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| Strain Wave Gear |
Marc sent me a video about Harmonic Drives this morning. Okay, cool, I've seen these before, but wait a minute, how can that inner gear be rotating when there are teeth engaged at both the top and bottom? Turns out there are two kinds of these gear systems. The first is the Harmonic Drive.
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| Harmonic Drive Also known as Strain Wave Gearing |
The inner gear on a Harmonic Drive (the red one in the GIF above) is flexible. You can tell that it is rotating by focusing on one of the red teeth. You will see that each time one of the lobes of the green cam comes by, the red tooth steps from one blue tooth to the next.
That's fine and dandy, but a flexible gear? I was pretty sure there was a Harmonic Drive that used regular, made of steel, rigid gears. There is, but it's called a Cycloidal Drive.
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| Cycloidal Drive |
In this one, the purple output shaft is connected to a disk with a bunch of pins that transmit the force from the yellow rotating gear. You could just hook the yellow gear to the output shaft, but then you are going to get some wobble. You could handle that using a pair of U-joints on either the input or output shaft. Probably the input, less torque there.
3 comments:
I ran across the Harmonic Drive in telescope mounts used in astrophotography. Large gear reduction with little back lash.
In the animation it's easy to see it works because the red ring is flexible, but looking at the lead photograph everything looks solid. Obviously it must work or they couldn't sell them but I wonder if there is a flexible ring inside the hard sides?
Helluva torque multiplication
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