Ball Magnets

[scawsome]

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.

[BJC]

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

[BIGWILLI2081]

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.

[Andrew Remmers]

Originally Posted by BJC

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

We use a FP on our ball magnet and we have no problems with it works great! I'm not sure what the ratio to the roller is but i know we use a FP motor on the roller and we have faced no problems with it besides the wires not being properly crimped.

just my .02

Andrew

[BJC]

Originally Posted by Joyride_67_1902

We use a FP on our ball magnet and we have no problems with it works great! I'm not sure what the ratio to the roller is but i know we use a FP motor on the roller and we have faced no problems with it besides the wires not being properly crimped.

just my .02

Andrew

I was refering to when you are using a pincher where the rollor (fisherprice motor) has to stop suddenly. Fisherprices can't handle this because they will stall. I'm not sure if you are using this ball possession method, but if you are you must have modified the motor in some way.

[NOV8R]

As the American Express ad says "Don't leave home without one" Here's a video of our ball magnet and shooter working together. Btw, the ram light on top tells the driver when he's in possession of a ball. http://www.rambotics.com/video5.html

[BJC]

Originally Posted by NOV8R

As the American Express ad says "Don't leave home without one" Here's a video of our ball magnet and shooter working together. Btw, the ram light on top tells the driver when he's in possession of a ball. http://www.rambotics.com/video5.html

Very nice, we have a light for that purpose on our robot too. On a side note did you model after that robotic soccer league ball magnet. They look very similar.

[Chris is me]

Originally Posted by BJC

I was refering to when you are using a pincher where the rollor (fisherprice motor) has to stop suddenly. Fisherprices can't handle this because they will stall. I'm not sure if you are using this ball possession method, but if you are you must have modified the motor in some way.

Friction-based power transfer (polycord, timing belt flipped upside down, etc) that works like a clutch when sufficient resistance to spinning is met can do this without modifying a motor.

[Tom Ore]

Well they also work going backwards depending on if you gear the thing properly. The trouble really occurs when you are turning. We find that if we turn too quickly the ball slips out.

One thing we do to help this is to adjust the speeds of the Mecanum wheels so the center of turn of the robot is near the center of the ball.

We use a FP on our ball magnet and we have no problems with it works great! I'm not sure what the ratio to the roller is but i know we use a FP motor on the roller

We also use and FP and I believe we use about a 4:1 speed increase to a 1" diameter roller.

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)

We covered our roller with a small diameter bicycle inner tube. To get the inner tube stretched over the roller, we put the aluminum roller inside a steel pipe and stretched just a bit of the inner tube over the pipe. Pressurizing the pipe inflates the tube and the roller drops right in - then trim the inner tube to length.

A couple of other notes. To get variable shot selection we reverse the direction of the roller just before the kick to push the ball out in front a bit. By varying the lead time, we can get a good shot from all three zones even though the kicking force is the same all the time.

Also, when driving forward with the ball magnet pulling the ball into the robot, our robot would start to "power hop". We reverse the roller with speed propotionate the forward speed to avoid this.

[Andrew Remmers]

Originally Posted by BJC

I was refering to when you are using a pincher where the rollor (fisherprice motor) has to stop suddenly. Fisherprices can't handle this because they will stall. I'm not sure if you are using this ball possession method, but if you are you must have modified the motor in some way.

i guess i misunderstood what you said we just have a roller no pinching systems :/ sorry for the misunderstanding

[MarkoRamius1086]

Oh... so they are flexible enough that they have a low enough friction coefficient that the ball follows the bar instead of bouncing away?

[Zach O]

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.

[ttldomination]

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.

[Jeffy]

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.

[Tarzan19]

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.