This touches on why the gearset doesn’t work, but isn’t true. Right now, disregarding friction and if you have the correct gears dead, the carrier is completely independent from the suns. Imagine holding both suns still, you’ll be able to roll the planetaries without fighting an input, and if the planetary is an output to find the gear ratio you have to divide by 0.
Now, there are two ways to solve this:
- Make the gear ratio between the suns negative, as weilin said.
- Keep the gear ratio ratio positive, but with a magnitude different than 1.
For your application (a variable mechanical advantage drive), you’ll want to have magnitude different than 1 regardless (which you can do with a negative ratio as well), or have a different input rpms. Otherwise one of your full power outputs would result in 0 rpm, rather than your ideal pushing rpm.
I personally would advocate for positive ratio, as it requires the least amount of gears, while a negative 1:1 ratio requires a custom carrier hole (and pinions meshing), and a negative off 1 ratio requires 3 pinions meshing - though if you really need the 60 tooth gear profile a 36 tooth planetary doesn’t work.
Here’s the clearest picture of my favored gearset. This current application is continuous power sharing, but its what I used for the multispeed drive designs too.