Stunning 4-Cylinder Solenoid Motor Should Be A Hit With Subaru Fans

As far as electric propulsion is concerned, the vast majority of applications make use of some kind of rotational motor. Be it induction, universal, brushed or brushless, these are the most efficient ways we have to do mechanical work with electricity. There are other, arcane methods, though – ones which [Maker B] explores with this 4-cylinder solenoid engine.

The principle of the solenoid engine is simple. Cylinders are wound with coils to act as solenoids, with the piston acting as the armature. When the solenoid is energised, it pulls the piston into the cylinder. The solenoid is then de-energised, and the piston can return to its initial position. The piston is coupled to a crankshaft via a connecting rod, and a flywheel is used to help the motor run continually. These are also known as reciprocating electric motors.

[Maker B]’s build is a 4-cylinder design in a boxer configuration. Produced with basic hand-operated machine tools, the build process is one to watch. Aluminium and brass are carefully crafted into the various components of the motor, and parts are delicately assembled with small fasteners and plenty of retaining compound. Solenoid timing is via a series of microswitches, installed neatly in the base of the motor and actuated by the crankshaft.

While solenoid motors are inefficient, they’re quite something to watch in action. This one is no exception, with the motor spinning up to 1100 rpm when running at 7.2 volts. We’d love to see some data on the power output and efficiency too. It’s possible to build solenoid motors in different configurations, too – this radial build is particularly fun. Video after the break.

[via Reddit]

44 thoughts on “Stunning 4-Cylinder Solenoid Motor Should Be A Hit With Subaru Fans

    1. In my experience when things are symmetrical there can be inefficiencies introduced. As an example I have built an immersion heater for chemical etch baths that used electrically heated water flowing through tubes to heat the chemicals indirectly. If I wound them into perfect coils it wouldn’t heat the bath evenly but a random jumble o tubing corrected that.
      Guitar pickups are rarely evenly wound , unless u look at Fishman Fluence pickups which are not “wound” but more etched like a pcb. If I was OCD those windings might bother me

      1. Can confirm, the windings of most guitar pickups look like they were done by some dude in his garage in a hurry. Well, at least those which you can see the windings in the first place.

    2. Actually it would.
      Now these solenoids have quite high stray inductance and stray capacitance, which generates losses. Also conductive “cylinder” adds losses caused by eddy currents, because it acts as secondary winding of transformer consisting of single loop of wire that is shorted. So to increase the efficiency and probably number of RPMs one would have to either cut a gap across the “cylinder” and make sure it’s not shorted or replace it with non-conductive one. Then one would have to rewind the coils properly, maybe even using basket winding to reduce stray capacitance and inductance even more…

      For further increase of efficiency one could play around with timing for the solenoids and/or turn them into LC resonant circuits at switching frequency…

      Also it would look cooler in form of radial or V engine…

      1. The shorted secondary makes the current through the primary rise quickly, yet when the current reaches steady state it doesn’t diminish the resulting magnetic field. In other words, it improves performance at the expense of efficiency.

        If the same was done by reducing the number of turns in the coil and cutting a slot in the bobbin, the current would rise quickly but the resulting magnetic field would be weaker.

  1. When you made the coils:
    Why did you cut the ends off the bobbins (for the coils) and not just leave both ends connected?
    (Basically cutting it out “H” shaped rather than “L” (or T if you want to be pedantic))

    Rather you make it, cut an end off, then glue it back.

    Just asking.

    1. If your pistons were magnetic passing through coils of wire, yes. Problem is reciprocating through a steel or aluminum bore would generate eddy currents slowing the piston down and generating lots of waste heat. And shortly afterwards the magnets would demagnetize due to the heat of combustion.

    1. I don’t honestly know but I think it’s a Sherline.

      Am going to give you some advice as a machinist…don’t settle for a “3 in 1” machine. They’re really not worth it in the long run if you take to machining, you’ll quickly outrun the machine’s abilities as your confidence and projects grow.

      If you search eBay and Craigslist long enough while continuing saving up money, you can get a knee mill (a Bridgeport or clone) and a decent sized lathe for a little more cash. A new “3 in 1” runs around $2K you can get a used mill and lathe for <$3K if you take your time…you'll know your machines when you see them. Remember that you're probably not going to be making aerospace parts and a clapped out dedicated machine is almost certainly going to be better than a cheap new "combination" machine for your uses.

      Just take your time and wait for the golden chance…i picked up a 3yr old cold saw for $3500, it was $12K new, and it's a beast.

      Also don't forget that you should expect "tooling up" to cost 25-75% of what the machine costs…Shars has pretty decent tooling for a fair price.

        1. Sherline mills are workable. I think their lathes are kinda limited. Look at craigslist for older benchtop lathes. Quinn Dunki has a lot of stuff about newer chinese 9×20 lathes, which she’s doing well with. I’m fond of older Atlas/Clausing/Logan lathes, which are pretty cheap and pretty solid. I know people who like Taigs, as well. But as other people have said, any lathe is better than none. Note that both lathes and mills throw chips like you wouldn’t believe, and the chips are often razor sharp and sometimes red hot, so you want to have an area that’s pretty closed off from the rest of your living space.

  2. I wonder why he chose to use Brass as the coil former’s, Brass from memory is a prety good shield against electromagnetic fields. its a bit like Aluminium and i believe it will reflect electromagnetic fields. Nice little project and some great machining work. love the addition of the micro switches although adding a little adjuster to them so you can adjust them forward and backward would allow you to adjust the timing.

    1. Andrew:

      You are absolutely correct that brass is very much like aluminum (and copper). Both are very much like air, having no affect on field. (When we start talking electrostatic that is very much a different story)

      1. Thanks Tom,
        I use brass inserts in the kicker coils for the vintage electro therapy units to dull down the inductive kick by sliding them over the iron core. Hence why I thought it would have an impact and why I have used wood formers. I may have to try one with a brass former now. That would make things so much easier :)

      2. Those brass formers act as one-turn shorted secondaries, and may very well have an effect on the speed for a given applied voltage. Back in the day, Bell used a whole assortment of relay coils with copper cylinders on either the top or the bottom of the coil — one position made for fast pull-in, slow release, and the other end was the other way around (I forget which was which, and I no longer have the book).

        1. hehe, reminds me of a client who was having huge issues with the AMP he just built with some high powered toroidal transformers. he made some copper strips and shield that went around the outside of the transformer then wondered why the transformer got hot real fast and seemed to loose power.

  3. “Produced with basic hand-operated machine tools, the build process is one to watch”…

    If you consider a 3-axis CNC mill a “basic hand-operated” tool, I have to ask what you consider a non-basic tool…

  4. I dream of a retrofit kit where we shove solenoid cylinder inserts into LS engine blocks and add batteries. :) yeah yeah I know. iron block, magnets, inefficiencies, oil, the list goes on

    1. I don’t see replacing pistons with solenoids doing the job, but it doesn’t have to be a lot harder than that; just pull the engine out and mount an electric motor to the transmission input, or to the driveshaft(s). ‘Course, you still have to power the accessories. Still, it should be possible to make conversion kits that are direct replacements for the popular engine blocks, that have all of the accessory mount points already in place. People were doing VW conversions to electric (and whatever other kind of powerplant they could rustle up) in the 1960s.

  5. I owned a Subaru for many years. My wife also owned a Forester. Subaru makes great vehicles. Loved the pancake engine. It was a dream to work on for a little maintenance that it did require. Got awesome gas mileage.
    This is a great project. Loved seeing all the macining of the parts. Great job!!!!

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