# goBILDA 5103 Planetary Gearbox 139:1

> goBILDA 5103-0024-0139 5103-series 3-stage planetary gearbox, 139:1 (exactly 139.138:1), steel gears, sold as the replacement gearbox for 5203 Yellow Jacket motors: Ø36 mm × 50.3 mm body, 8 mm REX output shaft 23.5 mm long, M4 goBILDA pattern on the face, 237 g. No torque or backlash rating is published.

- Manufacturer: goBILDA
- Part number: 5103-0024-0139
- Category: Reducers
- Canonical page: https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-139-1-1c3f
- Structured JSON: https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-139-1-1c3f/data.json
- Source: Xirkit structured parts catalog — every value traced to a cited document; unknowns are explicit.

## Key specifications

| Property | Value |
| --- | --- |
| Reducer type | planetary |
| Gear ratio | 139:1 |
| Stages | 3 |
| Input | replaces the gearbox on goBILDA 5203 Yellow Jacket motors (RS-555 motor, input pinion) |
| Output shaft | 8 mm REX, 24 mm long |
| Output shaft diameter | 8 mm |
| Weight | 237 g |
| Dimensions | 36 × 36 × 50.3 mm |

## Where to buy

| Supplier | Price | Stock | Checked | URL |
| --- | --- | --- | --- | --- |
| www.gobilda.com | 34.99 USD | in_stock | 2026-10-01 | https://www.gobilda.com/5103-series-planetary-gearbox-139-1-ratio-24mm-length-8mm-rex-shaft/ |

## FAQ

**How much does the goBILDA 5103 Planetary Gearbox 139:1 cost?**

From $34.99 at www.gobilda.com. Prices are observed unit prices before tax and shipping.

**What are the goBILDA 5103 Planetary Gearbox 139:1 dimensions?**

36 × 36 × 50.3 mm. A STEP model is available for enclosure fit checks.

**Where does this goBILDA 5103 Planetary Gearbox 139:1 data come from?**

Every value in this record is traced to a source — 2 documents including the board and chip datasheets — with the page and table cited per value. Unknowns are left explicit, never guessed.

## Sources

- [goBILDA 5103 Planetary Gearbox 139:1 datasheet](https://www.gobilda.com/5103-series-planetary-gearbox-139-1-ratio-24mm-length-8mm-rex-shaft/)
- [www.gobilda.com listing](https://www.gobilda.com/5103-series-planetary-gearbox-139-1-ratio-24mm-length-8mm-rex-shaft/)

## Part graph

### Alternatives (by use case)

- [goBILDA 5103 Planetary Gearbox 26.9:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-26-9-1-4c3b) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99
- [goBILDA 5103 Planetary Gearbox 50.9:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-50-9-1-541f) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99
- [goBILDA 5103 Planetary Gearbox 5.2:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-5-2-1-ed7b) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99
- [goBILDA 5103 Planetary Gearbox 99.5:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-99-5-1-019e) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99
- [goBILDA 5103 Planetary Gearbox 19.2:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-19-2-1-1cb5) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99
- [goBILDA 5103 Planetary Gearbox 188:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-188-1-3a30) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99
- [goBILDA 5103 Planetary Gearbox 13.7:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-13-7-1-486e) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99
- [goBILDA 5103 Planetary Gearbox 71.2:1](https://www.xirkit.io/products/gobilda-5103-planetary-gearbox-71-2-1-9650) — Both serve robot joints and actuation — check the trade-offs; $34.99 vs $34.99