Hi,
I am working on a planetary reduction and I am using Taylor’s formulas. Taylor stated that the ring gear teeth have to equal two times the planet teeth plus the sun teeth (2xNr+Ns=Nr). The gear company gives me a tooth count that doesn’t fit Taylor’s formula, is this possible? This is a quadruple reduction and it’s getting very complicated but the tachymeter speed works better with the company’s tooth count but there’s not enough difference to really rule out. I joint the info and I would appreciate if someone could sort it out. Thanks

Simp_drive,_4.2.pdf (128 Kb, 33 downloads)

Hi Marcel,

Just had a look at 4 different planetaries, 3 single & one 2 stage. The formula produces a result which is one less than actual ring gear number in all but 1 example (which equals). All gearmeshes can be confirmed by vibration data. These are major gearbox manufacturers. Guess they threw in a spare tooth incase it lost one!! Would love to be enlightened about Taylors formula.

To sort out your 4 stage will take a bit of work. If you are lucky enough to be a CSI user it has an excellent epicyclic gearbox calculator (up to 6 stages)that takes care of everything, you will need to refer to instructions under help (calculator found under "Frequency Calculations" icon). First thing is to carefully go through drawing identifying which parts rotate and which parts are stationary, that is not very clear to me. If you post that info I'll run it through for you, otherwise it will take more time than I can afford at the moment. Rgds.

Marcel, review the attached, specifically page 3. It is an extraction from the manual for some gear design software. You'll note that it is not necessary (or even desirable) that Nring = Nsun+ 2·Nplanet and the reason why.

In addition, should you want to really get into this I would recommend the book Gear Drive System Design and Application by Peter Lynwander. With that book you'll soon get an appreciation for sequential vs. simultaneous meshing and how that might affect the tooth numbers, as well as several other variables.

Planetery design is very complex. At my previous employer, we had a group that did planetary work and another group that did predominantly parallel shaft designs. On one occasion, a parallel designer did a design for a planetary driven valve operator. On test the device just couldn't develop the design seating force. Upon closer examination, he had totally "missed" the ratio, hence the thrust just wasn't going to be developed. The valve operated very swiftly I might add.

In summary, don't trust the canned formulas often presented for epicyclic designs. In the real world, they will very often be wrong due to efforts taken in optimizing the gearset.

John from Pa

This message has been edited. Last edited by: John from PA,

Simple_Epicyclic_Gear_Design.pdf (152 Kb, 23 downloads)