Cat 303.5 mini ex brush cutter build

backwoodstractor · Dec 5, 2021

Hey guys, looking to build a bush hog for my cat mini ex , 303.5 Gonna take a 4-5 ft mower an down size it to a 36” cut, need help trying to determine what hyd drive motor I need to turn the pto gearbox. Built one few yrs ago for my bobcat 763 skid steer an I had found a guy on here that recommended me a hyd drive motor with my build at the time, hopeing to hear from someone again for advice on my build. Thx for any help

4570Man · Dec 5, 2021

You need to determine your aux flow then size the motor to achieve the intended RPM. Keep in mind if you shorten the blades you’ll have to increase the drive RPM the keep the same tip speed.

backwoodstractor · Dec 6, 2021

this is what I found online dealing with the specs for the 303.5 mini. Regular ole square body tail. Hope maybe you can share ur thoughts on what I’ll need for my hyd drive an take in consideration me cutting it down to a 36” cut. Will actually just cut of the ends of the bar that holds the blades

4570Man · Dec 6, 2021

Was the mower originally intended to be 540 rpm driven? If it was a 540 mower that was originally 6’ wide and you cut it down to 3’ you’d optimally drive it at 1080 rpm but with only 6 gpm you’re going to be pretty low on power so a slower speed might work better. Edit. It appears your second circuit is 15 gpm. With that flow I’d probably make a wider mower. That’s in the range of a low flow skid steer mower and they seem to work fairly well. I’d have to look up the formula but a hydraulic motor rpm is an easy calculation between the motor displacement and the flow volume.

RickB · Dec 7, 2021

Flow per minute / displacement = RPM
Flow rate needs to be converted to the same unit of measure as the displacement. EG: cc or cu.in.
1 gal = 3785.4 cc
1gal = 231 cu.in.

backwoodstractor · Dec 7, 2021

4570Man said:
Was the mower originally intended to be 540 rpm driven? If it was a 540 mower that was originally 6’ wide and you cut it down to 3’ you’d optimally drive it at 1080 rpm but with only 6 gpm you’re going to be pretty low on power so a slower speed might work better. Edit. It appears your second circuit is 15 gpm. With that flow I’d probably make a wider mower. That’s in the range of a low flow skid steer mower and they seem to work fairly well. I’d have to look up the formula but a hydraulic motor rpm is an easy calculation between the motor displacement and the flow volume.

Yes sir it was original 540 pto drive , thx for ur time an help , just don’t wanta buy a motor that’s too big or too little. An when talking to the part guys that sell the drive motors kinda look at ya like a deer in the head lite look when ya start asking them what I would need