Running a pto bush hog off excavator

fourwheelinj1 · Oct 20, 2020

Let me start off by saying that my knowledge of hydraulics is very limited. I have a bobcat 442 excavator that is plumbed with auxiliary hydraulics. I currently have a hydraulic thumb and have an additional set of remotes along with what i am pretty sure is a large case drain line. I would love to have a commercially made mulcher or brush hog specially made for excavators but the budget isn't there for that. I do however have a couple of old tractor 540 pto bush hogs I would like to convert to run off the excavator so we can mow pond banks and other hard to reach areas. I would like to add a hydraulic motor to the existing bush hog to turn the factory pto gearbox. My specs on my machine say the auxiliary system has a max working pressure of 4,060 psi and a flow (adjustable) maximum 26.4 gpm. Can someone help me figure out what I would need in the way of a pump and cushion valving to make a working system that won't harm my machine? I am really just looking for a little education so I can get this designed. I am not expecting the performance of a commercially available unit but I would like it to be able to knock down thick brush. I have found a few motors that might work but the psi ratings are usually only 2500-3500. Can I lower my psi on my auxiliary to be able to use a lower psi motor?

ruffdog · Oct 20, 2020

fourwheelinj1 said:
Let me start off by saying that my knowledge of hydraulics is very limited. I have a bobcat 442 excavator that is plumbed with auxiliary hydraulics. I currently have a hydraulic thumb and have an additional set of remotes along with what i am pretty sure is a large case drain line. I would love to have a commercially made mulcher or brush hog specially made for excavators but the budget isn't there for that. I do however have a couple of old tractor 540 pto bush hogs I would like to convert to run off the excavator so we can mow pond banks and other hard to reach areas. I would like to add a hydraulic motor to the existing bush hog to turn the factory pto gearbox. My specs on my machine say the auxiliary system has a max working pressure of 4,060 psi and a flow (adjustable) maximum 26.4 gpm. Can someone help me figure out what I would need in the way of a pump and cushion valving to make a working system that won't harm my machine? I am really just looking for a little education so I can get this designed. I am not expecting the performance of a commercially available unit but I would like it to be able to knock down thick brush. I have found a few motors that might work but the psi ratings are usually only 2500-3500. Can I lower my psi on my auxiliary to be able to use a lower psi motor?

If you are trying to cut "hard to reach areas", I don't know if I would want to reach out with a heavy tractor cutter (add weight of hydraulics) next to a pond. A rotary cutter will have side forces as it hits solid objects too.

fourwheelinj1 · Oct 20, 2020

weight shouldnt be a problem. My excavator weights about 17k pounds and can easily handle that weight stretched out. The tractor style bush hogs are actually lighter weight than most of the excavator cutters/mulchers. I am only looking at either a 4' or 5' bushhog.

ruffdog · Oct 20, 2020

This guy was converting old cutters to hydraulic.....

Skidsteer 5' brush mower - farm & garden - by owner - sale

deereman75 · Oct 26, 2020

Owner of a hydraulic shop, so take it for what that's worth.
What you want to drive it is a Char-Lynn orbital motor. Look for an Eaton hydraulics dealer near you, phone them, and explain what you're doing.
There is math you can do to calculate hydraulic motor displacement to give a specified RPM (540) for a given GPM (your auxiliary flow rating)
You'll also need to plumb in a pressure relief as those motors tend to prematurely blow out shaft seals over 3000psi or so, and a seal kit is over $100.

There are other options such as piston motors, but an orbital motor is PLENTY good for this application at roughly 1/5th of the cost.

Your motor will output 540 rpm, and then it's just a matter of fabricating the necessary mounts and making (or having a machine shop make) an adapter to connect the motor onto the input shaft of the mower gearbox.

Or at least that is how I'd do it if I was building one. Information provided for reference only, use at your own risk