Shooter Help for 2nd Year Team
 

Hey everyone,
Team 4186 is reaching out hoping that some of you can help us. Our problem is simply this: We can't get our frisbee launcher to work. We initially built a launcher using a single drive motor and a 9 inch wheel with an enclosed chute. We tried different speeds, different amounts of pressure between the wheel and Frisbee . . our results were very poor. Then we built a curved shooter to keep the frisbee in contact with the wheel longer, hoping it would impart more velocity. That didn't work either. We now have a straight launcher using two C channels and three drive wheels propelling the Frisbee. It's very much like the one constructed in the Robot in 3 Days videos. Initially we started with only two wheels, but it was only throwing the Frisbee fifteen feet and couldn't even propel it high enough to hit any of the official sized targets. We thought it might need more power, so we added a third drive motor and wheel, but it didn't really improve our results. We're using five inch wheels by Bane Bots with the orange tread, all three rotating at the same velocity. Do we need to vary the speed between wheels? Is the rotational speed of the 5 inch wheels too slow? Do we need larger wheels? Is there any way we can drop a wheel and motor so we will have a better chance of keeping it all under 30 pounds? Any suggestions, advice, or knowledge you can share would be very greatly appreciated. Last year (our first) we were only able to field a 'defensive robot" that had no shooter at all. This year we would very much so like to participate more fully in the competition. Thanks again.

Re: Shooter Help for 2nd Year Team
 

Step1 would be to spend an hour reading the threads here on CD that have in-depth discussion about shooters.

Step2 would be to provide more detailed specs (and some pictures) about your present design: what motor(s), what gear ratio, what speed and voltage, etc etc.

Re: Shooter Help for 2nd Year Team
 

What speed are you running at? Can you post pictures of what it looks like? What motors are you using in your shooter? What angle are you having difficulty propelling the frisbees at?

Re: Shooter Help for 2nd Year Team
 

Maybe you could try using a CIM motor instead of a BaneBot motor.

Re: Shooter Help for 2nd Year Team
 

Do you think you could post a picture of this shooter?

Re: Shooter Help for 2nd Year Team
 

I see a trend here.

Re: Shooter Help for 2nd Year Team
 

Thanks for the replies!

We are going to do some more work this afternoon and I will make sure I get pics to post along with other pertinent info. I will also task the team members with utilizing the resources here at Chief Delphi better.

They are currently using 3 of the large CIM motors with no gearboxes. The motor shafts are just linked directly to the wheel hubs.

I believe they have just been hooking directly in to one of the robot batteries.

There was talk that any sort of variable speed control would have to be programmed?

So far we do get a bit of distance, but as it stands we would have to sit right next to the low goal and hope for the best. Angle doesn't seem to affect things much at this point.

Our regional is next weekend and we don't have a lot of time to finish this so we really appreciate the assistance.

Re: Shooter Help for 2nd Year Team
 

Hello everyone!
I've got photos of the shooter in question... here:






We're using CIM Motors, with no gearboxes, I'm not sure about speed, all of our electrical is inaccessible, so we have the motors linked directly to a circuit breaker and battery.

Thanks!

Re: Shooter Help for 2nd Year Team
 

It looks to me like your wheels aren't getting enough contact with the frisbees. Any chance you have anything else to show us? A CAD file? A video?

Re: Shooter Help for 2nd Year Team
 

Several thoughts come to mind:

1) In the world of shooting frisbees with spinning wheel(s), you reach a point where faster is not better. In fact, some teams have reported a *loss* of frisbee exit speed once the wheel(s) were spinning faster than some experimentally-determined optimum point. So, it's hard to "tune" your shooter if all you have is an on/off switch for the motor voltage.

2) I don't see anything preventing the frisbee from riding up the side of the fence (the guide rail opposite the wheels). If that is happening as the frisbee passes through, you won't get sufficient compression

3) The fence looks shiny and slippery. You want more friction on the fence so that the frisbee has to spin its way through the shooter. Without adequate spin, the frisbee won't go far.

4) The wheels are narrow compared to the chute height. There's nothing preventing the frisbee from climbing up over the exposed part of the wheel.

Re: Shooter Help for 2nd Year Team
 

It may be that little compression (looks to me like .125-.25 at most) paired with immediate high speed is not enough to impart much velocity on the disc. Since you appear to have the materials handy, I suggest you look into a Spectrum (Team 3847) esque shooter. You would be able to sub the BAG motors for 2 CIMS, the smaller wheels for your bigger wheels, and also I suggest looking into slowing down the first wheel that the disc contacts.

Re: Shooter Help for 2nd Year Team
 

1. Ask a local team for some hands-on help, there should be no shortage of good teams in your area.

2. From my measurements you have almost zero compression, we run our orange banebots wheels at 3/8" compression, but up to 1/2" works well.

3. I'm not sure how you are connecting to the CIMS, but I don't see any keys in there, are the wheels slipping on the shafts?

Re: Shooter Help for 2nd Year Team
 

I'll do my best to reply to everything in order...
Here's a video: http://www.youtube.com/watch?v=e7zD_Qd1mG0 we've made some modifications since taking this video, and have dealt with some of the Frisbee jumping and slipping on the fence.

We've replaced one of the big CIMs with a smaller one, and will probably take off the third wheel...

As far as the wheels slipping on the shaft itself, we're using shaft collars with locking screws and the wheels aren't going anywhere.

as far as local teams, MVRT has been helping us, but they aren't close enough to be of much help at this point (they're the closest at about a 1.5 hour drive away)

Thanks!

Re: Shooter Help for 2nd Year Team
 

These seem like your two best bets to me. In addition to this, add something sticky to the wall opposite the wheels.

And one more suggestion, playing with wheel speeds can help a lot. A variable voltage power source is ideal, but a poor man might try wiring the first two CIMs in series and the last one in parallel. Or, mini Cims spin at ~6.2k rpm to the CIMS 5k and have the same mounting and shaft size.

Re: Shooter Help for 2nd Year Team
 

Try some different types of wheels as well. My team went through a few different sets of wheels to see which worked best. It turned out the same wheel we used on our shooter last year worked best for this year as well.