Which would be better for detecting a rocket's apogee? An accelerometer or a gyroscope?
None of my parachute deployment timers have been reliable enough, and so I've stopped developing for a while. I would like to get going again, though, with a much more reliable system. Preferably, one that activates at the highest point of the flight profile, to protect the rocket and the parachute from damage.
I know from research that acceleration profile of a rocket doesn't have any specific point tat marks its apogee: the rocket experiences a large amount of G-forces (Z-axis) when accelerating, but that value goes negative as soon as burn-out occurs, which happens long before apogee occurs. I assume that, at apogee, the G-force would be zero, but I'm not sure how easy that would be to detect.
The only way I can think of to use gyroscopes to detect apogee is to detect the turnover of the rocket as it begins falling back to Earth, but I'm not sure how accurate that is either.
Eventually I would like to mount a camera in my rockets, but that can only be done once their safety is ensured.
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M$3 Answers
The problem is no device can measure the rocket's trajectory vertex ("apogee" applies to orbiting objects not to ballistic) from inbetween the rocket itself.
It can be calculated in real-time per aproximation by instantly measuring acceleration (accelerometer), linear motion divergence (three axis gyroscope) and correcting the forecasted trajectory by recomputing it.
There are too much variables influencing the "rocket's flyght" to correctly define the trajectory in advance.
So if your problem is 35$ are too much to invest for your camera's safety... then forget an electronic solution.
You can use mechanical or electromechanical solutions.
Take in mind you have at least two distinct situations to manage:
1. (near) vertical trajectory;
2. parabolic trajectory.
This may cause you to have to study different detection methods.
Some mercury switches may be of use for solving your problem...!
Or a magnetically locked mass connected to a switch or actuator.
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M$Hope this helps,
Jaymz
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M$The accelerometer won't work well because you have the rocket going neutral, literally in free fall, as soon as the engine runs out of power. You will have a small amount of negative acceleration due to air resistance actually and could possibly read that and when it goes to zero then you have reached apogee.
The gyroscope method should also work to detect physical turnover.
So any of the three, given the proper hardware and programming, should be doable.
Enjoy,
Ray
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M$
So you are saying that I would need a multi-DOF IMU to get reliable results?
The $35 was for the highest accuracy barometer that Sparkfun had. Many of their accelerometers are cheaper than that.