We built ourselves a dynamic Newton meter to safely measure the thrust our engines produce.

We can sense downward thrusts as large as ~50N in increments and as small as [[0.1N|Newton weights] (assuming it is properly set up and calibrated).

With an iPhone you can record data and extract it.

Set up

Put the book case 10m from the wall, adjust clamps & align it.

Calibration

The laser is aimed at multiple meter sticks, which are taped end to end against a shady wall. Small changes in the force pressing downwards on the board should move the red dot on the meter sticks a measurable amount. By placing known weights at a designated spot we can calibrate it. We figured out that one nickel ways approximately one Newton, making it much easier to calibrate the meter.

1. Note the location of the red dot.
2. Gently add 1N and measure the distance (in cm). This gives you the conversion from cm to Newtons. Write it down.
3. Repeat this process to find the smallest weight that produces a measurable change. This is the sensitivity. Record this too.
4. (Optional) repeat with a weight that is roughly twice the expected maximum and confirm that:
   • The dot is still visible.
   • The ratio of Newtons/cm computed from this value is close enough to the value computed for the 1N weight.
   • This maximal position is still in range of the camera.

Use

We have multiple steps leading up to the use of our dynamic Newton meter:

1. Make sure the engine is in place. We drilled a spring into the wooden plank that holds the laser.
2. Call roll. Make sure everybody is ready for the test.
3. Light the engine safely using a fuse. Make sure to take extra caution during this step.
4. After the test is completed, make sure the engine is fully done before removing it from the dynamic Newton meter.

Data Extraction