Team 3081 Prototype Launcher - Final
Hello Chiefdelphi, this is a semi in-depth report on shooting frisbees. We have spent the last week prototyping shooters and I aim to report what we found here.
Selection of wheel - We prototyped with two wheels, one being the AM Pneumatic wheel and the second being the AM 8" 2010 wheel. We attached these directly to the CIM motors using AM hubs creating a 1:1 drive. We modified the speed of the wheels using a Jaguar controlled by a C++ program.
AM 8" 2010 Wheel - We initially started testing with this wheel because it was the only one we had on site. While it worked well it simply was not accurate enough for our liking. We used multiple different types of material on this wheel during our testing, from friction tape to plaction. For range plaction worked best in this application.
AM Pneumatic Wheel - In the end we chose to go with the AM Pneumatic Wheel because it was much more accurate then the AM 8" 2010 Wheel. My personal speculation is this is caused by the tread on the wheels.
Tread
The Pneumatic wheel has tread go farther around the wheel while the AM 8" 2010 Wheel only has tread straight out from the wheel. We used this fact to our advantage, instead of putting the frisbee linear with the wheel we actually placed the frisbee under the wheel. http://i669.photobucket.com/albums/vv57/Team2470/WheelCompressionexit_zps49d75b8b.jpg You can see it in action in the above picture. When we placed the frisbee under the wheel not only did we launch farther and faster but we were also more accurate.
PSI of the wheel
We tested two levels of PSI, 15 PSI and after filling it, letting as much air out as we could. We will call the second level 0 PSI. The first level shot the frisbee pretty far, at 70% speed we could hit the 3 pointer from ~30 feet away. Unfortunately it was highly inaccurate, making only 4 shots out of 24. Next we tested the second level (0 psi) http://i669.photobucket.com/albums/vv57/Team2470/Wheel_compression_zps4d6c0c42.jpg we noticed a small decrease in range of the shooter at this point so we increased our test speed to 80%. After shooting another 24 shots and making 18/24 we decided this was the design we would go for.
The below tests are all results with the AM 8" Pneumatic wheel. The wheel is not perfectly beaded.
Compression
We did not test many different types of compression but the entry compression is less then the exit compression.
Exit compression:
Entry compression:
Saw blade
Why is there a saw blade on top of our wheel? It takes awhile to take the saw blade on and off so for all of the above results the saw blade remained on our wheel. The sharp edges were grinded(ground?) off before the saw blade was attached and it adds a lot of mass to the wheel. Initially the saw blade was attached on the underside of the wheel but we found it was not as effective as it being on top. The wheel has a lot of momentum because of the extra mass, it takes a lot longer for it to slow down and speed up.
Velocity
We measured velocity over about 18 tests using limit switches and an Arduino board. The average velocity was 17.62 feet per second.
CIM voltage/current?
We did not measure either.
Guiderail
During our initial testing we found adding a small guiderail to the arc of our shooter increased our accuracy and shooting distance. It is just some C-channel we bent to fit in our arc.
The Arc
We found that a 90 degree arc works just as well as a 180 degree arc in our prototype.
I most likely forgot to include something in this report so please ask questions if you have any.
I do not have a video at the moment but I hope to upload one later tonight.
Evan