Please help - launcher issues.

Technical Technical Discussion
#1

Hello everyone.

We’ve been prototyping our launcher since build season started, and we’re not happy with where we are.

We’ve done a variety of things from changing wheels, changing gear ratios, speeds, changing compression, putting on a roof, changing angle, using double wheels, etc… all to no avail.

We’re getting meager distance out of these - 20 feet max. That may not be too bad, but the 20 feet max is only achieved if we fire the frisbee at a height of about 3 feet: in other words, not fast enough to get into a 3 pointer if aimed upward.

Here’s a few images of the launcher… hoping we can have some guidance. Thanks a ton.




Gear ratio on the front wheel is roughly 1:2.375
Gear ratio on the back wheel is roughly 1:2

Both being run at a bit over 12V via direct battery hookup.

We’re just getting a bit frustrated because we’ve seen very very very simple prototypes work much much much better and have not been able to achieve a satisfactory result with hours upon end of adjustments and changes.

#2

Without seeing a video, it looks like you might be seeing a lot of slippage. A CIM(?) geared like that at that kind of voltage seems waaaay too fast, especially using a non-compressable wheel. Faster != better.

I would say start with what has worked for other teams so far. Pneumatic wheels, 1:1 ratio first wheel 1:1.25 ratio second wheel, 10-11 volt range on both. If that yields better results, start tweaking one variable at a time until you find something that works well for you.

#3

1.2 off what motor - I can’t see them in the pics.

My best guess is you are getting a lot of slippage using those wheels. And those wheels are not very wide - very little room for alignment errors. Our mock-up is very close to yours but we are using an old 2" wide IFI high-traction wheel.

Try cleaning that wheel (scrub it hard, they get stickier when you do) and try other higher-traction wheels.

Good Luck!

#4

From what is shown in the photo, I would guess that you are getting a LOT of slip between the wheels and the disc - those wheels are pretty firm, and you only have a single squeeze point for contact in a linear shooter. What other types of wheels have you tried?

Part of why the Ri3D shooter used pneumatic tires is because they can compress a lot and significantly increase the contact time for a linear shooter. As has been discovered by many now, those particular AndyMark pneumatic tires have weaknesses for high speed use, but the principle of a more forgiving tire and greater compression for a longer contact is sound.

Does anyone on the team have a camera with a high speed video mode so you can try and see what is happening? (many newer point and shoots have low res, high speed video modes)

I am not terribly familiar with the Modulox gearbox system, but based on the small gear I can see on the CIM, and the larger gear mated to it I think you have a gear reduction set up, is that correct? You can check by slowly turning the output wheel by hand and counting the revolutions of the motor shaft - if the motor spins more than once for one turn of the output, then you have a gear reduction.

Our team always likes to start prototyping shooters by directly connecting a CIM to a wheel, since it keeps things simple (too much squeeze can be rough on the motor bearings though). There has also been some talk online this year about teams wanting to gear up their CIM to make the wheel spin faster (as Ri3D did).

Some suggestions to test: higher grip wheels, more compliant wheels, greater squeeze/compression (to a point), and start with 1:1 off the CIM to keep things simple.

#5

http://www.chiefdelphi.com/forums/showthread.php?p=1216070#post1216070

#6

It seems that using the FIRST wheels is problematic, since they do not compress. This would distort the frisbee slightly when going through the shooter. Next the linear design can also be imparting only a little of the momentum, since the frisbee will only be given momentum from the wheel at a single point.

#7

This thread may help

#8

Thanks for the feedback guys. To address a few questions:

We are indeed using CIM Motors.

We are not doing a reduction or 1:1, both gearboxes are geared up; 1:2.375 and 1:2.

We’ll try 1:1 tomorrow and try to put on pneumatic tires. We have them, but it’s been challenging to get the hub on them to stay straight and not have them wobble on the shaft.

#9

You maybe spinning the wheel TO FAST. Causing slip between the wheel and the disk, which would decrease performance. Try adding a victor and running at slower speeds.

#10

This may or may not be your problem, but it was our problem.

Make sure you test with the official FIRST discs. We got a bunch of generic frisbees to test with ad we were really disappointed with the horrible distance (about 5 feet) that the discs were flying. Then I tried loading in one of the FIRST frisbees and those flew over 50 feet.

Most likely one of the previous posters already identified your problem, I just thought I’d post this here just in case it could be helpful to you or someone else.

#11

Use pneumatic wheels!!!

#12

Try different wheels, not necessarily pneumatic but try KOP wheels etc. Put more compression on the frisbee.

#13

Agreed, or go for something with more grip, like some plactions ( what our team is using for a prototype)

#14

Absolutely too fast. Try 1:1 and 80% speed (~10 V), at least on the first wheel.

#15

slipping is a problem with those wheels we made a arc shooter with just a single wheel the wheel was directly connected to a CIM. when the frisbee went through it scuffed the frisbee and the wheel was shedding thin rubber strips. a wheel with better traction and a a wall that is slippery should work fine don’t use a placation wheel as the tread around it will fly off and possibly hit someone like that almost happened to us

#16

You don’t want a slippery wall.

If the bee slips on the wall, you won’t get the spin you need for accurate and consistent shooting.