One horse walking a gin puts about 490-735 W on the sweep arm and 397-595 W on the millstone, which grinds roughly 6.6-39.7 kg of wheat an hour (0.24-1.5 bushels), well below the 2-4 bushels an hour sometimes quoted. A pair working in turns of 2-3 hours can supply a village of 100 only if the stones need little energy per kilogram, so build the gin for coarse meal and keep the water or wind mill for fine flour.
Part of Community Grain Mill
A horse or ox walking a circle to turn a millstone through a vertical shaft and crown gear: how much power the animal gives, how the gearing turns a 3 rpm walk into a 100 rpm stone, and what it costs in feed.
An Animal Gives Power By Pull Times Walking Speed
Power is force times speed. The community grain mill note describes a horse hitched to a beam on a central vertical shaft, driving the stone shaft through a crown-and-lantern gear. The animal’s force is its sustained pull, usually put at 10-15% of its body weight at a walk (a rule of thumb recalled from draft-animal practice, not a measurement here); its speed is the walking pace in the circle.
| Animal | Weight | Pull at 10-15% | Speed in the gin | Power at the sweep |
|---|---|---|---|---|
| Horse | 500 kg | 490-735 N | 1.0 m/s | 490-735 W |
| Ox | 600 kg | 589-883 N | 0.56-0.83 m/s | 330-733 W |
The horse and ox weights are the ones the corpus uses in its feeding tables (Horses for Draft Work, Oxen); the ox walks at the 2-3 km/h that page gives, 0.56-0.83 m/s. The horse’s 1.0 m/s is a slow gin walk, below the 5-6 km/h it covers on the road.
Gearing Takes The Walk From Three Turns A Minute To A Hundred
The carrier gives a circle 20-30 ft across (6.1-9.1 m), so the sweep arm is 3.05-4.57 m long. At 1.0 m/s the shaft turns at 1.0 / 3.05 = 0.33 rad/s (3.1 rpm) on the short arm and 1.0 / 4.57 = 0.22 rad/s (2.1 rpm) on the long one. To spin a stone at 100 rpm the train must step up 100 / 3.1 = 32 to 100 / 2.1 = 48. That needs two gear stages, and two stages at 0.90 each leave 0.81 of the power.
At the stone: 490 x 0.81 = 397 W up to 735 x 0.81 = 595 W for the horse; 330 x 0.81 = 267 W up to 733 x 0.81 = 594 W for the ox.
Method: Throughput And Shifts
Step 1: Take the watts at the stone. Use the row above.
Step 2: Divide by the grinding energy. The energy per kilogram of wheat ground is 15-60 Wh/kg (Bushels per Hour by Power Source). One horse: 397 / 60 = 6.6 kg/h up to 595 / 15 = 39.7 kg/h, which is 0.24-1.46 bushels an hour at 27.2 kg a bushel. One ox: 267 / 60 = 4.5 kg/h up to 594 / 15 = 39.6 kg/h.
Step 3: Set the shift. The carrier says to rotate every 2-3 hours. Two horses alternating for a total of 5 hours a day grind 6.6 x 5 = 33 kg to 39.7 x 5 = 198 kg of flour.
Step 4: Compare with the need. A village of 100 eating 1.5 lb of grain each a day needs 150 lb, which is 68 kg (Community Grain Mill). The pair covers it at the lower grinding energy (198 kg a day, nearly three times the need) and about half of it at the higher (33 / 68 = 0.49).
The carrier’s 2-4 bushels an hour for one horse is 54-109 kg an hour. At 397-595 W that requires only 3.6-10.9 Wh/kg, below every figure derived in the linked article, so plan on the lower rate.
Feed Is The Running Cost
A 500 kg horse in heavy work eats about 7 kg of hay and 5 kg of grain a day, and a 600 kg ox in heavy work about 15-18 kg of hay and no grain (corpus feeding tables). A horse working 2.5 hours at the grain-mill rate grinds 17-99 kg of flour a day while eating 5 kg of grain; an ox costs hay land instead of grain land. See Feeding Working Animals for the full ration.
Common Mistakes
- Quoting bushels with no animal in the sum. One horse is under 600 W at the stone; any rate above that is a claim without a power source.
- A tight circle. The smaller the gin, the tighter the horse’s turn and the faster the gearing must run; build the largest circle the site allows.
- No spare animals. A lame horse stops the mill, so keep at least two and rotate.
Gears, sweep arm and kicks
The sweep arm and the crown gear above the animal strike and crush. Wall off the gear with a guard, keep the circle clear of children, and never reach into the train while the animal is hitched. The stop is the driver at the animal’s head with a halter, and the animal’s own momentum is small, so it halts in a stride or two; unhitch before any adjustment to the stones. Flour dust is explosive in a cloud: no open flame in the mill, sweep often, and never test for dust with a flame.
What’s Next
- Learn next: Hand-Cranked Backup Systems - the next step down in power
- Combine with: Lantern Pinion - the gear a bare workshop can build for the train