A simple parachute deployment system for machines having "brick-like" flying characteristics when losing power.
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I want to use a device which doesn't require the needs of pyrotechnics, something fast to reset. I'm thinking about a spring-loaded ejector, the hatch being closed by a 9g servo. The servo itself should be triggered by a simple ATMega328 checking an accelerometer.
Here's a small presentation video, in the most terrible english you've ever heard.
The project isn't moving on as fast as I wanted to, others things got in the way...
I finished the print of the first casing for the parachute, based on rough dimensions I took from the parachute, and I made it waaaay too big... Lesson learned.
It took 18 hours to print, but it allows me to make sure my system works correctly before making the definitive casing.
I just came back from my testing facility (ok, I just tossed the parachute from the highest window of my house), and the results seem pretty interesting: with a 500g load, the parachute slows down to about 2.5m/s, and with a kilogram, the speed is still decreased to 6-7m/s, which is slow enough to avoid major damage.
Now that I know how big the parachute needs to be, I'll fold it up correctly and size the compartment.
I also made a small presentation video to hit the requirements for the Hackaday Prize. Gosh, listening to myself makes me realise how terrible my english actually is...
After sizing the parachute I needed, I took some plastic sheet I had lying around and cut it into a circle of 45cm in diameter.
I then attached 4 strings, making them into eight parachute lines:
The mock-up is ready for some testing. It will allow me to check whether I have enough suface to slow it down, and size up the compartment that will hold it when folded.
I want a system that has the following requirements:
-Be able to install easily on a any kind of multicopter (sub-750g)
-Be lightweight (Under 50g would be great, I still need to figure out how light this actually needs to be)
-Be cheap (If not under $10, at least under 30 bucks)
-Be totally independent from the main system: I want something that deploys the chute when it detects an abnormal drop in altitude (or a g-variation, I have both sensors)
The first thing I have to figure out, is how big the chute needs to be. If I follow a matching table (on page 17 of this PDF: http://www.planete-sciences.org/espace/publications/techniques/parachutes.pdf ), I need a spherical parachute of 43.8cm in diameter to slow down a 1kg body at 10m/s. Now, we will be braking only 750g, but I want it to be slowed down a bit more, so I'll round this diameter up to 45cm.
With this in mind, I'll first make a mock-up of the chute using simple trash bags, to get a feeling of how big the compartment needs to be.
re: gwtting a ball of strings. look at how real emergency chutes are packed, in paragliding for example. Do the same. Also, I suggest you use (synthetic) fabric for the chute. It's lighter & packs more tightly, unfolds faster and has almost identical, if not better, aerodynamical characteristics compared to plastic.
Prop avoidance will be a bit hard, yes, but not too hard, especially if you add some sort of motor-cutting function and activate it, say, 200ms before deployment.
M.daSilva
Giovanni Leal
SapoRano
Douglas Miller
Tommy Gunn