The solenoid engine RC project

Loud, fun, a mish mash of this and that and all held together with 3D printing!

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I always see lots of folks making solenoid engines, but they always just sit there looking pretty. Over the years I made plenty myself that just sit there and run. For the last few years I have been making them move themselves, and doing something fun. With a surplus RC controller I got'em driving around old timey style, and with surplus leftovers of balsa, wire, and whatever, turned them into flashy vehicles. I will be adding more pictures and history as I go.
This project is certainly not everyone's cup of tea But I really enjoy making them and hope some others will have an interest too.

Pardon me if my updates are a bit skewed/slow/sluggish I have cancer bad(no sympathy required) and am very low energy these days.

 I started making solenoid engines in 1972 at the age of 12. Been making them ever since and they just keep getting more bizarre.

The engine is a single solenoid type(a round tubular type from ebay), and just use a microswitch and chip driver for timing. The crankshaft is 1/8 steel rod, but the offset and cam and flywheel are 3D printed as well as most of the engine. The battery holder is out of a junked toy and holds 4 AA batteries for engine power. It rests on a balsa wood frame with leftover balsa when I used to make model aircraft. The steering and throttle motors are china leftover from other projects. The tires are old dubro wheels for airplane use but I made hubs to attach the to the rear end differential made from surplus worm gears. I ended up making my own printed u joints because they just cost too much.

The geardown for the motor to transmission uses those cheap plastic gears you get for a few dollars a bag off ebay. The belts are O-rings from some plumbing mess I had a few years back.

There are 2 vehicles shown in the pictures. One is an open frame version and the other has a balsa wood bus body. Using the extra channels on the rc remote I made the horn work, headights,  turn signals and even the bus destination light function light up.

The rc system is an 11 channel(they say its 12 but...) 2,4 gig unit that can be had off ebay for about 15$. I bought several and finally found a use. All of the parts for this project are available for building more. Most are from ebay that I bought here and the as extras or to sample. The real good news is for US folks they can all be sourced here now so no waiting.I will provide a detailed list if anyone cares to indulge but solenoid engines are really just a novelty to most., but so much fun if you make them do things. It is of important note to make the engine and drive train efficient so you can just use a small power source to run it. In this design I am running the engine off 4 AA batteries but the RC system has a rechargeable pack that is super light  .Engine RPMs can be varied between 300-650 Rpm.

I always try and build my engines so they resemble a real fuel burning motor with exhaust pipes, carburetors, air cleaners etc to make them more interesting and fun to look and play with. I started building them in the early 1970s, and have ever since, so as you can imagine I have built many and still have pretty large pile of them on shelves and cubby holes. In the last few years I began 3D printing them  as it allows for easy reproduction, and to make revisions and add ons. 

I 3D printed everything in ABS but any will do. I generally indicate suggested infill on critical parts.

Interesting factoid! I once made this engine run a pencil sharpener! Quite a hoot...Several more apps come to mind but never got around to it yet.

Driver module for solenoid engine R.E.M.

x-zip-compressed - 5.54 kB - 05/02/2020 at 00:25


  • 1 × Solenoid 5-12 volts Tubular type with cone plunger
  • 1 × Chip driver pcb Link to compressed file shown in files
  • 1 × Chassis/frame printed parts see files section
  • 2 × 3 1/2 inch DuBro wheels
  • 2 × locking collars 3/16 tower hobbies

View all 25 components

  • Another solenoid engine powered vehicle!

    castvee805/25/2020 at 18:45 0 comments

    Here is a video of a crane/forklift I built that is powered by a solenoid engine.

    This one uses the clear acrylic version of the engine and you can see all the parts working. This earlier version uses belts to transfer power from the engine to the driveshaft. It moves slow but is pretty torqued up and can climb bumps in the rad. Magnificent loud running motor noise if you like that sorta thing. It all runs from 4 AA batteries like the newer 3D printed version.

  • The tale of the crankshaft

    castvee805/14/2020 at 01:51 0 comments

    The heart of this engine is certainly the solenoid, but the soul is the crankshaft/camshaft.

