PARACHUTE anyone ?

Maybe someone has encountered a small scale parachute ?

I'd like to add a safety parachute to the Arducopter !! help me decide....

As part of the project is to use an expensive DSLR on the copter,

My GF said i must have some kind of emergency parachute... after joking at it, i thought deeper -

I'd rather feel much safer having a parachute as backup to all electronics (even though i plan on 6 or 8 motors)

Just imagine an emergency button that will immediately turn off all motors and shoot a parachute.

questions:

as parachute takes some time to open (=some free fall height), the benefits are sure and obvious for a 100m fall.

but if i'm around 5m above ground, (which can still be nasty to the DSLR) - would i have enough "falling time" to open the parachute and having enough braking force ?

think i better make one by myself ? is it rather simple as cutting and connecting wires to a cloth,

or it is more complex design that i could hardly achieve and i better get a ready one ?

i came across this as the only parachute i could find:

http://cgi.ebay.com/NEW-40-SPEED-RUNNING-POWER-CHUTE-training-parachute-/220760637799?pt=LH_DefaultDomain_0&hash=item33665c0167

It looks sturdy and well balanced & stuff... it's totally affordable !

they say the 40" version has 7KG resistance. i'm safe on this side, i dont want a much bigger one.

how about the opening technique ?

i could stuff it in a small plastic tube attached to the top of the dome, using a small solenoid or servo to kick it out...

how do i ensure it opens reliably ? i guess it depends on the folding inside the storage tube...

Squalish, those 30-120 g are averages, not peaks. Peaks could very well be within the 10,000 g neighborhood, and that's enough to develop hairline fractures in the structure and definitely enough to reliably kill gyroscopes, accelerometers and lipos (and when a lipo goes, everything else does).

Then there's the DIY aspect. Reaching aerospace quality is exceptionally hard. A certified pyro cutter (a device that cuts a 5mm nylon rope with fire) for use in space costs $800. A DIY version costs about $1. Ponder the differences in quality control involved. Without access to substantial know-how and tools you won't be able to DIY an airbag system that I would have my machine rely on. A parachute on the other hand? Much easier. Why? An airbag has to deploy within milliseconds to be effective, and it has to be strong enough to 1) survive the inflation and 2) dissipate highway-type velocities inside of a couple milliseconds. A parachute on the other hand can deploy comparably when it wants to (~seconds of time) and has more seconds to dissipate the velocity in (a ten second sightseeing drop?). All in all a chute has to deal with orders of magnitude lower mechanical stress, which makes it the emergency system of choice in resource constrained development environments.

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Overwatch March 27, 2011 at 10:32pm

There are a number of ways. Mechanical (springs, pistons, levers... actuated by servos) that are heavy and slow, natural (drogue chute positioned to open on its own when the airspeed reaches a certain level) which is dangerous because you never know when it opens, and pyrotechnic (a very small BP charge together with a commercial fireworks electronic igniter) which is by far the lightest, most reliable and safest of them all.

There are even chute designs with forced inflation - a system of weights and strings designed so that when ejected out of the chute tube it forces the parachute open, making it effective within meters from the apex of the free fall.
ARHEXA March 27, 2011 at 10:22pm

imagine that the first thing to hit the ground would be the DSLR mount.

i might put foam or polystyrene on the outer side of it to absorb some G's

it's still not very friendly to the DSLR,...

but let's said im less worried on the 5m height falling (where the parachute won't have time to open) or from the relatively aggressive landing with the parachute...

i'm more worried of 100's meters free fall from the sky...
I.S. March 27, 2011 at 4:08pm

How people usually "fires" its parachute? (I don't know the proper term for that)

Which mecanism is used?
Overwatch March 27, 2011 at 2:39pm

Squalish, those 30-120 g are averages, not peaks. Peaks could very well be within the 10,000 g neighborhood, and that's enough to develop hairline fractures in the structure and definitely enough to reliably kill gyroscopes, accelerometers and lipos (and when a lipo goes, everything else does).

Then there's the DIY aspect. Reaching aerospace quality is exceptionally hard. A certified pyro cutter (a device that cuts a 5mm nylon rope with fire) for use in space costs $800. A DIY version costs about $1. Ponder the differences in quality control involved. Without access to substantial know-how and tools you won't be able to DIY an airbag system that I would have my machine rely on. A parachute on the other hand? Much easier. Why? An airbag has to deploy within milliseconds to be effective, and it has to be strong enough to 1) survive the inflation and 2) dissipate highway-type velocities inside of a couple milliseconds. A parachute on the other hand can deploy comparably when it wants to (~seconds of time) and has more seconds to dissipate the velocity in (a ten second sightseeing drop?). All in all a chute has to deal with orders of magnitude lower mechanical stress, which makes it the emergency system of choice in resource constrained development environments.
Ersin Acar March 27, 2011 at 1:34pm

http://diydrones.com/forum/topics/dronechute-1
Marcus Vickers March 27, 2011 at 1:24pm

Check out the high power rocketry sites
http://www.apogeerockets.com/parachutes.asp
http://www.madcowrocketry.com/servlet/the-Rocket-Components-cln-Chu...

I wonder if a streamer would slow / stabilize enough?
Squalish March 27, 2011 at 1:21pm

Kicking the dead horse:

*Airbags function to limit terminal velocity *as well* as reduce impact forces.

*30-120 G's is really not a lot for a light, strong object like this. Rubber landing gear legs experience impacts like that on hard landings all the time without damaging the copter.

And as was mentioned, airbags are primarily considered in combination with chutes.

IMO, 5m from the ground is not enough for a chute to provide reliable protection, when its opening time is combined with human threat assessment and human reaction time. Airbags *might*, with enough development. Improved landing gear and roll cage *would*.
Overwatch March 27, 2011 at 11:56am

Yea, apart from being heavy, clumsy and expensive and that they don't work, airbags are a fabulous idea!

Seriously now: the chute doesn't need to bring the falling quad to walking speed. We're talking damage control here, which means getting it down to a reasonably safe speed is enough. Some 25 km/h (7 m/s) is still safe for a quad with good landing gear, it might get broken but electronics/motor damage is unlikely.
ARHEXA March 27, 2011 at 11:36am

who's talking about airbags ? thats behind us...

these chutes on the rockets site are nice,

but i think 40" (the sports one i found) is not ENORMOUS relatively to the copter, and remember it will be a heavy one - 2-3kg...
Matthew Coleman March 27, 2011 at 11:25am

so, apart from being difficult to implement and mostly ineffective, an airbag is a good idea.

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