Jammed Ball Bin-Storage Help!

[=Martin=Taylor=]

At the Silicon Valley Regionals our team had problems getting the balls to come out of our bin.

The bin was gravity fed with no agitators. The bottom and sides were both sloping, directing the ball towards our 1pt shooter.

(You can sort of see it in this picture)



The problem occurred when 3 balls would try to exit the shooter at once causing a triangular pattern to form.



We fixed this at the regionals by simply jerking the robot back and forth to loosen the balls. This is fine, but it makes aiming difficult! I'm hoping to design a new bin in time for nationals that will solve the problem but I'm not sure what to do.

Agitators are out of the question because additional motors would require additional programing and wiring, which we don't have time for.

Here are my ideas so far...

=>Note that the ones labeled 1,2 & 3 are back views looking towards the front of the robot.<=



Which do you think is least likely to jam?
Have any better ideas?
What did your team do?

[Jeremiah Johnson]

This is why our team didn't make a basket like this. But I think of all the designs... #2 would be the most likely not to jam but would also hold less balls.

[Billfred]

Originally Posted by Budda648

This is why our team didn't make a basket like this. But I think of all the designs... #2 would be the most likely not to jam but would also hold less balls.

I wouldn't offer guarantees on even that much. 1293 had our hopper shrunken down thanks to some acetate from another team to get the hopper one ball wide and stacked, and it still didn't work.

The solution, annoying as it may seem, is to completely eliminate the possibility of jamming. The best way, it seems, is to keep narrowing parts of the ball-moving process as upstream and easy to fix as possible. Look at 95's setup--three ball channels, each can only hold so many--but it doesn't jam. Or 1902's dumper, whose ball hopper stays at two balls wide the whole time through once it gets past the basket.

Is it possible to remove some of those side guides? Or do you have weight to add an agitator around where the jamming happens?

[artdutra04]

Almost anytime you have to funnel Poof balls down from a wide hopper into a small opening [without an agitator / sorter / indexer of some sort] you are going to jam. Period.

Funneling works well for some types of balls, but it only does so because the lack of a lot of surface friction on the ball. Pool or ping-pong balls would be good examples of this, as the surfaces of the balls will just slide past each other. But because of the compression and surface friction of a Poof ball, they would rather compress themselves than roll past each other.

No one said that this would be easy. And if they did, they were obviously refering to a little red button from Staples and not to FIRST. The fact that the Poof balls do not funnel down easily is just another design challenge.

If you need inspiration, I would suggust looking through CD-Media. There have been hundreds of pictures of robots uploaded so far this year, and I'm sure at least one of them used an idea that you might be able to "borrow" to suit your robot.

[s_forbes]

We have a 1 point shooter on our robot as well, but have had no ball cloggage problems even when full at the begining of the match. The secret: Shoot more than one ball at once.

The clogging problem occurs when you try to funnel the balls into too small of an opening, so you want to make your opening as wide as possible. Ours shot out a stream that was two balls wide and they still shot fairly straight. Just make your hopper funnel down to the width of your roller and that will eliminate some ball clogging problems.

[Greg Marra]

Originally Posted by artdutra04

No one said that this would be easy. And if they did, they were obviously refering to a little red button from Staples and not to FIRST. The fact that the Poof balls do not funnel down easily is just another design challenge.

Actually, we have one of those little red buttons from Staples on our controls. When you push it, it turns on our agitator to unjam the balls

[razor95kds]

If you saw our hopper at Davis, it jammed but required only minor shaking of the robot to unjam it. it holds about 15 balls, but yours would be mounted lower, allowing more capacity

Stop by our pit at nationals to take a look at our hopper.

[=Martin=Taylor=]

Thanks for all the input!

It seems like the most widely held opinion is that gravity-fed bins will always have the potential to jam.

Realizing this, I think my best bet is to make some kind of agitator (probably like the one drawn by BurningQuestion).

Despite my preliminary misgivings I am beginning to see how using an agitator might actually be easier than redesigning the bin.

Based on people's ideas (and the bins of other robots) I created a CAD model of the new bin. It is similar to the bin most people thought was least likely to jam (bin #2), with offset angles (as recommended by Jonathin Norris).





Looking at the design I am already beginning to see new jamming issues. There is also the problem of how to transport the plastic to Atlanta...
Overall it looks more difficult to build than an agitator, which is probably what I'll wind up doing.

Does the new design look workable/less likely to jam?

[razor95kds]

Originally Posted by Hachiban VIII

Thanks for all the input!

It seems like the most widely held opinion is that gravity-fed bins will always have the potential to jam.

Realizing this, I think my best bet is to make some kind of agitator (probably like the one drawn by BurningQuestion).

Despite my preliminary misgivings I am beginning to see how using an agitator might actually be easier than redesigning the bin.

Based on people's ideas (and the bins of other robots) I created a CAD model of the new bin. It is similar to the bin most people thought was least likely to jam (bin #2), with offset angles (as recommended by Jonathin Norris).





Looking at the design I am already beginning to see new jamming issues. There is also the problem of how to transport the plastic to Atlanta...
Overall it looks more difficult to build than an agitator, which is probably what I'll wind up doing.

Does the new design look workable/less likely to jam?

The design is very similar to 254's hopper. theirs still jammed and required shaking to unjam it

[s_forbes]

We found that the most jamming came from balls being stacked vertically, just like in the pictures you just posted. We made the bottom of our hopper large so that none of the ten starting balls were stacked on top of each other. If the balls are put in in the same pattern at the beginning of each match, then it will work every time (it did for us)

I highlighted the funneling parts of the hopper in our picture. The bottom of our hopper is at about a 30 degree angle and the two strips near the bottom just keep balls from getting hung up on the walls near the bottom. We also tried to put a shelf in right over the exit to prevent stacking, and it did it's job perfectly.

[Jizvonius]

Originally Posted by Hachiban VIII

Agitators are out of the question because additional motors would require additional programing and wiring, which we don't have time for.

Not true. If you can run the agitator off the motor running your front roller (directly or off the roller shaft), it would at the most require some chain/belt and mounting.

Also, if the jamming point is close enough, you can run flex shaft to it. And mount the agitator in any orientation you want.

[Lisa Perez]

We had the same issue at GLR. We ended up using the format you drew in picture 2, made out of taut netting, and it's worked great for us since.

If you want to keep ball capacity high, you could design a spiral ramp. It may take longer, but if built right, it pretty much guarantees that balls do not get stuck.

[Travis Hoffman]

The #2 method works for us as well. Reduced capacity but reliable performance for a passive hopper system.

[Jonathan Norris]

We have a hopper which is very much like #1 but to fix the jamming problem we found that If we off-set where the two angles become strait by a few inches the jams are reduced to next to nothing. Our simple solution was to just put across a 1" diameter plastic rod across one of the edges, but If you are designing a new hopper you could make something better integrated into the design.

If you look closely you can see it here: http://www.chiefdelphi.com/media/photos/23277

[Derek Bessette]

I know you said it is "out of the question". However, my vote would still be with adding an agitator. The programming is only a few lines of code and the wiring is not that big a deal. We were able to implement an agitator at the end of the build season in a matter of a couple hours. It has worked great for us. We initially tried making channels for the balls to flow through, but this just moved the ball jam to a new location. We used a van door motor with a piece of 3/4" square tubing attached to the output shaft. We then covered it with a poof noodle to keep from damaging the balls.

If you are really certain that you cannot go with an agitator then definitely go with option 2. The balls jams will get moved to the inlet of the channel at the top, but if you only keep 1 to 2 balls up there you should be OK.

Good luck!