Hey r/robotics,
I’m trying to upgrade the joints on open-source platforms (like the Berkeley Lite and ALOHA) because I keep destroying 3D-printed plastic gears under dynamic loads.
I’m currently designing a full CNC metal cycloidal drive to replace them, but I need a reality check on the physics before I spend a ton of money at the machine shop.
My plan is to standardize all joints to a single size with a 30:1 gear ratio and a 48V architecture (to keep machining costs sane).
Here is my main dilemma: At 30:1, is this still technically QDD (Quasi-Direct Drive)?
My goal is to achieve good proprioception (sensing external forces via current changes) without expensive inline torque sensors, utilizing Dual Absolute Encoders and FOC. But I’m worried that the added friction and inertia of a 30:1 metal cycloidal will kill the back-drivability and ruin the impedance control.
Has anyone successfully done sensorless force control with a 30:1 metal cycloidal? Does this actually work for humanoids, or am I just building a stiff industrial joint by accident?
Also, I'm trying to use one universal actuator size for the whole robot to simplify the BOM. Is this a terrible idea for bipedal swing dynamics?
Would love to hear some harsh truths before I pull the trigger on prototyping! (Exploded CAD view attached).