Solenoid Engine

I got the solenoid engine working tonight. I filmed a video of it in action, starting out around 5.5v and increasing to 7.5v. This has a dramatic effect on the engine’s RPM.

The solenoids only got a little warm during the filming of the video, so that’s a good sign. Next steps will be to diagram the circuit in EasyEDA and get a PCB made, then mount the whole thing on a pinewood derby car body. But this is good for now.

Optical Commutation

I finished putting together an optical commutation circuit on a breadboard tonight. It uses an IR emitter/detector pair to trigger timer chips that ultimately turn on power transistors to drive solenoids. The solenoids are logically opposite, so they alternate as the IR beam is made and broken.

The timer chips aren’t strictly necessary, but they prevent the solenoids from staying on too long and burning up. You can see this in the video below when I am blocking and unblocking the IR path using a playing card–I sometimes leave the card in or out for a few moments, during which time whichever solenoid is powered returns to a resting state after about one second.

I’ll use this circuit to drive the two solenoids in my solenoid engine, which will have a rotating half-moon to block and unblock the IR beam.

Solenoid Engine Prototyping

I’ve started thinking about how I might build a solenoid engine. I bought a couple solenoids on Amazon, Uxcell brand, and they seem to have quite a bit of zip to them, so I’ve been looking into how to mount them to a block in a way that would allow them to rotate around an axis, eliminating the need for the connecting rod to rotate with the piston head, which in this case is just the armature of the solenoid.

Pictured below is the first three attempts at printing a little box to hold a solenoid. The little wings on the side have 1/8″ holes in them that will fit over a rod, allowing the solenoid assemblies (I plan on having two of those) to lie directly over the crankshaft and rotate back and forth with the cranks.

You can see the design process as it unfolded, first with no venting on the sides, then with vertical venting and finally diagonal venting to allow the solenoids’ windings to cool off better during operation. I don’t know how much of a problem heat will be, though, since I’ll be running somehow around half the rated service voltage of the solenoids, at 50% duty cycle to boot.

I did melt the diagonal vents a little with a heat gun while trying to de-string the object. Oops.

Steam/air engine

I finally built something like a steam engine. This one runs on compressed air, but it’s the same idea. It uses a single cylinder, a flywheel, and a valve arrangement that looks like a cylinder.

The blue parts are all 3D printed, including the flywheel, the crank, and the collars/caps on the brass tubing (which serves as the cylinders for the piston and valve).

The valve works by moving 90 degrees out of phase with the piston and alternately trapping the supplied compressed air and admitting it to the cylinder. When the air is admitted the piston pushes on the crank, and when the air is trapped, the piston pushes the spent (exhaust) air out of the cylinder, back through the airway, and out through the bottom of the valve’s brass tube.

The valve is like a two-headed piston with an air chamber between the heads.

Below is a picture of the air supply system I rigged up. It allows the user to pump air into a soda bottle and then open the blue butterfly valve to allow the air into the engine. This is all just PVC, plastic tubing, and a brass airtank fill valve.

Finally, here’s a video of the engine in action. Future improvements include a more compact air system and actual piston rings that should help the piston and valve seal better inside the brass tubes.

Piston/crank test

I have redone the pistons and rods quite a bit since the last post. The rods now connect to a pin I installed through the middle of the piston head and rotate in a slot I cut in same. This is more like how real pistons work and limits (or ideally eliminates) the ability of the rod to impart a torque on the piston head, which would cause it to bind.

Additionally, I used a longer rod and removed the lever between the rod and the crank. This lessens the angle of the rod to the side of the cylinder, reducing the risk of the rod contacting the cylinder, and also reduces piston head torque/binding.

Below are two close-up pictures of the piston/rod connection, and there is also a video showing the motion of the piston when connected to the crank.

Steam engine taking shape

I worked more on the rods and cranks tonight, and I now have a picture to show of the parts laid out.

The steel-colored parts from left to right are the piston cylinder, the piston itself with rod and crank lever, and the valve with its two heads, rod, and crank lever. I also put the crank itself along the top the way it will be arranged in the final product.

To do yet:

  • Cut out a cylinder for the valve
  • Cut out new thicker risers for the crank
  • Glue the crank parts and remove the sections of the 4mm rod that shouldn’t be there
  • Drill steam ports in the cylinders and run some kind of pipes or hoses between them

Rods and cranks

I continued working on my steam engine tonight. I fashioned a rod or lever to connect the piston rod to the crank in a pivoting fashion (first two pictures). These are made from 1/8″ steel rod I ground and drilled to accept a 2mm pin (jumping back and forth between measurement systems, sorry about that).

The crank (third picture) is a 4mm rod (so chosen because my old Erector set pieces have 4mm holes in them) with little plywood risers that also accept 2mm rods. The latter 2mm rods will be what the piston rods ultimately connect to. Once I get things more permanent, I’ll cut out the pieces of the 4mm rod that would interfere with the motion of the piston rods.

I’ve had a good amount of success drilling through these thin steel rods by first grinding a flat spot with my Dremel, centerpunching a guide divot in the desired spot, then carefully applying the drill press until the bit finds the guide divot.

He did what in his cup?

I have been working on several things since my last post. First, I made a vertical shooter game on that LED matrix. I don’t have a good video of the finished product yet, but for now below is a video demonstrating the custom controller.

I also stumbled onto some really nice craft steel material at my local fleet farm store. These metals are from K&S Precision Metals ( and they are fantastic. I got a stainless steel rod and a stainless tube that would fit around it, and the fit is about as perfect as a non-machinist can get for making homemade pistons. Then I bought a cold-rolled 1/8″ rod to use for a piston rod.

Why make pistons? To make a model steam engine, naturally. I managed to craft a rough cylinder, piston, and rod (complete with mounting hole in the end) using just my Dremel (for cutting and grinding) and my drill press. The mounting hole I accomplished by grinding halfway through the 1/8″ rod on one side to make it flat, then drilling a 1.5mm hole. Below are some pictures, followed by the promised LED video.