I need to build a mechanism that moves a pin to release a payload from a drone. The drone is very small (150 grams) and the payload will be very light, something like 2 or 3 grams. I can't use any digital circuit, battery... it has to be purely mechanical and light.

At first I was thinking about a hook that I would attach to my drone and when I make a very strong movement sideways the hook would release and drop the payload, but I couldn't find a good design to work reliably.

Then I thought about creating a mechanism just like a timer: after 30 seconds it would move a pin. The way I thought about it, would be like a small balloon with a tiny hole releasing air, and when it's completely empty it would become small/shorter and would pull a pin. But having a balloon hanging in a drone would not be good (it would become a kite even using a small balloon).

Still using the timer idea I thought about folding a paper, when you fold a paper and release it, you will see that slowly it tries to get back to the original position... maybe attaching a string to the paper and make it pull a pin while it's trying to get back to the original position... but I think that must be a better way.

So I ask you: is there some way to build a "timer" (it does not need to be precise) that after sometime it can move a pin?

  • $\begingroup$ There are several questions on here asking about quick release mechanisms - all in the last few days… $\endgroup$
    – Solar Mike
    Commented Nov 3, 2022 at 13:30
  • $\begingroup$ Do you have any mechanism currently part of the drone that you can move? A DJI Phantom III has a camera on a gimbal; anything of that nature? I realize that a 150 gram UAV is not going to have much payload capacity. $\endgroup$
    – fred_dot_u
    Commented Nov 3, 2022 at 14:08
  • $\begingroup$ @SolarMike Really? I searched and couldnt find! I signed up today in this forum so I can assure you I am not spamming this forum with similar questions :) $\endgroup$ Commented Nov 3, 2022 at 14:13
  • $\begingroup$ @fred_dot_u I thought about using the gimbal but as I read online, I can easily overload the gimbal if I try to do anything other than its main purpose... $\endgroup$ Commented Nov 3, 2022 at 14:14
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    $\begingroup$ Not a full answer, but I wonder if you could do something with ice, which could release a pin or the payload itself as it melts. Might be finicky to work with in the field, though. $\endgroup$ Commented Nov 3, 2022 at 14:39

1 Answer 1


First I was thinking about a hook that I would attach to my drone and when I make a very strong movement sideways the hook would release and drop the payload, but I couldnt find a good design to work reliably."

That's good. Do that.

You could try a sudden momentary descent or up/down shaking dislodges a free pin sitting shallow grooves. You could rely on airflow of a sudden descent to blow the pin off by having it sit with an open air path above and below and giving the pin some flat "wings" for surface area. Or even wings on just one end so it flips up when it dislodges.

How agile is this quadcopter? It can't do a crazy flat spin on the spot can it? Then you could have a loose fitting plastic screw thing with fins for air resistance with only a couple of loose threads engaged, maybe even fewer like 1/4 or 1/2 turn and maybe spin it loose against air resistance. That's just a crazy proposal though and might not work. But it should be impressive looking and reliable if it does.

If tilt based, the pin could sit in a shallow half pipe so it could roll out when tilted enough.

  • $\begingroup$ Thank you! It's not a powerful quadcopter, it's actually very slow but I can move it sideways/tilt with a good amount. However moving it up/down would be not very fast, but I could try designing a mechanism to make use of that. I just didnt understand well your 1st paragraph... I was thinking about a simple hook but I dont thing it would be easy to unhook it moving the drone... $\endgroup$ Commented Nov 3, 2022 at 14:17
  • $\begingroup$ @EricaShumander I'm thinking of a completely free and disposable pin like a tooth pick. One-shot deal. No resetting. If it's a slow quad another crazy idea is a spiral (or square spiral groove that holds a ball captive and you sort of tilt the quadcopter in a spiral to get the ball out. Sort of like those games where you tilt a wood maze with a steel ball in it to get it out. Unless you can find a mechanical tiny egg timer, pocket watch mechanism, or wind up toy mechanism to use. $\endgroup$
    – DKNguyen
    Commented Nov 3, 2022 at 14:25
  • $\begingroup$ You said no electricity, but can you apply heat or a heating current to something prior to take off such that it cools while in the air? There are Nitinol/Muscle wire springs and wires (use the spring, much more contraction) that can be used against a regular bias spring that stretches them back out as they cool. Thicker diameters can take 10-15ss or longer to cool (I can't find the specific numbers anymore). The springs seem to imply even one minute. Time can be adjusted by how much you heat it up by. $\endgroup$
    – DKNguyen
    Commented Nov 3, 2022 at 14:39
  • $\begingroup$ If not by air resistance, pin release by centrifugal mechanism when yawing $\endgroup$
    – user12750
    Commented Nov 5, 2022 at 2:25
  • $\begingroup$ @qqjkztd That would be preferable if it can yaw fast enough. That can a big if though. $\endgroup$
    – DKNguyen
    Commented Nov 5, 2022 at 2:51

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