Re: Curved Shooter help
 

Those of you running direct drive to a 6-8" wheel using the CIM, are you running the CIM at max RPM or something less (eg. 70-80% power)?

Re: Curved Shooter help
 

One thing we noticed with chain drive, is that chain tension is critical...if it's just a little too tight, the binding will really reduce rpm (and distance).

987 uses a 6" smooth tread kit wheel from a few years ago, their curved shooter is spectacular. It might have something to do with the quality of the rest of the robot, too.

Re: Curved Shooter help
 

We hadn't considered or observed the side-loading force as being a problem; however CIM motors are cheap enough that it's not a burden to replace as long as it doesn't die completely mid-match, just bring a few spares :).

We use a hall-effect sensor to determine our RPM (surprisingly easy to setup hardware for, code isn't too bad either, I can share details if you want to give it a go), and shoot at 3900 RPM (we can get up to 4400 RPM with the wheel).

Aside from consistency, the closed loop (using a fairly simple bang-bang controller) provides a huge benefit to spin up time. We went from at most 1 shot per second (with inconsistency depending on how long we let it spin up), to one shot every .4 seconds, and much more consistently.

Re: Curved Shooter help
 

90 degree curved shooter. Two mini-CIMs driving a 4" wheel geared up to 9700 RPM. I think we have about 1/4" of compression against black roughtop tread. Shooting from the far side of the pyramid without issue. Ours didn't shoot far at all until we added more compression (had 1/8" before).

Re: Curved Shooter help
 

Yes, the smooth surface is supported by an aluminum wall on the back. We support it with L aluminum brackets. It needs to be pretty rigid. There can't be much flex at all

The only reason we angle it was to make sure the frisbee didn't curve on the flight pattern. When you increase the angle when it comes out, it doesn't curve as much when flying through the air. We are shooting full court so that is the reason we wanted that.

Think of a shotgun. The more accurate shotguns have a longer barrel to keep the bullet from moving much when it comes out. The is exactly what we are doing. That as a short barrel so the frisbee stays as straight as possible.

Re: Curved Shooter help
 

We currently run at 100% power for our direct drive with a mini-CIM (more specs here).

Re: Curved Shooter help
 

We have a "combined" shooter:

A mini-CIM directly drives a small ~2" "starter" wheel, giving the disc an initial velocity and rotation before it comes in contact with a 6" AM performance wheel with wedgetop tread. This main wheel is driven by a full CIM sped up to a 1:1.2 ratio by a belt. The curved part of the shooter is about 70 degrees and has wedgetop on the curved wall.

Both motors are run at a "fixed" voltage of around 11 volts to account for battery voltage varying during the match. (We read the battery voltage and adjust the input to the speed controller accordingly.)

I don't know what the compression is, but it is not that much - perhaps .25". The wedgetop and the starter wheel really reduce the amount of slipping.

It shoots full court easily and accurately as seen in San Diego. In fact we were very surprised by how well this combined system works.

Good luck!

- Mr. Van
Coach, Robodox

Re: Curved Shooter help
 

Here is a slow motion video of our prototype shooter. We are running it direct drive with a CIM at full speed. Our real shooter uses 2 RS775 motors controling to 4000 RPM, so similar. We have quite a bit of disk compression. It is hard to force the disk through the shooter with your hand and you have to spin the wheel to get it out. We were definitely one of the hardest shooters at our past regional. We shoot full court.

http://team2052.com/Slow%20Motion%20Shooter

Re: Curved Shooter help
 

We have our curved shooter set up like this.
Direct drive mini CIM driving a 4 7/8 in banebots GREEN wheel.
We keep the rpm down to 4500 and easily shoot from behind the pyramid and much further. We use about 3/8 inch compression which humps the disk up about 1/2 inch. We use a progressive compression. At entry to the shooter there is only about 1/8 inch and at max it is about 3/8. Shot to shot is something like .4 seconds or less. Yes, the green banebots get eaten up but the funny thing is it does not seem to matter. New wheel or half eaten up wheel shoot to the same place from the pyramid. We do have a "few" extra wheels just in case.
Our frisbee wall is 1/4 inch laser cut polycarb with a rubber U channel over it for grip. There is a wider piece over the top to keep the frisbee from walking up and we angle the wheel down about 3 degrees at the exit. This keeps the bee from turning to one side.
Hope that helps.

