I'm planning to build an air-dropper for a small drone - a device to release small payloads hanging under the drone.
This is a commercial example of such a system, used with a much bigger drone - for heavier payloads, pretty heavy itself, and using the drone's built-in systems for control:
(7:18 - system in action. 5:44 - the part, for which counterpart I'm asking.)
I'm planning to build something similar, but much smaller. Payloads of up to 100-150 gram (but often smaller too), a completely independent control system. I already have working remote control electronics capable of outputting 3.3V at 40mA (driving a tiny coreless motor like this; I also have such motors), under 10 gram together with the battery.
I still have no idea what sort of actuator I could use to release the payload. I'd prefer it to remain unpowered when 'latched', needing only power to open (drop the payload). It should be as lightweight as possible, because any of its weight takes away from payload capacity of the drone. And not being very expensive would be a big plus.
For the ideas I had so far:
- Most servos I've seen are rather on the heavy side, or provide so little torque I'm afraid any latch I come up with won't suffice.
- I considered pairing a permanent magnet and an electromagnet that would cancel out the magnet's field, but first I'm not sure if I can output a field strong enough, and then the cancellation won't be perfect and if my payload is very light, it won't drop.
- I don't think I have the current to drive a linear electromagnetic actuator to unlatch a hook (not sure about that though).
- I don't have means to build more complex gearboxes to convert the high RPM of the tiny motor to torque - at least from scratch; if something of that kind is commercially available and small enough, it might be good.
- ...also, it would be great if it was fully reusable and safe. I seriously considered just a small relay to put full current from a battery through a resistive spiral to burn through the line with the payload. I'm not enthusiastic about this idea.
I'm not specifying the housing, 'hook', line, attachment methods etc here - these are to be made such as required for it to work.
(also worth considering: a fully mechanical connector with no electronics; disengaging on a maneuver not encountered in normal flight, e.g. a rapid drop. I can't generate negative-G, but I can make the drone -almost- drop out of the sky. If this could disengage the hook, that would also be a workable solution. This is not as preferable as it requires considerable vertical space and is rather risky.)