Help feeding from stack of 4 discs

[jspatz1]

From our experience and from the description of your problem, my guess would be that you are not guiding the disc stack closely enough. The stack needs to be contained so closely that the discs are not capable of tilting and nesting any more than they do when stacked vertically.

Special attention must be paid to how the exit slot controls the bottom two discs. The lower edge of the exit slot needs to be exactly the height of one disc (1.5"), or even lower if it is flexible. The second disc is prevented from tilting forward in front of the bottom disc only by this lip, so it must be right. Once again it must fit the diameter closely. Leaving a sharp, rough, or rubber edge on this lip helps in retaining the second disc.

The bottom disc must be prevented from being shaken or jarred forward (through the exit slot) when other discs are on top of it. Some additional friction in a limited area at this location is helpful. The width of the exit slot can be reduced so there is some slight interference with the edges of the disc when it exits, just enough to prevent it from exiting forward prematurely.

The height of the plunger which pushes the bottom disc is critical so that it does not attempt to go above or below the rounded profile of the edge of the disc. We push on the disc about 3/8" above the shooting surface. If you are pulling the disc from the inside, try to reach up into the interior about 3/8" rather than pulling on the lower edge. Of course a pulling hook must somehow go away before the trailing edge of the disc passes over it.

It is best if the entire feeding and shooting surface is a smooth, solid surface. Bad things happen when the circular discs can tilt slightly in grooves or rails. Be sure that debris can not accumulate in the feeding area. The slight tilt of a disc resting on a piece of debris can mess things up.

[sanddrag]

Thank you all for the help. We had spent quite a few hours just trying to understand the dynamics of the problem, and with your help, I think we're moving closer to a solution for our particular mechanism. We were very close to independently developing something similar to Team 1884's spurs but didn't quite hit this final mark. We tried a fixed pin, and a servo-moveable pin, but the spur looks like it just may be the perfect thing for us. Thank you 1884!

The one problem that still remains for us, is we don't have space in our existing design to use the spurs. You all have been generous in sharing what you have, so here is a picture of our setup, to receive some feedback and advice on. Sorry, I don't have a better picture of the feeding or a video, but they are pulled from the right side of the picture with a pneumatic cylinder with a wedge shaped hook. I'd still like to use the spurs, if we can somehow do it without remaking the whole shooter. I'm willing to remake the "hopper" if we need to. That's an easy fix.

Also, I'm still interested in seeing how others are doing it.

[Curt Henderson]

We had a similar experience with the disk stack jammimg when the bottom disk is indexed to our shooter wheel. For us it was a fairly simple fix, we attached a back pivot mounted short stroke cylinder to our hopper side that get extended prior to the disk flippers. The cylinder has a small wedge on its rod to ride up the side of the lowest disk and lifts/jams the upper disks to the side wall and relieves all pressure and interfence from the upper disks on the lower disk. We fire the side cylinder first and then 200ms later we fire the flipper cylinder to launch the disk and simple retract both to allow the stack to drop and then repeat the sequence.

[JChang]

Our team had a similar problem too, and one of our mentor came up with a simple fix. We added a lip on the exit side, so only the bottom most Frisbee lay flat, the rest sits on the lip. When the bottom one exits, the diagonal length allow the second Frisbee to fall through, getting it into position. This process repeats until all Frisbees are fired. The concept is very similar to team 2073's system:

Originally Posted by billbo911

In this video you can see clearly how we addressed the nesting issue. http:// http://www.youtube.com/watch?v=hdhlDQX2DQ4&feature=youtu.be

Our prototype showed that it works with a stacked hopper system, but we ended up using a linear shooter and loader system. Hopefully this solution will work with a curved shooter.
This concept is illustrated by the poorly made animation on the attachment.

Edit: After thinking how it worked on our robot, I realized that the animation is somewhat inaccurate. The back piece should be angled a little towards the exit so that it realistically works.

[Jeffy]

We saw both kinds of "nesting" that you described.

We only found the type of nesting where the upper frisbee tries to go out the output slot in front of the lower frisbee to be a problem.

If the frisbees nested so that the upper frisbee was between the "plunger" and the frisbee in the "chamber" we noticed that when the plunger was fired the upper frisbee would slide at an angle upwards and the lower frisbee would slide into the shooter just fine.

As per how we solved the other kind of nesting:

Originally Posted by JChang

We added a lip on the exit side, so only the bottom most Frisbee lay flat, the rest sits on the lip. When the bottom one exits, the diagonal length allow the second Frisbee to fall through, getting it into position.

Edit: After thinking how it worked on our robot, I realized that the animation is somewhat inaccurate. The back piece should be angled a little towards the exit so that it realistically works.

We use something very similar that I can advocate for.
What we have is that the bottom frisbee is shifted about 1/2" off center from the other frisbees. Then, the other frisbees lay on top of it at an angle.
When you push one frisbee out of the "chamber" another slides down into the chamber with the other frisbees still resting at an angle to the frisbee in the chamber. The key here is that this "chamber" only be small enough for only one frisbee to fit in at a time, but large enough so that a frisbee will slide into it from a position "staged" above it when no frisbee is in the chamber.

Also, vibration of the entire plate from the shooter wheel, or from the bot driving is more than enough for any loose frisbees to fall into place.

Sorry I don't have any good pictures of the device and the kids took the prototype apart. If you have questions, please ask.
Best of luck.

[Gary Bonner]

We had the same problem; even a minimum-sized exit slot allows movement of the second Frisbee in the stack, which could then tilt into and partially block the exit. In addition, the bottom Frisbee would occasionally prematurely slide out toward the wheel (we have a 90 degree shooter) from vibration or impact. This would allow the second disc to tilt to the back and block the firing mechanism. We solved both problems with a lightly sprung retainer in the middle of the exit slot that swings up and out of the way when pushed by the bottom Frisbee as it exits. The retainer both holds the bottom disc in the hopper and keeps the second disc nested parallel to, and centered on, the bottom one, preventing jams. We have had no jams since installing the retainer. Here's a clip:
http://www.youtube.com/watch?v=2hVpz...e_gdata_player

[Coach Norm]

We had a similar problem to the stacking, nesting in both the forward and back positions when frisbees were fired.

We actually did not have the problem in an early prototype. As we moved through testing, we moved to a more rigid method and it was a major problem.

Our solution, the opening the frisbee slides out of is smaller than the height of the frisbee. The top part of our hopper system is mounted on a hinge at the side opposite the frisbee exit position. The upper part of the hopper moves up as the bottom frisbee is pushed out. The hopper slides back down into position as the bottom frisbee moves out. As is mentioned above, the hopper does not allow the frisbees to stack but in one way without overlap on any edge. We are using a Jason's Deli pickle bucket of the 6 gallon variety. It has a slightly smaller draft on the side than a regular 5 gallon variety bucket. We are using the very top portion of the bucket down to just below the second rib (about 3" worth of the bucket).

Hope this helps and good luck.

Norman