Picture of Make a parachute ejection system
make an electronic, tilt activated latching parachute ejection system for model rockets from just a few simple components.

Finished Product:

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Step 1: Parts

Picture of Parts
Here is a list of the parts you will need:

-Soldering iron
-2 different coloured standard LEDs
-2 100 ohm resistors
-2 330 ohm resistors
-1 220 ohm resistor
-9V battery clip
-Ball bearing (tilt) switch
-Basic electronic knowlege
-Stripboard or PCB or something to solder the components on to
-9V PP3 battery
-Hot glue gun (optional)
-Screw terminals (optional)

Step 2: The schematic

Picture of the schematic
Here is a schematic of the circuit. You could etch your own PCB following the schematic, or modify it sligtly for stripboard (I did) I mangaged to fit it on a 5 hole by 8 hole piece of stripboard (with breaks and joins in the lines)

Step 3: Putting it all together

Picture of Putting it all together
Now all you have to do is put it together. I would suggest starting with the resistors, then the thyristor, then the battery clip, and finally the LEDs. I just soldered some short wires for the off board components and attached some screw terminals, so I can mount it in the rocket easier and to attach an actual parachute release mechanism. You can do this by attaching a servo or even a piston to where the red LED would normally be, but I will probably make another tutorial showing you how to make that. When you have finished, make sure you check the circuit over, since the battery and thyristor can overheat if there is a short in this circuit. Once you have it all done, you can think about making it fit inside a rocket. I hot glued the curcuit on top of the battery clip so it will sit on top of the battery, and shortened some of the wires. Then, mount the tilt sensor somewhere so it is standing upright. I mounted mine on the side of the battery, although you could put it nearly anywhere. Make sure you test it to make sure it is up the right way. when it is done, you should have something that looks something like this:
admin5 years ago
This is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that and leave me a message when you have so that we can publish your work. Thanks!
izzy darlow5 years ago
 Can this be made smaller, and to utilize a smaller power source? Say for use in a paper rocket like this one?
andy70707 (author)  izzy darlow5 years ago
unfortunately, no it can't. I tried to make the actual circuit as small as possible, and I tried making a power supply out of 3x3v coin cell batteries, but they are only 80ma each, giving a total of 240ma, which isn't enough to run the circuit. I had to settle with a 9v PP3 battery because I couldn't find anything smaller that gives enough power. It it fairly small as it is though, it fits nicely in my 4cm PVC rockets (and about 7cm long, not including the parachute). Also, for a paper rocket like that, it would be very nose heavy, even though in my PVC KNO3+FE2O3+Sucrose rockets it is fairly light.
Thanks for the info.
kevincai965 years ago
Um, I thought the negative acceleration forces right before apogee prevented tilt switches from working? Doesn't the mercury float and not make a connection?
andy70707 (author)  kevincai965 years ago
well it all depend on the type of switch. I used a ball bearing kind, in a cylinder sealed with argon to try and minimise this, and you are right it will be weightless for a second or two, but it will definately deploy the parachute before it hits the ground. I might update this soon since I have made yet another version with the servo and a prachute and a vido of it working.