A brake used in cranes and hoisting machines

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

The brake-wheel (radius 9) is on the crane's barrel shaft. The load turns it clockwise with a constant torque (0.6 N·m, the one driven joint) against a little friction in its bearings, so with the brake off it runs at a steady speed. The strap is leather, modelled as a chain of 48 links 0.8 cm thick on real contact with the rim (friction 0.4). It runs from a pin on the lever below the fulcrum, clockwise round about 267° of the wheel, to a pin above the fulcrum. The operator's hand is a damped spring on the lever, and he sets its free position: off holds the lever up (the strap slack), on pulls the long end down. The viewer's Brake control switches between the two. The automatic run puts the brake on at 2.5 s and takes it off at 6 s.

Measured

With the brake off the load runs the wheel round at 1.62 rad/s (15.5 rev/min), faster than 0.2× the mean all of the time. Pulling the lever down swings both pins away from the wheel, drawing the strap's ends toward each other. The strap tightens on the rim and the wheel stops within half a second; while it is held its speed stays at 0.0009 rad/s (limit 0.05). When the lever is let up the strap slackens and the wheel runs at 1.62 rad/s again. The deepest contact is 0.19 mm, and 0.02 mm after the first half second.

Notes

Brown gives no sizes, so the lever, the pins and the fulcrum are placed as on the plate. Both strap ends are on the lever, either side of the fulcrum, so a pull on the long arm takes up strap at both ends, about 4.4 cm per radian of the lever. In the off position the lever holds the strap about a centimetre slack, or its weight and pretension drag the wheel nearly to a stop. The strap's links must be soft enough to stay stable at the 0.1 ms step.

Film (MP4) · Still (PNG) · Spec (YAML) · Model (MJCF)