On a completely unrelated note, be aware that "stainless steel" as you know it is stain-less only when subject to air and moisture. I have heard that there are cheap washing mashines and dish washers that have "stainless steel" drums and walls, but the grade of the steel is not the one that resists houshold salt, chlorine, and all the other washing chemistry you will inevitably use, and they will actually last less than the plastic equivalent.

 

When I started this thread, all I wanted to know was if there were some rules-of-thumb
for solenoid construction. Would I have better luck making them closer to square than
elongated, would I want so many turns for certain gauges of wire, and so forth and so
on. I can see that I am not missing much, or that I'm missing almost everything. Something
as simple as a solenoid is pretty complex.

Specifically, I wanted to use as solenoid to wave a flag to tease my cat. I have a house cat that
doesn't like the grinding noise that many gear-motors make, and neither do I. Also, I have been
making models of linkages of steam engines. Again, replacing linear steam power for linear electric
power is kind of cool to my way of thinking. Using a gear motor is cheating, anyone can do that.

All this and more. I like kinetic sculptures; as I develop ideas, it would be nice to know what is
and isn't a likely path to success when I am musing something up. Trial & error is acceptable path
to gaining this experience. I eat my own cooking.

How long a throw are you talking about? How big is the flag?

I don’t know the answers to this question, so I can’t tell if a solenoid is the best solution.

Note: I’ve done a few “art” animation projects. That’s where my questions come from.

I would have first considered one of these options, several of which have been mentioned.

• Rotary to linear motion converter
• Worm drive
• Stepper Motor
• Geared motor direct drive
• Hobby Servo motor

Several of these do not require any complicated electronics. Others use standard techniques. So what are you exactly trying to do? And several are simpler than a solenoid.

And I’m sure that there are others. So what exactly are you trying to do?

 

An the 400 series of stainless steels are magnetic and rusts BTW.

 

I was thinking of opening another thread for the following question, so as not to give the impression that I'm trying to hijack this one. But then I thought that the question is not only on-topic, but it will also add valuable info to the TS, once it's answered.

I have a small solenoid designed for 5V operation, it measures about 11 x 11 x 21 mm, with a 4 mm diameter plunger. I disassembled it to take a closer look, and noticed that the plunger has a tapered tip on the back side, and the armature has a rivet at the bottom with a conical hollow matching the plunger's tip. See the following image.

View attachment 176273​

A plastic barrel around which the coil is wound is shown in green, the steel armature is shown in blue, the plunger is magenta, and the coil (#32 ga) is shown in orange.

The solenoid's force is definitely at its maximum when its plunger is 1.5mm away from completely reaching the rivet (as exactly depicted in the previous image). I'm sure that the arrangement has to do with concentrating the field lines passing through the rivet and the plunger, magnetizing both, and thus maximizing attractive force.

The solenoid's housing is made of steel, and it's "U" shaped (the rivet is installed at the bottom of that housing). See picture.

View attachment 176274​

My question is, is said housing also necessary to concentrate the field lines? Or would the solenoid function just as well with a plastic housing, provided that the steel rivet is installed in the same place?

For the solenoid in the picture the short answer is YES!! That steel housing is a very large part of how it works, as it collects and conducts the magnetic field hundreds of times better than air. A plastic housing would do no better than air, and so it would be totally worthless. REALLY, you need to read a textbook on magnetism and electromagnetism, so as to have a bit of understanding. And for kinetic art a solenoid is a worst choice, both because of the motion speed profile and also because of the power dissipation problem. A motor and crank arrangement can provide similar motions that are far more gentle, use much less power, and usually are far simpler to control. Also, they are usually less expensive, and less likely to start fires.

 

Very sage advise indeed. FWI, I am not enamored of, nor am I a supporter of "efficiency". Life is meaningless, but use fuses just in case.

And for kinetic art a solenoid is a worst choice, both because of the motion speed profile and also because of the power dissipation problem. A motor and crank arrangement can provide similar motions that are far more gentle, use much less power, and usually are far simpler to control. Also, they are usually less expensive, and less likely to start fires.

 

REALLY, you need to read a textbook on magnetism and electromagnetism

I have... and I still have lots of questions that remain unanswered... magnets and magnetic fields sometimes behave counter intuitively

 

Just an added thought. Without the noise of a geared motor another possible solution is a nitinol or memory wire motor.

• Extremely simple
• Smooth motion
• Silent (not even a solenoid thunk)

Available on Amazon and many other sources.

 

Very sage advise indeed. FWI, I am not enamored of, nor am I a supporter of "efficiency". Life is meaningless, but use fuses just in case.

