With the arm roughly finished, I could design the rest
of the machine. I made a chipboard prototype to decide on the dimensions
of everything and the ergonomics, so both small kids and large adults
could use it.
If you drop too many fuel pellets, I thought a
lead shutter could descend, so you then had to complete the task ‘on
video’ (watching the monitor with a video feed from a camera inside the
chamber). Sadly, it was impossible to find a perfect place for the camera.
The arm sometimes obscures the view and the perspective is quite odd, both
of which make it hard to use. I had originally thought everyone should try
to insert pellets by video, but I had to give up and set it so you only
get to try the video if you’ve already successfully inserted most of the
pellets. The good thing about the camera is that the view looks identical
to a real reactor cooling pond.
Real nuclear fuel pond
My-Nuke camera view fuel pond
At the end of each go, I wanted to dispense a bit of
edible nuclear waste. The idea came from the ‘nuclear electric mints’
I’d bought from the visitor centre of my local nuclear power station,
Sizewell. Finding the right sweet to dispense was tricky. Several
marketing companies sell packets of sweets with your own logo printed on,
but they were too expensive. I thought of rock sweets early on, but the
samples had smeared letting and didn’t look good. I was stuck for
several weeks, and in desperation phoned another the rock company. They
told me the smearing was due to old machines and that their new machines
didn’t smear. Their samples were great, so I had 10,000 ‘edible
nuclear waste’ rock sweets made. It will take me years to get through
them so I had a lot of them vacuum packed to extend their shelf life.
Making the mechanism to dispense the sweets wasn’t
straightforward. After a few failures, the key was a magazine which
allowed the ‘wings’ of the twist wraps to stick out the sides. A bar
then pushes out the bottom sweet and drops it into the ‘waste fuel
box’. At this point I made my life over complicated. I decided it would
be better if the machine could hold more sweets, so I added a second
magazine and mechanism to swop from one to the other when the first one
was empty. It works, but it took ages.
The gripper works by compressed air, and as
most of the other movements were linear, it seemed sensible to use
pneumatic cylinders. This is not a cheap option, roughly £100 per
cylinder, including the control valve and fittings. Almost half the cost
is the control valve, so I decided to buy a second hand valve manifold
from ebay. There weren’t any in the UK, so I got one from the US. I
forgot that the US use eighth inch tubing instead of 4mm and its not easy
to convert the two. Also the valves themselves were exotic, with double
solenoids. I ended up having to epoxy glue makeshift fittings and add an
extra relay board to make the exotic valves behave like ordinary 5/2
valves. It wasn’t worth the struggle, I should have bought new valves.
The translucent casing of the machine is made
of polypropylene. The panels are joined by ‘plastic welding’. I’d
never tried this before but its fun. Its done with a special heat gun with
a nozzle that both heats up the edges and the polypropylene filler rod
that feeds into the nozzle while you move the heat gun along. It didn’t
take long to get the hang of this. We put together the whole casing in a
couple of days. I’m not sure how well the polypropylene will wear, it
seems to pick up dirt easily, but its also easy to clean, so maybe it will
be OK. The advantages of polypropylene are that its relatively cheap, its
strong (although a bit bendy) it can be planed and sanded to a reasonable
finish, and its translucent, so lights inside can look great.
After all the major components were installed,
the machine took ages to finish. It seemed to be jinxed, so many parts
failed along the way. When two things fail simultaneously, it can be
really hard to work out what’s gone wrong. Eventually though it did all
start working. The final element is to put together the video introduction
and instructions. I wanted the introduction to be animated atoms
(historically there have been so many attempts to explain atoms with
animation). I realised atomic fission was surprisingly like sex. Atoms
collide, get very hot, and then produce new atoms.
Until I got it on the pier, I hadn’t realised how
different My-nuke is from my other machines. At first I thought it only
was wrong, but the people who are drawn to having a go with the arm, are a
minority. The most popular machines in the arcade hardly require any skill
machine had several teething problems. The worst was the push button that
operates the pneumatic gripper. People push it so hard when they are
concentrating that it stopped working after a couple of months.
I tried a more expensive button, but the same thing happened. Eventually I
replaced it with a bigger 'vandalproof' button - so far so good. The other
persistent problem was that the gripper jaws became increasingly slippery
with use. I tried different rubbers to no avail, six months later I tried
putting O rings in grooves on the gripper jaws. They still get slippery,
but they deform enough to still grip the nuclear fuel - its made a huge
difference to the fun of playing the machine.