NEMA17 Geared Radar Scan Turret

This is a desktop scanning turret for "Arduino radar" sweeps, ToF room mapping or a steady camera head. A NEMA 17 sits under a deck on four legs. It drives a 20-tooth pinion into a 60-tooth ring gear, a 3:1 reduction. That gives 0.6° per full step, or about 0.04° at 1/16 microstepping, so you set sweep speed and resolution in firmware instead of living with a servo's jitter. The ring gear's hub holds two 608 bearings that turn on a fixed 8 mm rod, so nothing grinds printed plastic on printed plastic. A turntable bolts on top of the gear. A U-shaped yoke on the turntable carries a sensor cradle that you tilt by hand from −45° to +45° and lock with a screw in an arc slot. The cradle face has a 10 mm M3 hole grid, so it takes almost any sensor board on standoffs.

It's aimed at hobby roboticists who want a sturdy pan head with a real bearing for scanning, mapping or pointing. It also fits as a sensor mast on a larger rover. All screw joints are M3. Threads come from brass heat-set inserts, and the same M3 clearance/insert sizes are used everywhere.

Assembly order:

1. Press M3 heat-set inserts into the leg tops, the rod boss on the deck, the top face of the gear hub, the turntable and the cradle flanges.
2. Screw the four legs under the deck with M3x12 screws.
3. Push the 44 mm length of 8 mm rod through the deck boss until it's flush with the underside, then lock it with an M3x8 grub screw in the boss.
4. Press one 608 bearing into the bottom pocket of the ring-gear hub and one into the top pocket. Lower the hub over the rod until the bottom bearing's inner race sits on the boss shoulder.
5. Put the motor under the deck with its pilot in the slotted recess and fit four loose M3x10 screws. Slide the pinion onto the shaft 1 mm above the deck and lock it with the M3 set screw and captured nut.
6. Slide the motor along the slots until the gears mesh with a hair of backlash, then tighten the screws.
7. Bolt the turntable to the hub with 4x M3x8 screws in the counterbores. Bolt the yoke to the turntable with 4x M3x10.
8. Fit the cradle between the cheeks with M3x12 pivot screws. Add M3x12 lock screws through the arc slots, set the tilt angle and tighten.
9. Mount your sensor on the grid face and run its cable through the turntable's cable hole.

Tuning notes: the gear center distance is 60.25 mm (60 mm pitch plus 0.25 mm of backlash). The motor slots give ±1 mm of adjustment, so you can take up slop without binding the gears. The pinion's set screw needs at least 21 mm of shaft sticking out from the motor faceplate, so measure your motor. The deck sits 55 mm up, which clears motor bodies up to 48 mm long. The head is held down by gravity, so don't mount it upside down. Because the sensor cable runs through the turntable, limit the sweep in software to about ±170°, or add your own homing switch.