Re: What is a 1,000 rpm PTO for?

Posted by ChrisL on February 24, 2005 at 15:26:46 from (216.254.224.232):

In Reply to: What is a 1,000 rpm PTO for? posted by Quebec Bob on February 24, 2005 at 13:30:10:

part of it is this - imagine this scenario

don't think tractors for a moment - think something like car driveshafts. well maybe think like a huge truck driveshaft.....

now picture these 2 scenarios -

the truck has all the rear wheels locked up (it has been setting for years) - you start it up - put it in super super low gear and slowly let out the clutch - with the engine only idling - oops twists the driveshaft right off.....engine was only putting out maybe 5% of its total power

so you go and fix the driveshaft , loosen up the wheels - get it all running and load it up with about 35 ton of stuff in the back - you take off cruising along in super super low at about 3 mph - you start to go up a hill the engine works a little harder so u give it some more throttle - the hill gets steeper - you give it some more throttle - the hill gets really steep - you have this thing all the way to the floor just to keep going at 3 mph - and you think to your self now the engine is putting out full power and the driveshaft isn't breaking - the difference is speed -
the faster a shaft spins the thinner it can be and still transmit the same amount of power - think about the last time you twisted off a shaft - did it happen at high speed - no - you always twist and break shafts at the very lowest speeds - once they have speed they can take a lot more

so now if you are an implement designer you can make all your shafts thinner as long as they turn faster - so any implement that is made to put on a 1000 rpm can be made cheaper and still transmit a lot of power.

For example look at silage cutters lets say the main driveline is some 1/8" 2.5" diameter pipe (I am making these numbers up) and you send it out as a 540 rpm unit - the farmer hooks it up to his 60 hp tractor starts to work it some and snap - the driveshaft breaks - he goes gets another one - but this time he puts it on a 1000 rpm shaft - he turns it on starts working it, a little harder, a little harder , and finaly the tractor has no more power to give - in other words that same driveshaft is more than capable of handling the power from the tractor - just because it is spinnging faster -

now granted all these implements need to be geared right - in the above example the silage cutter head (if not the whole thing) would be going too fast so it would have to be desinged with the speed coming in as a known factor - for example if the guy now knows he is going to tell people to use a 1000 rpm input he will change the size of some pulleys and gears somewhere to slow the head to the proper speed again.......but if the driveshaft is spinning faster he knows it will take all the power a certain size tractor will put out......

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