N20 Self-Locking Worm-Drive Winch

This is a small powered winch for robots, animatronic lifts, mini cranes and pulling a claw or sensor up and down. An N20 gearmotor turns a printed module-1.5 single-start worm, which drives a 24-tooth worm wheel bolted to a line drum. The worm's lead angle is about 7°, lower than PLA's friction angle, so the drive can't be back-driven: stop the motor and the load stays where it is, with no brake or holding current. The drum is fixed to an 8 mm steel axle turning in two 608 bearings in upright cheek plates. A fairlead brace across the cheek tops stiffens the frame and guides the line off the drum. The whole unit sits on one 146 x 105 mm base plate with four M3 holes for mounting to a chassis or frame.

Every printed part bolts to the base from underneath with M3 socket-head screws into brass heat-set inserts. The base therefore sets the positions of all parts, and the gear mesh depends only on printed heights. The worm and the motor sit together on one sled. The motor goes into a square channel against a stop wall, and the tail of the worm runs in a 624 bearing on the same sled, so the worm always lines up with the motor shaft. The worm wheel and the drum are printed separately so both print flat without supports, then joined with three M3 screws.

Assembly order:

1. Press heat-set inserts into the cheeks (4 in the bottom edge, 4 in the top edge), the sled (3 underneath) and the drum collar (3). Press an M3 nut into each set-screw pocket in the worm wheel hub, the drum hub and the worm collar.
2. Press a 608 bearing into each cheek, then bolt both cheeks to the base from underneath with 4x M3x10.
3. Bolt the worm wheel to the drum collar with 3x M3x16 so the two make one rotating unit.
4. Slide the 8 mm rod through cheek A, the wheel+drum unit, then cheek B. Push the shoulders against the bearing inner races and tighten both M3 set screws on the rod.
5. Press the 624 bearing into the sled post. Put the worm on the N20 shaft, set screw on the D-flat, with its tail pin in the 624. Seat the motor in the channel against the stop wall and strap it down with two zip ties through the under-channel tunnel.
6. Bolt the sled to the base from underneath with 3x M3x10 and check that the worm meshes with the wheel with a little backlash.
7. Bolt the fairlead brace to the cheek tops with 4x M3x12. Tie the line through the anchor hole in the drum, wind it on so it comes off the +Y side, and feed it up through the fairlead slot.

Tuning notes: the N20's body size (about 12 x 10 mm) comes from supplier listings and isn't a verified dimension, so the motor is held by zip ties in a 12.4 mm channel rather than a tight pocket. If your motor is loose, shim it with tape. The mesh centre distance is 24.2 mm, which includes 0.2 mm of backlash. If the gears bind, put a 0.2–0.4 mm paper shim under the axle cheeks. The wheel teeth are straight-cut, which a 7° worm lead tolerates. Grease the worm lightly with PTFE or lithium grease. With a 100 rpm N20 the drum turns at about 4 rpm, taking in roughly 0.4 m of line per minute. Wire the motor direction so the line leaves the drum on the +Y side, under the fairlead slot.