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

How?? Many small solenoids like that are made with the coil being "one size fits all", to get enough bobbin space in a small diameter to get enough pull in force. They then put a stop in the bottom of the coil for things not needing the full movement. That makes the part work in many applications without the need of the same number of bobbin sizes.

Kind of like some IC's that only need so many active pins that are put in a package that has extra pins that are then called out as NC, no connection. Saves making many odd sized molds to put on the plastic and making odd ball pin sockets.

 

Worthwhile educational video:

 

Worthwhile educational video:

Some of that only applies to that particular type of solenoid.

Back to your flag waving project. Years ago there were advertising displays that did what you want they would move a sign or picture back and forth to get attention and were powered by a single D cell battery. They some times come up on EBay, I looked for a short while but couldn't find a picture to show you. They used an electromagnet not a solenoid. Similar to how an old fashion door bell ringer worked, The magnet turned on attracting the arm which broke a set of contacts turning off the magnet. This allowed the arm to return to the original position turning the magnet on again, and it would repeat over and over. From - https://en.wikipedia.org/wiki/Electric_bell

Interrupter bells

How an interrupter-type electric bell works.
How it works
The most widely used form is the interrupter bell, which produces a continuous sound when current is applied. See animation, above. The bell or gong (B), which is often in the shape of a cup or half-sphere, is struck by a spring-loaded arm (A) with a metal ball on the end called a clapper, actuated by an electromagnet (E). In its rest position the clapper is held away from the bell a short distance by its springy arm. When the switch (K) is closed, an electric current passes from the battery (U) through the winding of the electromagnet. It creates a magnetic field that attracts the iron arm of the clapper, pulling it over to give the bell a tap. This opens a pair of electrical contacts (T) attached to the clapper arm, interrupting the current to the electromagnet. The magnetic field of the electromagnet collapses, and the clapper springs away from the bell. This closes the contacts again, allowing the current to flow to the electromagnet again, so the magnet pulls the clapper over to strike the bell again. This cycle repeats rapidly, many times per second, resulting in a continuous ringing.

 

Some of that only applies to that particular type of solenoid.

Back to your flag waving project. Years ago there were advertising displays that did what you want they would move a sign or picture back and forth to get attention and were powered by a single D cell battery. They some times come up on EBay, I looked for a short while but couldn't find a picture to show you. They used an electromagnet not a solenoid. Similar to how an old fashion door bell ringer worked, The magnet turned on attracting the arm which broke a set of contacts turning off the magnet. This allowed the arm to return to the original position turning the magnet on again, and it would repeat over and over. From - https://en.wikipedia.org/wiki/Electric_bell

Interrupter bells

How an interrupter-type electric bell works.
How it works
The most widely used form is the interrupter bell, which produces a continuous sound when current is applied. See animation, above. The bell or gong (B), which is often in the shape of a cup or half-sphere, is struck by a spring-loaded arm (A) with a metal ball on the end called a clapper, actuated by an electromagnet (E). In its rest position the clapper is held away from the bell a short distance by its springy arm. When the switch (K) is closed, an electric current passes from the battery (U) through the winding of the electromagnet. It creates a magnetic field that attracts the iron arm of the clapper, pulling it over to give the bell a tap. This opens a pair of electrical contacts (T) attached to the clapper arm, interrupting the current to the electromagnet. The magnetic field of the electromagnet collapses, and the clapper springs away from the bell. This closes the contacts again, allowing the current to flow to the electromagnet again, so the magnet pulls the clapper over to strike the bell again. This cycle repeats rapidly, many times per second, resulting in a continuous ringing.

The sparks on those contraption's contacts would be quite a sight, I'm sure...

 

I remember those! I recall being impressed with the design, using only one D-cell battery, agitating for months on end.

Some of that only applies to that particular type of solenoid.

Back to your flag waving project. Years ago there were advertising displays that did what you want they would move a sign or picture back and forth to get attention and were powered by a single D cell battery. They some times come up on EBay, I looked for a short while but couldn't find

 

The sparks on those contraption's contacts would be quite a sight, I'm sure...

There is a restoration project on youtube of an interrupter alarm-bell, and near
the end, the demonstration shows a bright green flash emanating from around the clapper arm at the case opening.
I suppose that is so the bells could be used in the schools for the deaf, with the olfactory cue of ozone
signaling the end of the class period.

