hydraulic questions and mower build

Code54 · Jul 5, 2016

I am picking up a mini ex in a few weeks and been thinking I would like to get a mower for it BUT after seeing the cost I now think I may make a winter project building one.

I have build a lot of 3 point stuff but nothing hydraulic so that part is new to me. Can someone explain what kind of hydraulic drive "motor" I need for a brush hog style of cutter.
I have a hair over 10 GPM to power it and would like to shoot for 36-40" mower. Want to build the deck out of plate but that is easy part, I just am not too sure where to start with the hydro stuff. I presume I need a certain RPM and torque rating but not sure what that would be. Do I need some type of shear bolt or something in the system? I am just starting to research this so any help, photos or explanation would be very helpful. (or links to drive units)
THANKS

2458n · Jul 5, 2016

Looking at a bobcat bush hog mower today. It is 48 inches and takes a 20 gallon per minute flow. That was the end of my looking because I believe my 743B aux. is more like yours at 10 gallons.

GLyford · Jul 6, 2016

OK, so here's my thinking...a 48 inch lawn (finish) mower takes about 20 HP to run. A 30 inch lawn mower takes about 10 HP to run. So if a 48 inch brush mower takes 20 GPM, then assuming brush mowers scale about the same as finish mowers that would imply 10 GPM could swing about a 30 inch mower?

oldnslo · Jul 6, 2016

Hydraulic horse power = (GPM x PSI) /(1714 x %efficiency) Based on this it requires approximately 20 HP to drive a 10 GPM pump @ 3000 PSI. Figure minimum of 20 - 25% loss in HP when driving a motor with this pump so you now have around 15 HP available at the cutter head. Actual losses depend on several factors some of which include:
Line losses
Pump and motor efficiency

Dirthog · Jul 6, 2016

The only problem with a rotary brush mower on ANY excavator is they throw things the ones we have installed on larger excavators the machine all have cabs and we put extra guarding on them. Even then that is sometimes not enough also most mini do not have cabs so ??

Code54 · Jul 6, 2016

Good point there - they do chuck a lot of crap!
Maybe I will find an old flail mover to convert. Wondering out loud - run a hydro motor to drive the the old PTO driven gear box perhaps???

Arc weld · Jul 7, 2016

I don't think you have enough flow or pressure to run a mower. A tractor PTO will have way more power. The HD brush cutters and mowers usually use hydraulic motors with case drains. I have almost 17 gpm on my skid steer and demo'd a rototiller. No comparison to the pto tiller on the tractor. It worked but you had to go awfully slow and left a much coarser tilth.

BrinkME · Jul 8, 2016

The type of motor required would most likely be a wheel type or fan type motor (large bearings to support the intended load) or it may even require an overhung load adapter (large bearings in a sealed case that is lubed/flushed with hydraulic fluid)

A wheel type motor would probably be more in line with the load that a cutter would encounter (mostly radial with some thrust) vs a fan type motor (mostly thrust with some radial)

ozzie tractor · Jul 11, 2016

just be careful, when a digger is travelling, it uses nearly all of the aux oil flow. we strike it occassionally with flail mulchers where people think they are going to reach out and then drive along with the machine to mow a verge etc. the flail mowers slow down massively.
also 10gph at what pressure. most digger pumps drop flow as pressure increases, so while they can make 3000psi or 10 gpm, they dont do both at once. so at 2500 psi you might only have 4 gpm. i honestly dont think you have the oil flow.

Code54 · Jul 13, 2016

Thanks all. I will do some checking. I know Kubota shows the machine with a mower but may have to see exactly what is possible. Not sure of how they figure their flow numbers