Calculating Epicyclic/Planetary gear ratio

[Neil WyattModerator @neilwyatt]

Posted by john carruthers on 18/05/2016 08:48:23:

I've seen a couple of old lathes that use a Sturmey Archer 3 speed hub as a back gear ?

This is actually a rather good idea – see the Rollo Elf recently featured in another thread.

Bullet proof units, albeit a bit small for your intended use.

Neil

[RainbowsParticipant @rainbows]

Never been a cyclist. That said I can see the application for my Wizard lathe if its too small for the new one. Perhaps it would be good for the Mega Adept (or did John Stevenson nick the Adept out of spite and melt it into a TOS lathe accessory?)

[Nicholas LeeParticipant @nicholaslee]

Hi,

For calculating epicyclic/planetary gears, I have found the free software at the following page to be very useful:
**LINK**

The following is also useful to remember:

Let
R = Number of teeth on the Ring Gear

P = Number of teeth on each Planet Gear

S= Number of teeth on the Sun Gear

Then R = S + 2P

If the ring gear stays still, then the gear ratio is just S / (R+S)

The software lets you draw the gears an tells you what combinations fit nicely.

In general, the more planet gears you have, the more teeth are engaged overall, and so the greater the torque capability.

Best Wishes

Nick Lee

[Author]

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