This video provides a detailed project update on the CAD and mechanical design of "Ball Butler Vzero," a robot designed to throw balls. The creator has shifted focus to completing a minimum viable product (MVP), temporarily postponing more complex features like a spring-powered throwing mechanism and a side-mounted hand.
Key design advancements include the integration of a slip ring to enable infinite yaw rotation, which eliminates cable twisting but necessitates a redesign of the absolute encoder's placement. The encoder is now mounted on the rotating arm and will function as a "load encoder" for the ODrive motor controller. The creator also details the physical modification of a DC motor by removing its built-in encoder to save space. A comprehensive walkthrough of the current Onshape CAD model covers the assembly process for the base, the large bearing and gear system, and the arm structure. The design addresses previous stability issues with a more robust clamping mechanism and considers serviceability by ensuring access to all fasteners.
The video also discusses ongoing challenges, including the wiring plan, potential signal integrity issues with CAN bus cables running near power lines, and the unresolved issue of how to safely handle the regenerative energy from braking the throwing motor. Finally, the creator outlines the next major design problem: creating an automated hopper and a mechanical escapement system to load balls into the robot one at a time.
Ball Butler Vzero: A Deep Dive into the Latest Mechanical Design and Assembly Plan
0:00:45 Focus on the MVP: The creator is now concentrating on completing a minimum viable product (MVP) of the Ball Butler Vzero, postponing more complex solutions to get a functional prototype working.
0:01:19 Avoiding Electrical Braking: To prevent regenerative power from damaging the electronics, the creator intends to use a mechanical braking system (e.g., a TPU block or shock absorbers) for the throwing arm instead of relying on the motor's electrical braking.
0:02:55 A Postponed Design Idea: A concept to mount the hand "collinear" with the arm (on its side) was explored. While this would prevent collisions with the base, it adds significant complexity to the motor and string placement and has been shelved for now.
0:11:15 Slip Ring for Infinite Rotation: A slip ring has been incorporated into the design to allow the main yaw axis to rotate infinitely without twisting and breaking the power and data cables that run to the upper section.
0:14:46 Redesigned Encoder Placement: The addition of the slip ring forced a redesign of the yaw axis's absolute encoder. It is now mounted on the rotating arm (instead of the static base), and its data will be fed to the ODrive as a "load encoder" to ensure accurate positioning.
0:24:46 Motor Modification for a Tighter Fit: The creator successfully removed the built-in encoder from the brushed DC motor used for the base. This modification shortens the motor, allowing it to fit within the compact design.
0:31:34 Improved Base and Gear Support: The base is designed to support the slip ring and features an added bearing to counteract the axial forces produced by the helical pinion gear, preventing it from walking off the motor shaft.
0:49:26 Designing for Disassembly: The assembly is designed to be serviceable. Unlike previous ideas, it does not require rotating the non-backdrivable arm to specific angles to access the bolts, preventing a situation where the robot could become impossible to take apart.
0:54:48 Robust Clamping Mechanism: The arm is mounted on a solid M8 stainless steel shaft, held firmly in place by a new clamping design that uses T-nuts for a much stronger grip, aiming to eliminate the wobble seen in previous prototypes.
0:58:58 Onshape Pro-Tip: A warning for 3D printing from Onshape: users must remember to manually update "contexts" between parts to ensure that corresponding holes and features remain aligned after design changes are made.
1:04:47 Complex Wiring and Signal Integrity: The plan for routing the CAN bus and power cables is detailed. There is concern about potential signal noise since the cables will run parallel to each other in a tight space, likely without room for a ferrite core to mitigate interference.
1:29:37 The Next Big Challenge: The Ball Hopper: With the main robot design nearing completion, the next major task is to design a system to load balls into the hand. Ideas include a vertical tube or a shelf-mounted bin that uses a mechanical escapement mechanism, inspired by the Wintergatan Marble Machine.
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