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Solenoid Engine

Nigel Taylor

I've been thinking about a solenoid engine for sometime. They feel like a bit of a cheat as they are not really an engine, more like an electric motor. However, this runs so sweetly that I may have caught the bug and think about some other configurations. Sorry I didn't take images whilst buidling it, but have made it in a total of about 2 days - a fast build.

The flywheel was machine from pewter (just happened to have a lump laying around. Once machined I then carefully hammered the outer surface to give the beaten effect you sometimes see on pewter.

The engine runs using a simple 9V (PP3) battery and just a simple flick of the flywheel. See youtube video at the bottom of this article.

I do like the ease with which you can construct a base using wood (as you may have noticed lots of my engines have been like this.

The brass mushrooms along the top of the frame are there purely to wrap the connecting wires around to keep them tidy.

The copper wire is laquered and so no worries about shorting.

The connecting rod was made using two brass bushes (the big-end has a ball race in the centre) and some thin copper tube flattened and then soldered to the brass bushes.

The switch is a small micro-switch with an arm that has a roller on it (I bought this one from Peco train accessories).

The piston (armature) and cylinder (electromagnet) are both machined from ebony. The piston is a loose fit and has a 6mm hole through the centre into which I push 5 magnets (cut from the ends of geomag bars).

Using magnets means that if you get the polarity correct when you apply a current to the electromagnet it always pulls the armature to the middle of the electromagnet - this way the engine is double acting with just a simple switch and cam that operate as the piston goes just over TDC and BDC.

Just to prove it runs here is a video on youtube of it:

If you have made a similar engine and would like to share your experience we would love to hear from you - ed.

Have just started making another solenoid engine, this time a V-Twin solenoid, and thought I should try and improve it in the process. One area of particular concern was that for this one I used small permanent magnets in the armature, useful as it means I can make the engine double acting, but the downside is that it only acts over half the stroke and the force drops to zero when the armature is centred in the solenoid.

So first thing is to measure the force. Below is the contraption I came up with: 2x pulleys, some digital scales and a weight.

The idea is you place the weight on the scales and zero them, this means that when you turn the solenoid on you get a negative weight on the scales.

I made some small pulleys with ball races so that they are very free running. Quite frankly these could be just plain bearings.

The measurement. With a fresh battery the peak was 33g, this dropped to 22g max with use and as the armature moved to the centre of the solenoid this rapidly dropped to 0g.

33g is 0.033kg, multiply this by 9.8ms-2 to calculate the force. This gives 0.32N

22g = 0.022kg -> 0.22N

So there is my new target I have to beat. To make this simple you can just divide the mass in grams by 100 to get the force in Newtons - rough, but pretty good.

All of the parts for this can be made with hand wood working tools and a small lathe such as a Unimat 3.