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ORRERY Link back to the MSF Google docs page
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| (1) This shows the Northern section of the Railyard. The water tower is in the lower left, downtown to the right. We are not in the dirt lot just behind Sky Coffee, but in the next triangle, enlarged here: | 
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| (2) This is a park with fine gravel. The green dots indicate trees, which limit what we can do. The red circle shows our spot. The largest trunk-to-trunk circle you can make there is about 27-F¢ in diameter. These are young trees, and the tips of the lowest branches are are about 7¢ off the ground. The biggest circle that clears the branches is about 15¢ diameter. We can probably do a little trimming, but not much.-A As indicated, there is a power panel, with a double 110V outlet on the outside. No water. There will be two other installations in the rest of the triangle, and there will be fancy lights all around. | 
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| (3) We need a number of concentric axels/tubes. Our objects will be heavy, so we probably need good bearings. You can use ball bearings, but these get big fast as you nest 1,2,3... tubes. | 
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| (4) Instead, use lazy-susan bearings between stacked plates. Each unit consists of a plate, a tube and a lazy susan bearing. These are easier to construct and (dis)assemble. | 
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| (5) A traditional orrery has horizontal arms, with the planets on vertical posts. We could have arms above, with planets suspended, perhaps at eye level. I also drew some counterweight, which reduces the friction between pipes, and makes the orrery more balanced and stable. | 
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(6)Standard black pipe size OD wall ID ---------------------------- 0.125 0.405 .068 0.269 0.250 0.540 .088 0.364 0.375 0.675 .091 0.493 A 0.500 0.840 .109 0.622 0.750 1.050 .113 0.824 B 1.000 1.315 .133 1.049 1.250 1.660 .140 1.388 C 1.500 1.900 .145 1.610 2.000 2.375 .154 2.067 D 2.500 2.875 .203 2.469 E 3.000 3.500 .216 3.068 F 3.500 4.000 .226 3.548 G 4.000 4.500 .237 4.026 H ---------------------------- ID = OD-2*wallPipes A-H can be nested. A is probably the minimum diameter we would use. On 4 May, I found A (at Ace), B and C at Peter's nextdoor, and D at Helmut's further down the street.
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| (7) 5 May: Justin welded up the first unit. Not visible is a hole in the plate so that we can pass a power cord up the central tube. | 
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| (8) Next things to do:
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| (9) Drill and tap 1/4-20 holes and mount a lazy susan bearing to the bottom of the plate.
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| (10) The protruding bolt stubs are then used to mount the pulley disks
A narrow ring (laser cut by Stefan out of scrap ply) centers the lazy
susan bearing of the next higher unit.
On top, the tubes are centered by 3D-printed bushings (printed by Stefan). You can also see the powe cord (for the 'sun') sticking out the top.
(19 May 2018) | 
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| (11) Gearing and delays:
Kepler's 2nd law states the the orbital period scales as the 3/2 power
of the orbit's radius. So if we make orbits that are roughly equally
spaced, by how much need they be delayed relative to each other?
ratio to
radius period previous period
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1 1.00
2 2.83 2.8
3 5.20 1.8
4 8.00 1.5
5 11.18 1.4
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This shows that the relative gearing down is quite moderate.
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| (12) The gearbox uses 5/16 threaded rod, which fits the ID of skateboard bearings, which in turn happen to fit inside 3/4" copper unions.
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| (13) Move them! I used the concept on top, but without the motor. | 
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| (14) These are 3 pairs of pulleys (see previous sketch). The 3 different heights correspond to the heights of the 3 horizontal disks (see section (10) above. The pairs are placed at slight angles, pointing to the sides of the big horizontal pulleys. | 
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| (15) Temporary assembly: The pulleys are angled to send and receive the cords from the big disks, and send them up to the gear box. 25 May 2018 I devised a simple way to keep the ropes tensioned: I attach a (paperclip)- wire loop to each end of the rope, and hook a bundle of 5 rubber bands.
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| (16) To make the whole thing go, I wanted bike pedals, which would be operated by hand; I found this Barbie bike at the thrift shop. It got all chopped up - sorry Barbie. What's left of the bike gets mounted such that the pedals are at waist level, and the mount is tipped forward at 15°, so you don't step on the support platform. I also plan to have a low box at hand to children can work the crank also. (29 May)
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| (17) The crank assembly, the gear box and the pulleys put together.
