The schematic of DR-110 is:

For this circuit, each percussion element seems to sound when you put a negative pulse of width 1 ms. I’ve put oscilloscope to observe the pulses come as expected.

Here are the pulses to the bass drum and output:

The pulse width looks to be around 1.3 ms.

These are the pulses to the snare drum and output:

For the hand clap, I only took pulses:

This is a simulated output of the bass drum circuit:

The output would be weaker when the pulse is narrower:

A wider pulse gives a stronger output, but the waveform starts distorting significantly at certain point.