Constant force opposing hydraulic winch

Question

I have a situation that I am hoping to solve with the use of electric motors, and a variety of controls. I have a hydraulic winch which turns at speeds from 0-60 RPM. This winch is coiling and uncoiling a rope. Under normal operation, it would have anywhere between 200-300 pounds of pull on the rope it is coiling or uncoiling. There is a situation, in our shop, where we would like to simulate the working conditions of our hydraulic winch. I would like to attach another electric winch that would pull 200-300 pounds on the rope as the hydraulic winch is unspooling and also keep a pull of 200-300 pounds on the rope as the hydraulic winch in coiling. What would the simplest way of achieving this be? Thank you very much for your support.

Hello Everyone, I would like to thank you all for your great input. As much as I would love to hang a weight off the end of this winch, which would work out perfectly, there are situation where that setup would not work. I need to be able to simulate this 200-300 pound pull. The best way I can describe the situation is this. Lets say you are on a boat traveling though the water pulling in a rope with a buoy attached in the middle of your rope. As you are sailing though the water there is a constant pull on your rope but if you stop there will no longer be that constant pull on your rope. If you are sailing and you winch in your rope, the buoy will reach the winch and get wrapped up nice and tight the way it is supposed to. If the boat stops, there will be no pull on the rope that is in the water allowing buoy to fall forward on the winch as it passes over the top of the winch. This will cause big problems. So with all that said, I am trying to build something that can be used in our shop and on the ship to retrieve the system if they have a propulsion failure. So it needs to be relatively small, shouldn't be a problem with only 200-300 pounds pull and i can attached as much feedback \ encoders on either unit I want. I have been looking at some oil shear technologies but would much rather do this electrically. Thanks and I look forward to hearing more about your suggestions.

Answer 1

As others have said, an electric motor load solution could be quite expensive, but depending on your budget you could look into brushless DC motor torque control.

Due to the low rpm requirement you could get away with using a relatively small motor (something on the larger side of hobby size brushless motors) and gear it down with either a gear box or a belt system. You would want to look for a controller that has torque control which basically means it can sense the current through each phase and convert that current to a torque and use that in a feedback loop to maintain a set torque.

Another possibility cheaper control option would be to use a similar motor and reduction setup but to use a regular ESC to control the power to the motor and implement a large torsion spring between your pulley drum and the inner drive shaft. This would allow you to use a relatively simple encoder feedback to measure the relative angle between the outer drum and drive which would translate to a certain torque on the spring. Maintaining that angle with the control loop would effectively keep a constant force on the rope.

Once you start down the path of one of these methods I would consult with others to verify the specs of your motor and controller choice. It can be very thermally demanding on a motor to maintain that force at very low or no speed and you would need a considerably beefier motor and controller to hold that static load indefinitely.