Design goals
v6.5 builds on the v6 foundation while moving more of the arm’s weight away from the shoulder. NEMA 17 motors drive every degree of freedom except the gripper.
Transmission and wrist
A fiberglass-reinforced GT2 belt drives the elbow and adds a 3:1 pulley reduction. The wrist uses differential helical bevel gears, so its motors can sit further back, belt-drive the wrist, and act as counterweights for the payload. The actuators reuse the stackable 5:1 planetary gearbox I designed for v6.
What came next
The lessons from v6.5 went into Robot Arm v7, which switched to custom cycloidal drives, added a sixth degree of freedom and closed the loop on the big joints.