If you're noticing double the expected RPM or excessive fluctuations in the RPM measurements, which may trigger a safety cutoff, this is likely due to environmental disturbances or reflections being picked up by the RPM sensor.
To resolve this issue, try the following:
Electrical Tape: Add a black strip of electrical tape around the motor's outrunner to reduce reflections that may interfere with the sensor readings.
Ambient Lighting conditions: Conduct the experiment in a room with less ambient lighting, as excessive lighting can cause unwanted reflections.
These steps should help minimize interference and provide more accurate RPM readings.