boom mower project

[J_J]

Thanks everyone for your input. I sure wish I could glean all the helpful info in to formulating a hydraulic design. I guess at this point it's honestly over my head. I just don't know enough about hydraulics, there are so many choices and mistakes are too costly.
I refuse to give up! I have yet to find anything similar to get earnest ideas off of. Some how I need to drill down on the variables. If I use a high rmp motor, which one? If I go with pto pump, what is the list of components to make that system, and still, which motor? Why is there no impact to the scenario if there is a belt and pulleys to change the rpm's?
The physical build exceeded all my expectations. It was an idea I'm sure everyone has thought about. I expected it to be too heavy to extend so I slapped it together expecting to fail. But its not too heavy at all.
As far as the danger of debris, I designed the adjustments so it never can aim horizontally at me. I also will put a rubber shield on the side facing me and of coarse wear proper fighting gear. :laughing:
Thanks to TBN there's a place to talk it out.

There is impact to the scenario by using belts and pulleys. If you increase the rpm of the blades, the torque goes down.

 

[nealfris]

JJ, If I were to use the 11.4 GPM PTO pump as you suggest, could you please tell me what you would recommend for a motor???

 

[J_J]

With 11.7 GPM's, a 3 cu in hyd motor will turn at around 900 rpm. I believe that is the size hyd motor that is used on the 48 brush cutter below. It runs on 8 GPM, at 3000 psi .

The PTO pump max pressure is 2200 psi.

The object is to get the blade tip speed up high and still have enough torque to do the work.

 

[nealfris]

JJ, this is the only one with RPM as high as you described. Would this do the trick?

Surplus Center - 3.15 cu in DYNAMIC BMPH50H2KP HYD MOTOR

 

[ns_in_tex]

We built something similar for our front end loader about 10 years ago. We don't like to run our engine full throttle, so we figured around 5 to 6 gpm on flow. I think this may have figured to around 5 HP on our 30" mower deck. We used a Barnes Hydraulic motor, purchased from WW Grainger, P# 4F657-3. We used belt drive, I think for 2 reasons. To get blade tip speed and we were afraid the motor bearings would not stand up to direct drive pressures. The mower deck already was set for belt drive & it was just easy to do this.

Of course, we always want more power, but it probably performs as well as a 5 or 6 HP gas engine mower would.

 

[J_J]

JJ, this is the only one with RPM as high as you described. Would this do the trick?

Surplus Center - 3.15 cu in DYNAMIC BMPH50H2KP HYD MOTOR

That would probably work, but it does have a case drain line that needs to go to a cooler or tank. Three hoses.

Continuous pressure is only 1840 psi. What is your tractor relief set at?

 

[Tenn_Blue]

Been following this post with interest. I have been considering a similar idea for my miniX. Its a small one (4k lbs), too small for the commercial exc. mowers I have seen (more money than I want to spend as well...).

The x has good aux. hydraulics, and the tracks let it go places the tractor can't (safely). The reach of the boom would be good to clear culverts and hill sides I do now with a weed eater. And would be great for clearing brambles and brush at the fields edge.

I'm considering using a (don't laugh...) push mower. Leave the bottom half of the engine case on the frame (roller bearings and crank shaft). Then use a pulley/belt and hydraulic motor mounted on an adapter plate screwed on the top of the engine case (roller bearing for the other side of crank as well). Cut off the skirt on 1/2 of the mower deck (the part away from you) and fab a 2 part blade like a bush hog.

But I'm trying to figure out the hydraulic needs and motor size before I go any further with the idea.

