uMAD Micro Magnetic Apogee Detector

This MAD is a descendant of the great work done by Bob Galejs (the inventor of the MAD) in the 90's:
http://www.aeroconsystems.com/electronics/magnetosensor_images/Magnet3.PDF 

In a nutshell, the device senses the attitude of the rocket by measuring the earths magnetic field. When the rocket arcs over, the field (from the perspective of the rocket) rotates 90 degree's and the ejection charge is fired.

The u in uMAD stands for micro and is there because this MAD has a small computer running things. This gives you:

• A 2 minute safe period after you power up. During this time the uMAD will beep when the rocket is tilted over allowing you to test it before flight.

• A re zero after the one minute has expired to null out the effect of the launch rod.

• A glitch filter to stop noise and small changes in field strength (like clearing a metal launch tower) from prematurely firing the charge.

• Much more accurate tip over detection in all directions.

The uMAD is designed to work in conjunction with low power deployment charges and having an exceptionally low power draw, the unit will fire many charges on a single charge of a low mAh single cell Lithium Polymer battery. (We recommend the 130 mAh batteries used in many micro remote controlled models)

Hobby King carry these for $1

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8864

Full details on the design, development and testing of the uMAD can be found in this forum thread:

http://www.ausrocketry.com/forum/viewtopic.php?f=32&t=2359

Installation:

If you live in the southern hemisphere, install the uMad with the terminals towards the aft end of the rocket.

If you live in the northern hemisphere, flip it so that the terminals are towards the nosecone.

If you live near the equator, we’d really like to hear how you get on with this product!

The uMad has 2, 3mm mounting holes. But the terminal block is a bit close to one of them. We’ll fix that in the next batch.

I reckon the best way to mount the thing is with a bit of 3M double sided tape, (the foam stuff) and a thin cable tie (this method works really well when you have a 138mAH LiPo battery installed).  Try to keep the magnetometer (the chip the farthest away from the terminals) at least an inch or two from any ferrous metal.  A steel bolt acts like a magnetic lens, distorting the earths magnetic field and making it hard for the uMAD to work out which way is up....

Using the uMad:

• Walk confidently to the pad with your uMAD equipped rocket. Remember, people are watching!

• Point the rocket (or just the bit with the uMAD in it) upwards and power up the unit. You’ll hear three beeps.

• <optional> Wait a couple of seconds and then tilt the rocket/uMAD over and check that it starts beeping within +-45 degrees of horizontal.  If it doesn’t, power off and retry, making sure the uMAD is vertical and at least an inch or so clear of any ferrous metal.

• You now have 120 seconds to get your rocket on the pad. During this time it’s OK to tilt the rocket over, it’ll just beep.

• After 120 seconds, the uMAD will start beeping once every couple of seconds telling you that the system is now armed. DON’T TILT THE ROCKET OVER WHEN THE UMAD IS BEEPING LIKE THIS. If something went wrong and you haven’t got it on the pad at this point. Carefully power the unit down and try again.

• Wait until 120 seconds has passed since you powered the uMAD then launch.  Don’t worry about it sitting on the pad for ages. On a 130mAH battery, the uMAD will run for 10 hours before needing a recharge...