Tuesday 21 November 2017

AstroMedia Copernican Orrery kit - part 2

In part 1 I described the first half (approximately) of the construction of a cardboard Orrery kit from AstroMedia. In the second half things get more interesting, and more complicated, as the majority of the pulleys and shafts are assembled.

AstroMedia Copernican Orrery kit

The first part to be constructed is the "planetary gearing". This will eventually roll around the ecliptic disc, held in place by drive bands above and below the ecliptic disc.

AstroMedia Copernican Orrery kit

As you know, Earth's rotational axis is tilted and the Orrery has quite a clever system to keep the axis pointing in (roughly) the same direction as the Earth orbits the sun. The Earth rotates on a steel shaft which runs through a brass tube attached to a small bracket. The bracket is attached to a hollow shaft that passes through the planetary gearing to a drive wheel below.

The Earth's rotation is driven by another pulley and shaft that passes through the planetary gearing. A round magnet attached to the top drives the Earth's rotation via a small piece of silicone tubing. Unfortunately I didn't get the magnet exactly centred on the shaft and so the drive occasionally slips.

AstroMedia Copernican Orrery kit

Above the ecliptic disc are two large discs supporting Mercury and Venus. The orbit of Venus is driven by a belt around its large support disc, and Mercury is driven from below by a hollow shaft through the Venus disc. After fitting all the drive belts the moon and remaining planets are attached with steel support pins.

AstroMedia Copernican Orrery kit

There are five drive belts holding the planetary gearing in place. The topmost one drives the orbit of Venus, the next drives Mercury's orbit. The bottommost one drives Earth's rotation, the next keeps Earth's axis pointing in a constant direction and the last drives the planetary gearing to roll around the ecliptic disc. Does it all work? Watch the video and see for yourself.

AstroMedia Copernican Orrery kit

PS More pictures of its construction are available on Flickr.

Tuesday 14 November 2017

AstroMedia Copernican Orrery kit - part 1

AstroMedia Copernican Orrery kit

For a long time I've fancied having an Orrery but have been put off by the high price of traditional style brass ones with all the planets (and Pluto). Something much more my style is the cardboard kit from AstroMedia. This only has the inner planets, but I get the fun of building it.

I bought the kit a few months ago from Sherwoods Photographic Ltd, a company I've bought a telescope and accessories from in the past. Two weeks ago I finally got round to starting to construct it.

I soon discovered that one of the die-cut thick card sheets was missing (and I had a duplicate of another sheet). I emailed Sherwoods and they arranged for the UK arm of AstroMedia to send me a replacement, which arrived the next day. Top notch service from both companies.

At the time of writing I'm about halfway through building the kit. So far I'm very impressed with its quality, and with the instruction leaflet, although it occasionally reveals its German language origins. Construction is quite slow as you have to allow glue to set before moving on to the next stage. I'm also doing the optional painting of some cardboard edges on partly assembled components, so I have to wait for that paint to dry as well.

There is a temptation to read ahead and start constructing later parts, but with so many similar looking wheels it could get very confusing. One thing I have done in advance though is to paint the small wooden spheres used to represent the planets and our moon, after temporarily mounting them on cocktail sticks.

AstroMedia Copernican Orrery kit

The first component to be built is the pedestal. This uses spacer rings between two sheets of card to make a strong, light structure. Strips of printed paper are used to cover the gap — a fiddly bit of glueing but the result isn't too bad.

AstroMedia Copernican Orrery kit AstroMedia Copernican Orrery kit AstroMedia Copernican Orrery kit AstroMedia Copernican Orrery kit

Next is the drive crank and pulleys, followed by the pedestal base and the central shaft with three pulleys.

AstroMedia Copernican Orrery kit AstroMedia Copernican Orrery kit

Today I finished the ecliptic disc, another structure using spacing rings. It's beginning to look like something now.

AstroMedia Copernican Orrery kit AstroMedia Copernican Orrery kit

PS Part two is now available. More pictures of its construction are available on Flickr.