In answer to Christian Tedesco's question [210120 MMD], a second
clockwork drive was regularly used to operate the bass drum beater.
In Imhof orchestrions the barrel and feeders were operated from
the main drive, using a large weight behind the instrument. To my
knowledge, all instruments of this type used a single drive to run
the feeders and barrel.

The bass drum was hit by a pair of hammers, alternating in their use,
and set by a smaller weight driven motor. The barrel's key would
trip the mechanism, allowing the next hammer to hit the drum under
the influence of a strong spring, and then the motor would slowly
pull the hammer back into its ready position for its next hit. Two
hammers were used in case the time between bass drum hits was less
than the time to reset the mechanism.

The side drum was usually operated by a four-way cam, allowing
four hammers to repeatedly hit the drum when set off by the barrel.
This cam was continuously rotated by the main drive, by means of
a chain.

Nicholas Simons, UK