Planetary gear mates

stu_croysdale

Hi there.
I have been playing with the onshape app on iPad,  I've been modelling up a planetary gear (just for fun) but I'm struggling to get the gear mates to mesh or run correctly. I'm wondering if there is something I am missing. 
Any tips very welcome. 
Many thanks 

florian

Hi Stu,
I guess we need a bit more information. Can you share the doc or post some pictures of the setup? I guess you will need to

1. Create revolute mates for the parts that are turning
2. Then constrain the revolutions with a gear constraint

You will need some math for the ratios as there is no "no-slip tangent rolling mate". Depends whether you want optics (constrain what is necessary) or mechanical simulation (needs mates for all the parts).

bradley_sauln

On top of what @florian said, if the gears are not meshing after you've set the gear constraint. Go back and edit the revolute mates and rotate the secondary axis, this should be enough to get the right alignment for meshing. Let me know if this doesn't work.

jakeramsley

Here is a planetary gear system that our intern Ethan Rejto did that I made a copy of/modified a bit.  It is a good example of how to mate together a planetary system.

https://cad.onshape.com/documents/578650ece4b02dc672b6313e/w/ce0a528bc931fb830cc89f7a/e/7ae73e028d75c0aaa7b99358

ethan

They are tricky. It all comes down to teeth number when getting it to mesh correctly. Follow these governing equations. And remember that the ratio you are calculating is the ratio of the input "the sun gear", to the output "the carrier". So set a gear ratio between the sun gear to the carrier. Follow these general equations.

Situation:

Ring Gear Stationary

Sun Gear Input

Carrier Output

---

Variables:

R = Number of Teeth on the Ring Gear

P = Number of Teeth on the Planet Gears

S = Number of Teeth on the Sun Gear

---

Governing Equations:

R = 2P + S

(R + S) / # of Planets = Even Number

Ratio = S/(R + S)

ethan

This might help you also, https://www.onshape.com/cad-blog/tech-tip-assembling-gears

florian

Hi Stu,
I guess we need a bit more information. Can you share the doc or post some pictures of the setup? I guess you will need to

1. Create revolute mates for the parts that are turning
2. Then constrain the revolutions with a gear constraint

You will need some math for the ratios as there is no "no-slip tangent rolling mate". Depends whether you want optics (constrain what is necessary) or mechanical simulation (needs mates for all the parts).

bradley_sauln

On top of what @florian said, if the gears are not meshing after you've set the gear constraint. Go back and edit the revolute mates and rotate the secondary axis, this should be enough to get the right alignment for meshing. Let me know if this doesn't work.

stu_croysdale

Hi guys. 
Thanks very much for your comments.
@florian I'd got as far as setting all  the mates and gear constraints but I think because I've already set mates for the sun and planet gears, trying to set a second mate with the planet gears to the ring gear is causing issues ???  I've tried to cheat it by making a gear constraint with the sun and ring gears  (only because I thought it might be easier) but of course it still means applying two constraints to one gear. 
@bradley_sauln , top tip about editing the revolute mates, I didn't know you could do that. I will let you know if this works for the meshing issue. 
I will share the doc when I'm next working on it. I think my main problem is understanding if its possible to make planetary gears in onshape and if my theory of applying two mates to one gear is an issue. 
Much apreciated 
stu

jakeramsley

Here is a planetary gear system that our intern Ethan Rejto did that I made a copy of/modified a bit.  It is a good example of how to mate together a planetary system.

https://cad.onshape.com/documents/578650ece4b02dc672b6313e/w/ce0a528bc931fb830cc89f7a/e/7ae73e028d75c0aaa7b99358

ethan

They are tricky. It all comes down to teeth number when getting it to mesh correctly. Follow these governing equations. And remember that the ratio you are calculating is the ratio of the input "the sun gear", to the output "the carrier". So set a gear ratio between the sun gear to the carrier. Follow these general equations.

Situation:

Ring Gear Stationary

Sun Gear Input

Carrier Output

---

Variables:

R = Number of Teeth on the Ring Gear

P = Number of Teeth on the Planet Gears

S = Number of Teeth on the Sun Gear

---

Governing Equations:

R = 2P + S

(R + S) / # of Planets = Even Number

Ratio = S/(R + S)

ethan

This might help you also, https://www.onshape.com/cad-blog/tech-tip-assembling-gears

stu_croysdale

This is brilliant ! Many thanks @jakeramsley for the model, very helpfull. Every thing I could possibly need is right there for me.
And @ethan, you spotted my error straight away. I had totally overlooked the fact that I should be creating the final gear ratio from the input to the out put. That is exactly where I've been going wrong. This is my first real go with any 3D CAD software and I guess a planetary gear set was a bit ambitious but it's prooved to be a great learning exersise so thanks again every body.
Best wishes
Stu