How to calculate inner/ring gear profile and matching helical pitch

david_fisher031

I am trying to create something like this http://tim.cexx.org/?p=1282 It is a gear driven 3D printed peristaltic pump using helical gears.

How do I design the profile of the ring gears. In the Planetary Gear Set Simple how was the profile of the ring gears teeth arrived at (sketch 3)? The tooth from this sketch is then extruded and transformed. The transformation used is xyz, it is transformed in the z axis as well as the x axis. Shouldn't a transformation have been to rotate it around the gears axis instead of just the x axis for xy transformation ?

How do I match the helix of the planet gears with that of the ring gear ?

many thanks

daniel_splawski

I've only worked with double helical (herringbone) gears in OpenSCAD.  In that program the process for making these gears is to take a normal gear in two dimensions and move it slightly in the z direction and then rotate it slightly and perform a loft.  Depending on the thickness of the gear you may have to do this several times to achieve a smooth surface.  The double helical gear is simply the single helical mirrored.  The ring gear in OpenSCAD is created using a similar method, but by the time I figured out how the normal gear worked I just gave up and used the pre-built module.  

Unless someone has developed a feature script to create helical gears in Onshape, I would suggest installing OpenSCAD and generating the gear with that program and just importing it into Onshape.  It's cheating, but you'll save a ton of time.  

david_fisher031

There is a much easier way in onshape using a helix and a sweep. Take a look at this example https://cad.onshape.com/documents/53082dd4775c4696a9a20c57/w/49204547641d44a88924e24a/e/33b2b54e12f04155a7d5f148

What I would still like to know is how to work out the profile of the ring gear.

daniel_splawski

That a vastly superior method.