We thought that we would have to resort to building eight or nine hammers, but now we have a design that only requires four hammers, one for each chime. The red thing is a cam that turns clockwise when the crank is turned. Each lobe of the cam lifts the hammer (green) and pawl (yellow), and then releases them in that order. When released, the hammer swings once toward the chime on the left (not pictured) and then swings back toward the cocked position. By the time the hammer returns, the pawl has been released and is able to catch the hammer mostly cocked.
If the crank is turned too fast, the pawl is released in time to catch the hammer after only a fraction of a swing, preventing the hammer from hitting the next lobe on the cam with damaging force. The pawl limits the tempo at which the tune may be played, catches the hammer to prevent damage caused by repeated swinging, and preserves much of the energy of the hammer, making the whole thing more efficient and minimizing wear.
Unfortunately, the pawls are four extra moving parts and an additional axle, but they help us avoid making eight or more moving parts that we would need if we were to use more hammers.