Discover the Power of Magnetic Locks: 650-1000 lbs of Force

[mfb]

It has "1/2 of a commutator". Half of the turn is unpowered, but the other half is sufficient to keep it moving through the whole rotation.

 

[oquen]

It has "1/2 of a commutator". Half of the turn is unpowered, but the other half is sufficient to keep it moving through the whole rotation.

Maybe it can move it faster, but it's not necessary. For example. Watch the following video especially at the 2:30 mark (just jump to it if you don't have time to watch the entire video), you can see the guy removing all the insulation around the end.. not just the 1/2 and the winding still runs:



I guess the reason it still rotates is because it's so light that it can overcome 1/2 of resistance, right?

 

[NTL2009]

Maybe it can move it faster, but it's not necessary. For example. Watch the following video especially at the 2:30 mark (just jump to it if you don't have time to watch the entire video), you can see the guy removing all the insulation around the end.. not just the 1/2 and the winding still runs:
...
I guess the reason it still rotates is because it's so light that it can overcome 1/2 of resistance, right?

Interesting. He clearly strips all the way around. I might build one to try myself.

My initial theory is the magnetic forces at some point push the coil up and away from contact, providing just enough switching to keep the force alternating, but I can't quite work that out on paper.

 

[davenn]

It's not that. Nurgatory didn't want to give the answer so we can figure it the simple solution. The answer the video doesn't need commutator is because it's so light and it can make one full resolution even if only one half cycle is making it turn! (this is correct, other experts, right?)

wrong
you are clearly not understanding what the commutator(s) is
both your videos clearly show the commutators of each of those motors
in your post #26 --- it's the 2 loops that the armature wires run through
in your post #32, they are shown as hooks rather than loops

the commutators in these 2 videos are serving a dual purpose
1) they are the bearings for the armature to run on and
2) they are the commutators ( the power transfer point ) the point where power is transferred
between the fixed sections and the rotating sectionsDave

 

[NTL2009]

...
both your videos clearly show the commutators of each of those motors
in your post #26 --- it's the 2 loops that the armature wires run through
in your post #32, they are shown as hooks rather than loops ...

Yes, but in post #32, how do the hooks provide any switching? If power is just transferred, with no switching, the armature will move towards, or away from the magnet (depending on polarity), and just "stick" there. But that motor spins. That is normally done by switching the polarity with a commutator, but in these simple motors, they just connect half the time and let inertia carry it through.

Maybe it's obvious and I'm just missing it.

 

[arydberg]

Today I just learned the concept of magnetic lock.. where pure electromagnetic force was used to lock doors.. My experience with magnets shows you can still pull two magnets apart.. but for magnetic lock.. there is no moving part, the door is closed just by the turning the electromagnets on and it is just small pieces and small voltages.. so powerful stuff! Specification says 650 lbs to 1000 lbs of force. Would anyone know the electrical patterns the magnetic lock make compared to ref magnets? How could something so small able to hold or pull 1000 lbs?

This may help,
https://www.mcmaster.com/#electromagnets/=17m1fk0

 

[oquen]

This may help,
https://www.mcmaster.com/#electromagnets/=17m1fk0

Thanks. I want to see the schematic of the coiling inside a magnetic lock. The other day when I went to a convention, I brought the lock to see how it would look like when it passed thru x-ray machine similar to that used in airports:

It didn't show any details.. just one solid rectangular block.. so if anyone in the future find a schematic.. just share it here. I bought the magnetic lock for $50 and it would be a waste to burn the plastic away.. and I'm fast losing interests in all this anyway. So I may just resell it to get back the $50. Thanks and would appreciate so much anyone in the future who could provide an internal details of the coiling of such electromagnet locks.

 

[NTL2009]

I'm pretty sure the schematic is... a coil of wire.

You seem to be looking for magic. I think this is simply a coil of wire around a pole piece. I'm sure there are some specifics to the design of the pole piece to optimize the force where they want it, but that's all.

Did you do the calculations of current and forces and determine how many turns would be required for that force? Will a wire of that current capability fit into that space with that many turns? Bring that calculation back to the forum, and I think you will get your answer. Hint: for the calculations I found, all else equal, the magnetic force is directly related to the number of turns (in theory - there will be practical matters that influence that).

http://spiff.rit.edu/classes/phys213/lectures/amp/amp_long.html

 

[oquen]

I'm pretty sure the schematic is... a coil of wire.

You seem to be looking for magic. I think this is simply a coil of wire around a pole piece. I'm sure there are some specifics to the design of the pole piece to optimize the force where they want it, but that's all.

Did you do the calculations of current and forces and determine how many turns would be required for that force? Will a wire of that current capability fit into that space with that many turns? Bring that calculation back to the forum, and I think you will get your answer. Hint: for the calculations I found, all else equal, the magnetic force is directly related to the number of turns (in theory - there will be practical matters that influence that).

http://spiff.rit.edu/classes/phys213/lectures/amp/amp_long.html

I know an electromagnet is simply a coil of wire around a pole piece. The specific of how they can just make one surface magnetic while all the other sides are not magnetic is what I'd like to know.. like how they optimize it. that's all.

 

[NTL2009]

I know an electromagnet is simply a coil of wire around a pole piece. The specific of how they can just make one surface magnetic while all the other sides are not magnetic is what I'd like to know.. like how they optimize it. that's all.

It should be fairly obvious if you have ever played with a magnet and a piece of iron. From wiki, iron (depending on composition) can have thousands to hundreds of thousands higher permeability than air:

https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials

So that magnetic field is contained almost completely to the pole piece. I've got some strong magnets from hard drives that are mounted on a metal plate. Super strong on the magnet side, but it won't even hold a paper clip on the other side of the metal piece. I'm sure you can find some web sources discussing electromagnets and their pole pieces and how they are adapted for different purposes.

I think it's time for you to do some reading and research on your own, rather than coming here for answers.

 

[oquen]

It should be fairly obvious if you have ever played with a magnet and a piece of iron. From wiki, iron (depending on composition) can have thousands to hundreds of thousands higher permeability than air:

https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials

So that magnetic field is contained almost completely to the pole piece. I've got some strong magnets from hard drives that are mounted on a metal plate. Super strong on the magnet side, but it won't even hold a paper clip on the other side of the metal piece. I'm sure you can find some web sources discussing electromagnets and their pole pieces and how they are adapted for different purposes.

I think it's time for you to do some reading and research on your own, rather than coming here for answers.

All my magnets since a child were small so I thought they equally attract iron at all area. So it's only the pole. Now the videos in youtube makes sense why the fillings where only attracted to the poles (I thought they just did it that way). Thanks for mentioning permeability. Everything finally makes sense. It's good you mentioned it or I could have missed that concept.