Mechanical Movement 17 — Spanish Burton, Second Form
How does the second Spanish burton reach five to one?
Mechanism No. 17 from 507 Mechanical Movements, the second of the “Spanish bartons” (Spanish burtons). Rope 1 is tied to the beam, runs under the load pulley, over a fixed pulley and holds a runner pulley. Rope 2 starts at the axle of the load pulley, runs over the runner and down to your hand. Both parts of rope 2 pull on the runner, so rope 1 is twice as tight as your pull, and it holds the load twice; rope 2 adds one more share. Ideally the load hangs on 2 + 2 + 1 = 5 times your pull; the slanted strands in the drawing give a little less.
How it works, step by step
1. Two ropes, three pulleys
Rope 1 holds the runner from the fixed pulley; rope 2 runs from the load pulley’s axle over the runner to you.
2. The runner doubles it
Both parts of rope 2 pull the runner down, so rope 1 is about twice as tight as your pull: 328 N.
3. Five shares
The load hangs on two parts of rope 1 and one of rope 2: 2 + 2 + 1 ≈ 5. Pull 192 N for 785 N (the slanted rope gives a little less).
4. Lowering
The runner falls twice as fast as the load rises; your hand travels 57 cm for 12.0 cm of lift.
The key idea
F ≈ W / 5 — Rope 1 is twice as tight as your pull and holds the load twice; rope 2 adds one more share.
Taking rope 2 from the load pulley itself adds one more share: the second Spanish burton reaches about 5 : 1.
Model and assumptions
Mechanical advantage is taken from the geometry: hand travel ÷ lift, about 5 (the slant of rope 2 lowers it slightly). As the load rises 1 cm the runner drops 2 cm. Friction: lifting needs about W / (MA · η³).
Frequently asked questions
How does it differ from Movement 16?
The second rope starts at the load pulley itself, which adds one more share of lift.
Why is the measured advantage below 5?
The slanted rope pulls partly sideways, so a little of its tension does not lift.
How far does the runner move?
Twice as far as the load, in the opposite direction.
Part of the 507 Mechanical Movements series
This is Movement No. 17 from Henry T. Brown’s 507 Mechanical Movements (1868), redrawn and simulated by BCRUZ.
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