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Magnet for picker/dropper

Adonai

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Hello.

I am working on a project for a magnetic picking and dropping device.

My idea is to use a permanent magnet (neodymium or similar) that grabs stuff coupled to an electromagnet, thus a brief pulse of current will be enough to drop anything attached to it.
the magnet should have an attraction force slightly less or equal about to the maximum lifting capacity of the drone (1kg for the mavic 2), in order to release the payload by itself if it gets stuck somewhere.

and it should dangle from its support about 1.5 meters from the drone, (then leghts can vary), just far enough not to interfere with its compass/magnetometer, using the red and black paired cable as the wire to sustain magnet and payload, it has the benefit not to twist or spin while posing the payload. (assume you are placing down a gopro for example, you wont curse too much to place it in the right direction)

All the payload should have is a small metallic plate the size of the magnet for it stick into.

Compared to the actual dropper it shoud be smaller, lighter (about 35 grams on mavic 2) and easier to build: mangnet, wire, battery, a strap as support (or something "cooler" 3d printed) and the photocell/photodiode to command it (mavic 2 has no other ways to operate it) are all its required.

And safer: it offers a better way to pick up stuffs minimizing the risk of getting stuck, unlike hooks.

What do you think about, is it feasable?

What kind of magnet do i need?
 
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Not sure what sort of effect this might have on the drone hardware and functions.
Don't think the permanent magnet will play well with the drone, or that it would go well even with a short electromagnetic burst (it needs to be on for it to hold).

Maybe @sar104 or @slup or any of the other flight analytic people here can give you some advice.
 
It's difficult to picture what you are proposing. Can you post a simple diagram of it?
 
It's difficult to picture what you are proposing. Can you post a simple diagram of it?
Trying to better explain myself.
The magnet, when unpowered should normally attract.
When u briefly pulse a current in it, should release its load.
The cable should be as long as to keep the magnet far from the drone enough not to interfere with her compass/magnetometer.
 

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Magnets and drones are a bad mix. Period
If you do attempt it, I would keep it at least 20 feet away and you will get a warning of interference.
Good luck.
 
i vape and the pod magnets are pretty strong and as long as i,m not doing anything but flying it dosen,t bother the drone
 
Trying to better explain myself.
The magnet, when unpowered should normally attract.
When u briefly pulse a current in it, should release its load.
The cable should be as long as to keep the magnet far from the drone enough not to interfere with her compass/magnetometer.

That's a pretty interesting idea, but I think you might be surprised to find out how much current and how much wire it would take to overcome the magnetic field of a permanent magnet that can lift a kg. The weight of the battery and coil of wire is likely to be significant.

I'm no expert on magnets, but a little online searching says that an N52 neodymium magnet like can be found all over the place on eBay has a field strength of 5200 Tesla. If I correctly understand the online solenoid calculator in the link below, to generate an opposing field of 5200 Tesla would require a pulse of 100 amps through a 5 cm long coil with just over 10,000 turns of wire if the coil had an iron core. I didn't try to figure out if wire small enough to fit 10,000 turns on a 5 cm long coil could survive a 100 amp pulse, but I suspect not. Not to mention how much all of that would weigh.


If anyone with a better understanding of DC solenoids has a better calculation, please post it.

Here's another thought. With the permanent magnet and the release coil being at the end of a few feet of wire, they are going to swing around quite a lot as you try to maneuver over the payload you want to pick up, with the wind and any prop wash making things worse. I'd be very surprised if you could get it to attach to a small metal plate.
 
If you find a solution to developing an electromagnetic pulse to temporarily neutralize the permanent magnet, you could do this by NOT using a DJI drone. If you used a Skydio 2 (which does not use a magnetic compass), it may work. Also keep in mind that every time you "fire" your magnetic neutralizer, it is going to permanently remove some magnetism from your permanent magnet. And as AZDave says above, it just isn't practical carry a huge battery that can put out that much pulse current. Maybe slowly charge a bank of capacitors, then fire them into the neutralizer?
 
The other issue is that the item you want to pick up need to have metal, and most drones don't like metal or magnets
 
Trying to better explain myself.
The magnet, when unpowered should normally attract.
When u briefly pulse a current in it, should release its load.
The cable should be as long as to keep the magnet far from the drone enough not to interfere with her compass/magnetometer.
Rather than using a power eating solenoid, how about a small toy DC motor turning a cam which slowly pushes the load away from the magnet far enough until the weight falls away? Then continue (or reverse) the motor (and cam direction) until back in home position and ready to release again.
 
You will need power to hold the items for the duration of the flight and a way to turn the power on or off. Weight of the items carried and duration of flight will determine power requirements. Power requirements will dictate battery size. We are experimenting with an item drop relay for carrying a Ham wire antenna a distance and then dropping it. That will use a lot less power than the magnet.
 
To carry my example above a bit further, let's assume that 20 gauge wire could handle a brief surge of 100 amps. I don't think it can, but for illustration let's assume it could.

20 gauge bare wire has a cross sectional are of 0.52 square mm, and maybe you can find some that has a really thin insulation. 10,000 turns would be at least 52 square cm, and for a 5 cm long coil the radius of the coil would therefore be over 10cm ... that's more than 20 cm diameter and would weigh several kg all by itself.

