Make a Percussion Sequencer in Ableton Live

The front end of the Percussion Sequencer is the same as the pitch sequencer. A clip with one note in it is piped through an Arpeggiator and then a Random effect that steps through a predefined number of steps. Each one of these notes goes into a separate chain, essentially making a different step for each step.
In each step chain is a scale effect that forces every incoming note into a 'C', regardless of the incoming note.
Here's where it gets weird.
Now, each step chain splits into eight drum chains, one for each drum. On each of these chains is a Chord effect, the cumulative effect of which is that, if left to its own devices, each step will play all 8 possible notes. This is clearly not awesome.
The MIDI Mapping here is key. I'm assuming that you will be using some sort of grid controller like a launchpad or an APC, although a lot of different things would work. So, select the Step One Chain, then enter MIDI Map mode and map the Chain On button in each Drums Instrument Rack to a column of buttons on your grid controller. Exit MIDI Map mode and select Step Two Chain and repeat. This is not fun, but it's unavoidable.
Once you are all mapped up, load your drums into the first 8 cells of a drum rack and go nuts! In a good way.