Hi-torque Hydraulic motor question

[easygo]

I'm thinking of buying a winch that is powered by a hi-torque hydraulic motor. The seller says that it is hooked up so the motor directly drives the drum. I checked the specs on the said motor and according to the manufacturer it is a 250rpm @ maximum input of 20 GPM/3000psi. My tractor produces about 6-7 gpm around 2000psi that is well within the operational parameters of the motor. (It is detailed down to about 1gpm)

The chart on the manufacturer's site says that the motor at that input (6gpm/2000psi) produces 4970 in/lbs of torque that is roughly equal of 415 ft/lbs. The winch speed at this input is about 60 rpm.

My question is: How do i arrive to a pulling power number (lbs) on the cable, when presented with this data? I assume the winch drum is 3-5" diameter so that will certainly decrease the power but by how much? I'm waiting for numbers from the seller. It fits about 120-130ft of 3/8 cable.
If I get this thing it would serve as a log puller behind my tractor.
Thanks for your help.

 

[RodNH]

Divide the torque in ft-lb by the sum of the radius of the drum and 1/2 of the cable diameter in ft. That will give you the pulling force. For a 3" diameter drum with 3/8" cable, that equals 415/0.1406 = 2952 lb. As the first wrap of cable on the drum represents the smallest radius, that first wrap provides the greatest pulling force (and the slowest speed in ft/min). As the later wraps are at a larger radius, the pulling force decreases and the speed in fpm increases since the drum speed is constant at 60 rpm.

 

[easygo]

Thank you guys! With your help I came up with actual numbers. After I received the correct winch drum diameter (2.5") from the seller I did the number crunching.
Based on the formula posted here by RodNH in a perfect world the winch would produce 3464 lbs of pull on the bare drum.

However. Reality chafes, drags and restrict that perfect world even in the high power of hydraulics. I was unaware of the extent of this gash in reality until AKKAMAAN helped me out with some additional calulations via a PM.

So. Taking many of those into account the winch would have an actual pulling power closer to 3297 lbs on the bare drum.

Thank you both for helping me out. Now I just have to make up my mind if that is enough for me.

 

[GE222]

Maybe my brain is a bit foggy. Will a 60 RPM winch be ok? Seems a bit fast.

 

[LD1]

Maybe my brain is a bit foggy. Will a 60 RPM winch be ok? Seems a bit fast.

60PRM on his 2.5" drum is only ~ 45 feet per minute line speed on the first wrap. I thik that is about right. Any slower and it would seem TOO slow for skidding logs.

 

[easygo]

It would not be all that fast but my other option is to look into a winch intended to be used on a vehicle. Those are really slow. Something in the neighborhood of 10-20 ft/min. My concern is about the proper amount of pulling power and the no freewheel option on the winch. Any suggestions for a home made clutch that could be engaged/disengaged when no load on the winch line?

 

[J_J]

You can get your free wheeling from a hyd winch, but it will be extremely slow. If you connect a hose with a gate valve across the hyd motor, and you pull on the cable, you are causing the hyd motor to act as a pump, and it has to move so many cu in of fluid per minute. With the correct HP, it would turn OK, but you don't have the physical force /HP to make it turn very fast. Perhaps if the winch was driven by a clutch assembly, it would be feasible, and it still would be direct drive. Also, if the winch body had, say a square PTO shaft that the hyd motor could slide in and out on a sliding rail.

Square shaft adapter on hyd motor, and square female adapter on the winch body.

 

[easygo]

... if the winch body had, say a square PTO shaft that the hyd motor could slide in and out on a sliding rail.

Square shaft adapter on hyd motor, and square female adapter on the winch body.

Thanks for the idea J.J. This is actually quite doable. With a few inch piece of a square pto shaft on the motor and another on the winch side. Just stop the whole thing and slide together. Could be done simply and cheaply.
The motor has power in and out with equal speed and power in both direction. Now it is mounted directly on a home fabricated winch drum. Very simple and quite fail safe. It was built to be a lighter lifting unit in fishing application.

 

[Yoseph]

you are right EASYGO 60rpm is too fast, 10 rpm seems to be normal speed, if you have 3 inch radius drum the first wrap speed cable will be 2*3inch*3.14*10rpm=188.4inch/min average of 15.7 feet / min
in the case of 60 rpm the speed cable is:
2*3*3.14*60=1130inch/min = 94.2 feet/min
the speed increases at each wrap cable...
best regards

 

[Yoseph]

i have a question for you guys
if there is a reducer box like 1/37 ratio what will be the output torque of the drum ?