I chose a ten planet model, incorporating Pluto and Eris, with a modified scale (see step 1). Distances, for reasons that you know doubt understand, are not to scale. My model is not mechanical, although the planets can be rotated individually.

For more information and plans to build a true mechanical orrery, check out Clayton Boyer's beautiful designs here.

Edit: Thank you to everyone who voted for me in the Celestron Space Contest! As you might be able to guess, this is still a work in progress. I will post the final pictures after it is completely finished. Thanks!

**Signing Up**

## Step 1: Calculations

I set Jupiter's size at 7 inches (diameter) and scaled the other planets relative to it. Be aware that seven inches is a lot bigger than it sounds and a lot heavier than you think (Jupiter weights ~3 lbs). Many of my later design constraints came from Jupiter and Saturn's weight.

The terrestrial planets and earth's moon are magnified by a factor of 5 in order for them to be visible (In the photo below, Pluto at ~0.6 inches in diameter is approximately the correct size for Earth without the 5x magnification). The sun is essentially not to scale, for reasons that are unlikely to become clear at the moment.

The calculations below do not include Eris. Reports vary as to whether it is in fact significantly larger than Pluto or only slightly larger. I chose the smaller value for the radius as it is the most recent. All the data is from Nasa. The scale was calculated in excel and modeled in photoshop.

Now you can attack the subject of rotation axis. Your excellent design assumes the solar system is coaxial, but it is not thus. A good challenge!!

lo suficientemente cerca de coaxial para Instructables.

Tal vez una idea para nuestro próximo proyecto

Bill, terminé mi Longworth plate, successfully. Tengo ganas de volver to attack mi proyecto de Steam-Stirling Engine, cuando I finish los little proyectos que I have en portfolio.

If you have any ideas, let me know!

Very, very nice! Do you know how many people know the definition of the word "orrery"?

I see you included Pluto.

Regarding your question about the weight of the counterbalance, this is quite easy, as you only need to counter the momentum, which is distance by gravity force.

G-force planet x distance planet = G force counter-weight x distance weight.

As the gravity force applies to both your planets as well as your counter-balance you can simplify the calculation by neglecting the g-factor (9,81 m / s^2). Note how you could calculate the G-force from the weight by Newtons law: G-force = mass x g-factor, i.e. 1 kg experiences a gravity force of 9,81 m / s^2 which is close to 10 Newton. You can read up on the details at wikipedia, http://en.wikipedia.org/wiki/Kilogram#Nature_of_mass

Or simply use the following rule of thumb:

mass counter-weight = mass planet x (distance planet / distance weight)

Cheers,

isnoDIZ

love your mom

As for your question about the counterweights, each planet and counterweight section is basically a lever with the fulcrum being the rotating blocks. The rough calculation would be balancing a ratio of the weight of each side to the distance from the fulcrum on the horizontal plane.

The weight of planet and support over the distance from the center of the pivot out to the elbow would equal 'x' over the distance from the pivot to the center of the counter weight, where 'x' is the wood block and support plus the weight you would need to add to make it balance. This wouldn't be exact without finding the real center of mass for each side, but I think it would be close enough.