This post is about “planetary gears;” here is a photo of a real planetary gear set:
The center gear is called the “sun” gear; the surrounding gears are called “planets” or “idlers.” The outer gear is called the “annular” gear. (Nomenclature varies.)
From the point of view of the arithmetic, the outer gear (with the teeth inside) acts just like a large ordinary gear. As we learned before, the trick for laying out gears that mesh is to keep the ratio of the number of teeth to the diameter the same (and not a fraction) for all the gears. Here’s a combination that will work:
Here are the numbers for this combination including the relative rotations:
As I did in the first post, I added radial lines (corresponding to tooth positions) and an inner and outer circle to each gear layout:
Then I experimented with the tooth size and shape until I found a version that did not create too much interference where the gears mesh:
By the way, these “gears” don’t work in reality since there is some (unnoticeable, one hopes) interference and/or gaps where the gears mesh. Real gear teeth have a special curved shape so that the teeth “roll” against each other smoothly.
Again, I used the techniques in the first post to add the teeth to the gears. Briefly, for the gears with an even number of teeth I grouped a pair of opposite teeth together and duplicated and rotated the group around the gear layout. Use Drawing Guides and the Format Object/Size pane to center and rotate the tooth pairs. For the gear with an odd number of teeth, I temporarily added a line (in red) to a tooth to help with positioning:
To complete the inner gears, I deleted the layout lines leaving only the teeth and the smallest circle; then for each gear, I used Merge Shapes/Union to combine the teeth and circle into a single object:
For the annular (outer) gear, I merged the inward-facing teeth with a Donut shape:
Finally, position the planet gears at 60° intervals and add the simultaneous Spin animations: use the rotation numbers above and a common duration (10 seconds in this example). Voila!
It is worth noting that some people complain that PowerPoint animation can create dizziness or nausea in the audience – not a desirable effect. This may in fact be true for this example; you have been warned.
Undaunted, the brave folks over at Acme Services created this rather extravagant version to support their position that “Acme drives the universe!”
Well, here are some notes:
- The sun gear contains the Acme logo; the planet gears represent Acme’s experience areas (manufacturing, finance, etc.). The universe is represented by the star field.
- A larger Donut shape was merged with the outer gear (so that it fills the slide) and a star field photo was used to Fill the gear.
- If you use Fill/Picture for the other gears (the logo and icons), you will find that the result is rotated. This is because the gears have been rotated during construction and the Fill process remembers the rotation. Merging the logo and icon pictures with the gear shape retains the desired orientation. (See this post for more on this “cookie cutter” method.) Here’s a diagram showing the difference:
- Actually, the star field was rotated but it doesn’t matter.
- Using the Merge technique loses the animation; once the gears have been positioned, you can use the Animation Painter referring to the “plain” version to restore the animations.
As usual, if you want a free PowerPoint file containing these projects, use the form below: