A speed controlled pulsing electro magnet? - RC Groups
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May 06, 2010, 10:00 PM
Physics hate's my ideas
GreenAce92's Avatar

A speed controlled pulsing electro magnet?

So... first of how do you get a light to blink... ie pulsing.. is it done by a capacitor storing enough energy then firing, using a transistor perhaps...

Taking this idea, I'm working on developing an ornithopter wing drive system based on an electro magnet turning on and off (assuming one end is spring loaded) to create a bouncing effect (flapping).

But how would you setup a "brushed" speed controller, which would manage the voltage out put (magnetic force should go up in direct relationship with voltage going in) and perhaps the speed of the flapping of the wings as well.

Hmm... clarifying what exactly I'm looking for.

The electro magnet will have a continuous input of energy but something between the speed controller and the magnet will make it "pulse".

here's the thing I'm trying to do:
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May 06, 2010, 10:04 PM
Physics hate's my ideas
GreenAce92's Avatar
Apparently what I'm doing is close to how a buzzer works.
A circuit is completed for a coil of wires causing magnetic field to pull the piece of metal that will strike the bell, at the same time the metal when touching the bell will disrupt the circuit. Hmm I think I see where this is going. This could work, I wonder about changing the speed of this on/off (hz?)
May 07, 2010, 10:00 AM
Registered User
A brushed speed control just applies constant pwm to regulate the speed.

You need a cpu and a power switch, plus a diode across the coil. The cpu will turn it on when required. But solenoids have their own problems. You will
find the force generated is only over a short distance, it is best to have the magnet inside the coil, because when it gets too far out the force will diminish greatly. Non-linear function. There is something called

The Solenoid Equation

which you might want to look up!
May 07, 2010, 10:44 AM
Landings are not optional
DeuceTrinal's Avatar
I think you might find a solenoid is going to be less effective than a rotary setup for anything but full throttle. The solenoid won't be able to actuate proportionally - it's either enegized or not. This means that at low throttle your wings are going to snap up and down just as fast as full throttle, just with pauses in between. It seems to me (not an orinthopter flier) that this wouldn't be as effective as a motion that is proportional to throttle.
May 07, 2010, 12:29 PM
Oxford Panic
AndyOne's Avatar
I have an inkling that the solenoid method will be far from efficient enough to get into the air. The solenoid as drawn will have very little force at the beginning of the stroke as the poles are far apart and working against spring tension of the rubber band.

May 07, 2010, 03:30 PM
"Simplify, then add lightness"
Like the others have said, a motor with a crank arm or a cam would be much more efficient, lighter and easier to control.
May 07, 2010, 09:51 PM
Physics hate's my ideas
GreenAce92's Avatar
Well actually I changed the design too. Originally the idea was also based well on the roto saw and a buzzer.

The buzzer seems more feasable. Spring loaded in which ever stroke is hardest, then the electro magnet will pull the metal tab. (I figured they should be weighted (a like gyro motion or stabilizing effect)

Let me try to explain this verbally. When there is no load, the circuit is complete but off. When the circuit is turned on the electromagnet will pull the tab disconnecting the circuit, thus the electro magnetic field is cut, the spring will pull it again till it touches. Thus causing a "vibrating motion".

Take this idea, a flexible metal sheet (as part that goes up and down) like a parabola shaped flat sheet of metal(flexy) this would be what is pushed and pulled.

Sorry verbally explaining is not that great I'm going to work on a physical model tomorrow when I can.

Will post a "narrated video". It may turn out different I'm assembling it from scraps.
May 08, 2010, 02:52 PM
Registered User
Buzzers oscillate at an audio rate, ornithopter wings do not, unless building a..


You need a chip to control the rate, not ancient electromechanical gizmos.
May 08, 2010, 03:49 PM
Physics hate's my ideas
GreenAce92's Avatar
hmm..... ok well I still was wondering if my electro magnets would be strong enough to attract the metal end. I was wondering about the speed like how a "buzzer" would be. The main problem I saw was that, it would instantly be flapping like crazy (acceleration) so if anything it would probably destroy itself if it was powerful enough lol.

I guess the pulsing idea would work, by varying the time interval ooo calculus could be put to work here... still the electronic part deters me.
May 08, 2010, 04:04 PM
Physics hate's my ideas
GreenAce92's Avatar
Hmm looking around at the basics of making led lights pulse...

here's one I was looking at
May 08, 2010, 04:12 PM
Registered User
You can use a 555, as an oscillator, set the duty cycle for about 10% on time
to save battery power. Then just hook a FET to it, N-channel, ground the source pin, the drain pin goes to the solenoid, other side of solenoid to B+.

Also very important to have a fast recovery diode across the coil, like a 1N5817.
May 08, 2010, 04:22 PM
Physics hate's my ideas
GreenAce92's Avatar
holy crap haha.... hmm yes see I feel dumb now twice today! Haha, first time trying to understand a guy speaking in spanish (school only goes so far) that didn't get a anywhere...