 

shows a bright green flash emanating from around the clapper arm at the case opening.

Hence the need for BEMF diodes!
Max.

 

Hence the need for BEMF diodes!
Max.

How dare you polluting such a beautiful vintage design with a semiconductor!

 

How dare you polluting such a beautiful vintage design with a semiconductor!

I discovered back in the dawn of time, well before I had any understanding of why, that sticking your fingers in a bell was a good way of getting electrocuted.

 

Post # 63 tickles a memory from about 1938, 6th grade when I made an "electric steam engine" from a dual coil door bell. Coffee can lid for flywheel the remainder from coat hanger wire. Little yellow sparks, no diode. Yes I knew what a diode was, a little stiff wire that you probed around on a Pb-S crystal to get the best signal.

 

I recall the huge battery feeding the bell at home: Eveready, maybe 20 cm high which seemed to last for years.

 

I recall the huge battery feeding the bell at home: Eveready, maybe 20 cm high which seemed to last for years.

 

particularly long-throw solenoids...

I've been making solenoids for art projects. (Off the shelf solutions are short on availability, expensive and inadequate) .

I've had some luck, wasted a quantity of enameled wire, and ready for more.

I've used a number of online calculators, FWIW (for-what-it's-worth).

Is there any secret tips for what makes an adequate solenoid, or no?
My biggest concern is heat, not power. I'm not building pinball machines (but you never know...)

Hi,

It sounds like maybe what you want is a linear motion mechanism. That gives you better control over the movement.
There are different types. One of the cheapest is an automobile door lock mechanism. It has a motor inside and inside the rotary motion is turned into linear motion. They have a decent throw and also some strength behind them. They run on 12 volts DC.
Available in different places.

 

The sparks on those contraption's contacts would be quite a sight, I'm sure...

Not really, the same thing is done today in tattoo guns/machines.

 

I remember those! I recall being impressed with the design, using only one D-cell battery, agitating for months on end.

One could be made with an old relay, by drilling and tapping a hole in the movable armature for the flag pole. Since most electromagnets and solenoids move very fast, the relay coil could be powered by a 555 timer circuit feeding a transistor to the relay coil. This would allow adjusting the potion of the flag.

 

One could be made with an old relay, by drilling and tapping a hole in the movable armature for the flag pole. Since most electromagnets and solenoids move very fast, the relay coil could be powered by a 555 timer circuit feeding a transistor to the relay coil. This would allow adjusting the potion of the flag.

I have done that with relays when I was MUCH younger, and while it certainly does produce a great deal of motion it is very rapid and probably not at all suitable for a kinetic art sort of thing. What may provide a useful motion would be one of those electronic driven pendulum arrangements, where the motion speed is set by a mechanical resonance and the electronic part supplies just enough energy to compensate for the losses.

 

This video should answer our questions about "frame" or "no-frame".
Fellow makes a solenoid without, and then with, a opposing iron "concentrator", then adds external frame.
A small scale is used to measure pull force of the solenoid at each step. I skipped ahead and cued up
for relevant parts:

 

That is a good ,but misleading video. I say misleading because it isn't representative of how a solenoid is used, he measured holding force not pull in force. Also to say never use a solenoid without an end stop/magnet because it isn't strong is just BS. Look at how a car starter solenoid is made and works, it hasn't got one of those end stops, it stops on the contact ring at it's front. Look at how an Asco solenoid valve works, it's solenoid doesn't have one either. A fuel injection solenoid in your car doesn't have a metal frame on it and yet it is able to pull up its armature/pintle against 45 t0 90 PSI of fuel pressure, depending on the type of EFI. I could give more examples if you want, most of them in normal everyday use.

 

I have done that with relays when I was MUCH younger, and while it certainly does produce a great deal of motion it is very rapid and probably not at all suitable for a kinetic art sort of thing. What may provide a useful motion would be one of those electronic driven pendulum arrangements, where the motion speed is set by a mechanical resonance and the electronic part supplies just enough energy to compensate for the losses.

I said that, the part about moving fast, but it's the same with with a solenoid. The pendulum your talking about works slower because it has no spring involved like in a relay armature. and is dampened in it's pivot point to slow the speed.

 

Rapid movement of solenoid is not desired but what happens if we apply magnetic or hydraulic braking to slow armature ?