Go Down

### Topic: Solenoid Artistic Function - Magnet and Glass Tube (Read 3066 times)previous topic - next topic

#### encryptor

##### Feb 01, 2013, 07:24 pm
My brother is a glass blower and he mentioned an interesting idea to me, which I believe is similar to a solenoid.  The idea is to seal a glass tube with a magnet inside.  Then wrap the glass tube with a copper wire from end to end.  The copper wire will be spaced so that you can still see into the glass to see that magnet.  On each end of the wire there would be an electrical connection.  Then by reversing the electrical polarity the magnet can be seen floating back and forth.  What is the best approach for flipping polarity and circuit design with the Arduino Uno?  How much voltage and/or current do you think would be required for a 1 foot tube 2 inches wide, with a strong magnet from magnetic key box you'd stick under your car, and copper wire 2 mil thick?
peace*&^

#### PeterH

#1
##### Feb 01, 2013, 07:39 pm
Not sure that 'floating' is an accurate description since the magnet would be resting on the glass and (hopefully) sliding from end to end as you power the coil.

Impossible to say how much current/voltage the coil will require, partly because the magnetic flux needed to move the magnet is unknown and partly because you can trade off current versus number of turns to produce that flux - the voltage requirements would then be determined by the required current and the resistance of the required number of turns. However, the wire you're mentioning sounds far too thick unless you are planning a coil to take massive current. You would probably be much better off designing it for a few thousand turns of much finer wire, but how many turns, how much current is needed with those turns, and how thick the wire needs to be to support that much current, you will need to find by trial and error.
I only provide help via the forum - please do not contact me for private consultancy.

#### encryptor

#2
##### Feb 01, 2013, 08:04 pm

Not sure that 'floating' is an accurate description since the magnet would be resting on the glass and (hopefully) sliding from end to end as you power the coil.

Impossible to say how much current/voltage the coil will require, partly because the magnetic flux needed to move the magnet is unknown and partly because you can trade off current versus number of turns to produce that flux - the voltage requirements would then be determined by the required current and the resistance of the required number of turns. However, the wire you're mentioning sounds far too thick unless you are planning a coil to take massive current. You would probably be much better off designing it for a few thousand turns of much finer wire, but how many turns, how much current is needed with those turns, and how thick the wire needs to be to support that much current, you will need to find by trial and error.

Ok, very good.  Please explain more about the resistance of the required number of turns in the coil.  I don't quite understand that.  How would you know.  Isn't it dangerous to send electricity across a bare copper wire?
peace*&^

#### liudr

#3
##### Feb 01, 2013, 08:58 pm
Not sure if it will work. If you power the solenoid it will suck the magnet in to the middle if you power it the other way, it will try to turn the magnet, not really pushing it to an end. On the other hand, if you only wrap the bottom half with wire, you can use different current to repel the magnet so you may suspend the magnet at different vertical heights.

#4
##### Feb 01, 2013, 09:07 pm
Doesn't have to be "bare" copper wire - can be magnet wire, which has  an insulating layer of varnish or equivalent over it.

Google it - lots of choices.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### retrolefty

#5
##### Feb 01, 2013, 09:13 pm
Biggest missing element if you want the arduino to be able to control the position of the internal magnet is that you need a feedback measurement method to know where the magnet is at any given time so the controls know how much and in what direction to power the electromagnet(s). A software PID controller would have to be set up most likely. While the overall effect would be very cool and appear simple the complexity of control is much more difficult then what one might expect. And on being able to reverse the polarity of a electromagnet requires an H-drive much like used for DC motors where you want to be able to change the direction (polarity) as well as speed (amount of average power).

Lefty

#### Grumpy_Mike

#6
##### Feb 01, 2013, 09:36 pm
Quote
for a 1 foot tube 2 inches wide, with a strong magnet from magnetic key box you'd stick under your car

With these dimensions you have no chance to get it to work. Even if you could get enough magnetic field the magnet when it moved would break the end of the tube. What is likely to happen is that the magnet would not move along the tube but just flip over.

#7
##### Feb 01, 2013, 09:54 pm

Not sure if it will work. If you power the solenoid it will suck the magnet in to the middle if you power it the other way, it will try to turn the magnet, not really pushing it to an end.

I don't think so. When the coil polarity reverses the force will reverse as the magnet poles are still in the same position. The round tube will not allow the magnet to rotate to reverse its poles. Think about why swolenoids work. If the magnet and coil poles are opposite the thing will fly to the closest end as that will be the dominant attracting force and the closer it gets the stronger the force.\

The end breaking problem by the magnet when hit can be solved by using a small magnet covered in 2 layers of soft material on both flat sides.

The feedback signal for the control loop I'm still thinking on that one...
Perseverance is 90% of the solution. The remaining 10% is more perseverance.

