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.

Re: Shooter Help for 2nd Year Team
 

Compression, although not as drastic as last year, is quite important.

Take a shot at mounting the other side of the shooter (side without wheels) on 80/20 sliders so you can easily adjust the compression to find the sweet spot.

Re: Shooter Help for 2nd Year Team
 

Looks to me like your wheel isn't exposed enough to your frisbee. Try exposing them a bit more, and stack another wheel on top so the frisbee has no chance of skipping up over the wheel. I know quite a few teams had success with these wheels and motors, once you expose the wheel a bit more you just need to play with the compression. You should also be able to lose the 3rd wheel/motor.

Re: Shooter Help for 2nd Year Team
 

Why does it matter how much it's "exposed", as long as it sticks out far enough to produce the required compression without requiring the width of the chute to be less than the frisbee diameter?

Re: Shooter Help for 2nd Year Team
 

We've worked it out, thanks to all of you! We now have a two-motor shooter that shoots frisbees 20-30ft (depending upon how much juice the battery has) and we can hit the 2pt goal. I'll post video and specs ASAP.

Thanks so very much!

Re: Shooter Help for 2nd Year Team
 

Ta-Da! We have a functioning shooter!

Video: http://youtu.be/DASvBTc78GM

We're getting 20-30 feet from it with stacked wheels (as you suggested), two different CIM motors, a big one and a smaller one, the smaller one spins faster than the big motor, which apparently gave us the variance we needed. However, it was a little bit accidental, we put it all together and said "Let's see if it works!" and it worked fantastically! We also increased our compression and added some foam insulation tape for friction, which helped a lot.

Thanks again from the entire team, we look forward to the Silicon Valley Regional next week!

Re: Shooter Help for 2nd Year Team
 

Here's some photos of the final shooter, it was getting dark so the lighting's not great...





last one's a little blurry, but you get the idea :)

Re: Shooter Help for 2nd Year Team
 

Just curious...why two different sizes of wheels?

Re: Shooter Help for 2nd Year Team
 

Smaller wheel reduces tangential speed for entry. They don't have a speed controller.

Re: Shooter Help for 2nd Year Team
 

Is it just my imagination, or is the CIM not mounted perpendicular to the plywood?

Re: Shooter Help for 2nd Year Team
 

What Ether said. ;)

We only have one cRIO and it is on the bagged robot. That is the first thing we will be remedying for next year. This was the best method we could come up with to vary the speed between the two sets of wheels. We have had a really steep learning curve and a really small team. It has been a very educational experience in so many ways.

Re: Shooter Help for 2nd Year Team
 

They are supposed to be perpendicular, but one of the motors is indeed a little bit out of alignment. We will be replacing the plywood today since it got pretty chewed up while things were getting moved around yesterday. Today will be dedicated to cleaning up the design, adding the bucket frisbee hopper, and adding a pneumatic "pusher" that will feed the frisbees in to the wheels unless there is a way we can get it to just gravity feed.

Thank you (and everyone) for your patience and help. The team went from totally discouraged and not wanting to even go to regionals for fear that we would be the lamest team there again, to having a bit of hope that we can make a better showing than last year.

We did place 47th out of 50 last year, but that was primarily due to good alliances. We also received the Rookie Inspiration Award last year so the team wanted to show that we were taking that to heart and making progress.

Re: Shooter Help for 2nd Year Team
 

Glad to hear your shooter is working well.

One thing I noticed was that you had to push the disc into the wheels. Make sure the disc isn't dragging between the walls after the first set of wheels (i.e. the walls should be >11" apart). This would require moving the left wall to the left a little bit; it looks like the distance between the right wall and the wheels is good.

As far as local teams, usfirst.org has a search tool for finding teams in your area. Here are all the teams within 25 miles of Alameda: http://tinyurl.com/c9f5cw2

Re: Shooter Help for 2nd Year Team
 

Thank you! We have a pneumatic push rod to shove the discs, but I will be sure to share your comments with the team. The push rod has not been fully tested yet so your suggestion may be a good solution if we run in to trouble with it tomorrow at pit day. I will also make sure some of the team members reach out to the list of teams that you provided after we are done with the SVC Regional.

