How to Measure Motor Speed with our RPM Probe

By Lauren Nagel

Measuring motor speed is a key part of characterizing your UAVs propulsion system. Perhaps most importantly, it is necessary forcalculating the efficiency of your system, which our test stands do automatically.

Our optical RPM probe is a motor speed measuring device that is included with all of our Flight Stands (15 - 150 kgf) and with our Series 1580 (5 kgf) thrust stand bundle.

It works with a simple two-part ‘optical’ system.

The first part of the system is a piece of reflective tape that you place on your motor like in the photo below. It doesn’t necessarily need to be reflective, but it needs to be a color that significantly contrasts with the color of the motor, such as white on black or vice versa.

Figure 1: White tape on a black motor is sufficiently reflective for the RPM probe

The second part of the system is the probe itself. The probe plugs into the side of the test stand’s force measurement unit (FMU) and attaches to the motor mounting plate via standoffs. It is tightened securely so the probe sits between 5 and 15 mm away from the motor (figure 2).

Figure 2: The optical RPM probe is attached to the FMU and motor mounting plate

Once both components are secure, the system is ready to start measuring your motor’s speed. 

The principle is very simple: the optical probe has a sensor that counts how many times the piece of reflective tape passes in front of it. The Flight Stand’s optical probe can measure rotation speed up to 30,000 RPM with an accuracy of ±1 RPM.

For a full demo, here’sa video showing you how to install the probe on the Flight Stand 15/ 50: 

If you would like to characterize your motors, including measuring their speed, we encourage you to check out our thrust stands for motors up to5 kgf,15/ 50 kgf, and150 kgf.