Double three-legged gravity escapement

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

Gravity on. The escape-wheel is two three-legged locking-wheels on one arbor, ABC in front and abc behind, with their legs reaching to radius 2.6, and one set of three lifting pins between them near the center at radius 1.2. A constant torque turns it clockwise (the weight). The pendulum hangs from a pivot 10 above the wheel's axis. The two pallets A (left) and B (right) hang from arbors of their own near the pendulum's point of suspension, 2.6 either side of it and at the same height. The pallets lie between the two wheels. Each pallet carries a weight and a fork-pin, and the fork-pins lie against the pendulum rod 4 below the wheel's axis. A banking stops each pallet when it hangs against the rod. Each pallet has an upright lifting face in the pins' path, and a short stop-tooth right under its arbor: D on A, in the path of the front wheel's legs, and E on B, in the path of the back wheel's. A pin coming round pushes the face out and lifts the pallet's weight until a leg lands on the stop and the wheel is locked: a leg of ABC on D at the left, a leg of abc on E at the right. The stop is struck nearly through the arbor, so the locked leg does not push the pallet. The pendulum swinging that way takes up the lifted pallet by its fork-pin and raises it a little further, the stop slides from under the leg, and the wheel goes a sixth of a turn until the other pallet's stop catches the next leg, its pin having lifted that pallet in turn. The pendulum comes back with the first pallet resting on it, and the pallet's weight falls further than the pendulum lifted it, down to its banking: that is the impulse. The pendulum is drawn 4° aside to the right at the start, with B resting on its rod, and the only input is the torque on the wheel.

Measured

The wheel goes a sixth of a turn per beat (1.0472 rad; 1.0472 expected) over 15 beats, never going faster. The pendulum's period is 0.886 s against 0.899 s for the free compound pendulum, 1.4% fast. Its swing holds at about 3.9° either side (3.90° in the first third, 3.81° in the last). With 0.7 times the torque it swings 3.88°, nearly the same, as a gravity escapement should. The wheel turns back at most 0.8° (allowed 2.3°). The deepest contact after the first second is 0.36 mm.

Notes

Brown gives no sizes. Here the stops sit on opposite sides of the wheel and it goes a sixth of a turn a beat, so the two wheels' legs have to stand in line, and the motion is the same as No. 310's; in Lord Grimthorpe's clocks the stops sit above the wheel and the two wheels are turned 60° on each other. The pallets' weights bear on the rod for part of each swing, which makes the pendulum run 1.4% fast; the bob is made heavy so this stays small. With 1.4 times the torque the pins throw the pallets off and the wheel stops being locked each beat. The swing is measured about the pendulum's hanging position, 4° from where it starts.

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