The drone parachute

Let's talk about parachutes.

Multicopters can become deadly weapons if the motors stop spinning as they should. There are so many reasons for a failure to happen (bad motors, bad battery, radio problems,etc...)  that it is absolutely necessary for the pilot to anticipate it, especially if you intend to flight over people's head!  We made the choice to never fly directly above people, but if you're willing take that risk,  you might be interested into getting a parachute on your drone . That's why we designed last year a DIY parachute for our quadcopter  🙂

The principle is very simple : the parachute is carefully folded  in a tube on top of which lies a lid that a servomotor keeps closed. At the bottom of the tube, a big spring pushes strongly the parachute towards its top end. So if the servo lets the lid go, the spring will push the parachute in the air.

It may be hard to believe, but the parachute will fit in the tube !
It may be hard to believe, but the parachute will fit in the tube !
The spring is separated from the parachute by a CNC milled ring.
The spring is separated from the parachute by a CNC milled ring.

I recommend you use a strong spring, so the parachute is entirely pushed out when the servo releases the lid. The spring we used is 10cm long, has 8 turns and is 3.5cm wide. It can be fully compressed under pressure, which is what we wanted here, in order to get the smaller parachute we could.

A hook holds the string to the bottom plate
A hook holds the string to the bottom plate

One of the major problems with parachutes is that the air needs to get "under" the parachute envelope in order to make it act as it should. If it doesn't , the parachute will become useless. We followed the method described in the following video :

 

This is how the parachute looks before we insert the actual parachute. The spring will eventually be pressured until its minimum lenth
This is how the parachute looks before we insert the actual parachute. The spring will eventually be pressured until its minimum lenth
We used a glass fiber bottom plate as it needs to resist to a lot of pressure
We used a glass fiber bottom plate as it needs to resist to a lot of pressure
Bottom plate. It can attached to your frame by screws or zip-ties (we love them :) )
Bottom plate. It can attached to your frame by screws or zip-ties (we love them 🙂 )

Parachute surface calculation

 

Obviously, your parachute's surface needs to match the weight of your copter, and the desired landing speed you would like to reach. I think a commonly accepted falling speeds sits around 5m/s (18km/h).

We found in the past a pretty useful formula that gives the diameter of tissue to use depending on the weight you want to slow down and its expected falling speed:

 Diameter = \frac{70*\sqrt{m}}{V}

, with m in grams and V in km/h.

 

For our 1kg drone, it gives us a diameter of 122cm. As you can see, the parachute can quickly become huge compared to the size of your multicopter, and you should maybe start thinking about where to place it on your drone from the very beginning of its conception.

For our quadcopter, we used a slightly smaller parachute (taken from a distress rocket) than the 120cm recommended size given by the formula, which led to higher falling speeds than the expected 5m/s, but it stayed slow enough to keep the drone intact after many, many test flights ! 🙂

Parachute ready for insertion
Parachute ready for insertion
See, it fits ! :)
See, it fits ! 🙂
Ready to go!
Ready to go!
The servo arm is under a lot of pressure here.
The servo arm is under a lot of pressure here. We used the TGY-53317M servo for this parachute.

 

Here's the final video 🙂


Comment if you have any question ! 🙂

17 thoughts on “The drone parachute

  1. Where did you buy the spring from? What are the specs on it besides the length and number of coils, how did you decide on it?
    I tried at different local hardware stores and nobody carries springs like that you used.

    Thanks!

    1. Hi Dinos!
      We bought the springs from a dedicated french webiste selling springs. Honestly we kind of chose with our guts how the spring should be like in terms of size. It's important you get a spring that can fully be compressed, though.

    2. Just watching this, the springs that look similar may be like the ones in pop-up lawn sprinklers. A cheapy may cost ~$AUD1

      The one I have here is 11cms uncompressed/1 cm compressed, 1 mm wire, 2.5 cm diam. Most are similar dimensions

      They could be easily rewound & tapered to reduce compressed length. Tension I think would be just right.

      Casing of sprinkle may be good as well as primary container with a few mods.

      Hope that helps

  2. Where did you find the motor? I am assuming there is some sort of release aux button for the controller? Do you have any tips on that set up?

  3. Hey, I love this deployment system. I would like to replicate this project for my quadcopter. Could you be more specific on the dimensions and parts that you used?

  4. Did you make your own parachute or buy it? I tried using a runners parachute for mine but it was too bulky and heavy. Also, what was the load for your spring?

    1. Hi Tim,

      The parachute we used for this video was a parachute used in distress rockets for boats 😀
      I described the spring whe chose in the article but I would say that I was much stronger then what we actually needed.

  5. This is a great project. I am thinking of making something similar but I would like it so when the drone's battery dies or the motor malfunctions that the parachute deploys automatically. Would you have any knowledge as to how one would do that?

  6. Love the bent nail hinge. What are the plastic looking parts in the hinge or what could I use to make those hinges? Must be strong obviously. Thanks.

  7. Hi boredengineers!

    I am a 13-year-old boy who wants to build your awesome parachute but I need some information from you:
    1. I need the measures of the tube (diameter and height)
    2. In which webpage did you buy the spring?
    3. How does exactly the servomotor work? I am new in this “build world” and I have no idea how it works.

    I would appreciate if you could answer all my questions.
    Thank you very much in advance
    Timor

  8. May I ask what is the delay from turning of motor power to releasing parachute?

    If the delay is 0, or too short, the parachute string may tangle to the motor propeller. If the delay is too long, will the drone flip-over during falling (given condition the altitude is enough)? If the drone is in an up-side-down position, the parachute still will tangle the drone arms.

    Please correct me if I am wrong.

    Thank you!
    Liang

  9. hi!! i'm studying student!
    i have a question
    your parachute what material?
    and... you know weight & terminal velocity & parachute size relational expression ?
    plz answer :D!

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