Gearing Ideas and Notes at MROB

Gearing Ideas and Notes

This page discusses some ideas related to gearing mechanisms that came out of my other projects (primarily the orreries) but are only remotely or tangentially related (no pun intended) to them.

Hailfire Droid Wheel as Ring Gear

The large wheel in the picture was only ever used in one set, 4481. It is a ring gear with 168 teeth racing inward. This is exactly three times the 56 teeth on the outside of the Technic Turntable (part 48452cx1), which means you can just fit three across inside the ring. I looked for another way to construct a concentric planetary gear mechanism, and here is the result:

Dual Concentric Planetary Gear Arrangement using Hailfire Droid Wheel

The turntable in the center serves as the sun gear; the z36 and z40 gears are the planets (the planet carrier is hidden below the gears) and the Hailfire Droid wheel is the ring gear.

All pairs that should be meshed are just right, except two: the red gear is just a little bit shy of the outer ring, and the two black ones (the inner one being the turntable) are not meshing with each other at all. The rest move really well and really smoothly. Since 4 out of 5 is all it takes to keep the assembly centered and stable, the construction works as intended.

The z36 and z40 gears are all held together by a symmetrical arrangement of parts 6629 and 32009:

detail
detail

Inside the turntable is a normal planetary gear setup — here the sun and planet are yellow and blue z8's, and the turntable serves as ring gear.

Inside-Out Differential

Here is a way to construct a differential without a differential housing:

Normal and Inside-Out Differentials

In a normal differential (shown on the left) the rotation of the housing (dark gray) is the average of the rotations of the two gray axles. As used in a vehicle, the drive goes into the housing, and the wheels are driven by the two axles.

In the alternate differential (on the right) the two gray axles are connected (so they are the same axle), and the two pairs of dark grey gears move independently of the axle. The motion of the central axle is the average of the rotations of the two pairs of dark gears. In the vehicle application, the drive power would go into the central axle, and each wheel would be driven by one of the dark gray gears.

The little tiny teeth on the dark gray gears (not present on the differential housing) allowed me to make this somewhat whimsical orrery depicting a single planet with a moon, orbiting a triple star system:

Orrery Based on the Inside-Out Differential

Here is what it looked like after I added a stand:

Complete Version

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This means that you are free to copy and reuse any of this work (noncommercially) as long as you tell people where it is from.

That is, you don't need my permission to post these ideas on your website, just mention that (some or all) of the ideas came from here, and include a clear and obvious link back to this page. You're also welcome to use my ideas in not-for-profit publications, curricula for seminars, and other educational activities (all with appropriate attribution). If you want to use them in a commercial activity or event, or if you're not sure whether your use is noncommercial, feel free to contact me ("Email the author" link above) and ask.

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