It may be helpful so research a proney ( SP ? ) brake to measure power of rotating drum.
How about weight, pulley & rope? Use various diameter pulleys or drums. Properly sized a one pound weight can counter a 100 lb. pull.
Another thought- how about a windless ? I might have to look this up.
Pronay- inventors name. Windlass.

 

To provide a specific resistance torque all that is needed is to provide a specific DC current through the run, or run and start, windings. Then to retract, just apply some AC to run the motor. No extra parts and no additional actuators or mechanisms required. The only extra thing will be a sensor so that the controller will know when to retract and how far to retract. That is even simpler than controlling the motor in the stalled mode.

 

When I was thinking about this one option was to make brake which produce friction for part when user pulls the rope and then second part which is motor (any kind, no matter) which starts to pull once user stops to pull.
Then second option was to use only motor which pulls all the time, only to allow to go even reverse, but still to rotate. After checking details this second option seems better, but I still need to find person or company, which can offer setting it up.

 

When I was thinking about this one option was to make brake which produce friction for part when user pulls the rope and then second part which is motor (any kind, no matter) which starts to pull once user stops to pull.
Then second option was to use only motor which pulls all the time, only to allow to go even reverse, but still to rotate. After checking details this second option seems better, but I still need to find person or company, which can offer setting it up.

Certainly an electric motor can provide both braking and retraction/ tension on a rope and do it very well. But you are asking for a significant amount of design effort for a product that must also be safe, reliable, repeatable, and cost-optimized. That amount of effort is a "big Deal" indeed.

 

Thats correct. How many hours of work engeneer needs to invest to get results? this way I can calculate budget maybe..

 

Thats correct. How many hours of work engeneer needs to invest to get results? this way I can calculate budget maybe..

An engineer probably wouldn't do it the way you are requesting. There is no need to reinvent the wheel. What it sounds like you want to do has been done for, I'm guessing over a century, just like Bernard said, with weights and pulleys, it's known by a few different names, rowing machine, cable machine, chest fly machine and a few I'm not listing. A Google of those names will show you.

 

An engineer probably wouldn't do it the way you are requesting. There is no need to reinvent the wheel. What it sounds like you want to do has been done for, I'm guessing over a century, just like Bernard said, with weights and pulleys, it's known by a few different names, rowing machine, cable machine, chest fly machine and a few I'm not listing. A Google of those names will show you.

Weights and pulleys and even springs can certainly provide the functionality desired by the TS, BUT they would be rather complex, large, and subject to wearing out. AND, Worst Of All, they would totally lack the "Cool Factor", which is what sells products to the group of people with lots of money and in a certain social bracket. And the technical advantage is that such a machine will not be angle sensitive because it does not use gravity.

Probably the exact functionality already exists in a linear induction motor system already available from some established motor company. That could make the package even less complex and add even more to the coolness of the new product. What the TS would then need to create would be the user interface, which might possibly even run on a standard computer.
So there the TS has a few hundred dollars worth of consultation with no charge.

 

To provide a specific resistance torque all that is needed is to provide a specific DC current through the run, or run and start, windings. Then to retract, just apply some AC to run the motor. No extra parts and no additional actuators or mechanisms required. The only extra thing will be a sensor so that the controller will know when to retract and how far to retract. That is even simpler than controlling the motor in the stalled mode.

Hi, can this be repeated all over again, or it will damage motor?

 

What is your purpose for wanting to do this?

 

Hi, can this be repeated all over again, or it will damage motor?

Yes, within limits. Fortunately the braking force can be quite large with a rather low current, because the unwinding can have a small diameter and thus a low mechanical advantage, while the rewind can be much faster because the motor is capable of a higher speed. So this sequence can be repeated constantly if a motor with a continuous duty rating s used.
AND, for MrChips, this is for some sort of exercise machine, using an electrical load instead of weights and pulleys.

 

Yes, within limits. Fortunately the braking force can be quite large with a rather low current, because the unwinding can have a small diameter and thus a low mechanical advantage, while the rewind can be much faster because the motor is capable of a higher speed. So this sequence can be repeated constantly if a motor with a continuous duty rating s used.
AND, for MrChips, this is for some sort of exercise machine, using an electrical load instead of weights and pulleys.

Thanks.
Then what it needs is some kind of variable friction clutch mechanism which is not a simple thing to design.
On an exercise stationary bicycle they use electro-magnetic induction to present variable loads.

 

No, the system does not need a friction clutch or a mechanical brake. A bit of DC through the windings of an induction motor turns it into a very good brake. The system will need some sort of encoder to know when the load is in home position and when it has been extended, and how fast and how far it has gone. Then when the pulling has stopped the brake power can switch off and some AC be applied to retract the load handle. It can be programmed to offer some interesting variables not available with any mechanical arrangement, such as an increasing efort with each cycle and variablle effort within each cycle. Quite a few interesting options, and with the motor being an induction motor there would never be any brush wear. Plus the motor costs less for a given quality level.

 

TS wants to tie a rope around the motor axle. How is he going to do that?

 

TS wants to tie a rope around the motor axle. How is he going to do that?

Actually it will be a cable and there will be some sort of spool for it to wind up onto.

 

Actually it will be a cable and there will be some sort of spool for it to wind up onto.

How long is this cable going to be?

 

Quite a few interesting options,

Just how or where do you find a motor to do this, one that turns slowly so that on return/rewind it doesn't rip the handle out of the operators hands? Putting a gear box to slow it down also increases the power needed for pull out. The reason after all of these years of doing this with weight and cables is that you have pull on the operators muscles in both directions.

 

The system will probably be diect drive and the applied AC voltage for the return will be a whole lot less than the designed mains voltage. At a lower voltage the slip is much higherand so the toque is much less. So that part is what the TS is going to need to do. It may even be adjustable, Since I do not know the rest of the details it leaves a fair amount for the TS to develop. And that is good. We provided a scheme to have the motor work as a brake and as a retraction system, as requested.

 

Nice. Cable / rope length maybe 3 m, but it will "go out" and "in" only for 1 m. I ll attach rope on disc and then disc on motor axis. Then add some sensors and similar so system will know in what position rope / handles are.

I am thinking about moment when user stop to pull and before user losen rope... in case motor works like brake then in moment before motor starts to pull there will be 0 force on rope. Because of this I still try to find solution with motor which doesnt burn when pulled in opposite direction of its rotation.. such motor would pull constantly...

 

There is a variety of motor referenced as "torque motors" that fit that description exactly. I have never used one, but I have seen the specifications. They are not common, and so you may need to get the information from the manufacturer.

 

Honestly, I cannot see how a rope connected to the motor axle is going to work.
Imagine trying to pull back a car that is already running forward.
Why not simply a rope attached to a very large tension spring?