Lets see... Vocab review here..
555- timer Integrated Circuit.. variety of timing and multivibrator apps nice
Oscillator- produces repetitive electronic signal... huh..
Duty cycle- fraction of the time a system is in its active state...
FET-electrical field controlling shape and conductivity of one type of charge carrier in a semiconductor material.
N-channel is part of the High powered field effect transistor (FET)
Solenoid would be my electromagnet, controlling its field.

What do you mean by "across the coil" like halfway through it? I don't know...

Sheesh I had to google these terms, I need to create a simple flashing device, read and know some things I've got a bunch of parts though. I was looking at harvesting a radio dial/knob to see about using it as a speed controller on a small orni project.

Thanks for the help. I appreciate this please contribute more... perhaps together we can make this a reality haha.

Hmm.... looking at a diagram of the solenoid and the "magnetic field" it would theoretically create, it reminded me of like warp drive, compression of space... and expansion etc...
May 08, 2010, 06:36 PM
Registered User
Actually I would use a PIC chip to make the switching waveform, that is a signal that goes from 0 to 5V, in software you can control the on/off times, which is duty cycle. The PICAXE chip is easy to use, if you want to get into microcontrollers without learning difficult languages, it uses basic.

A good fet for this is the ZVN4206A from digikey.com. The gate is what turns it on and off, and connects to the output of your 555 osc or pic chip.

Whenever you turn off the current to an inductive load, like a coil, a high voltage is generated by the collapsing magnetic field (not dark energy or zero point energy, just regular physics) that can create a quite high voltage.

This is why the contacts in your buzzer arc. That mechanism is used in tattoo guns to make the needle vibrate, but they put a cap across the contacts to minimize the arcing, it burns them up. With solid state switching of coils, if you do not "clamp" this back EMF with a diode or snubber (R + C in series), the voltage excursion will blow out the transistor or fet.

Also known as a "freewheeling rectifier", this diode, best to be a fast recovery type (less heating when exposed to reversing polarity), regenerates the energy from the collapsing magnetic field back thru the coil. The cathode (band) of the diode must go to the B+ side of the coil, so it is normally reversed biased. When the current shuts off, the snap back voltage of the coil is reversed polarity, and the diode conducts. This is used in motor controls to keep the motor current more constant. The diode goes across the inductive load. But with some relays, for example, it will actually increase the time it takes for the relay to shut off, you can see it. If it bugs you, use a snubber to grab the energy.
May 08, 2010, 07:02 PM
Physics hate's my ideas
GreenAce92's Avatar
Wow... hehehe my mind is spinning hmmm
A diagram/picture perhaps? Lol

Also if I was to braid the enamel wires to make my solenoid would I be doing anything in crease the "magnetic pull" or would it actually be degrading it/cancelling it out.
Like take 3 equal lengths of wire, braid them, then wrap them in a spiral on a spherical magnetized piece of metal.

Hmm... I think I ought to make my blinker first lol. And read this nice book I have, it's kind of old but the basics haven't changed too much I don't think but it does talk about vacuums still being used.

Also is it possible to unrectify a rectified current, like DC to AC?

And I like that idea, not wasting the collapsing magnetic fields power, why is that? Why does the collapsing magnetic field create a voltage? So if our planet's magnetic field collapsed it would give off power?
May 08, 2010, 07:31 PM
Registered User
A diagram/picture perhaps?

I can make cad dwgs, but it takes time and am very busy.

Also if I was to braid the enamel wires

Bifilar or Trifilar winds of L's and xfmrs is done sometimes, rarely, due to cost, but it reduces eddy current losses in the wire, look up skin effect. Only at high freq. Litz wire is many fine strands randomly distributed, not just a simple twist. Forget it for simple apps.

Hmm... I think I ought to make my blinker first

Yes, build simple circuits and learn how chips and discrete parts are used.
Get a dvm and read about ohms law.

Also is it possible to unrectify a rectified current, like DC to AC?

Yes, that is called an inverter. Various ways to do it, most involve 2 or
4 switching devices, maybe a transformer. Easy to make a stepped ac wave that is not really a sine wave, those are more difficult, but rewarding.

And I like that idea, not wasting the collapsing magnetic fields power, why is that?

The first reason is to stop the collapse from generating a 200V spike on your 12V system, which blows out parts. Limiting or clamping. The "catch" diode on relay coils does channel the energy back thru the coil, which can cause unwanted opening delay. In motor controls it is required for operation, I am
talking about PM motors or series motors, not brushless.

Why does the collapsing magnetic field create a voltage?

Study the basics of electromagnetism, coils, magnets, cores, the field itself, and how it induces a voltage in a wire when the flux lines cross it. Inductors try to keep the current going, they resist changes by generating a voltage.

The real equation is calculus, L di/dt, which means inductance times the rate of change of current. The rise time of current is slew rate, sharp edges on signals can cause many problems. See ya tomorrow!

So if our planet's magnetic field collapsed it would give off power?

That would mean the molten iron circulating core which is conducting a billion amps, where the field comes from has failed. Then we are all dead.
The mag field stops cosmic rays from killing us.

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