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

That's not a soccer ball. And it's not being dragged backward on the ground.

BIG difference.


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

We homebrewed all the code from whitepapers... initially we had some code tested on a vex before we went full scale... PM me if you want more info...

Now to get this back on subject, Im interested to see the Techno-Ticks ball magnet working at CT!

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

I believe that it is roughly parallel. Perhaps the bottom one is a smidgeon behind the top one... as its primary purpose is to kep the ball from going back. We have it so the ball goes all 3 inches worth into the frame, so the top bar has the most grip possible.

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

We are geared to the fisher prices at I think up by 3:1. We get around 15,000 rpms at the vacuum impeller.

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

Are you running the motor at 100% PWM? If so, those numbers don't add up.

The no-load speed of the fisher-price is approx 15,700 rpm.

So if you are geared up 3:1 and you are getting only 15,000 rpm at the impeller, you are running the motor at 5,000 rpm which is less than 1/3 its max speed. This is way outside the acceptable operating region for continuous operation. At 100% PWM (12 volts) and 5,000 rpm, the motor would be drawing almost 48 amps.

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

I was in the stands at GVSU and noticed a bot with a particularly effective ball magnet. After the match, I walked down to their pit area and talked to them. They had a 2-roller design. The upper roller was powered and the lower was free-wheeling. The lower was set back from the upper about 1 to 2 inches.

As the team explained it to me, the top roller pulls the ball in, squeezing it ever so slightly as it does so, and the lower roller stops it at 3" inside the frame perimeter. Very effective.

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

Are you sure you weren't at VCU? Because that sounds an awful lot like us!:D

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

Do all these lower roller schemes have wheels ahead of them to prevent them being bashed into the humps? Or. perhaps they retract when traversing the humps? Then, if they retract, how can they prevent past 3" incursions when pressure from the ball pushing on them displaces them out of their proper incursion preventing location?
-Dick Ledford

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

Before going to the trouble of gearing it up (by "up" in this context I assume you mean higher speed at the impeller), you might want to measure your current draw with the 3:1 gearing when operating without a possessed ball. With a centrifugal impeller, the motor will be drawing more current without a possessed ball (more airflow).


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

Many of these lower rollers are in line with the first wheel's axles, so they will not contact the floor before the wheels do in any circumstance if both wheels are touching the ground.

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

You want the two bars nearly as far forward as you can get them. The ball should touch the top one just before the bottom one. The bottom one does not spin. The ball rests on the bottom bar, taking 90% of the normal force. The rest of the normal force is the ball just barely touching the ground. The robot is actually physically carrying the ball, but because the ball doesn't break ground contact it's not a penalty. That how, if you watch 217, 1114, 33, and others, they can whip around, back up, pick balls off the wall, etc because they are quite literally holding the ball.

Watch robowranglers video for a nice closeup of it in action.

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

It would be most interesting to hear from teams with effective 2-roller ball magnets whether their bottom bar a) is fixed and does not spin or b) is free to spin or c) is motorized


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

368 had a roller-type mechanism which was very effective. It is just as good, if not better, than anything else I have seen. I got a good glimpse of the space cookies 1868 one which I believe uses a clutch. I thought 368's one was better and they can literally move anyway they want using their swerve drive, without ever losing that ball.
I'll let them explain the materials and setup on how they achieved this. It rotates, but I wouldn't really call it a roller.

From what 1086 is describing, it sounds very similar to ours. Ours grabs pretty hard and I'd like to see a team knock ours out once we get it. No one is 3 regionals has done so yet. ;)

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

359... How is your upper mechanism set up? I am interested because we have a Fisher Price with the whole thing on a free-floating, spring tensioned, attachment.

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

The key for us was really wedging that ball in after it gets sucked in.
We dumped the FP because it would stall and have to swap it out after several test runs during build season, even with different levels of reduction.
Once we put in a CIM, it does stall and puts quite a strain on it. However, we swapped out only 1 CIM in 53 matches (3 tournaments) not including practice matches. Its an adjustable-height CIM driven motor driving a pool noodle with a swirl of duct tape with a 2:1 reduction running between 60-80%.
Our lower roller is an idler.
We have a picture of it on our website under regional flyer. Its so simple, a caveman can do it. :)