The Bucket Elevator: Lifting Grain by the Bucketful, and Where It Lands

Print eight small buckets, about 40 mm wide, 30 mm deep and 30 mm from back to lip, each with a flat back and two 5 mm holes. Bolt them to a loop of 25 mm nylon webbing at 60 mm spacing with elevator bolts: their flat heads sit flush on the belt side so they run smoothly over the pulleys. Make two drums from 50 mm PVC pipe on 8 mm steel shafts in skateboard bearings, one at the foot of an upright plywood board and one about 600 mm above it. Tension the belt by sliding the foot drum down in a slotted hole. Drive the head shaft from a geared DC motor on an adjustable power supply. Build a boot box round the foot drum that you can fill with lentils, and fix an open-topped chute on the down-going side of the head, just below the level of the head shaft, where thrown grain will land.

With the drum radius and bucket-lip radius of your build, compute the two speeds from the notebook: $n_c = \frac{60}{2\pi}\sqrt{g/r_1}$ and $n_g = \frac{60}{2\pi}\sqrt{g/r_2}$. With a 25 mm drum and 55 mm to the bucket lip they come to about 190 and 130 rpm. Fill the boot. Start slow, well below the gravity speed, and raise the speed in steps, reading each with a tachometer on the head shaft. Watch the head. At low speed the buckets tip their lentils out late and many fall back down the up-going side. Through the mixed band some are thrown and some dribble. Above the centrifugal speed the lentils leave in a clean arc into the chute. At each speed run for 30 s, weigh what reached the chute, and note what fell back. Plot grams per minute against rpm: capacity rises with speed as the notebook says, and the fraction lost down the leg drops to nearly nothing once the throw is clean.

**Oliver Evans** built bucket elevators into his automated flour mill in the 1780s, moving grain from floor to floor without carrying it; his milling improvements were patented in 1790. **Joseph Dart** and the engineer **Robert Dunbar** built the first steam-powered grain elevator and storehouse on the Buffalo River in 1842, working from 1843. Its marine leg was lowered into a lake boat's hold and lifted the grain out in buckets on a belt. No patent was taken; Dunbar went on to design elevators across the Great Lakes and beyond. **Honest limits.** Grain dust is explosive, and elevator heads and legs are where dust explosions start: real elevators need dust control, bearing temperature and belt-slip monitors. Belt speed is limited too — too fast and the buckets throw grain past the chute and damage it, so every head speed is a compromise.