I've always wanted to play drums but a real drum set has been impractical due to space required and loudness. Electronic drum sets seemed like a great solution but were too expensive. Then I saw the Alesis Nitro kit available for $300 and the reviews were mostly positive. So I ordered one and have been having a blast with it. I enjoy some metal music and thought it would be great to have a double bass pedal. The lowest priced one I could find was the Mapex P500TW. I read mixed opinions online as to whether or not this would work. My experience was that, with the original bass drum pad, the trigger area is too small for both beaters to get consistent hits registered. I ended up building my own bass drum pad very inexpensively to provide a larger hitting area and so far it's working great.
I've read online about people having problems using double bass pedals with the Alesis Forge kit due to the drum module (or perhaps the cable) preventing the bass drum input from handling fast hits. Fortunately for me, this problem doesn't appear to occur on the Nitro kit. And it costs less!
The only parts I had to buy were piezo discs to pick up the vibrations and 1/4 inch jacks for the cable to plug into. I only needed one of each, but multi-packs were so cheap that I thought it would be wise to have extras in case I screw one up or want to make more pads later. Oh, and I also bought a piece of metal flashing (I think it came as a 10 x 12 inch rectangle) and a 90 degree angle brace from Home Depot.
The other materials used were some scrap wood I had, wood screws, a piece of foam packing material that I had saved, and a piece of padding left over from our laminate floor installation. The packing foam goes against the wood, then I cut out a piece of the metal flashing and taped a piezo disc to the back of it. I cut a slit in the foam, and ran the wires from the piezo through the slit and then through the hole in the wood. The wires were then trimmed and soldered to a 1/4 inch mono jack which was attached to the back of the pad. A piece of the laminate floor padding is then placed over the metal and foam and finally I made a rectangular rim to hold those layers in place on the wood frame. I attached the angle bracket to the bottom of the pad frame to provide something for the pedal to clamp onto. I found that the bracket was a little too thin for the clamp on the pedal to get a good grip, so I taped an extra piece of metal to the bottom to thicken it up. I also needed some zip ties to help hold the pedal in place because the beaters are offset from where the clamp attaches and therefore want to twist the pedal away from the pad's frame.
Here are some pictures taking during assembly. Hopefully it's pretty self-explanatory.