In the simplest design, a minimum of two degrees of freedom are necessary to complete the designated task; the machine needed to be able to handle varying longitudinal distances as well as firing from different lateral offsets. Team Implausible was interested in taking this project to a new level; we wanted to add extra degrees of control to allow us to expand the ballistic trajectory control from planar space to 3 dimensional space. This would allow us to "hook" the ball through curves in 3d space defined by physical constraints (maximum achieveable rotational velocities, drag coefficient, etc). Due to the complexity of the design, simplifications were made towards meeting the required deadlines which occurred in two phases. In the first face, overall assembly and manufacturing was simplified. In the second phase we dropped an entire belt assembly from the firing subsystem. This was a disheartening in that rather than having control over ball spin around two axis, we only had control around 1 axis. This limited the theoretical aerial control effects to increasing or decreasing the net lift force experienced by the ball as it soars through the air. The evolution of the concept is depicted below, the final image being an actual photo of the final design.
2nd iteration concept: simpler manufacturing and assembly
Stephen Meade: electrical engineer/programmer
David Joffe: computer engineer/programmer
Ian Lenz: computer engineer/programmer
Christopher (CJ) LaMontagna: mechanical engineer
Automated degrees of Freedom (4)
Rotation at the base, independent open-loop velocity control for each of the 2 belts, ball-feed control
The base housed all of our electronics and the majority of our wiring. It has a two disc, friction driven 360 degree rotational aiming system. An ultrasonic rangefinder was attached to determine longitudinal distance to the target. With user input of lateral offset distance from the centerline of the target, the machine solves for the desired lateral firing angle and rotates the base until closed loop feedback from encoder values reaches the desired angle.
rotating base/platform concept
note: the concept used a direct drive rotational motor rather than the realized system's friction based one
The firing mechanism includes the pulleys, belts, and guide rails. Based on the rangefinder data (longitudinal distance), user input lateral distance, and fixed hoop height, we developed a lookup table to relate desired voltage at the motor in relation to the effective firing distance. (see original concept, 2nd iteration, and final assembly images)
We implemented a turnstile type device driven by a single hobby servo to release two balls sequentially with a fixed delay time before and in-between firing each of the two balls. The delay was necessary to ensure proper firing velocities were achieved and maintained after the firing sub-systems' inertial energies dissipate after the first shot.
Direct Link to Youtube Video