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 community COTS parts library (FRCDesignLib, inserted via the FRCDesignApp Onshape plugin) 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 FRCDesignLib. Place a 0.500 in ThunderHex output shaft (VexPro/WCP 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.