Re: Shooter Help for 2nd Year Team
 

Good luck at SVR, if there is a webcast I will watch you guys!

Try not to get too discouraged, being a 2nd year team is often world's better than a rookie but there is still a lot to learn. Know what your strengths are and what you can do to help the alliance. While you are at SVR, there will be a ton of great teams there. Try and make time to go talk to 254, 233, 118, 148, 846, or 973 (sorry if I forgot anyone, put yourself down if you want to be on the list!) they will definitely be able to help you guys develop as a program.

Good luck!

Re: Shooter Help for 2nd Year Team
 

You may want to have a look at the following thread started by my good friend Allen Gregory of Team 3847, especially post #16 where he describes how to make a 1:1 VersaPlanetary gearbox.

www.chiefdelphi.com/forums/showthread.php?t=111360&highlight=small+wheel+shoo ter


The gearbox will take the side loads off the motor shaft preventing premature wear/failure. We originally had a single wheel mounted directly on the shaft of a Mini-CIM. After about 20-30 shots (some with extreme compression), the rear bearing of the motor was worn into an oval and the motor armature dragged on the inside of the magnets. Since we did not want to wait for another motor, we ended up changing to RS550's with a CIM-ULATOR gearbox that I had left over from the previous year. The CIM-ULATOR also took the side loads off the motors.

Re: Shooter Help for 2nd Year Team
 

Side loads were not a problem for us this year direct driving off of CIMs and mini-CIMs with a very similar shooter. As long as your compression isn't insane (10.5 inches from tip of wheel to side wall is what we used) there shouldn't be any problems.

One tip I would give you guys to get a more accurate shot that curves less. It looks like your shots hook right, away from your wheels. We found this curve was a result of the frisbee being compressed but not constrained properly. The edge of the frisbee closest to the wheels was allowed to rise up, and thus discs left the shooter in a crooked manner. If you have some kind of physical guard (e.g. a piece of low friction plastic) mounted right above the shooter wheels to prevent this "popping", you may get a more consistent shot.

Re: Shooter Help for 2nd Year Team
 

The channel opposite to the wheels doesn't seem to have any friction, the frisbee will slip, loose energy and not fly far enough. Consider taping friction tape or at least soft sided velcro to the inside of the channel opposite to the wheels. This grip the frisbee and the fast spinning wheels will generate spin and push the frisbee out.

You can get 3M friction tape (cloth electrical tape) at home depot for about $4 or so.

Re: Shooter Help for 2nd Year Team
 

They already did that. Ya gotta read the whole thread:

Re: Shooter Help for 2nd Year Team
 

If you need the frisbees to go higher, add more foam tape (friction) and test, followed by speeding up the wheels if needed.

Re: Shooter Help for 2nd Year Team
 

The motors are already maxed out. The wheels may even be too fast as is.

They've already got tape on the fence. Where do you want them to put more tape?

Re: Shooter Help for 2nd Year Team
 

Our team had a simlar problem. We found that the surface between wheels acted as a brake. To fix this we moved our wheels as close together as possible and removed the wall between them.

We are running a com 1:1 first wheel 550 3:1 second wheel and 550 1:1 80% power third wheel

https://www.youtube.com/watch?v=qgMb...e_gdata_player

Re: Shooter Help for 2nd Year Team
 

Our team had this problem. We found that the wall between the wheels acted as a break slowing the frisbee down and it went through the shooter. We fixed it by moving the wheels as close together as possible and removing the wall.

We are running a cim 1:1 first wheel 550 3:1 second wheel and 550 1:1 80% third wheel



https://www.youtube.com/watch?v=qgMb...e_gdata_player

Re: Shooter Help for 2nd Year Team
 

Thanks so much! I will pass this along to the team. :)