You certainly don't need a 12" stack of magnets - the magnetic circuit just needs to be magnetically
soft iron or mild steel. The magnetic circuit is limited by the air gap, adding bigger magnets won't
do anything once that's dominating.
Often the coil has to have a lot of overhang of the poles, in order to have constant amount of turns
cut by the flux, which means wasting heat in the inactive part of the coil.
That or using a massive pole-piece area, and thus more heavy expensive magnets... No such thing
as a free lunch alas.
I was under the impression I had to stack magnets facing opposite poles in the tube. That was how the coil grabbed the next pole to move it in whatever direction. If it's just an iron shaft, than I'm confused as how the coils would actually push or pull the shaft in a predictable distance.
I just checked inside of a stepper motor. The ROTOR has embedded permanent magnets. The stator coils are wrapped around plastic, with metal through the center, extended out to a flat, with negative radius ridged edges. The edges equal the width of the permanent magnets. All the gaps and widths of the magnets are the same. When a coil is energized, it attracts all the like pole magnets and repels the opposite poles to the gap of the ridge - in each coil.
The largest "moving magnet coil" they sell is 14" long with only a 4" stroke. Peak force of 200 pounds, constant force of 10 pounds. 4" diameter coil. Though the website also claims at 100% duty it can only force 68 pounds - so there must be a threashold of power to strength ratio of a sweet-spot and is below 100% of it's electric capacity. Looks like the stroke is front to back, dual shaft through the coil, so it would have to extend 2" in one direction, then compress back 4" to make that stroke.
An interesting device, of course to tell me what can be done with a single coil actuator. I'm sure it probably cost more than I pay for my used cars.
The limits on electric motors are often thermal - the coils burn out or the magnet demagnetizes
due to the temperature. Water cooled motors have much higher ratings, for instance.
Boardburner2:
It is worth putting a search up on ebay.
Coil winders occasionally appear, often not complete though. Hope you have a lathe.
Yes I can buy one for about $60 on ebay, which is a shaft with a few gears, a hand crank and a counter. I can manually wind a coil on a lathe, if I'm doing just a few. Anyone can stick a wooden dowel in a drill press or hand-drill, mounted to a vise and do this too. If I don't get too distracted, I can build one in a few days, that will do alot more than a hand crank with some arbors.
MarkT:
The limits on electric motors are often thermal - the coils burn out or the magnet demagnetizes
due to the temperature. Water cooled motors have much higher ratings, for instance.
I'm not going to get into all of that. I will just build a shaft with 4 coils, try and match up to the same gauge and windings of a standard NEMA 23 bipolar stepper motor. So it will just be a stepper motor, with a long round shaft instead of a radial motor.
I finally got the courage to wrap up and go through the snow to the shop and try to find the article on the radial electric motor. I found the first and second installment issues of Home shop Machinist. The motor is a 3 cylinder radial motor. You may find some useful information there. The beginning is in the January/February 2003 issue and continues for perhaps 2 more issues. Too cold to find more than the second installment.
If I make a crank shaft and attach 1 or more solenoids to it, resembling a gas engine, it will function the same way. It is an interesting device, I have seen thrm build for class projects.
How much force is needed for your project? Using a stepper with a long arm and a connecting rod would move pretty quick, have predictable points, and should be easy enough to get code accomplished. You probably already have a stepper driver laying around, so required parts would be minimal on the electronics side, and some aluminum beam and rod for the mechanical side, probably in the neighborhood of 12" for the beam to keep the lateral loading down and make the stroke a little closer towards linear
Professor Eric Laitwaite came up quite a few times when I was searching for information. His videos on youtube were useful, until he started layering coils on top and over each other - the design was too complex for me to fully understand and try to re-create, at this point.
tinman13kup:
How much force is needed for your project? Using a stepper with a long arm and a connecting rod would move pretty quick, have predictable points, and should be easy enough to get code accomplished. You probably already have a stepper driver laying around, so required parts would be minimal on the electronics side, and some aluminum beam and rod for the mechanical side, probably in the neighborhood of 12" for the beam to keep the lateral loading down and make the stroke a little closer towards linear
I am past using steppers with levers, belts and ballscrews at this point. Now I am looking to build my own linear stepping device.
