5. Tie the end two long strings around the rocket body at the hang points
a. Try to use thin strings, fishing line, or something with very little resistance to bending.
b. Make sure they’re nice and tight!
6. Hang the rocket from the ceiling or a flat surface
a. First, ensure the two strings are parallel to each other. Measure their distance apart near
their attachment points on the rocket. It should be exactly twice the “String-COM”
distance.
b. Next, ensure the rocket is parallel with the ground. Make sure the distance from the
rocket to the ceiling is the exact same for both strings.
c. Enter this distance, in meters, in the “String Length” text box
7. Rotation testing
a. Now it’s time to rotate the rocket around its CM!
b. Using both hands, turn the rocket 10-20 degrees around it’s CM, then let go. Ideally there
should be no horizontal movement, just rotation
c. Let the rocket go back and forth a few times, then start a timer at on of the peaks of the
oscillation.
d. Let the rocket rotate back and forth a full 10 times during the timer, then stop it at the end
of the 10th rotation. For reference, check out this video. In the video, a translation test is
also performed, but that test is no longer required.
e. Divide the time that those rotations took by 10. This give us an accurate average time
that each full rotation took. For instance, if your rocket rotated 10 times in 18.5 seconds,
the average rotation time would be 1.85 seconds
f. Enter this averaged time, in seconds, in the “Rotation Time” text box
8. Average thrust
a. Depending on the average thrust of your motor, the stability of your rocket will change.
Using the average thrust, we can complete the tuning process. Try to use motors with
very small thrust spikes at the beginning of the burn, or with pretty flat thrust curves.
b. The average thrust for most commercial motors can be found either on the motor
packaging itself, or on http://www.thrustcurve.org/
c. If the average thrust is not listed in Newtons(N), please convert it to Newtons for the
tuning app.
i. Convert from pounds here
ii. Convert from kilograms here
d. Enter the average thrust, in newtons, in the “Average Thrust” text box
Copyright © 2018 Barnard Propulsion Systems, LLC. Version 1.3, July 12, 2018
www.bps.space
