Instructables
Hello fellow space-lovers!  Firstly, a little background.  An orrery is a mechanical model of the solar systems built to show the relative positions and motions of the planets.  A grand orrery incorporates all of the planets known at the time of its making (traditional orreries stop at Saturn).  The funny name comes from the Charles Boyle, the 4th Earl of Orrery, who I suppose probably liked this sort of thing.

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!
 
Remove these adsRemove these ads by Signing Up

Step 1: Calculations

For those who do not care about scale calculations, move on to the next step.  Nerds, stay with me.  

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.  

rimar20003 years ago
Very good work! Congratulations.

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!!
Bill WW rimar20009 months ago

lo suficientemente cerca de coaxial para Instructables.

Tal vez una idea para nuestro próximo proyecto

rimar2000 Bill WW9 months ago

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.

action pig (author)  rimar20003 years ago
Thank you! I have actually thought a lot about this. One possible design included putting two planets on one axis, then putting a vertical bar through the center of mass of the axis. The problem is, once you get past Jupiter the planets are rotating around Jupiter's center of mass, and not the sun's.

If you have any ideas, let me know!
Bill WW9 months ago

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

I see you included Pluto.

This is amazing. I want one!
isnodiy3 years ago
BTW, is this last picture in preparison for 2013 when all the planets align ? J
action pig (author)  isnodiy3 years ago
Well, you know, gotta get ready :) Thanks for the info on calculating the balance!
isnodiy3 years ago
Oh well reading your comment I neglected the weight of the bars in the above calculation. Well that is for some more math. Anyone around who wants to do the calculation with infinitesmals ?
isnodiy3 years ago
This is really beautiful, I wanted to do this as a webpage for years just to wrap my head around the distances and relations of the planetary system. But being a passioned hobby-carpenter I will definitely reconsider your design.

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
onrust3 years ago
I dig the use of the PEX 90's.
action pig (author)  onrust3 years ago
hey, thanks! I didn't even know that is what they were called :)
Well, I'm on the west coast. I've heard lots of different names...... and EVERYBODY IS A PLUMBER! I would not be surprised if there is not a correction by the time I hit the post button. REGARDLESS, great instructable, awesome use of material,..... and you did a smooth job bending your tubing.
anderlis3 years ago
I'm so proud of you!!

love your mom
action pig (author)  anderlis3 years ago
love you too, mom :)
juanjinjo3 years ago
Que bueno esta tu post, muy ilustrativo, me gusta asi podre tener un idea de como hacer uno para mis hijos.
action pig (author)  juanjinjo3 years ago
¡buena suerte!
depotdevoid3 years ago
That's absolutely beautiful, you've got my vote!
action pig (author)  depotdevoid3 years ago
Thank you so much! I enjoyed your 'ible (and needed it also :) Good luck! You got my vote too!
siamonsez3 years ago
Amazing, very detailed ible and ambitious project. I bet it looks even better in person. Nice detail on the planets.
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.
action pig (author)  siamonsez3 years ago
So helpful! Thank you very much. It is certainly an improvement over the trial and error approach :)
ChrysN3 years ago
Wow, that looks amazing, nicely done!
mikeasaurus3 years ago
awesome!
fretted3 years ago
This rocks now i can put my wood lathe to good use
foobear3 years ago
completely awesome. your idea to use a lamp for the sun is still a good one