Picking rocks out of a field

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When I was in Florida, I spent a day checking out some of the tractor dealers. I took pictures of this gizmo because it used a hydraulic motor (red rectangle that you can barely see) instead of a PTO and because I could not figure out what it was for. It turns out, it is a Schultze RS320 Jumbo Rock Picker. This video shows how it can be used with a windrower to remove rocks from a field and pile them along the side of the field. I discovered there are quite a few other brands of rock pickers such as this Kongskilde that has a windrower built in on each side. There are six hoses because two hydraulic circuits are used to control rams to change the height of the dirt separation platform and to dump the rock hopper. The third circuit is used for the hydraulic motor.

By using a hydraulic motor instead of the PTO, they save the time needed to design and manufacture the shafts, gears, and/or chains needed to transmit rotary motion from the tractor to the conveyor. Also, a hydraulic motor can reverse the rotation of the conveyor to help jiggle big rocks up the dirt separator platform. You can't reverse the PTO rotation.

SRW1400 Windrower

But note that the windrower shows in the above video uses the 540rpm PTO with shafts, gears, and a chain because of the higher speed and torque needed to rotate the 14-foot shaft through dirt. This video offers some more details about the drive shaft.