Splined like a gearbox shaft: ISO 4156 involute splines in module 1, with a flat root at 30° on the small pulley and a fillet root at 37.5° on the large one.
HTD-3M-24T+flange.stl — pulley 1, 24 teeth, without supportsHTD-3M-36T-P2.stl — pulley 2, 36 teethHTD3M-24T-Assembly.stl — pulley 1 with both flanges and breakaway supports: print this oneFree STLs are CC BY 4.0, printed size without print compensation. Open the design to change anything, tune the fit for your printer, or download STEP, DXF, SVG and the belt.
| Pulley 1 | Pulley 2 | |
|---|---|---|
| Pitch diameter | 22.92 mm | 34.38 mm |
| Outside diameter | 22.16 mm | 33.62 mm |
| Root diameter | 19.74 mm | 31.20 mm |
| Groove depth | 1.21 mm | 1.21 mm |
| Pitch line differential | 0.38 mm | 0.38 mm |
| Spline minor (the bore) | 8.27 mm | 15.17 mm |
| Spline major (its reach) | 10.50 mm | 17.40 mm |
| Sample shaft minor | 7.50 mm | 14.60 mm |
| Sample shaft major | 10.00 mm | 16.90 mm |
| Retaining ring | DIN 471 10 × 1, top face (McMaster 98541A118) | DIN 471 17 × 1, top face (McMaster 98541A420) |
| Ring counterbore diameter | 17.00 mm | 25.00 mm |
| Ring counterbore depth | 1.10 mm | 1.10 mm |
| Belt width | 10.00 mm | 10.00 mm |
| Face width (belt + clearance) | 15.00 mm | 15.00 mm |
| Minimum face width | 12.00 mm | 15.00 mm |
| Flange outside diameter | 28.16 mm | — |
| Flange past the OD | 3.00 mm | — |
| Minimum flange height | 1.59 mm | — |
| Belt | 104 teeth · 312.00 mm | |
| Centre distance | 110.85 mm | |
| Drive ratio | 24 : 36 · 1 : 1.5 | |
Read from the generator's Dimensions panel for this design, which opens with no warnings.
Ready for an FRC robot: the bore fits REV ½" rounded hex shaft, with SH-50 retaining-ring grooves on both faces and a splined washer under each ring so nothing walks along the shaft.
Built like a machined part: ISO 773 keyways sized to 12 mm and 20 mm shafts, M5 set screws to lock them, and flanges drawn as bent metal plates instead of printed rims.
Heavy-duty HTD 8M on splined shafts: straight-sided ISO 14 splines carry torque no set screw could, and the 36-tooth pulley is spoked around its spline hub.
Industrial scale: an HTD 14M drive for a 40 mm belt, keyed 35 mm and 50 mm bores, a spoked 36-tooth pulley over 160 mm across, and metal-plate flanges.