    The crankshaft consists of a small steel rod with a circular disc on one end (3D printed) that has an offset threaded hole which provides a means of taking the solenoid pull and converting it to rotary motion. In this case the dis has a 1/4 inch offset resulting in a total throw of 1/2 inch.

    The pull of the solenoid must be closely controlled from an off to on state so as to provide pull when the disc is in the correct position. This function is controlled by the cam which is mounted to common shaft. The raised lobe on the cam trips a microswitch for just long enough to move the crankshaft from just below top dead cent to top dead center, when the switch is opened as the cam edge abruptly ends. The rest of the cycle is carried through momentum by the flywheel spinning mass. The offset dis and cam are both secured to the shaft via set screws. I print those two parts at high infill and double wall for strength. Never had an issue or failure of either. The offset disc has a 6/32 screw that the connecting rod attaches to for operation. The other end of course connects to the solenoid via the connecting rod adapter.

    Here is how the crankshaft/camshaft is mounted and supported in the engine.

    It is important to note the microswitch does not directly power the solenoid. The hefty spikes of current would wear it out internally really quick. Instead the switch drives a chip that does the actual switching. The microswitches I selected for this project have excellent mechanical life when only running a tiny electrical load. I have never had one fail, and have run engines for 20+ hours(that's a lot of running time) and keep on going  and going. It is interesting to also note I discovered the switches I came to use in a junk box I keep under my workbench. I found a source and use them in all my engine projects. They cost a little less than a dollar each.

     I learned the hard way about switches for timing on these engines.The prototype I connected directly and the engine ran fine for about 5 minutes. Then the engine ground to a halt with the contacts seized. This thing runs from 4 aa batteries and the switch rated at 5 amps with a current draw of less than 200 Ma. It took me serval switches to finally saw the side off one to observe the contact to see the arc produced at break to realize the inductive loading was greater than I realized and that what lead me to a driver chip. It was a Duh moment, I should have known better, but there ya go.

  • Its all about the details

    castvee805/13/2020 at 23:33 0 comments

    More than a few folks have to be wondering....Why is there an exhaust pipe? An air cleaner? A fuel tank?

     Actually there are other things on the car and engine that just are not necessary like radiators, hoses etc. But I like modeling so I add things that fill out the details of a basic vehicle.

    (photo above shows air cleaner, fuel tank and exhaust pipe and panel.)

    The first time I added such details years back, I sort of questioned why also. But I soon took a real liking to it and now always do so. With three D printing its even more fun and interesting because you can make as many as you want and use them on different engine models.

  • Driving the beast!

    castvee805/04/2020 at 22:07 0 comments

    It is slow going indeed on top of a short and narrow counter top!

    So many things to watch moving and working together. It runs pretty slow but has climbing power over bumps in the road. I really geared it down a lot, and could back off a bit but it will never be really speedy and I am happy with that. It is getting pretty cluttered up too as I keep adding little details to it.

  • The prototype engine in acrylic

    castvee805/03/2020 at 19:15 0 comments

    Before I set off to 3D print the engine I made a functioning version in acrylic to model from.This is shown for historical/model purposes.

    It was helpful for scale and layout.

    Many changes were made along the way

    It gives a nice look at where everything goes in the see thru version.

    Top down-the transmission went thru some radical changes.

  • Wheels for the vehicles

    castvee805/03/2020 at 18:53 0 comments

    Wheels are made by DuBro and I always have a stash of these around from my model aircraft days. These are nice because they have some bounce to them, sort of a built in suspension. Since my vehicles have no real suspension and move very slowly, these work great. The fact they are pretty inexpensive is not a bad thing either. 

    The front wheels simply slip on the front axles and have a threaded retainer to hold them in place. The drive wheels need a way to hold them onto the differential shaft. For this I made a 3D printed hub which holds a locking collar. The hub adapter is cemented onto the rim of the wheel(E-6000) , the locking collar put in place and the thing is ready to go. I like the idea I can take the wheels off quick and easy and also experiment with various sizes. The wheels come in a large variety of sizes.