Any rotary motor has its linear equivalent, be it induction, permanent-magnet AC, BLDC, stepper,
even variable-reluctance (though that's probably incredibly niche). A voice-coil motor is the linear
equivalent of a galvonometer I suppose.
One problem with linear motors is the ends leak magnetic flux, so you lose some efficiency, and
ones with permanent magnets get quite expensive for longer versions. You also have to deal with
the strong forces invoved - they don't balance out round a circle (induction motors fare best with
this since there are only forces when there is current).
So there usually has to be a good reason to use one (zero backlash requirement for instance).
I'm not sure any device is 100% efficient, the steppers lose power too in iron and copper loss with heat, at a idle - over time decay the magnetic strength.
You bring up a good point with the magnets. If I buy these ones from a hardware store that are probably intended to be used as welding clamps, refrigerator magnets or whatever type of play toy. With a precision gauss meter, I can actually gauge the strength and field of each and every one, to make a matched array of them. Of course I can go buy a precision set from a distributor if I intended to produce products for resale, and had a budget to pay for all kinds of expensive materials.
Less mechanical parts, less friction, more speed, strength are also reasons to use a linear motor. For me, adding up the cost of these raw materials to fabricate myself makes it possible to do one customized for a task.
Hi,
This might help, its interesting in the maglev demonstration, but also mentions and shows a particular way to lay your magnets to bias the resultant field in one particular plane.
It gets the symetrical field to bend to areas where it will be more influential.
The maglev is a linear motor, with more coils and magnets to bind the other two axis of the carriage also to counteract the weight of the carriage. This is probably the most complicated structure of coils and magnets I ever seen.
If you take away the levitation balancing act from maglev and use traditional rail wheels - what is left is a linear motor. A long line of magnets facing opposite electro coils to shift the poles, inch-worming the carriage forward or reverse.
Hobby people are also experimenting with coil guns, which is also another array of coils to propel a simple aluminum ring, or slug.
My idea for the design is a round cylinder center, with 4 coils to alternate current to move the shaft. I have to have a bearing sleeve material between the shaft and coils to center the shaft.
The other way i see to design, is a flat bed of magnets, with the coils above it, attached to a linear guide rail. That is more complicated.
My skills with coils and magnetic fields arent as sharp as metal shaping, so I need help calculating the construction of coils. It would help me to explain, once i make a CAD 3d model of the structure to see how simple it works.
DocStein99:
Hobby people are also experimenting with coil guns, which is also another array of coils to propel a simple aluminum ring, or slug.
Certainly are
The required capacitors are unobtaniom in th UK though.
Occasionally on ebay but DOC restricted as parts for export unless as a a constructed defibrillator.
Tonight I finally found the project I was looking for. This took me a REALLY LONG time to sort through a whole bunch of information and videos, but I finally found it.
The basic coils, with a simple rod - to actuate a long variable distance with speed and strength:
DocStein99:
You bring up a good point with the magnets. If I buy these ones from a hardware store that are probably intended to be used as welding clamps, refrigerator magnets or whatever type of play toy. With a precision gauss meter, I can actually gauge the strength and field of each and every one, to make a matched array of them. Of course I can go buy a precision set from a distributor if I intended to produce products for resale, and had a budget to pay for all kinds of expensive materials.
Measuring the field around a magnet without putting it in a magnetic circuit isn't necessarily very useful,
you'd normally be wanting to know the magnetic flux density in the gap of the magnetic circuit its to be used
in. The surface flatness of a magnet matters when its in a magnetic circuit, but has negligible effect out of one,
for instance, and in a circuit its the total flux that normally matters.
