I already have an Instructable on how I made my main set of drums. This Instructable focuses on building a very simple floor Tom.
I was given an old pearl floor tom which then became the shell for the new electronic floor tom.
Building this type of drum is simplicity itself. You will need soemthing like an Alesis Trigger I/O or drum brain so you can get sounds out of these type of drums, you cant just plug them into a sound system.
They way they work is that a Piezo element, which costs about 50 pence, is struct by a stick or beater and generates a electrical pulse, which is in turn converted into a midi value which is then sent to the midi drum machine or sound generator. When a Drum is struck a sound will be produced.
If you were to constantly hit the piezo with a drum stick it would very quickly be damaged so you need to isolate it.
Because it is much nicer as a drummer to hit a drum skin that has some rebound and a nice feel it is best to design electronic drums with this playable feeling.
The Piezo is mounted to a cross beam fixed inside the drum. It is glued onto a small wooden disk which is connected to the cross bar via a height adjusting nut and bolt. Having this adjuster allowed the pressure placed on the piezo to be varied and as such alter the hit area and sound. Glued onto of the piezo is a second firmer foam cone or foam block which will absorb any initial hit from the sticks but still allowing vibration to travel through to the piezo to trigger the midi event. A TRS socket is fixed in the side of the drum and the piezo wired up, red to tip and black to ring. If you wanted to fit a rim piezo you might need to isolate the cross bar via rubber washers to stop cross talk between the rim and head. Fitting a rim piezo is simple, just glue one to the drum shell and wire back to the socket, blck to ring and red to sleeve.
Building these kinds of rums is very, very easy. The real Art is in the fine tuning, piezo pressure, cone material and head material.
My latest drums use a new drum skin which is made out of an old trampoline netting which is amazingly good. The rebound and feel is great and the centre hot spot almost eliminated. I have also changed the foam material fitted to the top of the piezo. The new foam is much more rigid and transfers vibration much better. In the floor tom I build here I started with a soft foam block but later changed it to a foam cone, taken from a kids toy, which works much better.
Have a go yourself and happy drumming.