It's been a while, but now a new project --- MARS.

a quick sketch of my Mars Orrery

It has been quite a while since my last entry, but I've been working through a few heavy 'life' things since October, and I'm finally ready to start up another major project.
The Karakuri plans are still very slowly chugging along, but I've been derailed as it were by a lack of spring steel that's an appropriate size. Until I have a source for this there really is no point in starting the construction, so for now I've begun to develop plans for a long overdue project. It's still good practice for the Karakuri, so for now I'm content with just making something complicated.
For the last ten years or so I've been floating the idea around of making an Orrery ( http://en.wikipedia.org/wiki/Orrery ) of Mars and it's two moons Deimos and Phobos. Made completely out of wood one would turn a crank, Mars would turn on it's axis, and the two moons would rotate at the appropriate orbital speeds. I'd design it to look old and use on Schiaparelli Mars maps, canals and all, as the design basis.
To make this work would require knowledge of Mars and it's moons (Check! - says the space geek), how to construct wooden gears (check!) and the hardest part, understanding and designing a gear train. Wait a minute, that's pretty hard. Well with much hair pulling I have figured this out, and made a mock-up to test it out.

the start of the process... what a mess

To the right here you can see I've started drawing out the concept. I figured out the wheel size and teeth numbers based on the orbital period of the two moons. I assumed that if Mars rotates one complete rotation on it's axis, one day, then the orbital periods of the two moons should be rough percentages of 360 degrees, one full rotation.

model made!

So here I have made a mock up of the Mars system and what I hope are the correct sizes of the wheels for this orrery. I carved them out of foam-core, and glued rubber bands to the edges with double sided tape. Carefully aligning and using toothpicks for pivots, I'm ready to test out my maths. 
It turns out that for every rotation on Mars, Phobos takes 1.26 times the rotation of Mars, while Deimos takes .32 times the rotation of Mars. Basically Phobos orbits very quickly, crossing the Martian sky in lest than a day, while Deimos just creeps along, actually looking like it moves across the sky in the opposite direction!
So here's the plan; I carefully turn the driver gear in the center (that could be any size, I designed this one smaller, you'll see why in future posts) allowing Mars to turn one full revolution, or one full day. I mark the start positions of the wheels. I carefully count how many times the Deimos wheel turns, which should be more than once because it's smaller than the Mars wheel. Then how many degrees the Phobos wheel turns; this should be less because the wheel is larger than the Mars wheel.
Results!

the results, not bad considering the slippage of the elastics!

I seemed to have pulled it off! It's not super accurate, but damn close enough!
I counted the Mars full rotation as 360 degrees. I then counted the Deimos rotation as roughly 2 3/4 rotations, or 990 degrees. Phobos as roughly 280 degrees. Divide 360 into 990, you get .363. The actual orbital period of Deimos is .319. Pretty close!
Divide 360 into 280, you get 1.29. The actual orbital period of Phobos is 1.26! Almost spot on!


So with this gear train designed and tested, allowing for a little bit of error, I am ready to start cutting wood. Well sort-of. Due to the fiddly-ness of the meshing of the gears, I will have to make a detailed 3D plan, as like the Karakuri doll, to make this work well. 
I'm so please I'm ready to make this I'm giddy, it's been ten years in the making.
Stay tuned!