Design Process: 2012 Shooters

[Chris Fultz]

I think #2 and #4 are worth noting.

#2 is to evaluate and agree that you want to score basketballs. Even though this seems really obvious, it is important to review the game and all of the scoring and confirm this is something you want to do.

#4 is to focus on the "what", not the "how". The intent was to get a ball through the hoop. As soon as you begin to say "shoot the balls", then you start eliminating other ways of getting the ball through the hoop and start thinking about shooters.


Step 1. Understand the game and how to win the match and the event.

Step 2. Determine if we want to score basketballs.

Step 3. Evaluate the benefits and challenges and risks of 1, 2 and 3 point scoring.

Step 4. Brainstorm ideas on general “ball scoring” ideas.
(We avoided using the word “shooting” as long as possible, since we determined we wanted to score the balls but shooting was just a way to do that.)

Step 5. Sketches and rough prototypes of scoring options.
• Conveyors – could we make something like a farm conveyor to take the balls up to the goals?
o This is most suited for 1 or 2 point goals, more of a challenge for 3 point goals.
• Launch tubes – could we make a tube to raise up, rolls the balls off into the goal?
o This is most suited for 1 or 2 point goals, more of a challenge for 3 point goals.
• Push Shooter – could we push balls through a tube (pneumatics, springs, etc).
• Wheeled shooter – motor driven wheels to shoot, similar to many from “Aim High”.

Step 6. We determined a wheeled shooting system was the best option for versatility and the ability to score from many places on the field.

Step 7. Research shooters. Reviewed baseball and football machines. Reviewed “Behind the Design” ideas. Evaluated our baseball pitching robot from the summer of 2011. Evaluated one and two axle (ball between the wheels) designs.

Step 8. Based on reviews of other designs and our experiences, we determined that a single wheel shooter was our preference.

Step 9. Prototype. We made a basic design in Inventor, and then made our first assembly from Plywood and Lexan and wheels we had from previous kits and robots.
• Questions to be answered included –
o Speed required to shoot from the fender, the key, the bridge, the sides by the alliance bridge.
o Exit angle to required.
o Could we run a single speed and vary the exit angle and be accurate.
o Could we run a variable speed and have a set exit angle and be accurate.
o What squeeze was required to minimize the ball size and density effects.
o How critical was “the load” process and location on exit speed, motor drain, etc.
o What size wheel was optimal.
o What wheel material worked best with the game pieces.
o What was the best way to “aim” the shooter and what accuracy / tolerance was acceptable.
 Options – Lazy Susan rotation, Simple single point pin with worm drive movement, No rotation and only driver adjustments of robot
• Several iterations of speeds, exit angles and ball squeeze were tested and recorded.
• Based on test results for a surface speed of the wheel and the motor / gearbox capabilities, we determined a wheel size.

Step 10. System integration and implementing prototype results into a design.
• Decisions made
o Variable speed wheel.
o Fixed exit angle.
o Approximately 50 degrees of wheel / ball contact.
o Bottom load, top exit.
o 2 – 3” Squeeze.
• System Integration
o Shooter as low as possible to keep CG low and increase robot stability.
o Shooter high enough that a shot ball would clear a 60” robot that was sitting directly in front of us.
o Simple ball collection and management.
 Balls collected and held in a single row inside the robot.
 Balls loaded / sequenced into bottom of shooter.
 Balls managed to prevent “jamming” in the collector or shooter.

Step 11. Continued development of shooter.
• Improved shooter design created to incorporate mounting provisions, supports for left / right rotation, motor and gearbox mounting and adjustments for ball squeeze.
• Motor decisions
o Initial Prototype used 2 CIMs, 1:1 drive
o CIMs required for drive to provide speed and power required for the field
o Determined 2 FP and 2 AM motors with similar output speeds into CIM-sim gearbox was best option
 Power and durability of FP’s was known. AM’s assumed to be durable.
o Direct Drive mount of CIM-sim to shooter wheel shaft for a durable and simple drive.
 One set each side
 No additional gearing, chain or sprockets required.

Step 12. Shooter, Production Version 1.
• Higher quality shooter built to match new design.
• Continued prototype activity with wide and narrow wheels, wheel tread surfaces, single wheel and “double wheel” (two narrow width wheels with space between) and ball squeeze.
• Shooter mounted on robot frame to begin determining accuracy, speed requirements, optimal exit angle, etc.

Step 13. Integration to Prototype Robot (R1)
• The prototype robot (R1) was built while the shooter system was being tested and modified and optimized.
• The shooter system was mounted to R1. Integration, testing and modifications continued.

Step 14. Shooter, Production Version 2.
• Changes and improvements from continued work on the prototype were incorporated into the design of the shooter, ball collector and loading systems. Weight reductions were made, the design was optimized.
• Production Version 2 was completed and installed on the Prototype Robot (R1) while the competition robot was being constructed.