Ball Magnets

Hi, everyone!
I am from team 230 and our team is trying to decide if we should put effort into designing a ball magnet. We were pretty sucessful without one at WPI but I saw that ball magnets were pretty useful at other competitions. I wanted to ask other teams several questions.

  1. How useful are ball magnets when shooting or pushing balls into the goal?
  2. What kinds of ball magnets (roller,suction,etc.) worked well?
  3. How have teams done with scoring and pushing balls into the goal without a ball magnet device?

Any opinions or suggestions will be very helpful.

I will put it this way.

I would rather have a good ball magnet then a good kicker.

That being said depending on where your kicker kicks you limit your options.

Also by far the best ball magnet is the pincher which is generally about as wide as the robot and uses a spinning top roller to pull the ball into a clamped position. When doing this you want to make sure that you use small diameter rollers and cover it with somthing that doesn’t slid on the ball (your choice). Also for best results the top roller should be spinning twice the floor speed and able to stop when a ball is possessed. Maby use a beam sensor. However, if trying this don’t use a fisherprice because it will stall.

For reference, 217 67 910 27

I’ll go ahead and answer in the same format you asked in.

  1. Ball magnets are incredibly useful when trying to kick (or shoot, whichever you prefer to call it) into the goal. They allow you to accurately line up the ball towards the goal and move around with the ball with ease. As for pushing a ball into a goal, they are not so helpful. Once a ball is in the “ball magnet”, you need to either kick of off or sometimes it will shake lose. If you plan on pushing a ball into the goal while trying to use a magnet, you might need something to get the ball out of you control first… if that makes sense.

  2. There have been several types of “ball magnets” that have worked well for teams this year. Rollers have been the best, with one roller on top rolling inward to your robot and one stationary roller on the bottom, keeping it from going too far into your robot. Some teams also use vacuums, which have worked to a certain extent. Some teams have paired the two together.

  3. Teams have had varying success when pushing balls without a ball magnet. It can be done, and some teams do it well. Others just can’t seem to put them in.

Via a search, you’ll find a thread that talks about the effectiveness of different ball controls. I believe the thread is called “All about Ball Control”.

I’ve seen plenty of the robots that done extremely well while pushing the balls. Teams 1466 and 34 only pushed the ball at Peachtree, they were pushing in 6-7 balls a match.

Really depends on what your ultimate goal is. My team has spent the better part of 2 months working on different ball control mechanisms because our design depends on it.

During autonmous, many teams have been successful without a ball magnet. After that, the only time I have seen it work with any success was for a zone 1 plow bot that can plow the balls along the wall and into the goal.

I would highly reccomend that if you have a kicker, you have a ball magnet to go along with it.

The simplest way to make a ball magenet is to have a roller towards the top of the ball and a wall 3" inside of your robots frame.

From what I have learned working for a week on the prototype and going through a competetion with it is that the roller type ball magnet has very small tolerances. To compensate for this, our team uses two foam wheels that deform and make up for some of this, and you can change the wheels or file them down accordingly. Also, you can add a slick substance such as electrical tape to your wall to change that distance.

Ours uses a fischer price in a 25:1 gearbox and 2.75" foam wheels. I would suggest that you try and gear it a little lower, or a little higher. Our gear ratio works, but only because of a clutch that saves it from stalling on the ramps and such.

edit: listen to the guy below me, one of the most impressive ball possesion mechanisms at KC.

We, from the start tried to implement a ball magnet, however we had complications from the start as well. During the competition, we started out with two motors turning a tube of pvc wrap with surgical tubing. about have way through this device broke, so we improvised. we stationized the motors, slid a pool noodle over the pvc, and it work better than we could have ever imagined.

Our team used a ball magnet, and it was extremely useful. It centered the ball in the middle of our robot and made it much easier to control the ball. Our robot could move backwards, move forwards, turn sideways, and sometimes move side to side (we had mechanum wheels) with the ball. As for pushing it into the goal, we just had a button on the control that we pushed to run the roller in reverse. This worked great because we could posses the ball and then spit it out as we started towards the goal. The most successful teams have had rollers as their ball magnets. They use a bar of some sort with a non-slick surface wrapped around it. Pushing the balls in without a ball magnet seemed difficult for many teams. As they would go up the little bump before the goal, the ball would go underneath them. So, if you are planning on pushing a ball in without a ball magnet, you will want to make sure there is a type of bar blocking the ball from going underneath.

