- Dual-range force sensor (measures up to 50 newtons, good for LPR and some mid power motors)
- LabQuest 2 interface/data collector
- Logger Pro 3 software
The next step was to incorporate the force sensor into some sort of test stand. I suck at building such things, so I turned to the able engineer Duane, who whipped me up a fairy nice contraption in a couple of days:
|The motor test stand, engineered and built by Duane (Click to enlarge).|
|The test stand plugged into the LabQuest2 unit. This is all I need to measure the thrust curve of a rocket motor|
(Click to enlarge).
Since I have a ton of Estes A8-3 motors, I figured Saturday's TARC practice launch would be a good time to make some thrust curve measurements. After I finished flying my rockets, I loaded an A8-3 (with igniter) into the motor tube, connected the launch controller and the LabQuest 2 unit, and placed the test stand on the ground. I set the LabQuest to record measurements for 10 seconds at 50 samples per second - I wanted to catch the ejection charge, to see when it occurred after motor burnout. As the count from 5 progressed, I started data recording on the LabQuest and saw the following plot appear as the motor fired:
|LabQuest2 screen capture showing the thrust curve of an Estes A8-3 motor. The sharp spike near the end|
is the motor ejection charge (Click to enlarge).
and zoom in on the motor thrust curve, at which point I could tell the software to integrate the area under the curve to get the motor's impulse (2.12 newton-seconds):
|The Logger 3 software can integrate the thrust curve to derive the motor impulse (Click to enlarge).|
|Thrust curve comparison (Click to enlarge).|
|A8-3 thrust test results (Click to enlarge).|