Trying to build a 42" Rotatary Mower

[FlyC17s]

Would please like some engineering help.

I have a Kubota KX 91 mini excavator that has a aux pump that puts out 10.9 GPM. I want to build a rotatary mower that uses a hyd motor that turns a single 42" blade. Was told I need to have a motor that puts out 3000 rpm at the shaft and turns the blade (at the tip, 15,000 Ft/Min) Am trying to cut heavy briars, stuff up to 1" thick.
I can build the deck and fasten the new deck to the mini. Just do not know what size hyd. motor to get to push the 42" blade. Can someone offer advice? Thanks

 

[BHD]

Basicily you take your GPM and size it to the RPM you need,

for some reason that seems a little fast to me, as even the smaller lawn mower at 30" is only 3400 to 3600 RPM using a standard engine,

I would suggest swinging blades for cutting that heavy of product,

two ways of doing it direct or nearly direct possibly a arbor that is driven directly by the HYD, motor, and the second is to use a standard mower gear box and drive that with a HYD motor,

possibly using a kit or parts Build Your Own 5' Medium Duty Rotary Cutter Kit Just Mount to Your Deck | eBay

 

[orangeandgreen]

for 15000 FPM at 42 inch diameter you would need 1364 RPM at the shaft.
Tip speed in FPM = RPM x 3.14 x diameter (in feet)
The safety police recommend 19000 FPM as the max tip speed for lawn mowers so that might be good for a brush cutter too, that would require 1728 RPM

 

[FlyC17s]

Thank you for the insight and suggestions.

 

[FlyC17s]

If I built a mower something like your saying, how do i find out what type of check valves, safety valves, by pass / pressure relief valves and everthing else that goes in between the hyd motor and the auxilary line to the machine?

Thanks for any help.

 

[TomSeller]

You might want to look up some skid steer rotary mowers and check them out. land pride has some pretty good details if you poke around this site.
http://www.landpride.com/products/165/sc26-series-skid-steer-cutters

Do a google search for others, you might even get one your size with a listing of the motor.

 

[tmc_31]

Hey flyc17s, Check out this link to Surplus Center. They have all of the hydraulic components you need and gear boxes too. This link takes you to the HYD motor calculator that might help answer your questions. I am looking at building a brush mower to go on my skid steer and have spent a good deal of time on the surplus center site.

Surplus Center

Good luck with your project

Tim

 

[FlyC17s]

Thanks for the help. Great site to look at to get some even better ideas.

 

[FlyC17s]

Surplus Center was a very interesting site to view. When time permits I will spend more time here.
Thanks,
Peyton

 

[tmc_31]

Are you a crewman on the C17?

 

[J_J]

FlyC17s ,

I really don't you have enough juice to run a 42 in blade with enough torque to do a credible job.

For example.

Using your 11 GPM, and maybe a 3 cu in motor, that will power the hyd motor to about 847 rpm.

Now, as far as the torque. 3 cu in, and 3000 psi, will provide about 1433 in lbs, or 120 ft lbs

If you go with a smaller cu in motor, you decrease the torque, but gain rpm.

 

[J_J]

FlyC17s,

If you stick with the 3000 rpm, , and 11 GPM, the cu in of the hyd motor would be about .847.

The torque using .847 cu in and 3000 psi = 405 in lbs or 44 ft lbs.

Here are some pic of a hyd blade attachment. Don't know all the particulars.

 

[tmc_31]

J.J, what kind of torque should we be looking for for an application like this. 42" blade? 72" blade? Or does the blade length even matter? It seems like I saw a torque spec that some manufacturer published for a brushcutter but I can't seem to find it.

Tim

 

[aczlan]

J.J, what kind of torque should we be looking for for an application like this. 42" blade? 72" blade? Or does the blade length even matter? It seems like I saw a torque spec that some manufacturer published for a brushcutter but I can't seem to find it.

General rule of thumb is 5hp/foot, so you would need ~17.5 HP to drive it. Hydraulics are ~80% efficient, so you would need to start with ~22HP used on the engine to get ~17.5HP at the deck.

Aaron Z