Let's Make Robots!

Powerful oxyhydrogen cannon - We have a lift-off!

Blasts small rockets into the sky
Spark_generator_circuit_diagram1.JPG125.24 KB
Functional_principle_cannon.jpg70.46 KB

I have started to build a more powerful oxyhydrogen cannon, something similar like Estes Hydrogen Fuel Rocket:

The igniter of the Estes Hydrogen Fuel Rocket is simply a nichrome wire, but I want to continue to ignite the oxyhydrogen via spark. The spark generator I have used for the mosquito rover was a HV PCB from a bug zapper and it works not very reliable, so I designed a new one with a certain flash over at a spark gap of 1 mm:

The circuit is very similar to the voltage multiplier of my Geiger counter design, but without voltage regulation and with one Villard cascade more, able to produce about 2 kV (see attachment).

How to get perfect graphite electrodes by dismantling an AA alkali battery (No NiCd or Li-Ion battery!):

Keep the manganese dioxide and zinc casing, you can make interesting chemical experiments with it.

The electrolysis is monitoredby a Picaxe 08. If enough gas is generated, a short buzzer sounds and a green LED begin to flash. The ignition than is remote controlled.

Cannon functional principle and design:

Details of the "rocket":

It's not really a rocket, it's a projectile, because it has no own propulsion.

The projectile weights 52.6g.

Due to the large electrode surface, the electrolysis chamber draw 400mA at 7.2V (electrolyte: 6g acetic acid 100%./100 ml water) and produces accordingly a lot of oxygen/hydrogen more than before.


All boards are assambled now and working fine:

Programming the cannon:

Now I just have to launch the projectile...

2010.7.18 First launch passed


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Nice and simple. Wonder what keeps the oxyhydrogen from leaking away from you while in the electrolysis phase. The seal between tube and rocket seems rather primitive.

Or do you simply ignore the problem and just run the electrolysis a few minutes longer?

I never head a problem with leaking. I had a problem that the over pressure by electrolysis was so high that the rubber plug with the projectile on it started to move.

:D :D :D

It's an amazing project. I realise it's a bit late, but would you give any consideration to mounting the launcher further away fro teh scooshy wet stuff? (Just in case.)

For heaven's sake no-one tell Fritz we're using explosives to propel robots.

I just love any kind of remote detonation! :P

One q: when the oxyhydrogen is ignited, doesnt it expand in both directions (up and down the tube)? I dont see the tube bursting, so I assume you have somehow sealed the electrolysis chamber tight but managed to bring the electrode wires inside.

And thanks for reminding about graphite electrodes. They would totally help me with one of my previous projects.

Hi ArvotroN,

Yes, the bottom side of the electrolysis chamber is moulded with epoxy resin.

nice building.i like chemical much more when i was in high school,ohh,that good times...

This reminds me of an experimental lava lamp I made once in my friends kitchen. His wife wasn't impressed when it "burped" and sprayed the kitchen ceiling in blue food dye, mineral oil / paraffin wax etc. To this day I don't know why (home made fussion reactor perhaps?) but I was banned from entering the kitchen for a week.

With all of your chemistry experiments / robots in the home have you had any mishaps?

My father was a chemistry teacher. I had my first chemistry lab at the basement of our house as I was 10 or 11 years old. In this age I discovered many chemical reactions more accidently than studying chemistry books.

Nowadays I read and calculate first and do experiments then. But my wife is still worried, I will blow up our apartment some day:)


Are you using a timer to figure out when enough gas has been generated?