Mudge’s gravity escapement
Mudge’s gravity escapement. The pallets, A, B, instead of being on one arbor, are on two, as shown at C. The pendulum plays between the fork-pins, P, Q, and so raises one of the weighted pallets out of the wheel at each vibration. When the pendulum returns the pallet falls with it, and the weight of the pallet gives the impulse.
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 five pins at radius 2 on its front face, 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, 2 either side of the pendulum's pivot and at the same height, as at C. Each pallet carries a weight and a fork-pin (P on A, Q on B), and the fork-pins lie against the pendulum rod 4 below the wheel's axis, so the rod plays between them. A banking stops each pallet when it hangs against the rod. Each pallet has a hook in the wheel's path: an upright face, and a short stop under (B) or over (A) its arbor. A pin coming round pushes the face out and lifts the pallet's weight until the pin lands on the stop and the wheel is locked. The stop is struck nearly through the arbor, so the locked pin 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 pin, and the wheel goes on until the other pallet's stop catches the next 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, and it is the same whatever the torque on the wheel. 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 tenth of a turn per beat (0.6283 rad; 0.6283 expected) over 15 beats, never going faster. The pendulum's period is 0.882 s against 0.899 s for the free compound pendulum, 1.9% fast. Its swing holds at about 4.1° either side (4.06° in the first third, 4.10° in the last). With two thirds of the torque it swings 4.03°, nearly the same, as a gravity escapement should. The wheel turns back at most 0.9° (allowed 2.3°). The deepest contact after the first second is 0.33 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 1.9% fast; the bob is made heavy so this stays small. With 1.5 times the torque the pins throw the pallets off and the wheel runs through. With lighter pallet weights (two thirds) the same happens at the working torque. The swing is measured about the pendulum's hanging position, 4° from where it starts.
Film (MP4) · Still (PNG) · Spec (YAML) · Model (MJCF)