#### liudr

#8
##### Feb 01, 2013, 10:04 pm

Not sure if it will work. If you power the solenoid it will suck the magnet in to the middle if you power it the other way, it will try to turn the magnet, not really pushing it to an end.

I don't think so. When the coil polarity reverses the force will reverse as the magnet poles are still in the same position. The round tube will not allow the magnet to rotate to reverse its poles. Think about why swolenoids work. If the magnet and coil poles are opposite the thing will fly to the closest end as that will be the dominant attracting force and the closer it gets the stronger the force.\

The end breaking problem by the magnet when hit can be solved by using a small magnet covered in 2 layers of soft material on both flat sides.

The feedback signal for the control loop I'm still thinking on that one...

You did this before? Any proofs beyond your reasoning that it would work? What is the expression of magnetic force on a magnetic dipole?

#9
##### Feb 01, 2013, 10:13 pm
Maybe the feedback siganl can be solved like this. Just maybe. Let' see what they find wrong with it and maybe we can improve it.

You can't touch the magnet with anything as it will affect the position and look awful; but..

You can place a round piece of reflecting something in top of the magnet thing. At the end of the tube you palce an LED and an LDR (light depending resistor) then you get the reflected light from the mirror and convert it to voltage with the LDR. The closer the magnet the more reflection you'll get and the higer the voltage. You will need to use infrared or something to avoid ambient light from affecting the thing.

Whatever you do with the magnet it has to move freely and you may need a hole in the middle or something to allow the air flow back and forth otherwise the piston efect it will create will slow it down or prevent it from moving altogether when the air gets compresssed. You can also vaccum the tube after done and seal it again as they did it the past with vaccum tubes. Vaccum tubes again? =(
Perseverance is 90% of the solution. The remaining 10% is more perseverance.

#10
##### Feb 01, 2013, 10:21 pm
You did this before? Any proofs beyond your reasoning that it would work? What is the expression of magnetic force on a magnetic dipole?

I haven't mentioned specific quatities or anything.. It's just simple reasoning, You just need to look at solenoids woking to realize about that. The cores don't rotate.

And you? have you done that?. Do you have poof of that other than your reasoning? What's the equation for magnetic force depending on the distance and current? Did you calculated that? With what values because n0 one here has nmentioned anything like specific numbers for currents etc. This is just brainstorming.
Perseverance is 90% of the solution. The remaining 10% is more perseverance.

#### Grumpy_Mike

#11
##### Feb 01, 2013, 10:51 pm
Quote
This is just brainstorming.

That is one word for it but it is another word beginning with b and a lot shorter.

You want to see this magnet and yet you want a coil around it, this means spacing between the turns, and so reduces the magnetic field.
Solenoids have hundreds if not thousands of turns and are not two inches in diameter.

All of a sudden your magnet goes from
Quote
a strong magnet from magnetic key box you'd stick under your car

To one that cannot rotate in a two inch diameter tube, .... that does not add up.
I am not sure what you are going to do with a feedback sensor for the magnet's position, what are you going to do with the information?

Forget the glass tube just try it in a cardboard tube, I bet it won't even move with the current you can put in it.

And no I haven't done the maths, I just have had many years of playing with large magnets.

#12
##### Feb 01, 2013, 11:01 pm
I did not posted this therefore I never mentioned any dimensions of anything. The author was. If he wants to make the magnet "float" it needs to be about the same diameter to avoid spinning. By the way I wasn't answering to your post. I think I know now why Grumpy is in your name. Maybe a similar word beginning with J will describe you be better.
Perseverance is 90% of the solution. The remaining 10% is more perseverance.

#### PeterH

#13
##### Feb 01, 2013, 11:21 pm

Ok, very good.  Please explain more about the resistance of the required number of turns in the coil.  I don't quite understand that.  How would you know.  Isn't it dangerous to send electricity across a bare copper wire?

Rather than me try to explain the theory of electromagnetism to you, I suggest you go do some research for yourself to learn about the theory behind electromagnets, and then look for practical examples of people who have made solenoids similar to the one you're envisaging.
I only provide help via the forum - please do not contact me for private consultancy.

#### encryptor

#14
##### Feb 02, 2013, 12:25 amLast Edit: Feb 02, 2013, 12:27 am by encryptor Reason: 1
very true.  Ok will do.  I believe I've heard of solenoid cannons that can shot out a magnetic rod from it.  This does sound like a high energy project b/c I want the magnet to float. I think the PIR detector set just right and timing to adjust polarity would work and use of magnetic wire.  Ok a H-bridge for polarity switching.  I like the idea about a coated magnet to prevent glass from breaking or hearing the "ting" noise constantly.  Ok a thinner wire wrapped more revolutions is ideal.  It would be awesome if this magnet had an led on it too.  What shape should the magnet be??  I was thinking a cylinder which wouldn't be able to flip in the tube.  I'm thinking it would have 3-4mm spacing between magnet and glass. :%
peace*&^

Go Up

Please enter a valid email to subscribe