A solenoid beam engine

[Zephyrin]

Hi,
I recently completed a solenoid beam engine of the vintage style with wooden frame witch now runs with a 4.5 V battery.
This model is inspired from an old article in "Model Engineer and Amateur Electrician" back from 1901 !.
It was a short and easy project, rated "for beginners" by the magazine !
the point is to find the proper coil (or to wind one) of low resistance, to cope with the low output of these batteries, since induction depends on Amp.
And as induction also depends inversly of the distance, I cannot remove this knocking sound without greatly reducing the driving force, already miserable...

[youtube1]https://www.youtube.com/watch?v=PdFA2R0Gq0s[/youtube1]

As the armature cannot touch the magnet owing to a gap of 0.3 mm, this noise does not result from the bump of the armature on the electromagnet, but more probably from all these small linkage when the armature is frozen by the magnet at TDC.

more pics on the build
https://goo.gl/photos/VZCZBSo2iAGyhvsn6

[b.lindsey]

What a nice looking and running engine Zephyrin. 

Bill

[Kim]

That is quite cool!  And a very handsome looking engine. 
I like the wood work (is that a bad thing to say on this forum?  )
Thanks for sharing the video and the pictures!
Kim

[PStechPaul]

Nicely done!  I'd like to see details of the switch, or "commutator", used to apply and remove power from the coils. It might be possible to reduce the knocking sound by adjusting the make and break points as referenced to the position of the armature and the coils. When the current is disconnected, it runs very quietly. Perhaps the current should be stopped a bit sooner. There also may be a problem due to the inductive kick when the switch opens, and this could cause a high voltage arc across the contacts, or voltage transients that could damage the insulation of the coil.

One way to help that would be a commutating or flyback diode across the coil, but that would not be in keeping with the early 1900 era. But perhaps a capacitor across the "points" would be something available at the time. Either method would extend the "dwell" by keeping current flowing in the coil after the switch opens. It may allow the timing to be retarded or the dwell reduced, each of which should affect the performance, and allow "tuning" and optimization. 

Another principle to consider is that the inductance of the coil causes the current to increase over a fixed time starting from the initial switch closure. Thus the current will be greatest at the end of the stroke, at which point the armature and coils are closest and the force is strongest. It might be better to charge a capacitor during the upstroke and then discharge it into the coil, which could be made with less turns and lower inductance so the current will quickly reach peak at the higher part of the stroke. As the armature gap decreases, the current will also drop, perhaps giving a smoother operation. 

I hope you don't mind the possibly far-out ideas. As an engineer, I'm always looking at ways to improve things that may already be "good enough". 

[Ian S C]

Many moons ago (late 1980s) I built a couple of these motors (I didn't know anyone else had done it before), the first one was a beam engine, with a full balanced beam, the armature in the solenoid had a 3/4" stroke, and little effort required to move the crank, unlike your one with a short stroke, and requiring to lift the full weight of the beam.  I put a small capacitor across the contact points.
Ian S C

[Zephyrin]

There are no far-out ideas as regards this hobby for me...
Many thanks for the input, Paul, I think I have got the principle so exposed.
At first, the contacts produced nice sparks loved by my 2 grandsons (10 & 7, but my associates in this project, apparently electromagnetisms is much more appealing to the youngster than steam engines !).
A 0.2 microF capacitor solved that, but as almost no sparks are visible now, the final version is without this capacitor.
i post a picture of the commutator : the circuit is closed by the contact between the 2 isolated copper spring blades when pushed by the cam on the shaft, a very conventional setup.  it is easy to change the position of the make and break point, and the dwell can be modified by a few filing strokes or with a new cam, a 10 min job.


The last point you raise reminds me many things learned in the past, I feel out of touch, but I have an oscilloscope in the depths of my garage...pretty heavy, I hope I could lift it on the bench !

Ian :
I also think that the unbalanced beam is very odd, I suppose it was to keep the stroke of the armature very short, but in fact the reasons are not clear.