If you enjoy model rocketry, you may wonder just what the thrust curve of the motors you’re using looks like. In order to answer that question, YouTuber ElementalMaker decided to construct his own test stand using an Arduino Uno coupled to a 10Kg load cell with an HX711 amplifier board. The test procedure is started with a little red button, and after warning LED blinks away for 10 seconds, it activates a relay and fires the motor under into the stand.
The experimental setup seen in the video yields successful thrust curves for both a ½ inch and ¾ inch motor. As you might expect, the ¾ produces more thrust than its smaller cousin, though at 2,683 grams versus the ½ inch motor’s 658, it’s an impressive difference indeed.
The heart of the stand is a common load cell (the sort of thing you’d find in a digital scale) coupled with a HX711 amplifier board mounted between two plates, with a small section of vertical PVC pipe attached to the topmost plate to serve as a motor mount. This configuration is capable of measuring up to 10 kilograms with an 80Hz sample rate, which is critically important at this type of rocket motors only burn for a few seconds to begin with. The sensor produces hundreds of data points during the short duration of the build, which is perfect for graphing the motor’s thrust curve over time.
Given such a small window in which to make measurements, [ElementalMaker] didn’t want to leave anything to chance. So rather than manually igniting the motor and triggering the data collection, the stand’s onboard Arduino does both automatically. Pressing the red button on the stand starts a countdown procedure complete with flashing LED, after which a relay is used to energize a nichrome wire “electronic match” stuck inside the motor.
The project is based on a paper archived here if you’d like to examine the design.