Acetone Smoothing Results in Working Motor

Here’s something only ’90s kids will remember. In 1998, the Air Hogs Sky Shark, a free-flying model airplane powered by compressed air was released. This plane featured foam stabilizers, wings, a molded fuselage that served as a reservoir, and a novel engine powered by compressed air. The complete Sky Shark setup included an air pump. All you had to do was plug the plane into the pump, try to break the pressure gauge, and let the plane fly off into a tree or a neighbor’s rooftop. It’s still a relatively interesting mechanism, and although we’re not going to see compressed air drones anytime soon it’s still a cool toy.

Since [Tom Stanton] is working at the intersection of small-scale aeronautics and 3D printing, he thought he would take a swing at building his own 3D printed air motor. This is an interesting challenge — the engine needs to be air-tight, and it needs to produce some sort of usable power. Is a standard printer up to the task? Somewhat surprisingly, yes.

The design of [Tom]’s motor is more or less the same as what is found in the Air Hogs motor from twenty years ago. A piston is attached to a crank, which is attached to a flywheel, in this case a propeller. Above the cylinder, a ball valve keeps the air from rushing in. A spring is mounted to the top of the piston which pushes the ball out of the way, allowing air into the cylinder. At the bottom of the stroke, the ball closes the valve and air escapes out of the bottom of the cylinder. Simple stuff, really, but can it be printed?

Instead of the usual printer [Tom] uses for his builds, he pulled out an old delta slightly modified for higher quality prints. Really, this is just a 0.2 mm nozzle and a few tweaks to the print settings, but the air motor [Tom] designed came out pretty well and was smoothed to a fine finish with acetone.

After assembling the motor, [Tom] hooked it up to a soda bottle serving as a compressed air reservoir. The motor worked, although it’s doubtful a plane powered with this motor would fly for very long. You can check out [Tom]’s video below.

20 thoughts on “Acetone Smoothing Results in Working Motor

  1. “All you had to do was plug the plane into the pump, try to break the pressure gauge, and let the plane fly off into a tree or a neighbor’s rooftop. ”

    This post reminded me of my sky shark and how we lost it on it’s first flight into a bunch of trees & never found it :(

  2. So I was thinking lately about compressed air – could you make an air compressor that works along a similar concept to a DC charge pump?

    “V++” is a low-pressure input, like maybe a cheap aquarium pump. “GND” is atmospheric pressure. Capacitors are replaced with pressure vessels, and rectifier diodes are replaced with check valves. Then your oscillating signal is just a relay controlling a solenoid valve switching between the “V++” tube and an outlet to “Ground”.

    …maybe?

    1. I was wanting something similar in an old project idea a few years back. I ended up looking at hydraulic rams and hydraulic accumulators, never found good design info like formulas you could just bam in the numbers for though.

      Mechanically, you could do it with a super large piston and a super small piston, you put 50 psi over 10 square inches and you’ve got 500lb of force, you push a 1 square inch piston with that and you’re creating 500 psi.

    2. Air powered hydraulic pumps are common to the point of cheap versions from horror fright.
      https://www.harborfreight.com/10000-psi-air-hydraulic-pump-98318.html
      Air boosters and air intensifiers are available as well, though they still seem to be the realm of specialty industrial applications ($$$)
      https://www.midwestpressuresystems.com/products-air-pressure-boosters.htm
      They also tend to be among the more expensive ways to make compressed air….

    3. The problem in thinking is that voltage is relative, while air pressure is absolute, so you can’t decouple your ground from your ground – all the pressure accumulators are always relative to the ambient pressure so you can’t “stack” them end to end like charged capacitors.

      But, you could fill a pressure reservoir with your pump, and then switch the inlet of the pump to that reservoir, so your “ambient” pressure is now higher and you can pump a second reservoir to an even higher pressure, and then switch your pump inlet to that reservoir and pump a third reservoir even higher. You’re essentially building a cascade pump, with only one pump.

      1. Of course, the pump will run harder and harder because the pressure against the piston is increasing relative to the free air on the other side, so the crank case of the pump would need to be pressurized by the intake air.

    4. Have a look at how portable medical oxygen machines build pressure.

      Ignoring the purifier part and the long time since I’ve seen one, I seem to recall they had some sort of dual reservior system to build pressure.

      Could be completely wrong, I didn’t fact check this.

      1. I got mine from an old friend who is a nurse, they replace them every 2000ish hours or so. They still are quite useful and full of great parts, just not up to medical grade. I’d reccomend asking your doctor for one over a beer.

  3. Haha…
    This completely reminds me of the helicopter version of the engine.
    I think I still have the engine sitting around somewhere.
    Had endless fun cutting up the fingers on the blade for all of a few sessions before secretly disassembling it and building an adapter for the gimbal part and hacking it onto the technics lego stuff.

    I made a small 1.5ft long “car” that ran at just about walking pace. Then had it as a power source for a gearbox (I Wish I’d knew about the more compact builds online at the time), Or I just made a lot of noise to irritate the care-workers ;), yet because it looked productive and experimental with design the carers didn’t consider it as obsessive.

    Any thought on converting those handheld electric pumps into one of these?
    I’ve got a broken one at work (Burnt out motor regulator) with a metal cylinder.

    Unferium: NV2325172011TTYDM

  4. In the animation in the video the spring holds the ball valve open until the piston is completely down. There is no expansion cycle for the air, much of it’s power goes down the exhaust and efficiency is low. I don’t know if this is just the animation or this completely shows the real engine. When you close the valve earlier, like e.g. half way down (make the stem and/or the spring shorter) the compressed air in the cylinder can expand and give off more energy. Probably the power will be reduced a little but the efficiency would be doubled as only half the amount of air per revolution is used. Of course some fine tuning can be done here.

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