The Box Collector v1.0
The Box provides both the energy and accuracy for the tracking system. It's effectively a small solar oven which boils and pumps the liquid ethanol in order to turn The Wheel, which turns The Gearing, which turns The Main Collector into the sun.
How does it do it?
The sides of The Box are parabolic curves, which means that the sunlight which bounces off them is focused to a point. When The Main Collector is pointed directly into the sun this focus sits just off the edge of The Box's copper boiler pipe, which contains ethanol (alcohol).
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|M6 nut driver
You'll only need it for one small step, but you'll be happy if you have it.
Take your 20cm length of copper pipe.
Drill a 6mm hole in the pipe, about 2cm from one end.
Take a cable tensioner bolt.
Cut the top bit off the tensioner bolt. This is so it takes up less space when you flatten the copper pipe.
Cut a small circle of inner tube rubber, just enough to be slightly larger than the head of the tensioner bolt. Cut a small circle in the center and push the tensioner bolt through it. This is to make sure the pipe will be airtight.
NOTE: if you are braising or soldering the pipe closed then you don't need to do this.
With a hacksaw, put two cuts into the top of the tensioner bolt, so that when it's pressed tight within the pipe liquid can still run through it.
Place the tensioner bolt through the hole you just drilled in the copper. Depending on the size of your pipe it might be a bit fiddly getting it in there, feel free to squash the pipe a bit to make more room.
Put an M6 nut on the tensioner bolt and tighten with pliers or a spanner.
In a vice, or carefully with a hammer (preferably the vice) squash the pipe to about half it's width, so that the bolt you just placed is in the middle of one flat side. This doesn't need to be too precise.
Flatten one of the corners in the pipe's opposite end. You want the flat area to be about 4cm long. The easiest way to do this is to put something metal about 1cm wide in the vice, place the end of the copper over it, and hit with a hammer until reasonably flat.
Drill a 6mm hole in the flat bit, about 2cm from the end.
Place a tensioner bolt, with rubber the same as the other one, through the hole and put on a M6 nut, tight. You don't need to cut the top off or make cross cuts.
(If you're soldering or braising you don't need the rubber.)
Cut two strips of inner tube rubber about 1-1.5cm wide and just long enough that they fit nicely into the inside of the ends of the copper pipe. A little bit of overlap is better than not being quite long enough.
(If you're soldering or braising you won't need to do this.)
Flatten the ends of the pipe. The easiest way is to squash them in the vice, then finish with a hammer. Make sure the rubber stays in place, poking out a couple of millimeters, and pay attention to the corners, making sure they're completely sealed.
If you're sealing the pipe by soldering or braising, do that now. Do both ends and the joins around the tensioner bolts.
Flatten the whole tube so it contains about 10 milliliters. This is easily done with a hammer on a flat solid surface, such as an anvil or your bench vice.
Check the volume by placing a short length of 6mm PVC tube onto one of the tensioner bolts, putting some water in your mouth, and slowly squirting the water into the pipe while holding it flat. When the water starts coming out the other bolt take off the pvc tube and drain the water from the pipe into a small measuring cup. Continue to flatten with a hammer until the volume is about 10ml, give or take. It's easier to decrease the volume than increase it, so take your time and don't overshoot.
You can increase the volume by placing the pipe in your vice flat side up, so that it squeezes the edges back together.
Don't suck water out of the pipe into your mouth, as it might not be clean.
Now test the seal on the pipe to ensure it's airtight. Do this by placing the PVC tube on one tensioner bolt, put you finger tight over the other, and suck as much air out as you can with your mouth. Without letting any air in, put the end of your tongue over the pipe so you can feel the vacuum and hold it there. If after 10-15 seconds or more the pipe is still stuck to your tongue then the seal is good, if you can feel the vacuum lessening and the pipe falls off your tongue then you have a leak.
If you do, put the pipe in a container of water and blow air into it, looking for any bubbles.
If the leak is at an end of the pipe hit it with a hammer until it stops.
If the leak is around a tensioner bolt, try tightening the nut.
When you're confident the pipe is airtight cover both ends and the joins around the tensioner bolts with Araldite or other resin glue. Allow to harden.
Or, if you're soldering/braising, just redo any areas that are leaking.
It's important that the pipe not leak at all, so take your time to make sure this is done right.
