Did some more reading.
A fellow made a small coil; unenergized a magnet stuck to the core; a pulse of the correct polarity and it "jumped" away.
Would this arrangement need less current (i.e. smaller lighter coil)?
It's ok with me if the magnet falls away; perhaps even advantageous.
Releasing a magnetic latch requires energy in joules or watt-seconds, not just current. That means some number of watts for some amount of time to counteract the magnetic field, for enough time for the payload to move out of the magnetic field before the field collapses. You could charge up a big capacitor and do that. The problem is getting the payload away quick enough, which usually means that it's spring loaded, which in turn requires more power to release.
I'm not suggesting you give up on your magnetic release idea, but I think you'll find that most model airplanes use servos to release some kind of mechanical locking mechanism. The servos interface nicely with the RC receiver. Most quadcopters have spare outputs to actuate cameras and accessories.
Perhaps the people on the ground that the falling magnet hits might not find it so advantageous.
A release mechanism that weighs less than 10 grams is going to be difficult, especially when the payload is undefined. 10g is the weight of 2 US nickels. Perhaps if you disclosed some more numbers, calculations, estimates, and sanity checks might be possible.
If such a low weight is a requirement, it might be best to store the release energy in something with a higher energy density than a battery or a capacitor. Above batteries are explosives, so that would be my first choice. Latch the payload with a magnet, and ignite some gunpowder to release. The size should be small enough not to produce an explosion hazard and certainly smaller and lighter than an actuator and battery.
Hint: The peel strength of a magnetic latch is much less than the pull strength, so placing the explosive at ONE end requires less explosive than in the middle.
Some oversized and overweight alternatives and ideas:
Good luck.
One more, which uses a servo: The problem is that the miniature servos typically weigh about 10g. (The regular servos are about 40g).
Oops. I forgot to sort the list by weight: Looks like there are some servos down to 1.5 grams. A servo might actually work.
I'm pretty sure it'll be heavier than an equivalent servo, but if you go that route could you please post your results?
I'd be interested to know if I'm wrong.
There's a company in Brazil with an AlNiCo (I think) permanent magnet that can be demagnetised and re-magnetised under the control of a command signal.
I saw it on Dave Jone's EEVBlog
Have something to add? Share your thoughts — no account required.
Ask the community — no account required