Mini-Project 2: A Single-Stage NEO/Kraken Gearbox

Almost every mechanism needs a custom gearbox. This mini-project builds a clean single-stage reduction you can waterjet from 0.190 in (3/16) aluminum plate.

Step 1 — Choose the ratio. Single-stage spur reductions are typically modest; for this example use 20 DP gears with a 14T pinion on the motor and a 50T gear on the output, giving 50/14 ≈ 3.57:1. Compute the center distance from pitch diameters: for 20 DP, pitch diameter = teeth / diametral pitch, so 14/20 = 0.70 in and 50/20 = 2.50 in; center distance = (0.70 + 2.50)/2 = 1.60 in. Write this as a variable #centerDist = 1.60 in. (If you need a larger reduction in one box, you generally move to a planetary or a multi-stage layout.)

Step 2 — Layout sketch. In a Part Studio, sketch two points #centerDist apart. Point A is the motor shaft, point B the output. Place the motor's mounting bolt pattern at A — pull the exact NEO or Kraken X60 footprint from the MKCad motor part rather than guessing hole positions. Place the output bore at point B sized for a 0.500 in hex bearing (a flanged hex bearing matched to 1/2 in hex stock).

Step 3 — Build plates. Extrude the front plate 0.190 in. Use Extrude Individual (Julia's FeatureScript) to create the matching back plate as a separate part in the same sketch region set. Add a ring of standoff holes (#10 clearance) so the two plates clamp onto hex standoffs.

Step 4 — Add the gears. Use the Spur Gear FeatureScript to generate the 14T and 50T gears at 20 DP so the model is dimensionally honest, or insert COTS WCP/AndyMark gears from MKCad. Place a 0.500 in ThunderHex output shaft (AndyMark hex shaft stock) through point B.

Step 5 — Sanity-check mesh. In the Assembly, mate the gears with Revolute mates to their bore connectors. Drag the pinion; the 50T should rotate. If they overlap or gap, your #centerDist is wrong — recompute pitch diameters. Because center distance is a variable, fixing it updates both plate bores at once.

This is also where you would consider a COTS gearbox instead: the REV MAXPlanetary and WCP VersaPlanetary systems offer stackable cartridge stages and are worth modeling-in when you do not need a custom plate.