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Gear Calculations

A project log for MPRT - Modified planetary robotics transmission

The reduction of strain-wave, but using a 'single' stage planetary gearset.

agp.cooperagp.cooper 04/19/2019 at 09:141 Comment

Gear Calculations

I could not be bothered tying to work this out, someone has done it before, I just have to find it.

On my search journey I found the gear system we are using are call Epicyclic gears.

Anyway I did find a website that published the equation for this specific gear system (http://www.efunda.com/DesignStandards/gears/gears_epicyclic_train.cfm).

If the gear train is Na/Nb/Nc and Nd/Ne (i.e. Sun1/Planet1/Ring1 and Planet2/Ring2) where Ring1 (Nc) is fixed ,and the planets (Nb and Nd) are locked the the reduction ratio is:

Here is the worked example from the website:

Gear Train – Worked Example
NA 21 Sun 1 Driven
NB 61 Planet 1 Locked to Planet 2
NC 141 Ring 1 Fixed
ND 41 Planet 2 Locked to Planet 1
NE 121 Ring 2 Output

Gearing 1 7.7143 Check

Gearing 2 0.2168 Check

Gearing 0.0281 Check

Reduction 35.5870

Here is Daren's design:

Gear Train – Daren
NA 18 Sun 1 Driven
NB 21 Planet 1 Locked to Planet 2
NC 60 Ring 1 Fixed
ND 21 Planet 2 Locked to Planet 1
NE 57 Ring 2 Output

Gearing 1 4.3333

Gearing 2 -0.0526

Gearing -0.0121

Reduction -82.3333


Note the sign change in the reduction ratio, this appear to be correct.

And here is my five planet version:

Gear Train – Alan v2
NA 25 Sun 1 Driven
NB 20 Planet 1 Locked to Planet 2
NC 65 Ring 1 Fixed
ND 20 Planet 2 Locked to Planet 1
NE 60 Ring 2 Output

Gearing 1 3.6000

Gearing 2 -0.0833

Gearing -0.0231

Reduction -43.2000


Realisation

The gear design has migrated such that the requirement for the two planetary gears to have the same number of teeth is no longer valid.

AlanX


Discussions

Daren Schwenke wrote 04/19/2019 at 14:28 point

First stage is 3.3~:1 for mine, not 4.3:1.

Yes, the negative sign is correct.  It switches directions depending on if the output has more teeth than the input or vice versa.

33:1 is a more workable ratio than the original.  Good job.

Also, at this point you have contributed more to the project than 90% of all contributors I have had for projects.  @Morning.Star is still winning in that regard, but the two of you may just change my mind about contributors...  :)

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