Mobile Platform
Drivetrain
A jameco 161382 dc brushed motor is face mounted onto the base. The duron mount inserts into the base, and is fixed using a #8-32 screw for maximum rigidity of this critical component. Onto the motor shaft we attached a fixed shaft coupler in order to mate with the 1/8" Vex square wheel shaft. We initially attempted to use spider couplers in order to account for shaft misalignment, but these introduced too much play into the system, so we decided that any additional radial load introduced by a fixed coupler was acceptable in our application and was greatly outweighed by the improvement in consistent drive performance. We ultimately designed our own 3d printed fixed shaft couplers and successfully integrated them, for a significantly reduced cost compared to those available for purchase. Our square shaft then passed through a 3d printed pillow block to support the inner side of the wheel. This pillow block was fastened to the base with machine screws, in a similar fashion to the motor mount. The shaft then passes through our omni wheel and is constrained at its far end by a roller blade bearing pressed into a vertical duron mount. Laser cut, duron shaft adapters were used along the length of the square shaft to create a cylindrical surface where the rotating shaft could be supported (ie at the pillow block and bearing), and these also served as spacers to constrain the position of the wheel along the shaft. A larger duron shaft adapter and a flanged bushing worked together to serve as a shim for the outer bearing, in order to constrain the wheel position without restricting rotation.
A jameco 161382 dc brushed motor is face mounted onto the base. The duron mount inserts into the base, and is fixed using a #8-32 screw for maximum rigidity of this critical component. Onto the motor shaft we attached a fixed shaft coupler in order to mate with the 1/8" Vex square wheel shaft. We initially attempted to use spider couplers in order to account for shaft misalignment, but these introduced too much play into the system, so we decided that any additional radial load introduced by a fixed coupler was acceptable in our application and was greatly outweighed by the improvement in consistent drive performance. We ultimately designed our own 3d printed fixed shaft couplers and successfully integrated them, for a significantly reduced cost compared to those available for purchase. Our square shaft then passed through a 3d printed pillow block to support the inner side of the wheel. This pillow block was fastened to the base with machine screws, in a similar fashion to the motor mount. The shaft then passes through our omni wheel and is constrained at its far end by a roller blade bearing pressed into a vertical duron mount. Laser cut, duron shaft adapters were used along the length of the square shaft to create a cylindrical surface where the rotating shaft could be supported (ie at the pillow block and bearing), and these also served as spacers to constrain the position of the wheel along the shaft. A larger duron shaft adapter and a flanged bushing worked together to serve as a shim for the outer bearing, in order to constrain the wheel position without restricting rotation.
Sensor mounts
Ultrasonic sensors were face mounted vertically on each side of the base. The geometry of the mount worked to locate the sensors exactly. After having trouble finding screws small enough to fit the sensor board, we simply used solid core wire fed through the mount and board holes to keep the sensors in place (the mount already provided such a precise, snug fit, that these wires were essentially a backup).
Ultrasonic sensors were face mounted vertically on each side of the base. The geometry of the mount worked to locate the sensors exactly. After having trouble finding screws small enough to fit the sensor board, we simply used solid core wire fed through the mount and board holes to keep the sensors in place (the mount already provided such a precise, snug fit, that these wires were essentially a backup).
Shooter
After consulting with many ME 210 and ME 218 alumni, we began by attempting a ruler / flicking design. They suggested that this was definitely the most precise method, and that fly wheels were difficult to control properly. We discovered that this method was difficult to implement and refine due to the accuracy required in the structure and geometry of the setup, which also made it difficult to test and adjust. Ultimately, we moved on to the flywheel design that most of the class had converged on. This allowed for much easier adjustment and testing by simply adjusting the voltage to change the wheel's angular velocity. This allowed us to start with a much higher exit velocity, which had the dual effect of reducing the impact of error on our ball's trajectory, as well as simplifying our trajectory to more closely approximate a straight line to our target. It also allowed us to very quickly and easily change the vertical impact point of our shots for testing and adjustments as needed.
Flywheel drive
Flywheel drive
Our flywheel drive was conceptually very similar to that of our drive wheels, this time using a 3d printed wheel powered by a smaller Sinotech 232040 dc motor motor. This motor was cheap, small, and provided up to 10krpm in order to shoot our projectiles as fast as desired. The 3d printed wheel allowed us to have the exact amount tangential speed and duration of ball contact we wanted (based on its diameter). It was also very rigid / reliable and allowed us to integrate shoulders and customize the drive shaft on either end for ease of mounting. An interesting failure that occurred during our testing was the shearing of one end of the wheel shaft. A close inspection showed that this was not due primarily to loading, but instead the heat from friction of the wheel shaft spinning at high rpm on duron weakened the plastic structure until it failed. Once a ball bearing was introduced at this support location (as initially planned), the wheel assembly proved to be very robust.
Ramp
The primary angle adjustment was integrated into our ball ramp. A simple foam core track was inserted into a curved guide (duron), and the length of this track was progressively shortened until we found our optimal shooting angle. Together with our modular fixing design (see below), this allowed for all the adjustability we needed.
The primary angle adjustment was integrated into our ball ramp. A simple foam core track was inserted into a curved guide (duron), and the length of this track was progressively shortened until we found our optimal shooting angle. Together with our modular fixing design (see below), this allowed for all the adjustability we needed.
Feeder
We initially hoped to use an inclined plane design to hold as many balls as possible and for quick-release shooting. After struggling to fit this design into our 12 inch height envelope, and seeing other teams struggle with balls getting stuck with similar designs, we quickly pivoted. We made a simple "revolver" design to hold and feed individual balls into our shooter ramp. Powered by simple servo with 180 degrees of motion, we were limited to loading 6 balls at a time. We were constrained by time and space restrictions, but a future iteration might use a stepper motor in order to feed 12 balls at once
Integration
1/4-20 threaded rods were used at 4 corners of the platform to connect all three stages of our robot. Additionally, the bearing mounts at the four sides of our base served to support and locate the vertical position of our shooter stage. A key breakthrough in our structure was the modular design of our feeder and shooter structure. With the threaded rods as primary supports, many identical slotted duron beams were used to create a gantry-like system. This allowed us to rigidly position the shooter and feeder at any x-y-z location, which proved invaluable for iteration and design without having to repeatedly develop an entirely new structure.