Re: Curved Shooter help
 

We did lots of prototyping of our shooter.

Our shooter:
CIM motor with wheel mounted directly to it.
Wheel is custom made out of HDPE
-8" diameter x 1" tall
-Wedgetop tread mounted to the HDPE wheel with rivets. Ends attached with AM clamps from performance wheels.
Shooter deck is made of HDPE sheet that is 1/2" thick. We had to brace the bottom of the deck to prevent sag which caused more compression on the frisbee.
Rails of shooter are made of HDPE with weather striping foam on inside edge. The rails are attached by machine screws about every 5" to prevent warping/bending when the frisbee moves around it.
The spacing from the shooter rail to the wheel is 11 1/16 inches. The foam is 1/4" inch thick so we get some compression on the frisbee but not much.
We also have a lexan cover over the top of the entire shooter.
You can see a picture of it here: http://www.chiefdelphi.com/media/img...ed21b3a4_l.jpg Notice that the wheel here is a performance wheel that has been replaced.

Here is an image with the shooter on the robot: http://www.flickr.com/photos/chaprob...57632928507774

Compression and surface on the wheel and rails were were the factors we spent the most time on. The diameter of the rails need to be determined by the size of your wheel so it is consistent all the way around.

Our shooter actually shoots better without full voltage. We have experimented with 9.2 - full voltage. I do not have any specific data but we mark the frisbees less with lower voltage and get more consistent distance and accuracy we think with the 9.4-9.5 voltage range. We competed at our first tournament and our encoder was not giving us the feedback we needed to control the shooter speed. We ran either full voltage or 80% for all the matches.

We can shoot from full court consistently at the two point goal.


Hope this helps.

Re: Curved Shooter help
 

What material is your "black frisbee guide on top of the slick surface"? How high above the frisbee do you have it and how far out does it protrude from the slick surface?

In your video it looks like your frisbees have black marks on them. Is that from this material or the wheels?

Thanks.

Re: Curved Shooter help
 

What my team noticed when experimenting with the shooter is that there are a couple of factors. First thing is that Higher RPM doesn't necessarily give you more distance. We are running a direct drive Cim to an 8" wheel. We have about 1/4 " compression on the frisbee from the side. We added a stop at the top with some more compression near the exit of the shooter.(basically it funnels a bit). The angle and height at which your shooting make a big difference as well. Greater angles give you less distance. For our full court shots we run the Cim at about 90% power. We put a weight on top of the wheel as well, pretty much just a steel coupler since we noticed stability and no wobbling when we added that. The interior is lined with plastic(the back end of the Regolith from Lunacy since we had a ton of it). Another thing that effects the firing is how you push in the frisbee. The angle at which its being pushed in and speed.

Re: Curved Shooter help
 

Do you know off hand what angle you shoot at for full court?

Re: Curved Shooter help
 

Off hand i would say the angle is around 20 degrees.Its something you need to play around with.

Re: Curved Shooter help
 

Info on our curved shooter:

https://www.youtube.com/watch?v=S5gVpo6PZh4

Check out 1:08

90 Degree wrap
8" 40A durometer rubber wheel
CIM motor direct drive running at ~2000 (normal shot) to 3000 RPM(full court)

We use very light compression and the reason is that when you compress the frisbee, it will bend which causes it to track vertically on the curved wall of the shooter. This can result in extra friction or a curving shot. Using a softer durometer wheel provides a lot of traction which permits significantly less compression.

Also, if you are shooting at full speed and you start to see a purple halo on your wheel, this will make you shooter almost nonfunctional. This happens
when you are spinning your wheel too fast and it is melting the frisbee upon initial contact. You have to grind the halo off as soon as it starts to appear. Once it gets fairly thick, its almost impossible to remove.

Hope this helps.

~Matt