Step-up gears for a generator inside a 2 in tri-clamp cross: 42 : 15, module 1 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-generator-step-up-gears/  (CC BY 4.0)
Basis: ISO 53 basic rack (20°, addendum 1 m, dedendum 1.25 m), involute flanks as the spur gears on this site; centre distance m (z1 + z2) / 2; tooth counts set by the room in the cross; rotor-top holes from the 2208 listing
Catalog version: 2026-10-20

Sizes: see table below
- The crank gear (42 teeth, tip Ø44) sits on the −X crankshaft beside the crank, in place of one flywheel disc and just as heavy; the 15-tooth pinion turns with the motor's rotor. Centre distance 28.5 mm, ratio 2.8 : 1.
- The pinion rides on an adaptor: a Ø18 × 2 flange bolted to the rotor top with four M2 × 4 (their heads on the flange's outer face) and a Ø6 stub through the pinion, which an M3 grub holds. The rotor's holes sit at r 6, inside the pinion's teeth, so the pinion cannot be bolted on directly.
- Why 2.8 and not more: the motor's Ø27.5 can lies over the crank, so its axis has to be at least 13 + 13.75 mm above the crankshaft (the crank's con-rod eyes sweep R 13), and the crank gear has to turn inside the Ø47.5 bore. 42 : 15 at module 1 puts the can 1.75 mm clear of the crank and the gear tip 1.75 mm inside the bore.
- Both gears are drawn at exact size with no backlash; their teeth are a mating feature (see Mating features).

part  teeth  pitch_dia_mm  tip_dia_mm  width_mm  bore_mm
crank gear  42  42.0  44.0  12.0  3.0
pinion  15  15.0  17.0  10.0  6.0
adaptor      18.0  14.0  

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- ISO: ISO 53 cylindrical gears, standard basic rack (20°, addendum 1 m, dedendum 1.25 m), as the involute spur gears on this site — standard — dimensions are facts [verify license at link] — https://www.iso.org/standard/22952.html
- GetFPV (product listing): Tiger GB2208-80 gimbal motor: 27.5 × 23, 4.5 hollow shaft, stator 4-M3 on 19 × 16, rotor 4-M2 on 12 × 12 — web — vendor page; dimensions are facts [verify license at link] — https://www.getfpv.com/tiger-gb2208-80-brushless-gimbal-motor-hollow-shaft.html
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/index.json
API: https://xemstudio.com/api/geometry?object=tri-clamp-generator-step-up-gears