A contrivance for transmitting rotary motion to a movable pulley
A contrivance for transmitting rotary motion to a movable pulley. The pulley at the bottom of the figure is the movable one; if this pulley were raised or depressed, the belt would be slackened or tightened accordingly. In order to keep a uniform tension on the belt, a pulley, A, carried in a frame sliding between guides (not shown), hangs from a rope passing over the two guide-pulleys, B, B, and is acted upon by the balance weight, C, in such manner as to produce the desired result.
Only the input is driven; every other part of this model moves by physics (MuJoCo), and its ratios are measured. Run it live, change its parameters, or switch the friction off to see the output stop.
- Modelled as
- a closed belt of 52 leather links (friction on the pulleys) round the driving pulley (r 8), the movable pulley (r 5.5, on a slide screwed at two heights: `low`, `raised` +6 cm) and the tension pulley A (r 4.5) in a yoke on a vertical guide; A hangs from a hemp rope of 34 links over the guide pulleys B, B to the 9 kg balance weight C on its own guide
- Measured
- movable/driver 1.409 (pitch-line radii 8.2/5.7 = 1.4386, slip 2.1 %); raised 1.380 (4.1 %); A rises 1.5 → 4.3 cm and C falls 1.2 → 3.2 cm when the pulley is raised
- Notes
- Only the driving pulley is motor-driven (30 rpm). Negative control, at a 0.5 N·m load on the movable pulley: normal 1.332, C weightless 1.088 with A dropped 3.3 cm (at the drawn 0.06 N·m load A's own weight alone still drives it, 1.389). Open: the raised variant slips 2 % more than the low one, and C falls 2.0 cm where A rises 2.75 (the rope's angle off B accounts for part).
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