Talk:Epicyclic gearing

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Why does a planetary geartrain have multiple planets? Is this about power transfer or stability or something?

See below.

Isn't the sun gear in the picture gray? --snoyes 22:36, 19 Nov 2003 (UTC)

yes, only the drive shaft of the sun gear is in yellow. This drive shaft goes through the (green) planet gear carrier and extends on the oter side into the sun gear. Maybe the OP should also make the sun gear yellow. MH 213.236.117.2 08:21, 24 May 2004 (UTC)

Kinda depends on your monitor, I guess. On the computer I created them on, it looks slightly yellow, but I checked it on a different screen and it's much darker and muddier. The same problem occurred with the images on Differential. I'll be uploading brightened-up versions soon - thanks for pointing it out! -- Wapcaplet 23:42, 19 Nov 2003 (UTC)

It seems that my version of galeon (or galeon in general) doesn't display pngs all that well. In both konqueror and mozilla the sun gear is clearly yellow, while in galeon the whole picture is significantly darker. (And the picture is viewed from a different angle - very strange). What browsers were you using? --snoyes 00:49, 20 Nov 2003 (UTC)

Hey, another Linux user! :-) The angle is something I changed in the last revision. I thought it showed the red arrows a little better. It may have been a browser issue - in Firebird under Linux on a newer 19" monitor, the colors were brighter; in Mozilla on Windows on an older 15" monitor, they were much darker. Could just be differences in gamma correction between the two monitors. In your case, maybe Galeon is still using a cached version of the image? That'd explain why one of them still shows the other angle. I've noticed that different software often uses different gamma correction on images - especially with things like Gimp and Photoshop, which are tweaked to get images to look closer to print output.

Anyhow, let me know what you think of the newer colors. I've used the same materials and similar lighting for the illustrations for Differential and Pin tumbler lock; I hope to make similar illustrations in this vein, and would like to find good distinct colors. -- Wapcaplet 04:47, 20 Nov 2003 (UTC)

Yip, you pretty much can't help avoiding linux users on wikipedia. Which is a good thing, since suggestions such as support for proprietary stuff like flash animations get struck down immediately. (A couple of days ago on the Village pump). Anyway, I cleared my cache and the pictures now look identical and the colours clear and distinct in galeon, konqueror, firebird, etc. --snoyes 05:35, 20 Nov 2003 (UTC)

Isn't the maximum gear ration always less than one? If so, it would be nice to note it in the descriptions.

Not necessarily. With the given scheme, sun gear as input and carrier as output, I think yes, but you could just as easily use the carrier as input and sun as output to get a ratio greater than 1. You could also hold the carrier fixed, and use the outer ring as output. But you're right in noting that a discussion of how the ratios work would be nice... -- Wapcaplet 16:50, 2 Jun 2004 (UTC)

Contents 1 Other uses for Epicyclic gearing than just gear ratios? 2 My math is rusty 3 Sun and planet gear article 4 Why planetary geartrains have multiple planets 5 Animated gifs 6 possible addition: advantages/disadvantages

[edit] Other uses for Epicyclic gearing than just gear ratios?

It seems that many combinations of power flow are available from the gearset. If power input is to the outer ring gear, wouldn't the "planetary" carrier rotate in the ring gear direction and the central "sun" gear in the opposite direction? Useful for driving grinding wheels in opposite directions?

• Yes, if the carrier is fixed. One of the gear units (outer ring, planetary carrier, sun gear) must be held fixed for any useful output to result. But yeah, this is sometimes used in simple transmissions to give two forward gears plus a reverse gear. Rather nifty! -- Wapcaplet 22:10, 22 Jul 2004 (UTC)

Further, what about its use as a "differential"? The whole article is written on the assumption that it is a way of achieving a few fixed ratios by holding one part stationary. In the Hybrid Synergy Drive, which is referenced, it's used as a 3-way power-split device, and all parts are usually in motion. --KJBracey 08:37, 18 November 2005 (UTC)

[edit] My math is rusty

OK, it's about time we got some examples of how the gear ratios work in this thing. Preferably a version that is easy to understand for the non-mathematician (namely, me). I found this site that attempts an explanation, but it leaves me somewhat baffled. Ideally, a thorough exposition of how the ratios are calculated would be nice, but a simple formula would suffice for now. Three cases:

• Annulus (outer ring) fixed
• Planetary carrier fixed
• Sun gear fixed

In each case, what is the ratio between the remaining gearsets, in simple terms of how many teeth each gear has? For the second case, it's fairly easy, since the sun and annulus simply turn in opposite directions, in the ratio sun/annulus = -teeth_annulus/teeth_sun (this is our reverse gear, as mentioned above). For the others, there's some angular velocity of the carrier involved, which taxes my brain. Assistance would be welcome. -- Wapcaplet 00:41, 23 Jul 2004 (UTC)

Nevermind. I found a much better explanation, which I will try to work into the article.

[edit] Sun and planet gear article

Hello, I just added a stub article on the above & got a message that it seems to be the same as Epicyclic gearing, looking at the page it seems to be the case that it is either the same thing or epicyclic gearing is a more advanced form of the original sun and planet gear. I am not an engineer & have some problems understanding technical articles (only created the s&pg as I'm working on the article of the engineer who invented it - William Murdoch) so I'm not too sure about the differences & the terminology. Does anyone know if the terminology 'sun and planet gear' is outdated or whether epicyclic gearing is the common modern (or American) phrasing for this? If so it might be better if I add a link from s&pg to epicyclic gearing as the s&pg article (while a stub) deals with the original invention. Otherwise it might be better to merge the articles & put in a re-direct. Can you please let me know what you think. AllanHainey 12:35, 6 September 2005 (UTC)

I'm a Mechanical Engineer. They arent the same thing at all. They do both contain sun and planet gears, as this just refers to one gear orbiting another. This article is about using them to make a gear train which converts shaft torques, the other is using them to convert piston force to torque.

[edit] Why planetary geartrains have multiple planets

Someone posted this question above: "Why does a planetary geartrain have multiple planets? Is this about power transfer or stability or something?"

The reason for having multiple planets is so that you can connect more than one shaft to the planetary gear. That's part of the ingenuity of planetary gears: you can input power from multiple shafts and output power in one, or more, shafts, as necessary.

Take, for instance, the planetary gear connected to two pistons on the right. Here a drive shaft inputs power into the sun gear, which in turn rotates the two planets, timed so the pistons move up and down one right after the other. (Note that the pistons are not actually pictured, but are connected to the "moving crankshafts.")

Of coarse stability is the first and main reason.

[edit] Animated gifs

Animated gifs, showing each locking configuration would be very helpful - its very difficult to visualise this kind of thing.

would this be any good? just the pic in the article now put together --Astrokey44 13:47, 26 May 2006 (UTC)

I like it. It would be even better with an intermediate frame; a little easier to follow. ike9898 22:45, 12 June 2006 (UTC)

Is it possible to do this with photoshop? When I try to do tweening the in between frame only changes the opacity of the two not the position --Astrokey44 12:33, 22 June 2006 (UTC)

What is method to calculate the maximum planet gears can involved in a Epicyclic gear system?

[edit] possible addition: advantages/disadvantages

To me, this article feels incomplete. I would expect to see a discussion of the advantages/disadvantages of planetary gears versus other gearing arrangements (i.e. when would you want to use planetary gears? when would you not?) For example, advantages include high power density, large reduction in a small volume, multiple kinematic combinations, pure torsional reactions, coaxial shafting. Disadvantages include high bearing loads, inaccessibility, design complexity. I have studied planetary gears in graduate school and could add such a section if others think it would add value... This would be my first attempt at contributing to wikipedia so I wanted to test the waters before jumping in... Kiracofe8 02:51, 6 February 2007 (UTC)