It seems to me that a better solution, at least for a one time pickup/dropoff, would be to put the magnet on the payload with the metal plate suspended from one of the inexpensive payload release mechanisms that are readily available for the drone. Some of those systems will even handle two drops instead of just one.
 
Rather than using a power eating solenoid, how about a small toy DC motor turning a cam which slowly pushes the load away from the magnet far enough until the weight falls away? Then continue (or reverse) the motor (and cam direction) until back in home position and ready to release again.

I'd bet that a magnet strong enough to lift a kg will cause any small motor with reasonable gearing to stall out.
 
I took a look around and bumped into this:

12v Dc Jsp-1212k Power On To Release Mini Electromagnet Lifting Electromagnets Holding Electromagnets - Buy Permanent Electromagnet,Electromagnetic,Small Electromagnet Product on Alibaba.com

Seems the JSP 1212K weighs 8 grams, lifts about 1 kilogram and consumes 6 w while on (0.5 A @ 12 V circa)
Numbers taken from the datasheets they published, which I don't know how reliable they are.

How many short (0.3-0.5 seconds) pulses can a small battery whitstand? (small circuit with capacitors maybe)

Maybe i'll buy one just to run some tests, or better have some friend lend me a non electric small magnet to try, and probably like @Capt KO said it will mess bird's magnetometers up, killing up this project :(

In my simple mind I thought an object so small, with a mag field so smal, if kept far away from the drone wont have been detected.

And like @AZDave said should find a way to avoid swinging or worse slinging it back into props when changing attitude, expecially if not carrying loads.

Other ways like @EyesWideShut suggested, will add weight and complexity, which is the opposite of this project purpose.

I'll keep you updated.
 
Toss the whole magnet idea out of your head. It's not gonna fly. No pun intended.
 
I underwent some tests helter skelter.

Strapped Just a wire , 1 meter in lenght and piled up 4 small ferrite magnets at the end, (lift capacity about 0.1 kg in total).

Results: magnetic interference error while on the ground, took off anyways, picking up stuff (small vials with a similari magnete attached on top) was difficult, because of the drone trying to compensate height.

No appearent mag interferences during flight

But not acceptable as the tool i intended it to be.

Looks like the cable is too short, too close, will try with a longer one and a neodimium magnet asap and posts the new results.

For now you were right.
 

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I underwent some tests helter skelter.

Strapped Just a wire , 1 meter in lenght and piled up 4 small ferrite magnets at the end, (lift capacity about 0.1 kg in total).

Results: magnetic interference error while on the ground, took off anyways, picking up stuff (small vials with a similari magnete attached on top) was difficult, because of the drone trying to compensate height.

No appearent mag interferences during flight

But not acceptable as the tool i intended it to be.

Looks like the cable is too short, too close, will try with a longer one and a neodimium magnet asap and posts the new results.

For now you were right.

Well, I still think that the reverse magnet you found on Alibaba was a nice catch. At the least it tells me that it doesn't take anything close to an N52 magnet to pick up a kg. I could imagine a lot of uses for those little things other than for a drone pickup.

You might try using some sort of thin, stiff fiberglass rod to hold the magnet under the drone. Not sure how you'd attach that to the underside of the drone, though. That being said, even though the camera gimbal makes videos look like the drone is really stable, in reality it is rocking all over the place much of the time. Certainly if there is any wind ... and probably even from the prop wash if the drone is close to the ground or some large object. Picking up a small object sounds like it would always be a hassle.

Good luck with your experiments, though.
 
...Results: magnetic interference error while on the ground, took off anyways

No appearent mag interferences during flight...
It's a couple thing's you miss here ...

When you power on your craft the compass will initialize the IMUYaw ... meaning, the compass will tell the IMU in which direction the craft is pointing. If the compass is interfered in this power on moment you will be in for a major surprise once you're airborne & the craft needs to counter wind drift to hold position for the first time. This is what we call a Yaw error ... the craft don't have the correct heading direction & apply thrust with the wrong motors to hold position = the positional error becomes larger instead of smaller ... & this is repeated over & over again leading to that the craft speeds away totally uncontrollable.

During flight it isn't mainly the compass that tells the direction ... it's the initialized IMU, so if the compass gets interfered during flight it will instead slowly feed in direction corrections to the IMU ... eventually the IMU over time will be either confused, this as the rate gyros tells a different story to the IMU & you risk having an IMU that gives up & going into ATTI mode ... or the IMU goes with the disturbed compass adjustments & the craft ends up with a Yaw error & again creates a undesired flight behavior.

It's a simple solution to all this ... keep the craft away from all sorts of magnetic interference at all time.
 
It moves alot, so does the magnet at the tip, but the rubber sheath of the cable somehow dampens its jolts.

Will see how It behaves with a longer cable. (And a proper mag)

If It pops interferences anyways I'll abandon the project.

Losing heading midflight would be too dangerous for the drone and for the payload.

@slup thanks for the deep explanation, im not gonna risk an erratic domino effect.
 
@slup is it right that if before take off, ensure the drone direction on the ground, matches that of the map, it *should* avoid the compass / IMU error ?

During take off if it gets closer, it may upset things, once airborne should be ok ?

I admire the OPs resilience in continuing his tests, even if something fails, you've learned another way that won't work, and can then get onto something else.
 
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