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| (18) The supporting arms for the three planets need to clear the Sun, as well as the first planet. Not a lot of space. I bought some metal conduit, and borrowed a bending tool from Rene down the road, and bent the three arms.
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| (19) Each arm is held be a pair of plates (Peter cut these on the plasma cutter), the plates are joined by a pair of strips that are tack-welded to hold the plates at a fixed distance. |
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| (20) Slaton made 2 planets, the 'cloud planet' and one that has skyscraper cities on it that are made of electronic components.
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| (21) Cecilia thought the Sun looked too much like a paper lamp, so she added flaming sunspots. Much better! Planets:
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| (22) In the Railyard, for the first day of the Interplanetary Festival, with Ginger for scale. The orrery was a success! After dark on the evening of the first day, we had a lot of traffic from people going to the Ozomatli concert. In the dark, the device takes on a different aspect, with the LED lights in the planets and all. Also, Artemy mounted a handheld projector which projected a moving image of a planet onto the ground. On Friday, we moved to the other side of the Farmer's market, across the street from Site - a much better spot, and we decided to stay till 23:00, since Currents opened at 19:00, and we decided to stay around and have the Currents crowd have a look and a crank also.
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(23)
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| (24) In addition to the Sun and 3 planets of this structure, two more planets would be supported from below, placed on rings which rotate much like planetary gears. Justin, Stefan and Zane worked on these - they got cut on the big ShopBot. Turns out, these work, but need a lot more power than can be provided by the string-and-rubber-band system. However, they looked real cool so we mounted them anyway, and they got pushed around by hand. The outer ring supported Katrina's planet. |
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A few technical details: | ||
| (25) I made use of some coincidences which saved a lot of time an effort: Skateboard bearings happen to fit nicely onto 5/16" threaded rods, and in turn fit nicely inside 3/4" copper pipe unions. The pulleys and the sprocket wheels are then fit onto the copper unions. |
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| (26) Another lucky coincidence had to do with the supporting arms. The first section was made out of (electrical) conduit (see (18) above). However, this was too heavy to reach out a further 5 or so feet. I made these extensions out of 1/2" CPVC (water) pipe, which - with a little scraping - fits tightly inside the conduit. Initially, the longest arm sagged too much, but a section of 7/16" dowel was slipped inside the plastic tube and provided enough stiffness. I did have to route a small channel into the dowel for the wires to fit through. |
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| (27) The ropes that ran from the gearbox via the pulleys to the central post were regular clothesline rope. To keep these under tension, I bent a piece of paperclip into a V, and then bent a few mm of the ends 90° so that these bit into the rope. I tightly wrapped this with (kite) string. Now I could attach these to loops that held a bundle of 5 rubber bands. |
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| (28) The rubber bands did not hold up well outside in the heat and sunshine, and a few of the attachments failed over the course of two days of use (they pulled out of the rope ends), so here is plan B: Starting with 5/32" Aluminum tube and a small file, file away until you have a piece as shown. This folds over the rope end, and the teeth can be pushed into the rope. Then it is wrapped with string and a bit of wood glue. Then instead of the rubber bands I use a spring. Looks better.
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| (29) After the festival, the orrery came back to Make, where there really was no way to store it. Fortunately, the Santa Fe Children's Museum had shown interest. I reworked some parts so that the device could be collapsed into managable pieces. All this fits into a Subaru Outback stationwagon (no passengers)! The orrery will now live at the Children's museum, where the plan is to bring it out several times a year. First showing: weekend of 7 July 2018. |
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| (30) I thought about the power distribution some more. For Interplanetary, we just had separate battery packs strapped to each of the rotating arms. However, it would be much more convenient to have a single power supply at the bottom, and send the power up to the moving parts. I think we can have sliding contacts in between each of the bottom disks: two sheet copper rings, about 0.5" wide, glued to the wodden surface of each unit, with sliding contacts on the bottom of the disks, where the lazy susan bearing is. The rings need to fit inside the lazy susan opening (~6.3") and the biggest pipe (2.375"). (27 June 2018) |
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| Since the first show at the June 2018 Interplanetary Fest, the orrery has ben set up several times:
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Hubert van Hecke Last modified Dec 2022