Let's Make Robots!

Making an variable strength magnet

I am in need of magnets where the strength of the magnet can be varied. Specifically I need 3 "settings", off, low and high. Low would be where the magnets have enough strength to connect but not more strength than they can be pulled apart. High would be where they connect but can't be pulled apart.

Now I'm wondering if such a magnet even exists, or if I have to make it somehow myself. If I have to make it myself, what would be the best solution? All I can think of, is making an electromagnet. However the magnets I need must be really small, no more than a centimeter in diameter, so I'm not sure it's possible to make an electromagnet out of that. Furthermore I have been thinking of using neodymium magnets, as they don't lose their strength but they are also very hard to pull apart from what I've heard, so they may not be the best idea.

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I aqm at work so cant go into detail here but there is a whay ro make your neo mags variable.

If you send me a nessage to remind me I will explain when I get home.

It involves shorting out the magnets mechanicaly. very simple but you may have to do some machining (not on the magnets!

Okay, so I just received some magnets I ordered online, which turns out to be Neodymium magnets which I tried to avoid (I guess I didn't pay close enough attention). So now that I have that, I can certainly tell that they are very strong, about as strong as I would want for my high setting. But if I make it into an electromagnet, will there be any way for me to decrease the current strength of the magnet alone, or will it only become stronger using electricity?

If you set the electromagnet to act against the neodymium magnet you could vary the apparent strength of it, but the electromagnet would have to be very strong to completely negate the other.

So I wouldn't really be able to make my magnet less strong, or even have so little strength so as to basically be turned off, correct?

It`s possible with a big electromagnet or enough current to counteract the neodymium one such that it can be considered off. You`re just limited by how you want to power it and how small you want it to be.

I think you should get some wire, a nail and a battery and create an electromagnet to see if it`s acceptable or not. If you have a multimeter measure the current from the battery. From there you can decide whether to attempt to make it smaller and more efficient, or go a different route altogether.

Is this even possible to do using a small button cell battery at say 5V?

I think that with a soo small battery the electromagnet will be very weak (indeed it depends on the number of turns you make around the magnetic core...), since it will require lots of courrents flowings in the spires. Moreover it will empity quite soon.

If you plan to put memories in your devices, they could be badly impacted by the electromaganetic fields (it depends how close they are to the source of the magnetic field).

 

 

Quite some interesting ideas being presented here. However, since the magnet can't be bigger than 1 cm, I'll have to stick to using square or round magnets. Fortunately I've found quite a few possibilities, so now I just have to read up on what all the data mean and figure out what I need.

@Oddbot: When you say that ferrite is better for high frequencies, what does high frequencies mean in this case?

@ezekiel181: That's actually a good question which I hadn't thought about. It only needs to be strong enough so that the average male can't pull it apart. How many Newton/lbs would that correspond to approximately?

Essentially, the idea of this is to have two metal plates, each with a magnet attached, attached to each other. Later on I plan on making a cube with a magnet on each side, so that I can put two cubes together.

I'm not very familiar with electromagnetism though, so that raises two concerns in the back of my head. Would the magnetic fields of each 6 magnets ruin any other electronics nearby it, and would it affect the magnetic fields of the other magnets in the cube, given that my idea is to have it strong enough at the highest setting as to not be pulled apart? Is this even possible to do using a small button cell battery at say 5V? And is this setup even feasible? I really don't have enough experience to judge whether or not it will, but I will order some magnets and wire and play around with this.

Btw, English is not my first language, so I was wondering what transformer wire means? I tried googling it, but couldn't really find anything.

• Transformer wire is also called enamel wire, winding wire, or magnet wire. It has a coating (usually reddish or orange) that can be stripped off at the ends. • Small button cell batteries have very low current drive capabilities, which doesn't match up well with the high current requirements of an electromagnet. You're probably going to have to either use permanent magnets or find a new power supply. • Unless your electromagnets are turning on and off rapidly they won't have a serious effect on most electronics. Some electronics are sensitive to stationary magnetic fields, but most are only affected by changing magnetic fields. For a more definitive answer you'll need to let us know what type of electronics will be near the magnetic parts. If you could give us a more complete idea of what you're building we could probably be more helpful.

I was just thinking, I haven't tried this, but it seems sound in theory...:

If you put a normal magnet in "piece A" and an electro magnet in "piece B", with both magnets of equal strength.

If the electro magnet is turned off, then the normal magnet would still attach to the metal core of the electro magnet (low strength).
If you turn the electro magnet on, then both magnets will attract each other doubling the force (high strength).
If you switch polarities on the electro magnet, then the magnets would push away from each other. This wouldn't be a normal "off" solution, if you need the two pieces to be able to stand next to each other without attaching or repelling, you will have to try some of the other solutions.

How strong your magnet is depends a lot on your magnetic circuit as well as your electrical circuit. A magnetic circuit is the path in which the mangetic flux travels. I would use mild steel rather than ferrite. Ferrite is better for high frequencies. You just have on or off. A "U" shaped piece of mild steel will be the best magnetic core. Think of 2 horseshoe shaped magnets joining together.