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E, Freestyle Version 2: Stronger 5^th Planet Arm

20071217

I rebuilt the arm for the 5^th planet to be much more sturdy. This entailed re-doing the drive train for the 5^th planet's moons yet again. I also decided to replace the copper wire and flex tubes with rigid parts — however, it uses one essential part, 4442, that LEGO hasn't made for over 10 years:

E. Reworked 5^th Planet

Stacked Turntables

20071218

I took a break from the main effort to research a method of driving between 3 and 5 stacked turntables from geartrains located below the bottom-most one. This picture and video explain:

Stacked Turntable Drive

I will be exploring the capabilities of this idea later; it should allow orreries of 6 or 7 planets, all with moons and each orbiting at an arbitrary rate.

Constrained 5-Planet Designs

20071220

After getting E to work well I decided to try to make my work more useful to others, and better suited to the Kepler group's purpose (a classroom demonstration: motor-driven, built from readily available parts, with a fixed budget, etc.).

That meant re-designing the orrery from current LEGO sets, preferably at the lowest possible cost. I ended up choosing Off-Road Truck (set 8273) and Motor Box (set 8287). The truck supplies the turntable and the structural elements; Motor Box has a lot of gears, the differential housing, pieces 6542 and 6539, and of course a motor; all of these are essential parts for meeting my goals.

After building the truck to ensure all the pieces were in the box (-: I quickly rebuilt it into model F shown here:

F. First Orrery I Built from 8273 and 8287

The tires are being used as non-slip rubber feet, and another wheel is being used to represent the sun.

This model uses a different technique to add a 5^th planet. Rather than adding the new planet outside (and below) the 4^th as was done in models C, D and E, this version adds a planet between the 1^st and 2^nd. This is done by adding an open-center z16 gear (part 6542) just above the 2^nd planet arm and making that arm turn it.

The more challenging part of this was to get the z16 gear to turn an arm to which a planet can be attached. It was done through the bizarre (yet legal to LEGO-purists) method shown here:

Attaching an Arm to part 6542

20071222

After getting the basic 5-planet motion working, I began to add moons and other refinements. I call this version G:

G. Interim Version with Some Moons

This version incorporates the following improvements:

• 5^th planet has 2 moons.

• Base contains motor and battery pack.

• A lever is flipped up or down to engage or disengage the motor.

• Everything you would want to touch (on/off switch, motor disengage, hand crank, and battery release) is red.

• With movement of one pin, battery pack folds out allowing access to its second battery cover.

• Crank can be installed on either side of the base, permitting right- or left-handed operation

• Motor and gears in the base are "hidden" using plates and other similar parts.

G's 5^th Planet and Moons

planet #	velocity	period
1	1.0000	1
2	121/147 ~= 0.8231	147 / 121
3	67/147 ~= 0.4558	147 / 67
4	1/3 ~= 0.3333	3
5	1/4 = 0.2500	4

Attaching a Planet and Moons to the Differential

20071226

With the switch to set 8273 it was necessary to find a new, secure way to attach an arm to the differential because part 3709 is not in that set. While I was doing this, I decided to also accomplish the secondary goal of being able to give the planet (the 4^th planet, in versions F and G) one or more moons. Quite a bit of time was spent exploring options. Here are 4 of them:

4 arm designs

The first one (on the left) is used in all the Ayres/Koch designs, and my versions C, D and E. It is quite secure but relies on part 3709 and does not allow the relative motion of the central shaft to be extracted for driving moons.

The two you see in the center are similar to the one actually used in F and G. They allow the central shaft motion to be extracted, but only in a rudimentary way. There is no provision for counterbalancing, and extending the arm and its gears would be difficult.

The design on the right can be made entirely from the parts in sets 8273 and 8287 that remain after model G has been built. It sends the motion via a radial shaft with bevel and crown gears, has easy attachment points for counterweights, and leaves enough clearance for both of the gears on the differential housing to mesh with the planet arms above and below.

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