Spraypaint the copper black. It's ok to also spray the tensioner bolts.
Take the plastic bottle and remove any wrapping. You'll need to pre-shrink the plastic, otherwise it will buckle and distort when heated by the sun. The easiest way is to just fill the bottle with boiling water.
Cut off the top and bottom of the bottle so only the flat walled area is left.
Cut what's left of the bottle vertically and flatten, then fold in half long-ways and flatten again. If it's somewhat bumpy and uneven from being shrunk, that's fine.
Cut two small holes so that the plastic can be wrapped around the copper pipe, with the tensioner bolts poking through. You want the fold in the plastic close to the edge of the copper with the tensioner bolt, and about 1.5cm of plastic past the bottom of the copper. There needs to be at least 7cm plastic on the top.
Staple the top, bottom, and side of the plastic, reasonably close to the copper. Since the plastic hardens when it shrinks you may have a little difficulty getting the staples through, but it should work.
It is possible to use glue or tape instead, but it will be damaged by the heat.
Cut off the long side of the plastic about 5 millimeters past the staples.
Put an M6 nut on the tensioner bolt coming out of the pipe's edge, and a small circle of innertube rubber. Tighten the nut until it just touches the edge of the plastic.
Take the metal tin and remove any wrapping or labels, and the lid. Drill a 6mm hole in a flat surface on the base, 2-3mm in from as close to the edge as possible.
Insert the tensioner bolt into the hole in the tin and hold in place with an M6 nut. If you don't have a nut driver this can be a bit fiddly, best way is using needlenose pliers and patience.
Drill a 6mm hole in a flat surface on the tin's lid, 2-3mm in from as close to the edge as possible.
Insert the Woods valve into the hole, with the thread facing inwards. Secure tightly with a circle of rubber and M6 nut.
The thread on the valve isn't quite M6, so some nuts will slip off. Find one that doesn't.
Place the lid on the tin so that the Woods valve is on the opposite side of it from the tensioner bolt. Fill the edges of the lid with Araldite or other resin glue, so that the tin is completely airtight.
Take the two pieces of corrugated plastic.
Print out the four template images (right click the links below, 'save link as' to download):
Angled Top Left
Angled Top Right
Flat Bottom Left
Flat Bottom right
Measure the printouts as below to make sure they've been printed full size and not distorted:
Tape the two tops and two bottoms together. Place them up on a window or screen to make sure they're lined up and overlap properly.
Tape the Tops to the smaller bit of corrugated plastic, and the Bottoms to one end of the larger.
With a craft knife / scalpel or similar cut the lines marked in red below, making sure to cut completely through the plastic.
Remove the paper templates.
Cut two pieces of aluminium plate so they cover the area within the cut lines of each piece of corrugated plastic and stick them down with glue or doublesided tape. This doesn't need to be super precise, as long as they don't overlap the cuts.
IMPORTANT NOTE: make sure you have the grain of the aluminium running sideways across the box, rather than from the front to the back.
This is because the grain scatters the light, but only in one direction. If the grain is running the wrong way it will disrupt the optical precision needed for the device to track accurately.
Cut two pieces of aluminium, measuring 29cm by 32cm, making sure the metal grain is running parallel to the 29cm edge.
Insert the short edge of both pieces into the curved cuts in the larger, bottom panel of corrugated plastic, with about 1cm poking through.
These will form the sides of the box.
Check that the aluminium grain is running across the curvature of the sides, ie pointing from the front of the box to the back, as opposed to vertically from the bottom to the top:
Insert the copper pipe + tin assembly into the same panel, so that the bottom tensioner bolt is underneath it. You will need to fold out the flaps of plastic around the cut (which may be easier if you cut rough one layer of the plastic board), and may need to cut a hole for the tensioner bolt to go through. You will also need to cut flaps in the aluminium sides to accommodate the tin. The size and placing of these will depend on the tin.
Make sure the front edge of the copper pipe is level with the focus point:
Insert the aluminium sides through the curved cuts in the top panel, so that the metal stuck to it is facing inwards. The top panel needs to be angled so that the distance between them at the back of the box is 21 cm, and 30 cm at the front:
which should give an angle of 20 degrees.
Cut the aluminium sides and the copper pipe's clear plastic housing in a line roughly parallel to the top panel, so that about 1cm pokes through.