Open-source autosteer on a legacy tractor
GPS steering that holds a line inside an inch, on a tractor built before the moon landing, for about a tenth of the dealer's number and no subscription at all.
What it is
Four pieces: an inch-accurate GNSS receiver on the cab roof, a Windows tablet running AgOpenGPS, a geared motor clamped to the steering column where the wheel used to sit, and a small control board that reads a wheel-angle sensor and tells the motor what to do. The original steering wheel bolts back on top of the motor. Push the knob and you have your tractor back.
The numbers
- Documented builds, not estimates. Peter Brookes, a Warwickshire farmer, built one for £700 — £430 of GNSS receivers, £100 motor, £130 of board components, £5 PCB — and runs it at ±1 cm on a 115 hp Massey Ferguson 5612. The forum consensus across many builds is £1,000–£1,500, or roughly $1,000–1,600.
- The dealer side is a stack, not a single number. On a legacy tractor the activation alone is $1,000 standalone (about $3,000 bundled) — but an older machine has none of the rest. A universal display lists around $5,495, a legacy steering controller runs $3,300–$4,100 plus parts and labour, and the receiver is extra again. That is how a retrofit quote reaches five figures.
- Then the signal, every year. Roughly $600 a year for corrections the DIY build can get free or from its own $300 base.
- Holds inside an inch pass to pass. Steering by eye, an honest operator overlaps 4 to 8 inches every pass. On a 10 ft implement, 6 inches is 5% of every acre worked twice — seed twice, fertiliser twice, fuel twice, hours twice.
- The software is free and so are the board designs. It runs on tens of thousands of machines, and the forum where people answer questions at ten at night costs nothing either.
Why it's here
This is the clearest case on the whole site of a capability being withheld by price rather than by physics. The hardware is commodity. The maths is fifty years old. What costs five figures is the permission.
The automation angle
It *is* the automation — but the part worth copying is the wheel-angle sensor, a $40 part that turns an open-loop guess into a closed loop. Nearly every automation on this site is the same shape: a cheap sensor that tells the machine what actually happened instead of what was commanded.
The catch
Budget above the headline figure. The £700 and $1,200 numbers are real builds by people who already owned a bench, and current build guides are blunt that first-timers land higher once mounts, brackets, weatherproof connectors, fusing, an enclosure and the crimp tool you didn't own are counted. The parts list is honest; the first build is always a little dearer than the parts list. You also stay in the seat — this is cruise control, not a chauffeur, and the seat switch and steering-wheel-grab cutout are not optional builds. It needs sky, so no heavy trees and no barn. It will not fix slop in a worn steering box; fix that first, with a wrench. And it faithfully repeats whatever first line you give it, so a crooked AB line gets you a field of crooked rows, perfectly spaced.
In the guide
Chapters 3, 5 and 7 of the Autofarmation guide are the full build, the calibration and the safety interlocks. Autofarmation →