GearHeads Corner

Hi,

I'm a total newbie to gearotic (purchased yesterday), and I'm trying to make a basic simulation of a sort of harmonic drive: https://en.wikipedia.org/wiki/Harmonic_drive. A 3d printable example is here: http://www.projectbiped.com/projects/harmonic-drive

I've created an non-circular/elliptical inner gear (order 2) and an outer circular planetary gear, but when I try to add the outer circular gear to the elliptical one it says "Differing Basic Types". I'm assuming that this means you can't have a circular gear mesh with a non-circular gear; is that right? Is there another way to do what I am trying to achieve?

Thanks,
Jeremy

Hi Jeremy:

  Yes, ellipticals cannot fit on a normal involute. In your example, notice the elliptical shape is not a gear, but is distorting as it gets revolved
much like a belt. Usually, a harmonic is made with gears that dont distort. but that requires an offset shaft center..

Use the cage gear screen for harmonics instead.. you can also stage them together for very high ratios..

  Select 14 teeth for the wheel, 13 for the pinion. Select "planetary" for the wheel and turn off spokes.

Simulate, and youll see the outer ring moves one tooth less than the pinion for each rotation of the primary.. Such levels are
stacked with offset shafts on each stage to make multi stage gears with very high ratios. ( look up this page
to get an idea of how that kind of ratioing works..

https://www.youtube.com/watch?v=ie2wwAnKDM0

  You have to watch that awhile to picture how its working. The back shaft is attached to a disk with 5 shafts in holes on
the wheel..  Gearotic can design the wheels and pinions as above, but youd have to do the shafts and disks to fit them
if you wish to stack them up.

It gives you the idea of how the hypcycloidic reducers work. The harmonic your attempting can only be done with
a belt that can be distorted in shape during rotation I think.

Art

Hi Art,

Yes it looks like you are correct. Sorry, I'm a bit of a gear newbie  ;)

In case anyone else finds this, here is a video which explains the principle: https://m.youtube.com/watch?v=nj1vO3cP7ug

No problem, common question.
A module for designing them is on the wishlist, (along with a million or so other wishes.. :) )

Art

I would love to see that!