    I am using 3 1/2 inch wheels on the back and slightly smaller on the front. You can see the locking system in the photo.

  • A quick test of the RC throttle and steering

    castvee805/03/2020 at 18:04 0 comments

  • Engine electrical system

    castvee805/02/2020 at 18:54 0 comments

    Simple but took a bit of scrounging to get it all together. Here are the basic parts:

    The battery pack is from a junked toy, but 4 AA battery holders are not uncommon but I didn't have so I robbed a bit. It was also nifty it has a switch built right in. The pot is a typical 10k along with a  mje3055 transistor allowing throttle control. The microswitch is a junk box part, but plenty of those in the wild. The PCB I had made for another engine years ago which replaced the original mounted on perfboard. It has a 16 pin socket mounted atop, and a ULN2003 Darlington array plugged in. The whole thing is really brute simple and I have never had a failure.

    The battery holder slides in the base of the engine in a printed motormount:

    The throttle control pot mounts on this printed plate:

    Then the plate mounts to this assembly with the transistor behind it.

    The current draw of the engine is 186 Ma @ 6.2 Volts at full throttle.

  • The radio system

    castvee805/02/2020 at 00:01 0 comments

    This is a handy RC controller which has 11 channels and was taken out of an excavator toy.

    You can buy this though on ebay for about 15$ They have a continuous supply of them it seems as I have bought some here and there over the last ten years. I made a small 3D printed holder for everything to mount it to the frame of the car. This will drive the steering and throttle motors directly.

    Here is a closer look at the receiver:

    I used these in other projects and made the battery pack store underneath. So when I placed in the car I left it in, although the battery in the engine would run it just fine too. The unit comes with everything you need including connecters etc to wire it right up quickly. Here is a link to the beast:

    good for lots of stuff!

  • Building the chassis for the vehicles

    castvee805/01/2020 at 22:58 0 comments

    The main frame is made from 1/2 inch square balsa wood. After mounting everything, I strip it down and stain and finish the wood with several coats of polyurethane to really toughen it up. Here is the bare frame with the differential/rear end mounted.

    Here is another look:

    The gearbox is shown here:

    The gearbox by itself with tiny printed leafsprings!

    The gears I had as surplus stuff but I found an actual source for them. Here is a link:

    Here is the 3D printed steering system.

    Another look:

    Everything screws together and the tiny motor is the same as the throttle motor. It is just a simple drag arm type but works very well. These had been lying in a drawer from another project, but are kinda handy to have around for things. Here is a link:

    Buy several, they are small and handy!

View all 12 project logs

  • 1
    The engine mount/battery holder

    The base and battery holder are 3D printed and supports the engine and holds the 4AA batteries used to run the engine.

    The battery holder I used in these engines were salvaged from toy cars and are slightly smaller than conventional off the shelf ones. No worries however you can just print the a bit larger by scaling it up in the slicer a few percent.

    This shows how the battery holder slides in the mount to allow access for changing batteries. It has an on/off switch, but new ones can also be had with the switch.

  • 2
    Mounting the lower block to the base

    The lower block houses the solenoid and top block which supports the crankshaft

    It is secured to the base with three 4/40 X 1/2 long screws.

    When assembled it also provides the top for the battery holder compartment.

  • 3
    Install lower block cover and battery retainer

    Install the battery holder tab to the lower block cover using a 4/40 X 1/2 long screw.

    Then install the lower block cover to the lower block assembly using 2 4/40 X 1/2 inch screws.

    This step is complete.

View all 11 instructions

Enjoy this project?



Ossum wrote 05/25/2020 at 07:42 point

This is wonderful! I have been fascinated with the beautiful brass solonoid engines I see on youtube etc. but frustrated that I'd never seen one actually doing work. Great job, I'll be following your updates.

  Are you sure? yes | no

castvee8 wrote 05/16/2020 at 23:38 point

It is SO quiet in here...What a shame!

  Are you sure? yes | no

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