This video provides a detailed progress update and CAD walkthrough for a robotic project named "Ball Butler," focusing on the mechanical design and assembly plan for its Minimum Viable Product (MVP). The creator discusses significant design changes, most notably the integration of a slip ring to allow for infinite yaw axis rotation. This addition prompted a critical redesign of the arm's absolute encoder system, moving it from the static base to the rotating arm and leveraging the ODrive motor controller's "load encoder" functionality. The video includes a step-by-step assembly guide in Onshape, covering the base, the large-diameter main bearing, motor mounts, and the arm structure, highlighting solutions like a new bearing support for the pinion gear and a robust clamping system using T-nuts. Key challenges discussed include wiring management, potential electrical noise, 3D printing artifacts on curved surfaces, and a crucial lesson on managing part "contexts" in CAD. The creator concludes by brainstorming the next major challenge: designing a purely mechanical, automated ball-loading hopper.
Ball Butler V0: CAD, Assembly, and Design Challenges
0:45 Project Focus: Minimum Viable Product: The creator has decided to focus entirely on completing a working "Ball Butler V0" (MVP), postponing work on a separate test rig for the throwing mechanism to accelerate progress.
2:55 Alternative Design Postponed: A design concept to mount the throwing hand on the side of the arm (collinear) was considered to solve potential collision issues. However, due to the added complexity, this idea has been shelved to maintain focus on the MVP.
11:14 Slip Ring for Infinite Rotation: Following a viewer's suggestion, a slip ring has been incorporated into the design. This allows the robot's main body to rotate infinitely on its yaw axis without twisting and breaking the internal power and data cables.
14:46 Critical Encoder Redesign: The introduction of the slip ring forced a redesign of the arm's absolute encoder placement. It was moved from the static base to the rotating arm to prevent its cable from twisting. The encoder will now send its data to the ODrive controller as a "load encoder" to ensure precise arm positioning.
24:46 Motor Modification for a Perfect Fit: To make space for the new slip ring assembly, the built-in encoder on the brushed DC motor for the yaw axis was physically cut off, and the shaft was shortened with an angle grinder.
30:35 Detailed CAD & Assembly Walkthrough: The creator provides a comprehensive tour of the robot's design and planned assembly process in Onshape, covering the 3D-printed base, the large main bearing and gear, the motor mounting system, and the two arms that form the main structure.
54:55 Robust Clamping with T-Nuts: To create a rigid and wobble-free arm structure, the design uses M4 T-nuts embedded in the 3D-printed parts. This provides a significantly stronger clamping force on the main stainless steel axle compared to previous prototypes.
58:58 A Lesson in Onshape Contexts: The creator highlights a critical lesson for 3D printing from CAD: you must update part "contexts" in Onshape after making changes. He failed to do this, resulting in printed parts with misaligned holes that had to be remade.
1:04:47 Wiring and Noise Concerns: The planned cable routing is detailed, with power and CAN bus signals passing through the slip ring. The creator expresses concern about potential electrical noise from brushless motor cables interfering with sensitive encoder signals, especially in a tight space where a ferrite ring may not fit.
1:22:07 The Challenge of Printing Smooth Curves: An ongoing issue is the "stair-stepping" or faceting on 3D-printed curves. The creator investigates whether exporting models as STEP files instead of 3MF can produce a smoother G-code path and a better final print.
1:29:37 The Next Big Problem: Ball Loading: With the main robot design nearing completion, the focus will shift to creating an automated hopper to load balls into the hand. The creator is exploring purely mechanical solutions, such as a vertical tube with a clock-like escapement mechanism.