9

Rocket Launcher Strandbeest

FEATURE

and painted it with grey (granite) spray-paint,
giving it a look that I was really happy with.
The 3D-printed face and launcher tubes
were also painted in the same manner,
though they would come a little later.

ELECTRONICS
I knew my Rocket Beest looked good,
and that I could get it to walk, but actually
stuffing all the electronics inside was quite
the challenge. I’d settled on a compact
Arduino Nano as the brains of this device,
along with a Bluetooth module to allow me
to steer it and fire rockets via a smartphone.
A pair of relays was used for rocket ignition,
and a motor driver board controlled – you
guessed it – the two leg motors. The
variety of electronics used meant splitting
everything into two small perf boards,
with components attached with solder and
hot glue.
While things worked outside of the
Rocket Beest’s body, stuffing it inside was
a matter of Dremel tool ‘adjustments’ and
careful wire-yoga. As noted earlier, the cut-

outs meant for time/filament savings came

in very handy here, as the circuit boards

were slightly wider than the body, and

ended up fitting nicely in these windows.

While testing its walking function with

the boards in place, powered by a pair of

3.7 V LiPo batteries in series, I was inspired

to design and print the distinctive ‘face’ of

the robot, painting it in the same way as the

rest of the body. Blue 10 mm LEDs were

used as eyes/headlights which, along with

its mouth-grate assembly, give it a lot of

extra personality.

ROCKET LAUNCHER!

With the face and rocket tubes strapped

on with zip ties, everything appeared to

be in place, but the design’s key feature –

automatic rocket launching – was still not

ready. A small disclaimer: I’m not suggesting

that you try this project, and can’t guarantee

its safety generally [Editor’s note: this is a

dangerous project, and could cause serious

injury. Just because Jeremy survived, it

doesn’t mean you will. Don’t attempt to

recreate it unless you’ve got the skill and

experience to work with pyrotechnics]. If

you do decide to build something that can

shoot a potentially dangerous projectile

[Editor’s note: we strongly recommend

you don’t], be sure it’s always pointed in a

safe direction when there’s a possibility of

ignition. As you’ll see later, following this

protocol helped keep me safe during testing.

I decided that Nitinol wire would be a great

choice for launching rockets, since running

electricity through a thin strand causes it to

glow red with heat. Actually holding the wire

was difficult, though, as soldering it proved to

be difficult, and I wanted this wire to be able

to be easily replaced when needed. I chose

to use alligator clips to hold short lengths of

Nitinol, with the positive wires connected

to the NO terminals of my dual relay board.

The idea was that when the signal was given

via Bluetooth, the Arduino would signal the

appropriate relay to close the NO terminal,

gloriously lighting its rocket payload.

As it turns out, it did gloriously light one of

its rockets... as soon as I plugged it in! No

damage to me or the surroundings as I had

it pointed ‘downrange’, but the relay wiring

was thoroughly melted. I’m still not entirely

Above

A rotary tool is great for making little modifications

to plastic kits

Left

Final assembly and testing

Above

A lick of paint can transform the look of

your build