Three-legged gravity escapement
Three-legged gravity escapement. The lifting of the pallets, A and B, is done by the three pins near the center of the escape-wheel, the pallets vibrating from two centers near the point of suspension of the pendulum. The escape-wheel is locked by means of stops, D and E, on the pallets.
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 has three legs reaching to radius 2.6, and three lifting pins near its center at radius 1.2, and 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. 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 (D on A, E on B) in the legs' path, right under its arbor. 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. 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 (3.91° in the first third, 3.82° in the last), and settles near 3.6° over 30 s. With 0.7 times the torque it swings 3.89°, nearly the same, as a gravity escapement should. The wheel turns back at most 1.0° (allowed 2.3°). The deepest contact after the first second is 0.42 mm.
- Notes
- Brown gives no sizes. The pallets' weights bear on the rod for part of each swing, which stiffens the pendulum a little and makes it 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 runs through. The swing is measured about the pendulum's hanging position, 4° from where it starts.
Film (MP4) · Still (PNG) · Spec (YAML) · Model (MJCF)
