Meshing gears are a useful metaphor for an activity or a process and can be used as an icon for thought, intelligence or expertise. Rather than search for gears clip art, you can create gears as PowerPoint objects and animate them for more impact. (Why bother? See this post.)
If you want a copy of the PowerPoint files associated with this post, use the form at the end of this post.
This video demonstrates some gear “physics:”
It’s pretty easy to generalize the relationship between diameters, number of teeth and number of rotations, but if you’re intimidated by the algebra, here are some combinations that will work:
Note added 8/2014: A reader sent me a gear animation with 8 (!) meshed gears that he used as part of a video introduction to his theater’s production of “Willie Wonka.” Kudos!
Drawing the Gears
Next, we’ll build the gears shown in the video. The design of real gear teeth is complicated and since we aren’t limited by reality, we’ll eyeball the tooth shape and size. Here’s the first step in adding the teeth; the blue lines are the center lines for the teeth:
Add some additional layout lines:
The outer circles (red) are 1/4 in larger than the original wheels; the inner Doughnut shapes are 1/4 in smaller (these dimensions are fairly arbitrary). Also, the small gear-to-be has been rotated half a tooth.
Now, create a Trapezoid shape, rotate and size it, and position it on the larger gear as shown below. Rotate and position two duplicates of the shape on the smaller gear:
The teeth are centered on the blue index lines and are positioned flush with the outer circle and extend into the inner shape. The tooth shape and size is adjusted so that there is space between them for the meshing teeth (but not too much space). Don’t obsess with this; it doesn’t need to be perfect to look OK in the final result.
Next, duplicate the tooth on the large gear and rotate/position it on the opposite side of the gear. Group the two opposite teeth together:
Now, copy, rotate and position this group at the appropriate locations on the gears. Repeat the process for the small gear. Use guidelines and the default Rotates and Flips to make this easier:
Now, delete the layout lines, group the gear parts and apply outline and fill colors:
The smaller gear can be moved to engage the larger gear at a different point:
You can create a three-gear train using the parameters in the table above:
Variations are possible; these use “3D” format and gradient fills:
And, you can apply “3D” rotation:
PLEASE NOTE: there are issues with animating these variations – see below.
You can combine the gears with other shapes; here’s my favorite icon for “expertise:”
Animating the Gears
Apply animation as shown below (click on picture to enlarge):
The Spin animation is applied to both gears. The larger gear rotates 360 degrees (1 rotation) clockwise. I have selected Very Slow (5 sec duration); slower speeds seem to look better. The smaller gear rotates With the larger gear – 720 degrees (2 rotations) in the counterclockwise direction at the same speed.
This video shows the result and includes a 3-gear animation based on the table (the smallest gear rotates once at a Very Slow speed):
To rotate the gears continually, apply the Repeat Until Click or Repeat Until Next Slide option (in the Effect Options pane). There are some problems with this – see below.
Spinning gears with gradient fills or “3D” effects are not, strictly speaking, realistic since the shadows and highlights spin with the gears. And, clearing the Rotate with Shape option doesn’t help (a different kind of rotation). You can ignore this particular nit with little danger. On the other hand, spinning an object with “3D” Rotation might make you ill; this video demonstrates these issues:
I suggested above that you can use the animation Repeat option to continue an animation. Unfortunately, this option resets the spinning object’s position each time it repeats. For some simple gears, this is not a problem. For gears with asymmetric features, this restart will be noticeable; this video demonstrates:
You can work around these problems by using simpler symmetric gears or by increasing the number of rotations for each gear (preserving the ratios) until each gear rotates one or more full rotations. By the way, the Smooth Start/End options will cause a problem here.
NOTE: This later post includes some additional gear effects.
As usual, if you want a free copy of the PowerPoint files associated with this post, use this form: