Electromagnetic crane

Question

I want to make a strong electromagnetic crane that would carry weights from one position to another. I am very unsure about the material. Do I use an old transformer? or What type of rods? What type of wire? Also, how can I make sure there is no short circuit occurring? Most important, How can I make the current cut off automatically upon reaching the specified position. I will be using LEGO for the motion and the crane and 12 V battery.

"Strong" - what does that mean? "weights" - what does that mean? — Andy aka, Nov 02 '15 at 08:49
Strong meaning would be able to attract the maximum number of screws(I think that is what we will be using for trial but we may use tiny weights like those for fishing) — Sarah Jamal, Nov 02 '15 at 14:57
@SarahJamal you should put the expected mass you intend to move in your question. — , Nov 15 '15 at 03:08

score 2 · Answer 1 · edited Jan 26 '23 at 19:07

Toasters often use a 12 V electromagnet it's on an E-core form (like a transformer), about 3 cm on the longest dimension. That sounds about the right scale and strength for a lego project.

On the other hand A search on digikey for "electromagnet" turned this up under miscellaneous, they have no stock, but seeed will sell direct. http://www.seeedstudio.com/depot/Grove-Electromagnet-p-1820.html (note 5V not 12V)

Another option is to modify a choke (which is constructed like a transformer but has only one winding), "Triad Magnetics C24-X" looks about right for your task. available though http://mouser.com/

12 V into 50 ohm is 240 mA - perfect.

score 0 · Answer 2 · answered Nov 02 '15 at 08:03

My advice is to locate a 12V DC continuous duty solenoid and use the factory wound coil. There is a similar 24V solenoid for sale on the Adafruit shop, it might work for testing and never get hot at 12V but will not be as strong as a 12V solenoid.

Remove the metal frame (they are usually clinched together and will require some force with pliers to lever open) leaving you with just the coil (on the bobbin) then place the supplied armature core into position and fasten it so it will not fall out.

This will be a lot more likely to work as you hope than winding your coil the first time (which is a fun experiment but getting 1000 turns of fine fire around a nail is not easy).

Remember the magnetic field is determined by the number of turns and the current. So bigger coils can have thicker wire (more current) or more turns and so will have more lifting power. If you are handy with a hacksaw and grinder a starter motor solenoid coil from the auto scrap yard will be really strong but may draw 30A at 12V and will get hot if used for more than a minute at a time.

Electromagnetic crane

2 Answers2