How does adding weight (load) to the propeller affect the spin rate? How does changing the size or shape of the propeller affect its spin rate?
Devise a way to measure the torque, or twisting force, of the motor. You might try attaching a string to the motor shaft and seeing how much mass it will lift. How does changing the voltage affect the torque of the motor? (Note: look up the equation that relates torque to the radius of the shaft and the amount of weight lifted).
Use a multimeter to measure the voltage and current in the motor circuit. Most models from a hardware or auto supply store will be suitable for this project. You can also buy one online; for example, the Equus 3320 Auto-Ranging Digital Multimeter, available from Amazon.com. How does the spin rate vary with the current through the circuit?
Can the motor be used as a generator? How does the spin rate affect the generated voltage?
Download Winscope and use your computer to analyze the voltage signals in your motor. This method is inexpensive, gives you very accurate readings for the rate at which the reed switch is cycling, and also provides graphic information about how the voltage varies with time. Two sites where you can download Winscope are provided in the Bibliography. You will need a wire and 3.5-mm jack that connects to your PC. The wire from an inexpensive microphone will work. What does the voltage-time curve look like?
Use a stroboscope to determine the spin rate. These tend to be quite expensive, so see if you can borrow one.
Another way to measure the spin rate is to record the motor's sound and then analyze the sound file. The sound file can be analyzed using various programs. For example, the program Audacity, a free audio editor and recorder, can be used. Audacity can be downloaded from audacity.sourceforge.net.