Thanks for all the replies. It seems everyone has a different definition of efficiency, haha.
A long-throw solenoid is inherently inefficient (poor use of power, heat, weak, non-linear).
However, it tends to be quiet, and that's important when you want to stress movement over
noise. And simplicity usually means longevity.

 

Using a solenoid to wave a flag or move an arm would result in very jerky unrealistic movement. Have you considered an AC synchronous motor or BLDC motor based mechanism instead? Either could run very quietly.

 

I recall visiting this site in the past or this

 

I recall visiting this site in the past or this

That's the first thing I thought of when Hamlet mentioned slower, smoother motion with the long throw. Google "cheap linear actuators" and you'll get links to Amazon and Ebay with units with under $20 prices. I'm assuming you don't want to spend $100's on kinetic art.

 

That's the first thing I thought of when Hamlet mentioned slower, smoother motion with the long throw. Google "cheap linear actuators" and you'll get links to Amazon and Ebay with units with under $20 prices. I'm assuming you don't want to spend $100's on kinetic art.

It is him who is into kinetic art, not me.

 

For an interesting read put " Why won't my linear stepper motor work?" in " SEARCH FORUMS" box. 513 entries on automated pool cue stick re post # 17.

 

To improve the magnetic characteristics of the solenoid, always have a complete magnetic path for the magnetic field through the solenoid.

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.

​

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.

​

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?

 

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.

The plunger is usually considered the Armature.
i.e. The part that is in motion.
The coil section is the stator.
Max.

 

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?

@cmartinez
Hola César. Sorry, I fail in identifying the rivet. Not even sure how it looks.

 

The plunger is usually considered the Armature.
i.e. The part that is in motion.
The coil section is the stator.
Max.

Thanks for the correction, Max ... technical English always gets to me...

@cmartinez
Hola César. Sorry, I fail in identifying the rivet. Not even sure how it looks.

The rivet can't be seen in the picture, but it's shown in the drawing.

​

 

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?

Thanks for hijacking my thread.

The inter-mesh between rivet/plunger leads me to think it was designed for strong holding force.
When the armature/plunger is seated, the frame/stator + armature
completes a magnetic circuit that is roughly doughnut shaped, where the armature is
occupying the space where the doughnut hole would be. The magnetic circuit is a torus shaped field
that is stronger when a magnetically permeable materiel is overlaid the region it occupies (metal frame/stator, + metal armature).
I think it would have stronger pull-in if the front part of the bracket were separated from the sides/rear&rivet,
and attached to the armature, so it was mobile. This wouldn't change the holding force, however.

So, in answer, it wouldn't be as strong with just a rivet and plastic body.

 

Thanks for hijacking my thread.

The inter-mesh between rivet/plunger leads me to think it was designed for strong holding force.
When the armature/plunger is seated, the frame/stator + armature
completes a magnetic circuit that is roughly doughnut shaped, where the armature is
occupying the space where the doughnut hole would be. The magnetic circuit is a torus shaped field
that is stronger when a magnetically permeable materiel is overlaid the region it occupies (metal frame/stator, + metal armature).
I think it would have stronger pull-in if the front part of the bracket were separated from the sides/rear&rivet,
and attached to the armature, so it was mobile. This wouldn't change the holding force, however.

So, in answer, it wouldn't be as strong with just a rivet and plastic body.

Sounds reasonable, but then again, why is the coil wound around a plastic tube instead of a metal one? Why is it more important to have a metal outside frame than a metal inner tube?

 

Here is a demo of the magnetic field completed by the outer metal frame.
Max.

 

It is the same reason why transformers use core on the outside of the coil as well as on the inside. You use the outside metal to "conduct" the magnetic field as efficiently as possible back to the other side of the solenoid, without scattering all around the outside of the core.
(added a clarification to the last sentence)

 

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?

 

Here is a demo of the magnetic field completed by the outer metal frame.
Max.

View attachment 176288

Thanks, I think I have a clearer picture now of how a solenoid works. BTW, I'm building a solenoid right now that is going to have to work submerged in water (plain drinking water) ... it's going to be a challenge to coat its frame to perfection to protect it from rust ... wish me luck

 

Thanks, I think I have a clearer picture now of how a solenoid works. BTW, I'm building a solenoid right now that is going to have to work submerged in water (plain drinking water) ... it's going to be a challenge to coat its frame to perfection to protect it from rust ... wish me luck

If you don´t need super efficiency, then think about epoxy coating the whole structure, just keep the barrel diameter clear. Something like the green current transformer here (with different insides of course) https://standexelectronics.com/wp-content/uploads/2014/10/current-sense-transformer-toroidal.png
Or a variation on impeller type aquarium pump.

 

May be do a test of a few selected products, one I have used in the past is RTV.
Max.

 

it's going to be a challenge to coat its frame to perfection to protect it from rust ... wish me luck

There are some magnetic stainless steels. https://www.greenwoodmagnetics.com/...fference-between-304-and-316-stainless-steel/

 

There are some magnetic stainless steels. https://www.greenwoodmagnetics.com/...fference-between-304-and-316-stainless-steel/

Yeah, I'm aware of that. But they don't react to a magnetic field with the same intensity as iron or carbon steel, and I need the solenoid's force to be as strong as possible using the same package size.