Have you considered a Magnetic Linear Actuator?
a) A moving coil around a fixed magnet or
b) A moving magnet inside of a fixed coil or several positioning coils
https://www.laserfocusworld.com/art...on-devices-what-is-a-voice-coil-actuator.html

The current when moving could ramped up vs the lower current required to hold the position

 

My question is, is said housing also necessary to concentrate the field lines? Or would the solenoid function just as well with a plastic housing, provided that the steel rivet is installed in the same place?

After thinking on this more, I don't think there is any advantage to a ferrous metal outside frame on the solenoid. While it would give the lines of force a complete path, it won't give the solenoid any more force in action. The plunger/armature when it is in the retracted mode(all or most of the way in) is using all of the magnetic lines of force available. And before that happens the outside frame doesn't react with the plunger. That said, the ferrous outside frame is usually just for mounting purposes, screws don't strip as easy as plastic.

The "rivet" is just a stop to limit the throw of the plunger.

 

Then try removing the frame and see if the force remains the same. My bet is it won´t be.

 

Then try removing the frame and see if the force remains the same. My bet is it won´t be.

That's exactly what I plan to do. But my bet is that the rivet does make a difference, but the metal frame doesn't. Stay tuned.

 

I think the rivet and conical housing piece are to provide a small amount of air braking, to reduce noise.

 

I think the rivet and conical housing piece are to provide a small amount of air braking, to reduce noise.

And I think that the rivet acts as a second (stationary) magnet that increases the force on the plunger as it reaches the end of its stroke.

 

Then try removing the frame and see if the force remains the same. My bet is it won´t be.

Mine says the force will be the same, or such a small difference it won't matter in the whole scheme of things. The main force is in the center of the coil, that is where the magnetic force is concentrated in a coil/solenoid.

"An electric current flowing in a wire creates a magnetic field around the wire, due to Ampere's law (see drawing below). To concentrate the magnetic field, in an electromagnet the wire is wound into a coil with many turns of wire lying side by side.[2] The magnetic field of all the turns of wire passes through the center of the coil, creating a strong magnetic field there.[2] A coil forming the shape of a straight tube (a helix) is called a solenoid

Much stronger magnetic fields can be produced if a "magnetic core" of a soft ferromagnetic (or ferrimagnetic) material, such as iron, is placed inside the coil.[1][2][17][18] A core can increase the magnetic field to thousands of times the strength of the field of the coil alone, due to the high magnetic permeability μ of the material" From - https://en.wikipedia.org/wiki/Electromagnet

 

Here's a couple of pics of the solenoid, disassembled. It gives a far clearer idea of what I've been talking about.

​

 

Certainly the force will be very much less without that surrounding soft iron frame. It is not there for looks, but to complete the magnetic circuit. If you have ever selected a solenoid for an application where both performance and efficiency mattered you would have learned that. And the benefit of efficiency is a lot less heat produced for a given amount of force delivered. For a cheap education on the subject look at the solenoid pictures in a catalog listing of solenoids. I think that Grainger and McMaster-Carr carry them and have both pictures and specifications.
For now it will be very interesting to see the results of having removed that soft steel frame.

 

Magnetic force/energy is concentrated in any gap in the "frame" or like in a transformer it's core. Some toroidal transformers use a split/gap core to increase current.

When that metal outside frame is intact on that solenoid it won't add any measurable power to the plunger/armature at all. It's main use is for the mounting of the solenoid, with secondary uses as a heat sink and to kind of but not completely keep the stray lines of flux from affecting other close items.

 

And I think that the rivet acts as a second (stationary) magnet that increases the force on the plunger as it reaches the end of its stroke.

The rivet at the bottom is there to prevent sticking caused by residual magnetism. Other solenoid types use other mechanisms.

And the results of the experiment with the disassembled solenoid will be interesting indeed. Probably the coil will overheat and burn out after a few minutes.

 

Probably the coil will overheat and burn out after a few minutes.

Current in DC solenoids is dependent purely on the resistance of the coil, they do not posses the Inductive reactance (frequency dependence) that AC versions do.
If the armature does not move under the coil, they do not suffer burn out as its AC counter part tends to do.
Max.

 

The rivet at the bottom is there to prevent sticking caused by residual magnetism. Other solenoid types use other mechanisms.

And the results of the experiment with the disassembled solenoid will be interesting indeed. Probably the coil will overheat and burn out after a few minutes.

I plan to perform the experiment under different configurations. It's actually something I need to do, since one of my projects depends on it. But I'll be more than glad to share my results as soon as I have them, which I estimate will be around the middle of next week.