Let's Make Robots!

Mosquito rover [new video now also on youtube]

Navigates around via IR, produces oxyhydrogen, shoots off mosquitos :)
H-Bridge_circuit1.jpg214.56 KB

Update 2010.06.10: New video to celebrate the 3rd 2nd place at the GoRobotics competition


Ni hao robot builders,  

If you ever see this baby in a store...

...buy it -- it is easy to hack and you get beside a tank track platform a lot of additional stuff like RC, sound chip, loudspeaker, battery pack, charger, bi-color-LEDs for around 180 RMB (Carrefour):

Unfortunately every motor draw around 1 A (and around 2 A if they block), so the L293D on the Picaxe board can not be used.I build up a TIP 122/TIP 127 double H-bridge on a perfboard and glued it with epoxy on the top of the gear box:


Today this little 20 RMB bug zapper caught my attention:

The small PCB inside is able to make big noisy sparks --- perfect as a spark generator for my oxyhydrogen cannon:

Handle this PCB with care, should you consider to use it too. Even you have a spark discharge, there is still a residual charge in the capacitor to fry your fingers instead of a mosquito.

Here is the finished cannon. The inclination angle of the barrel can be adjusted via servo from 90° to 45° .We know, that we will get the biggest range of fire at 45° (air drag neglected) :)


Thought about to name this robot Mosquito rover. Why? Ok, I want to give the cannon projectile the shape of a mosquito:

That's the theory so far. Now I have to build it.

Assembled the battery box and the Picaxe board on the rear of the tank platform today. Makes great fun to drive this robot!! Still a lot of place in the front of the tank for a second board and a photovoltaic array. I think I might use the same servo for adjusting the cannon and the photovoltaic array, because all output pins are already used.

The robot got its front board with spark generator driver, loudspeaker, astable oscillator 08M circuit, push buttons, power indicator LEDs and Sharp IR, driven by a micro servo HITEC HS-55:

Today I had to notice, that the timer settimer command in general not works if servo commands are used, so I replaced the 555, which I had used as an astable oscillator, simply by a Picaxe 08M. The 08M is now responsible to switch the mode after a defined time, when enough gas is generated to fire.

Here is the mosquito, build from a small plastic tube, plastic sheet, wire, heat shrink, epoxy glue, LEDs as eyes and a few other electronic components, just landed on a coconut:

To keep the take-off weight of the mosquito as small as possible, I only wanted to use a 1.5 V coin battery, so I needed a special circuit to make the LEDs flashing:

Today I ordered a 5.5V/90 mA photovoltaic array (9 RMB/piece at taobao.com) and started to build the holder for it:

The photovoltaic array holder has been finished. A micro servo HITEC HS-55 adjusts the gradient angle of the photovoltaic array according to the brightness, measured by a LDR. The basic position of the photovoltaic array is 0° (parallel to the ground). If the LDR gets shadowed, the photovoltaic array moves to 45°. If the photovoltaic array is still shadowed in this new position, the robot initiates an evasive maneuver to escape from the shadowed area. After the evasive maneuver is done, the photovoltaic array moves back to the 0°-position.

The mosquito rover has been finished. Now the robot takes a sunbath at my roofgarden to charge its oxyhydrogen cannon:

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How long does it take to accumulate enough gas to fire?

I wrote it below already: It takes around 15 minutes to generate enough gas to fire ;-)

Hey Markus, the photos look great but I can no longer view the videos with any of the proxy servers I was using including "Hide Fap". Can you post them on youku for me and any other Chinese viewers.

Hi Oddbot,

Ok, no problem, I will ask my wife to upload the vid's as youku has no English menu :) BTW, photobucket should also work in China. I am using it to dispaly the vid's on our web site.


Thanks for that. I like the idea that it makes it's own explosives. Would be cool if you could make a self loading version. Probably need to replace the rubber stop with something like squash balls and give it a small hopper to store them in.

I get the spark generator and that it's igniting the gas to fire the gun. Where's the gas come from? You just put water in the cannon, and the graphite rods separate it into HHO gas (when powered, via electrolysis)? If that's the case, how long does it take to generate enough gas to fire?

Another "if that's the case"; Cool ;) Simple and effective. I probably would've overkilled it with another servo actuating a butane lighter or WD-40 can to refill the chamber.

Hi Rudolph,

Yes, electrolysis is used to produce H2 (hydrogen) and O2 (oxygen). I do not use pure water as an electrolyte, because the conductivity is too low. I use a mixture of water and vinegar essence. If you electrolyse vinegar you actually get also C2H6 (ethane), but this gas burns explosively with oxygen too. The robot has a NiCd battery with 700 mAh and 4.8 V (delivered with the toy tank) for electrolysis (and motors). Later I plan to power the electrolysis chamber with a photovoltaic array, assembled on the top side of the robot. The electrolysis draw about 30 mA at 4.8 V with graphite electrodes and the mentioned electrolyte. It takes around 15 minutes to generate enough gas to fire. I am planning to use an external counter (555 and settimer count command). I can not use the internal Picaxe timer, because this timer can not be used at the same time as servo commands. After 15 minutes the robot will stop, adjust the cannon to 45° and fire automatically.

I have finished a test video of the cannon yesterday, just waiting that a friend will upload it on youtube, because here in China I am not able to upload videos on that or many other video sites.


Great  bot !!! Original Idea :)

Was just wondering, how much "power" do those gases have and would they be enough to shoot a ping pong ball or maybe even a tennis ball !? "(when leave the electrolysis on a bit longer off course).    

An oxyhydrogen explosion is very powerful. You can shoot a ping pong ball or tennis ball as well. The problem with cannons is, the higher the weight of the projectile, the higher the blowback. I have done some calculations for my Google Lunar X Prize project regarding oxyhydrogen cannons: http://www.seleneteam.com/files/oxyhydrogen_cannon.pdf

It shows that you just need to electrolyze 0.0154 cm³ water to shoot a 0.5 kg projectile 500 m (air drag neglected, launching angle 45°).

Just noticed that even the external counter can not be used in the same time as servo commands.