All the gears are in gears.scad.  I made a brief effort to determine what
exactly a "planetary gear" set is, and didn't achieve enlightenment.  It
does appear that they usually (?) include a ring gear around the outside,
though, and that type of gear doesn't appear in gears.scad.  You can post
an issue on the github requesting support for such gears.

On Sat, Jun 17, 2023 at 11:19 AM jon jon@jonbondy.com wrote:

It might be possible to create the ring by difference()ing a normal gear
from a slightly bigger cylinder but I haven't tried so don't know how well
it would work

-Daniel

On 17 June 2023 16:50:14 IST, Adrian Mariano avm4@cornell.edu wrote:

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On Jun 17, 2023, at 9:19 AM, Adrian Mariano avm4@cornell.edu wrote:

That seems unlikely to work well. The gear needs to have properly shaped teeth to mesh with the teeth of the other gear and allow the teeth to rotate past each other.  It seems like differencing away a different gear won't leave the right tooth form.

On Sat, Jun 17, 2023 at 12:06 PM Daniel <daniel@puggsy.net mailto:daniel@puggsy.net> wrote:

Actually, BOSL2's spur_gear() module already lets you make
interior-toothed ring gears.  You just need to set interior=true and
difference it from a larger diameter cylinder.

Here's code for a full animatable planetary gear assembly:

 include <BOSL2/std.scad>
 include <BOSL2/gears.scad>

 $fa=1; $fs=1;
 rteeth=56; pteeth=16; cteeth=24;
 pitch=5; thick=10; pa=20;
 prad = 31.8;

 cp_ratio = cteeth / pteeth;
 pr_ratio = pteeth / rteeth;
 rdiam = outer_radius(pitch,rteeth,interior=true) + 5;
 diff()
 cyl(r=rdiam,l=thick)
     tag("remove")
         spur_gear(
             pitch=pitch, teeth=rteeth, thickness=thick+1,
             pressure_angle=pa, interior=true);

 for (a=[0:3]) {
     zrot($t*90+a*90) back(prad) {
         color("green")
         spur_gear(
             pitch=pitch, teeth=pteeth,
             thickness=thick,
             shaft_diam=5,
             pressure_angle=pa,
 spin=-$t*90*rteeth/pteeth);
     }
 }

 color("orange")
 zrot($t*90*rteeth/cteeth+$t*90+180/cteeth)
 spur_gear(
     pitch=pitch, teeth=cteeth,
     thickness=thick,
     shaft_diam=5,
     pressure_angle=pa);

Screenshot 2023-06-17 at 9.03.41 PM.png

• Revar

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Actually, BOSL2's spur_gear() module already lets you make
interior-toothed ring gears.  You just need to set interior=true and
difference it from a larger diameter cylinder.

Here's code for a full animatable planetary gear assembly:

 include <BOSL2/std.scad>
 include <BOSL2/gears.scad>

 $fa=1; $fs=1;
 rteeth=56; pteeth=16; cteeth=24;
 pitch=5; thick=10; pa=20;
 prad = 31.8;

 cp_ratio = cteeth / pteeth;
 pr_ratio = pteeth / rteeth;
 rdiam = outer_radius(pitch,rteeth,interior=true) + 5;
 diff()
 cyl(r=rdiam,l=thick)
     tag("remove")
         spur_gear(
             pitch=pitch, teeth=rteeth, thickness=thick+1,
             pressure_angle=pa, interior=true);

 for (a=[0:3]) {
     zrot($t*90+a*90) back(prad) {
         color("green")
         spur_gear(
             pitch=pitch, teeth=pteeth,
             thickness=thick,
             shaft_diam=5,
             pressure_angle=pa,
 spin=-$t*90*rteeth/pteeth);
     }
 }

 color("orange")
 zrot($t*90*rteeth/cteeth+$t*90+180/cteeth)
 spur_gear(
     pitch=pitch, teeth=cteeth,
     thickness=thick,
     shaft_diam=5,
     pressure_angle=pa);

Screenshot 2023-06-17 at 9.03.41 PM.png

• Revar

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On Jun 18, 2023, at 7:19 AM, jon jon@jonbondy.com wrote:

Revar:

prad of 31.8 seems suspiciously specific.  Is there some magic for creating that number so that things work properly?

Thank you!

Jon

On 6/18/2023 12:05 AM, Revar Desmera wrote: