For some applications, maximum power density is worth the cost and difficulty of a complex epicyclic or “planetary” design. If, like me, you prefer simplicity, it is tempting to think you can outsmart the conventional thinkers with multiple stages of very high-quality single helical gears. But sometimes temptation leads you in very unproductive directions and you would be wise to do your research before making any wagers.
One of the references that might turn up is my paper from the 2009 AGMA Fall Technical meeting entitled “The Effect of Gearbox Architecture on Wind Turbine Enclosure Size.” I was so convinced that there was a way to beat the helical primary/epicyclic secondary designs that dominate the wind turbine field that I “built” a huge collection of math models to determine the likely volume and weight for comparison purposes. Those estimates were then used to determine a rough cost comparison.
You can cut right to the conclusion page to see that my hopes for a breakthrough were soundly dashed by the science. For maximum power density, smallest envelope, and lowest cost, the marketplace of ideas had made the right choice, i.e.: helical primary with epicyclic secondary were the way to go. You might disagree on the number of helical stages or the number of epicyclic stages or the number of planets, but the “right answer” will be found within that design scheme.
This not to say that all applications should move in this direction, it’s just that if you need compactness or light weight you will have to deal with an epicyclic arrangement. Many of the math modeling techniques and design suggestions contained in that paper are applicable to other fields as well.
Nine years may seem like ancient history to some people; in “gear years” it is only a few “minutes.” One of the reasons we are so proud of the online archive is that good information is preserved for use by an entirely new generation of gear people. Every issue we have ever published is there for your reference.