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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

direct vs planetary

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Brian

12-09-2003 20:11:01




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Can someone explain direct drive vs planetary- pros & cons?




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don

12-12-2003 07:58:44




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 Re: direct vs planetary in reply to Brian, 12-09-2003 20:11:01  
the orbit of the planet gears accounts for about 25% of the reduction and can be braked for a higher gear ratio without disengaging the drivetrain. Brakeing the planet gears shifts to a 1:1 reverese like a Ford model T transmission. most planetary gearing doesn't control the orbit so added torque automatically lowers gear ratio slightly. Dresser built a differential steering crawler with hydralic powered planet gears.

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Bob/Ont

12-10-2003 05:23:29




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 Re: direct vs planetary in reply to Brian, 12-09-2003 20:11:01  
Not exactly sure this is the answer you are looking for Brian but planetary gear sets give the most gear reduction in the smallest space and are stronger because they have one tooth engaged for every planet pinion in the set where as a regular gear reduction has one. If you are wondering why some machines have them in the wheel hub and some don't it,s because they have them inside by the diff like a lot of ag tractors do. When they are inside you need a much heavier axle shaft 4" or 5" dia instead of 1 1/2" to 2" dia with out board planetarys on the same size of machine. Later Bob

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Wayne

12-09-2003 21:34:40




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 Re: direct vs planetary in reply to Brian, 12-09-2003 20:11:01  
Hey Brian, with a "direct drive" setup, if I'm understanding your terms here, your gonna be driving through a final drive gearset with is basically a small pinion gear driving a larger bull gear (increasing input torque) which in turn drives the axel which is connected to the drive sprocket. There's usually more gearing between the pinion and bull gear, but you get the idea. With the planetary setup you have a sun/center gear driving the planetaries, driving the outer ring gear which drives the drive sprocket. The benefit of a planetary setup is you can get a larger torque output/increase, in a smaller amount of space, for a given amount of input torque than you can with a "direct drive" gear train. Most of your hydrostatic drive machines, for example a 953 CAT loader or most brands of excavators, have a hydraulic motor driving the track through a planetary gearset housed in the actual drive sprocket. This allows them to use a drive motor small enough to be practical yet still get the desired output torque. Basically you can get more power out of a smaller package with a planetary drive setup. As for pros and cons to each, personally I don't know of anything actually for or against either design. Both are tried and true designs and in my experience working on one is no harder than working on the other. As far as life expectance, as long as they are kept well lubed, again in my experience, one will last just as long as the other. Hope this helps.

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Wayne

12-09-2003 21:31:13




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 Re: direct vs planetary in reply to Brian, 12-09-2003 20:11:01  
Hey Brian, with a "direct drive" setup, if I'm understanding your terms here, your gonna be driving through a final drive gearset with is basically a small pinion shaft driving a larger bull gear which in turn drives the axel shaft which is connected to the drive sprocket. There's usually more gearing between the pinion and bull gear, but you get the idea. With the planetary setup you have a sun/center gear driving the planetaries, driving the outer ring gear which drives the drive sprocket. The benefit of a planetary setup is you can get a larger torque output/increase in a smaller amount of space for a given amount of input torque than you can with a "direct drive" gear train. Most of your hydrostatic drive machines, for example a 953 CAT loader or most brands of excavators, have a hydraulic motor driving the track through a planetary gearset housed in the actual drive sprocket. This allows them to use a drive motor small enough to be practical yet still get the desired output torque. Basically you can get more power out of a smaller package with a planetary drive setup. As for pros and cons to each, personally I don't know of anything actually for or against either design. Both are tried and true designs and in my experience working on one is no harder than working on the other. As far as life expectance, as long as they are kept well lubed, again in my experience, one will last just as long as the other. Hope this helps.

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