Intern’s Corner: Test-firing the HHO rocket

Fun & Games Technology
Intern’s Corner: Test-firing the HHO rocket

MAKE: Intern's Corner
Every other week, MAKE’s awesome interns tell about the projects they’re building in the Make: Labs, the trouble they’ve gotten into, and what they’ll make next.

By Steven Lemos, engineering intern

Making the Hydrogen-Oxygen Bottle Rocket (that Adam Savage is posing with on the cover of the new MAKE, Volume 20) was a pretty basic endeavor, with the exception of the circuit. The original schematic diagram had a flaw in it, but only after we breadboarded the circuit – twice — did we catch it.

I guess that’s the reason we MAKE interns build the projects that run in the magazine, so it’s us who bang our heads against the table and not you. I will kindly take that cookie now.


The experience showed me that, sure, when working with electronics it’s easy to misplace a component or wire, or completely miss something, which I already knew, but it’s just as easy to have a diagram be the culprit. So a word to the wise (a word I’m sure all the experienced hobbyists have already discovered for themselves): if you take care when putting together these tedious circuits it will pay off, for if you can trust in your work, then you’ll know the culprit lies in the plans, and you won’t spend hours chasing that metaphorical wild goose.

Twice we breadboarded this bad boy before discovering an error in the schematic — so you won”t have to.

But on to the actual launch. :) We had talked to the local electronics store owner, who at the time was making his own hydrogen using a more sophisticated apparatus, and who was interested in what we were doing with ours. So he came to watch, and brought along his professional pyrotechnician friend, who showed us how to make fuses with 12V and tiny resistors (basically the resistors pass so much current that the wire heats up and can act as a fuse to light stuff — voilà, cheap fuses).

Our beautiful 2-stage HHO rocket ready for test launching — before being crippled by a crash.

The first launch was a success, with the two stages going off rather quickly in succession, so we dialed in a little more delay time in the circuit before the stage 2 ignition. This was good and bad. We got more height out of the rocket on our second launch, but on its return it landed electronics side down. This resulted in our circuit behaving oddly.

So, not ready yet to call it a day, we began firing off only one stage at a time, adjusting the proportions of HHO (hydrogen and oxygen gases), water, and air, and testing the makeshift fuses, which worked fine for a single stage, but due to the time they take to ignite (3sec@12V) might not work for 2 stages.

We probably launched 12 times that day, attracting passersby. Good weather, new friends (who like blowing stuff up), and multiple launches. All in all, a good day. Houston, we have liftoff.

• Related: MAKE, Volume 20: “For Kids of All Ages”

9 thoughts on “Intern’s Corner: Test-firing the HHO rocket

  1. Bob D says:

    As a former chemistry major at the graduate level, I’m extremely annoyed when people call water “HHO”. This implies a bond between the hydrogen atoms where none exists. Calling it dihydrogen monoxide is equally as bad, again, implying a bond where there isn’t one. Structurally it’s H-O-H, hydrogen hydroxide, or even hydronium hydroxide depending on your point of view. It’s time to start getting this right after so many years of doing it wrong! The empirical formula of H2O is correct because there are two hydrogen atoms and one oxygen, but H2O is NOT a structural formula and is NOT the same as writing HHO.

    1. Keith Hammond says:

      Hi Bob, actually this rocket does run on HHO gas — it’s not a regular water rocket. Click through the link to Hydrogen-Oxygen Bottle Rocket and you’ll see the original MAKE article explaining it all.

      By means of electrolysis, water is split into hydrogen and oxygen gases (2 H and 1 O). This combo gas is commonly known as HHO, and it’s our rocket fuel. The rocket is filled partly with HHO gas, partly with liquid water, then the gas is ignited electronically and boom — the HHO gases recombine explosively to become water vapor, and the sudden pressure pushes the liquid water propellant out the nozzle.

      1. Bob D says:

        It’s filled with H2 and O2 gasses. Trust me, It’s H2 and O2. You’re not creating monatomic hydrogen and oxygen with electrolysis even with a fancy Hofmann apparataus.

        I see plenty of references to “HHO gas” when doing google searches, aka, oxyhydrogen. It’s H2 and O2 gasses mixed in a 2:1 molar ratio (respectively). This is especially disturbing to me that it’s so prevalent and is still being perpetuated. Oh well, not much I can do about it!

        1. Keith Hammond says:

          Yep that’s precisely why it’s called HHO gas — two parts H2 to one part O2 (molar).

          “HHO” is not a molecular formula, it’s just a common name that rocketeers call their fuel mix.

        2. Wilson! says:

          So, Bob, what’s the correct nomenclature for a mixture of 2 parts H2(g) and one part O2(g)? H20 it ain’t, because that’s the symbol for the compound commonly known as Water…

          1. Bob D says:

            It’s 2H2 (well, 2, H, subscript 2) + O2 (O subscript 2)

            2H2 + O2

            I tried to use HTML tags to show this (SUB and /SUB) but it doesn’t seem to work here.

  2. Dave Bell says:

    “how to make fuses with 12V and tiny resistors (basically the resistors pass so much current that the wire heats up and can act as a fuse to light stuff — voilà, cheap fuses)”

    Fuses are electrical circuit protectors.
    Fuzes ignite things.

    It’s field-specific jargon, just like calling a mixture of H2 and O2 gasses “HHO”.

  3. brushyfork23 says:

    I’ve been having extreme trouble getting my circuit to work correctly. Are you saying that there’s an error in the schematic diagram that Make links to? If so, what’s the error? My igniters are firing almost at the same time, not waiting for a full clock pulse between each ignition. Was the error corrected, and I have some other problem, or is my circuit wired wrong because I followed the online schematic?

  4. Malcolm Maude says:

    The schematic for the electronics does not appear to be on the project page for the rocket. Does anyone have it?

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