Home brew altimeter and chute release

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jnobels

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Wrapping up my first mid power DD build... As part of this, I wanted to try my hand at a home made mechanical chute release. I considered and tested pyro options too, but the added complexity of the firing and arming circuits seemed unnecessary when a simple mechanical release would do the job just as effectively. I love the simplicity of the JLCR but my personal philosophy is that before you’re allowed to buy it, you have to build it - or at least fail gloriously in the attempt.

The electronics are an Arduino Nano with a BMP280 pressure sensor. I had originally added an SD card and Bluetooth module and a 6 axis accelerometer but ditched these to keep things simple, light-ish, compact and (fingers crossed) reliable. The onboard 1k EEPROM can store a few flights worth of basic data, USB works fine for downloading that and the current generation of cheap accelerometers are not particularly useful (the new Bosch 9 axis ones that give you absolute orientation look promising though)

IMG_3330.jpg

I managed to cram all the electronics onto a single small perfboard including LEDs and a peizo to read out the unit status and apogee upon landing. The electronics alone will run on a pair of 2032 button cells. The servo sled draws a lot of current though and requires a 2s lipo. 1s at 4v might work too but it’s borderline.

IMG_3331.jpg

The chute release is just a simple 9g servo mounted to a plywood sled. The chute attaches directly to the sled to prevent tangling with the sled tether. I’ll likely modify the mechanism slightly to eliminate the rubber-on-plastic friction but the idea is to keep it as simple as possible. If things do fail, my hope is that worst case - the chute deploys early. The elastic band pulls in the release direction of the servo so the servo isn’t stressed and is routed so that the sled pops away from the chute. After testing some pin based releases I settled on this as the least complex and therefore - hopefully most reliable option. Nothing to bind up, no complex mechanisms.

The whole unit is a bit large. Requires a 2.2” airframe with a payload bay long enough to hold the electronics. Component cost here (if you’re willing to wait 4 weeks for parts from China and buy them in bulk) is less than the cost of the motor you’ll need to launch it though. Weight could be better. ~100g ish.

Now if winter can just hurry up and go away so I can test/fly this with something other than my shop vac...

Impressive that the guys at jolly logic managed to cram all of this into something a fifth the size though...



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