, seems to be really close to spec. The HS500's shiny surface works, if anything, better, on this surface than the matte (and now partly melted in places) finish on the old soccer ball we borrowed from the PE department. They'll get a nice shiny HS500 in return after the season ends.

Re: Ball Magnet
 

Do you have any more details on this "magic tape"? It sounds interesting. Have a link?

Re: Ball Magnet
 

Is it also known as "grip tape" that is found on baseball bats?

-RC

Re: Ball Magnet
 

Looks like you are getting closer. We have found mixed results.. its very sensitive to the friction on both the rug and soccer ball. Some balls stick like crazy to both the rug and roller and stall the roller. Others hardly stick. We have fooled with different roller surfaces and geometries but I think our rug must be too sticky compared to what I see in your video. So we have a design that will prevent roller stalling and is tolerant of friction variations...maybe.

In your video you mentioned shelf paper. How would you legally bind that to a roller?

Re: Ball Magnet
 

*gasp* that looks wildly familiar :yikes:

Re: Ball Magnet
 

Members on my team are talking about using a brush roller instead of the solid type shown here, but I doubt that it will put the required back spin on the ball. Has anyone tried brushs yet?

Re: Ball Magnet
 

Very interesting idea, thanks for sharing the video with everyone.

A few quick questions -

1) What materials on the rollers have people found works best when using this kind of setup?

2) How high from the ground do you have your roller mounted? During your trials, have you found a roller position that works best?

Re: Ball Magnet
 

We used clear packaging tape to attach the inner end, and a bit on the outer corners after wrapping the shelf liner around the roller a bit more than one turn.

I have not found any rules prohibiting the use of packaging tape. If you know of one, please let us all know! (rule number)

We sort of tried a brush, it was flaps of the shelf liner, like we used on last year's robot to lift the balls up the helix. It did not work at all. But we didn't use "real" brushes. I think it needs more friction than you can get with brushes.

1- We tried wheel tread and it works well to grip the ball, but it seems to need to have a full surface, not individual strips...the ball falls off when it encounters a significant gap. Shelf liner seems to work well, but we are concerned about it's life. It might be just fine, and it is cheap and can be replaced easily if it's secured with tape like we did on the latest video.

2- seems to need the roller pretty far up the ball to get enough traction on the ball to be able to spin it.

Re: Ball Magnet
 

Your first video convinced me ball posession would be easy, so I stopped worrying about it...

*grumble grumble grumble*

What motor / RPM are you driving the motor at? What speed variations have you tried? You might see something very similar from New York...

Re: Ball Magnet
 

We were messing around with our roller yesterday and we using a drill that outputs about 1000-1500 rpms. We found out that the faster the roller the more backspin it puts on the ball. Therefore causing the ball to come back to the roller causing it to "stick"

We will be using 2 mabuchi's to power our roller.

-RC

Re: Ball Magnet
 

Do you have a mock up or pic on how you are going to be using the mabuchi's? like a gearbox, etc.?

we are going to be working on this design type this weekend but we don't have a ton of resources and zero "extra" parts (no stock pile from previous years like veteran teams tend to have).