Mechanical Design

CAD Drivetrain

Moonwalker chassis is made up of ¼” clear acrylic top and bottom plates supported by 1” hexagon standoffs. There are three standoffs spread throughout the body to provide mechanical strength and equally carry the weight attached on the top.

CHASSIS

The bottom plate has three 12 V brushed DC motors with encoders (167 RPM) mounted to the 3.25” VEX omni wheels. It also houses two L298N motor drivers and a terminal block to facilitate external power connections to the system in a safe manner.

The top plate has the flywheel shooter mechanism with high speed 1620 RPM brushed DC motor and other major electrical components such as Teensy board, an IMU sensor, and the IR sensor.

WHEEL TO MOTOR DESIGN

The powertrain of the robot consists of three 3.25" VEX omni wheels, mounted 120°apart. Each omni wheel is connected to the brushed DC Motor via a 3D-printed nylon wheel hub, which allow for efficient torque transmission.

Ball Shooter

Shooting Mechanism

For the ball delivery system, we decided to use a flywheel shooter to deliver balls quickly without the need of driving all the way to the press stations. The system was designed for a 4 ⅞” BaneBots T81 30A hardness wheel. The main design considerations for the shooting mechanism were the angle of output of from the ramp, the rpm required by the motor, and the amount of compression on the balls. The angle of output was determined by plotting various trajectories based on the dimensions of the field and selecting the shortest path of travel that would work from both the good press station and the bad press station. The angle we decided on was 30°. Using this angle we determined the output velocity with basic kinematic equations. Using the relationship that v = ωr, the linear velocity was converted into angular velocity to determine the required rpm of the motor. The required rpm for the motor was 1184 rpm. Therefore, we selected our motor to be the Gobilda 5202 Series Yellow Jacket Planetary Gear Motor because it provided 1620 rpm and included an encoder. The compression on the ball was determined experimentally with a prototype that allowed us to increase or decrease the compression. The additional rpm specs allowed us to account for losses in the system due to friction etc.

Initial Calculations

Using an angle of 30 degrees we determined we would need the flywheel to spin at 1184 rpm

Initial Prototype

3D printed ramp with mountings that allow for adjustment of compression

Using the specs from our calculations we 3D printed a ramp for the ball to roll on and laser cut supports to mount the wheel shaft at the required height. In order to test the shooter, we initially hooked up a hand drill to the shaft to see if the ball would be launched. Once we were confident in the design, we build a more stable prototype and hooked in up to the motor. Using a power source, we varied the motor speed and were able to consistently deliver the balls to both the good and bad press.

Intake Mechanism

The last aspect of the shooter that hand to be designed was the method of storing and releasing balls into the flywheel ramp. We decided on a simple ramp that the balls are stored in. A servo motor is used with a 3D printed door that releases the balls onto the ramp when the door spins up out of the way. The ramp was prototyped initially in cardboard to determine the optimal angle (6°) as well at the distance from the ramp. The final design was laser cut out of acrylic.

Final Design

For the final design, the ramp and flywheel mounting were cut out of acrylic to give an aesthetic and clear view of the shooter. The motor was also mounted with acrylic plates that slid around the motor tightly. A 1/4" to 6mm shaft coupler was used to connect the 1/4" shaft to the 6mm motor output shaft. The flywheel was secured to the shaft using a hub and set screws. The two ball bearing and wheel were all placed on the shaft with shaft collars to maintain their location.

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