I am building a machine that will be able to play multiple pre-recorded samples from audio tape attached to the outside of a rotating cylinder. In concept this is something like a mellotron which is a keyboard that plays a different tape for each key. On the Mellotron the samples were typically the same sound at a different pitch for each key. My machine will not have a keyboard but instead a tape head that can be slid back and forth to rest on different tape samples. The different samples will probably consist of different pitches but will probably have various sound sources. One note might be a violin, the next a singing voice. Some of the tracks may have beats but these will probably have to be made up of bits of tape arranged in a regularly spaced pattern rather than a prerecorded beat on a continuous tape because the physical length of the beat on the tape would have to exactly match the circumference of the cylinder.
the machine:

Mechanically the machine is coming along fine. The cylinder is rotating on its axle. The motor is mounted and driving the cylinder via a rubber belt. The tape head is mounted on a small swing arm that slides back and forth across the surface of the drum. The little arm swings freely up and down so that gravity will keep it in contact with the surface of the drum. The user will slide it back and forth to select the tape. I am mounting the entire mini-cassette player that I took the head out of on the machine since I don’t want to figure out which parts of the circuitry are needed and which aren’t.
the tape head/arm:

Three important things remain to work out.
1. I need to make a speed control. Currently it’s running on a cell phone tranformer which gives a very
steady 5.2 VDC. The motor can run on up to 12VDC, maybe more. I need to get a higher voltage tranformer and put a simple voltage divider with a potentiometer to give me variable speed control. This is going to be important because if this thing will have any possiblity for expressive performance, it will probably come from having subtle and sensitive speed control. I will probably run it through a (homemade) volume pedal as well for a little extra performance control.
2. I need to record the content, the actual sounds. This is obviously going to have the largest effect on the ultimate sound of the machine. If I can lay my hands on a reel to reel taper recorder I hope to try that out in order to get wider and perhaps higher output tracks on the tape. The recorded tracks on a cassette are extremely narrow. There are actually 4 tracks on a tape abut 1/4” wide. I think a two track ¼” tape such as most reel to reels would make it easier to really get the head over the recorded sound.
The choice of sounds is more of a question at this point. I plan to record the sounds myself but some of them could be samples of existing music.
3. I need to figure out the best way to attach pieces of tape to the surface of the drum. I’m thinking of spray mount.
Some technical details:
The motor is a “gear head motor” which is like a normal DC motor but with a gear assembly that reduces the RPMs. This is an excellent type of motor for many applications because it delivers much more power at a more useful speed. Most DC motors run at hundreds or thousands of RPMs. Motors with gear reduction can run at much lower speeds. I got mine on eBay. Its range is between 100 and 200 RPMs.
For the drive belt I used a piece of a bicycle inner tube. Inner tubes are a great resource for any type of rubber belt or band. Cross sections make a very strong and super-durable rubber band of whatever width is needed. Using a tire patching kit, any strip of inner tube can be glued to itself to form a longer band of whatever size (not as strong as a cross section).