DIY Apogee Detector using 3-axis magnetometer

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ZenonDorin

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Hi guys I'm a beginner in high power rocketry but I'm quite experienced with electronics so I thought I'd share this with you.

For now it's not a complete solution (needs a MOSFET and some more robust software) but it's a proof of concept and open for DIY.
Details on my blog: https://zenontech.blogspot.ro/2014/10/diy-rocket-apogee-detector-using.html

I'll post only the video here (if you really want I can also post the whole content):

[video=youtube;MZUnnsldayk]https://www.youtube.com/watch?v=MZUnnsldayk[/video]
 
I am gonna use this method in my next rocket (for which I was planning to use mercury switch and delay).
Parts needed:
arduino compatible board (nano/micro for 13$)
HMC5883L board (3$)
power driver with mosfet/relay (1-5$)
 
https://www.aeroconsystems.com/electronics/mad.htm This version of a Magnetic Apogee Detector was developed by Professor Robert Galejs of MIT and former CMASS member in the late 1990's and published in 2000. The kits are still available.

Bob

I thought mercury switches are a no-no or is that only for staging? I would think one would be at risk for premature deployment if something goes haywire.

The Aerocon kit says "Call for price" Don't know if that means anything. I gorked one of mine 7 years ago with a homemade ematch and Professor Galejs graciously repaired it for me. I've never had a problem since by using commercial matches only.

This OOP device: https://www.whooshtronics.com/products-t83/umad.aspx

There is this Zeptobit device that is actually quite comprehensive. Device can be turned on and is armed by acclerometer. Also can calibrate the angle of charge firing from the device: https://www.zeptobit.com/zeptomag/

I fly two Galejs units from Aerocon in two Aerospace Specialty Products WAC Corporals. One yellow one white. One has to be very cognizant of these units as once turned on, cannot tip over. I use a locking toggle switch on the bulkhead to turn the unit on at the pad and lower the nosecone back to the bodytube. The switch hasn't had any failures in a dozen flights. This rocket was accidentally designed for a MAD unit. The noscone has a coupler "stuffer" tube with a bulkhead that's easily modified to carry the electronics. Could do dual deploy with
a cable cutter and an Accel/Baro unit. Kurt
 
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How are you going to deal with the potential for magnetic glitches at launch?

I flew a 3 axis sensor a few times and the data (with glitches) can be found here

There aren't many launch rods/rails made with iron pipe, but it is something to worry about.
 
Oh, I wasn't aware this was done before.. Then why do these barometer expensive solutions still exist?

Btw, whooshtronics says "If you live near the equator, we’d really like to hear how you get on with this product!". Are they for real or just trolling?! This obviously won't work at the equator unless you launch the rocket tilted to the north/south or the wind blows so, which is unacceptable!

As for the glitches, they are fine, I don't think a launch rail could invert the z component. Besides, the measurement can be averaged to filter the fast insane readings, and also an accelerometer can be added to start reading the magnetometer only after motor burnout (deceleration detected).
 
Magnetic sensors can be used for apogee detection, but they are not as reliable as barometric altimeters.

What's expensive? The Adept22 and similar barometric altimeters cost between $35 to $50. Since they measure altitude not magnetic field, they are likely to be more accurate than a magnetometer instrument. Additionally some rockets do backslide and not flip over.

Bob
 
https://www.aeroconsystems.com/electronics/mad.htm This version of a Magnetic Apogee Detector was developed by Professor Robert Galejs of MIT and former CMASS member in the late 1990's and published in 2000. The kits are still available.

Bob


If you contact Aerocon, you will find they are not in stock. I have been bugging them for over a year and still no MADs in stock.

I have two Galejs MADs and have used them for more than 15 years . . . no failures/glitches yet. Now, also have two of the Zeptomags designed by a guy in Norway ready to try out.
 
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If you contact Aerocon, you will find they are not in stock. I have been bugging them for over a year and still no MADs in stock.

I have two Galejs MADs and have used them for more than 15 years . . . no failures/glitches yet. Now, also have two of the Zeptomags designed by a guy in Norway ready to try out.

Only thing with the Galejs is one has to be cognizant of the "active" state of the device. Once turned on, CANNOT tip over for any reason.
MAD is good for apogee only without any kind of reporting ability. Nice for a sport rocket. Won't replace standard DD electronics for higher fliers.
The ZeptoMag is the most comprehensive MAD unit available. A primary AND backup channel with programmablity of the deployment angle.
If one just wants apogee only with a unit that can be sealed up inside, MAD is a good option. Kurt
 
Since they measure altitude not magnetic field, they are likely to be more accurate than a magnetometer instrument.
A barometer measures altitude ideally in a static environment, however the air surrounding the rocket is not static at all, generating pressure spikes inside.
Things get really tricky around sonic speed, because the pressure waves can falsely trigger a catastrophic deployment without some complicated filtering on the barometer and even with one I wouldn't rely on that for a supersonic rocket.

Additionally some rockets do backslide and not flip over.
Which serious rocket with CP behind CG would do that?
 
There IS a lot of noise in a baro altimeter, but it's not that hard to filter out. Once you take care of the issues that might lead to a premature main deployment because the baro pressure is increasing when the rocket is still moving up (due to the buildup of a shock wave), apogee detection isn't tough. There's very little noise near apogee because you're not moving very fast, unless you're going horizontally or looping. And since all of your rockets have the CP well behind the CG, it's all good.
 
Which serious rocket with CP behind CG would do that?

Rockets that are under powered have a tendency to slide backwards at apogee before tipping over. Of coarse as soon as it tips it will activate the MAD.

ZenonDorin we encourage your interest in HPR and don't take this the wrong way, but since you mentioned that you are a beginner I think some homework on the subject is needed here.:)

Steve G
 
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A barometer measures altitude ideally in a static environment, however the air surrounding the rocket is not static at all, generating pressure spikes inside.
Things get really tricky around sonic speed, because the pressure waves can falsely trigger a catastrophic deployment without some complicated filtering on the barometer and even with one I wouldn't rely on that for a supersonic rocket.
Supersonic flights are not an issue as most the modern barometric altimeters employ Kalman filters to eliminate false deployments due to Mach wave transients.

Bob
 
Rockets that are under powered have a tendency to slide backwards at apogee before tipping over.
Oh, that's true if the rocket is still quite vertical near apogee (unlikely). The rocket has a moment of inertia and if the parabola is too sharp then the aerodynamic torque won't be high enough to keep the body tangent to the trajectory in real time.
But yeah, my point is that it will eventually tip over and I don't think it will gain substantial speed until that happens.

As for barometer yes, Kalman filtering is a must.
 
One problem is the use of a mercury switch in a rocket is prohibited in the US by NAR and TRA.

I thought that was only prohibited in motor ignition. Isn't there some rule if the mercury switch is connected only as a sensing element it is allowed?

Steve G
 
There's this pretty comprehensive MAD deployment unit available: https://www.zeptobit.com/zeptomag/

Has two channels primary and backup. Kurt
Agreed. Looks like a nice system. My previous objection was the use of a mercury switch which represents an environment hazard if lost or improperly disposed with is one of the 2 reasons why they are banned.

Robert original circuit was novel in 2000 but is a bit dated by the new electronics. I saw him use it several dozen times and it worked well but the 1 D unit is a bit tricky to adjust and it was sold only as a kit IIRC.

Bob

Bob
 
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