So let us know how you figure things out! I got this ratty old push mower just sitting here..... :laughing:

 

[boggen]

when i initially saw thread title. then saw the mower deck pictures. i was surprised it was not a sickle bar.

perhaps. i have just seen a few to many sickle bars with side mounted on a tractor to deal with ditch mowing.

anyhoots. my concern is with tubing size. if ya go to small say 1/2" vs going 3/4" or 1" size. you may end up with hyd oil over heating. and less power at the pump on the mower deck. i honestly haven't done friction loss for hydraulic hoses. but i would imagine over the length of hose you are talking about. going to small could cause you problems. go bigger hose and reduce at the ends.

as far as pump/motor sizing, i would expect to be able to call manufacture and get some sort of flow chart. for RPM to GPM for any given pump/motor over a range of RPMs. once i got a enough charts. i would overlay them all into a single chart. then if doing pullys / belt drive. were pully on blade is smaller than pully on the pump/motor. i would work out the difference and plot the blade tip speed on the one chart. to find the best pump to suit given needs. ((in regular water pumps for say sizing a pump for a pond or well)) this would be more known as creating a system curve and applying different pump curves to the system curve to find correct pump for the given setup.

 

[dfkrug]

To size hoses for continuous motor duty, you can use the equation
D = sqrt(Q/2.45V), when D is in inches, Q is the GPM flow rate, and
V is the fluid velocity in ft/s.

A max velocity for a pressure line is about 25 ft/s, but that's pushing it.
If you went to half of that and 7GPM, a half inch hose is fine, if not
absurdly long.

You can get PDF catalogs for commonly available motors. The designer
must find his operating conditions on a manufacturer table like the sample
I posted. This is a White RS motor, which is not the ideal one for this
task, but they are commonly available. RS motors are slow speed, so
getting the right final load speed would require a step-up belt/pulley.
Understanding the use is important, too. Will the load be at max pressure
intermittantly or for longer periods? I would try to use a motor that
made use of the max pressure available from the implement pump.

 

[boggen]

To size hoses for continuous motor duty, you can use the equation
D = sqrt(Q/2.45V), when D is in inches, Q is the GPM flow rate, and
V is the fluid velocity in ft/s.

i would assume this is inside diameter of hose?

if Q = 7 GPM
if V = 12 ft/s
D = 0.49 inches.

A max velocity for a pressure line is about 25 ft/s, but that's pushing it.
If you went to half of that and 7GPM, a half inch hose is fine, if not
absurdly long.

continuous duty, and i am going to assume once he tacts on clamps and extra hose to get around joints of the back hoe and then the extended arm. 30 to 40 feet of hose one direction. plus double that for return hose, for a total of 60 to 80 feet.

i would consider that a pretty good length. then again. i don't know hydraulic specs. just water specs for ponds and wells. and don't know how much friction loss or rather PSI loss that would occur. but i would assume a good amount of psi loss, perhaps i am in the wrong.

You can get PDF catalogs for commonly available motors. The designer
must find his operating conditions on a manufacturer table like the sample
I posted. This is a White RS motor, which is not the ideal one for this
task, but they are commonly available. RS motors are slow speed, so
getting the right final load speed would require a step-up belt/pulley.
Understanding the use is important, too. Will the load be at max pressure
intermittantly or for longer periods? I would try to use a motor that
made use of the max pressure available from the implement pump.

*scratches chin*

if the you know the GPM and PSI of the pump and a motor of like equal size. you should have approx equal. RPM's and torque at the motor. with exception of pressure loss form hoses and efficiency losses of motor and pump.

if you had a bigger hydrualic pump on tractor. that sent more GPM and had more PSI than motor can handle. then there would be a good chance of the motor over heating. due to spinning way to fast. or not able to handle the pressure.

if you had a smaller hydrualic pump on tractor, and a bigger motor, that could handle GPM and PSI. the motor will not spin as fast. BUT, you would not be over spinning the motor to a point of over heating. or cracking it due to much pressure. to deal with motor not spinning as fast. it would just require a bigger pully on motor and a smaller pully on the blades.

to me "dfkrug" you are stating for a motor = to or bigger than the pump on the tractor for both GPM and PSI. if so i would be in agreement.