After configuring QjackCTL and ttyMIDI you will be happy to know that Hydrogen is the simplest of all three to get running. Install it using Ubuntu Software Center. Launch it and tap your piezos. That’s it!
I’ll include a few screenshots and some changes that I’ve made just in case you want to verify or customize your own setup.
Tools > Preferences > General Tab
Tools > Preferences > Audio System Tab
Tools > Preferences > Midi System Tab
You should see the MIDI-IN button light up in the toolbar when tapping the triggers.
Customize a DrumKit
In Hydrogen, select the Sound Library tab on the far right of the screen about halfway down the page. By default the first six drums in the GMKit Pattern 1 will be mapped to the DrumKit Kit AI triggers. I like to keep the GMKit as is so I can refer back to it later. To create a custom kit select Instruments > Save library and give it a name. Once saved you will see your new kit displayed in the User Drumkits under the sound library. This is an easy way to copy the existing drumkit instead of building a new one from scratch.
Right click your custom kit and select Load. Your custom kit now displays in the left pane. Then drag and drop, add and delete the drums until you like the way they map to the triggers. Follow the same steps to save your new kit, but give it the same name as you did before instead of renaming it.