The hobbyist Mishin Machine has developed the ROAR forearm, a compact, high-performance 3D-printed robotic forearm that integrates three fully custom-designed gearboxes. This advanced build features a smooth Wave Drive V2 with rolling elements for improved contact surface and reduced wear, a powerful Three-Ring Cycloidal Drive for high reduction ratios in a slim profile, and an innovative Angular Crown Gear that transmits motion at precise angles without traditional bevel gears. The entire structure was designed in Onshape CAD software and precision-printed on a Formlabs Form 4 resin 3D printer using Tough 2000 resin for structural strength and Clear V5 resin for transparency, allowing clear visibility of the internal mechanisms operating like a living machine. Carbon fibre tubes provide excellent rigidity while keeping weight low, and magnetic encoders on the output shafts deliver ultra-precise position feedback.
The technical excellence of this 3D-printed robotic forearm lies in its clever integration of interdependent mechanisms. Each custom reducer was optimised for minimal backlash, high torque, and compact packaging, solving common challenges in DIY robotic arms. The Wave Drive V2 uses a specially profiled cage for better ball-bearing alignment, while the cycloidal drive ensures smooth high-reduction performance. The forearm’s split-body design with a dedicated belt cover simplifies assembly and maintenance.
By choosing professional resin printing over standard FDM, Mishin Machine achieved superior dimensional accuracy, strong layer bonding, and flawless gear meshing, critical for the smooth, fluid motion seen in the final build. This ROAR forearm project provides practical insights for makers and robotics enthusiasts interested in custom reducers, cycloidal drives, wave gearboxes, and professional resin 3D printing.