It’s better to do one thing well than two things average. The position no one wants to be in is that you can do neither well because you tried to do both.

In my mind, what made you guys win WPI is that you did one aspect of the game well. You kicked balls from every zone and scored consistently doing so. Your game routine made it very hard to turn the tide of the match after the first 10 seconds of teleop. You let your partners deal with the nuances of the game involving possession and set up a balanced alliance.

My team was an example of the latter. We wanted awesome kicking, possession, and hanging, and it took us until Saturday to even kick a possessed ball at all.

So with that warning… Do you guys have a practice robot? Are you able to build something around your kicker without modifying it? How much weight can you play with? If you have a practice robot, then you get to prototype changes before you make them - significantly less risk. If you have one, you can just try it and see if you like the results. If you need to modify your kicker and don’t have a practice robot, that’s a very significant risk. Is that one you’re willing to take? Weight dictates changes, too.

If you need help with a vacuum, drop me a PM and I’ll tell you what my team did wrong and how to do it right.

For a simple ball magnet that works well just apply a layer of duct brand carpet tape before every match to the front of your robot on a metal bar or rectangle of poly-carb. It is 100% legal as long as you use certain brands. Duct being one of them.

Ball magnets are super useful especially when you are trying to gain control of balls that are in the middle zone. However a ball magnet could limit how high or far you kick and I know that a huge part of your game plan is scoring from the far zone in autonomous.

This was determined to be illegal at the Detroit event this weekend because it was leaving residue on the balls and causing them to stick in the ball returns.

I would not suggest using tape as a way to control the ball. Engineer something that would not affect the balls in the negative way that tape does.

What my team did during the last week of build when we realized that we needed a ball roller was attach a pvc tube to a 64:1 FP motor and covered the pvc with surgical tubing. This was mildly effective, but always let us have pretty good ball control without the risk of carrying.

I’d like to think the decision is a bit deeper than “yes, maintaining possession of the ball is a good thing!”. Of course one would rather have possession than none. Whether or not you want it or can implement it is the real question!

Engineering isn’t about whether or not it would be nice to have a feature, but the cost / benefit analysis of implementing said feature too.

When we were formulating our pick list for west mich, ball magnet robots were ranked higher than non-magnet ones. IF we saw two teams as equals, the one with the ball magnet got ranked higher always; so if you are debating about developing one, I highly suggest that you do. It could mean the differance between being in the playoffs and not.

My team will be re-doing our ball magnet in the upcoming weeks. What we are doing is a dual roller setup. On the bottom, we are putting a square shaft at angle with dycem on it. On the top we are using the Entrapption Star rollers from AM. This will be awesome and already proven deadly from numerous teams.

They stated at Detroit that only certain brands were allowed. We used Duct Brand Carpet Tape during the Elims.

Basically you have to use tapes that are proven to “hold their shape” and not leave residue.

If you are going to give a team credit for the name then you have to credit team 1018 The Pike Robo Devils and Mike Trapp. They developed the Entrapption star sold by AM and used by 45.

Actually it was a Scotch brand carpet tape that was supplied by the inspectors and deemed legal. As said above, we used it the entire second day. I dont think it worked quite as well, but it didnt leave the residue.

If others use this dont do it if you just have a pusher bot. We received a penalty during the finals because if you push a ball into the goals the ball will not come off and you will receive a penalty for carrying a ball. You have been warned.

Here is an example of what it is, it should be available at a Home Depot:

On the subject of tapes, my team found two types of material very effective. The first was pipe insulator, very cheap and effective. The second was grip tape, the kind used in stairwells. We ended up using the grip tape, only because it was very very rugged, for the pipe insulator tended to discintegrate after awhile due to the high rpm we had our spin bar moving at.

As Kyle stated it is a terrible Idea to use it if you don’t have a decent kicker!

230’s kicker is certainly “decent”, they won a regional with it… :rolleyes: