LEGO NXT Motor Analysis

In anticipation for various projects, we performed our own analysis of the NXT Motors. To test the motors, we used a pulley attached to the output axle of the motor to lift a known weight a known distance and measured the time. Through knowing the weight, distance and time, we were able to find the mechanical power, torque and rpm. While the motor was lifting, we also recorded the RMS current and voltage to find the electrical power and find the motor efficencies. Here are some photos of our setup: 

The pictures show the setup for our tests. One NXT is suppling power to the motor with the probes measuring the voltage drop and current draw. The other NXT has two light sensors attached to a meter stick. The Light Sensors record the time it took to lift the weight, and sends a bluetooth message to the first NXT to stop hoisting the weight once the second light sensor has been reached. The time is displayed on the screen of the NXT. Since the signal sent to the motor is in PWM, the oscilloscope was used to find the RMS values of the voltage and current.

Our motor behaviours are similar to results found by Philippe E. Hurbain, but with slightly different numbers. The Blue and Yellow data points are with the motor running at 100% power, Blue with a small hub for the pulley, Yellow with a large hub. The Red data points are with the motor running at 50% with the small hub.