Horsepower needed to raise curtain 1

[Tudelu]

Hello,

New to forum. Would anyone be able to supply the equation to determine what hp would be needed to fully raise from floor a: 60 foot by 18 foot by 2 lb per square foot curtain mounted to a 4" tube resting on rollers?

Would be most grateful for your help.

 

[waross]

Does it matter at all how long it takes to fully raise the curtain?
Will the 4" tube be spring loaded?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[3DDave]

In the old days they were counterbalanced with sandbags.

I guess, since many large curtains are this way, that it is 60 feet wide and you want to wind up 20 feet of material?

Anyway power = force times speed in the direction of the force. Speed is distance divided by time.

Without the time required, there's no way to determine speed and without speed, no way to determine power.

 

[waross]

As I understand the sand bagged curtains, they were gathered, not rolled.
With a gathered curtain the load remains constant.
With a rolled curtain the load reduces as the curtain rises.
But the OP wants the formula.
550 ft lbs per second = 1 HP.
You just have to add in the speed and gear reduction.
Then use a very generous factor for efficiency.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Tudelu]

Most kind of you all to answer. I would like the curtain material to roll up in approx one minute. It is a chain drive system with 60' steel tube. No spring loading.

Thank you again

 

[waross]

60 ft x 18 ft x 2 lb x 18 = 38.880 ft-lb per minute, = 1.18 HP.
Allow a generous margin for low efficiency.
A rolling gate operator with a chain drive to the roller tube will do well.
It will include settable end limit witches.
If the losses are not too great you may be able to use a 1 HP motor.
The load will be decreasing as the curtain rises.
An RMS HP calculation of the lifting cycle may validate the use of a smaller motor.
Before you settle on one minute, sit and watch the stage for a timed minute.
Few people will be happy with a curtain that slow.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LittleInch]

Which way is the 60ft? Width or height? I'm taking a guess from the 60' roll that it's 60 ft wide.

How thick is your curtain?

Does the curtain roll itself around the 4" tube?

If so, at a fixed rotational speed the curtain velocity will increase as the curtain is rolled around the tube and the circumference for every revolution gets bigger and bigger.

This is probably more than matched by the fact that as you raise the curtain you have less and less work to do.

I agree about the speed. At one minute for lets say 20 ft to make it easy, that's an average of 4" (100mm) per second. Fairly glacial.

But lets run with it - So 18' x 60' x 2lb/tf^2 is a weight of 2,160lb. that is being raised 0.33'/sec.

I work in metric so that's 1000kg(!!)or 10000N being raised 0.1m, so 1000J of potential energy per second. So 1000W or 1kW or 1.3hp.

Now add in some inefficiences and you're looking at an initial power of probably 1.5 to 2kW or 2-3hp. The last foot only needs a small fraction of that power if you're wrapping it around the pole.

Waross - 60 x 18 (not 12) x 2 is the weight (2140lb) Then you need to multiply the height it is being lifted. At worst the whole curtain is being lifted 0.33 ft/sec, so =642 ft-lbs. /550 = 1.16hp

Think about it - you're trying to lift a ton of curtain 4 inches a second and you think you could do that with a 180W motor?

But if you factor in the increasing circumference than you might only need a smaller motor and the vertical speed gets faster and faster so for a total of one minute, the first section might only climb 1" per second. Now that's really glacial.

So Tudulu, it's the wrapping it around the pole thing that is making this complicated and we don't have the information ( curtain thickness) to work it out.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[waross]

Thanks for the heads up, Little Inch.
Corrections made.
Note to self: Refrain from posting in the morning before at least two cups of coffee.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Tudelu; We have assumed that you intend to wind the curtain on the tube.
If this is not the case, please advise.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Tudelu]

Thank you very kindly Waross and Littleinch for the time spent and guidance offered. The curtain is being wrapped around a 4" steel tube which is 60 feet long. The fabric is 7mm thick. The motor is in one end only and is attached to a gear sprocket then chain then sprocket attached to tube.

 

[3DDave]

I keep thinking that a 60 foot tube, 4 inch diameter, is not going to remain straight and this will not end well.

 

[davidbeach]

Oh, no, please do tell...

 

[Tudelu]

I truly hope you are wrong as to not ending well. The tube is built by going 6 foot sections with an internal steel tube coupler which is bolted through and through. Motor system secures one end with idler securing other end. Entire roll cradled from under by rollers on 24" on center arms.

 

[3DDave]

So now there is the friction of rollers on fabric? Go with 10 hp. The difference in cost isn't enough and any additional durability will be welcomed. I suggest building a 10 foot long test piece of the final concept to check the loads.

 

[LittleInch]

OK,

An interesting little bit of calc and excel sheet working for a Friday morning.

So starting at an OD of 100mm, this roll takes 13 revolutions to roll up the curtain at 7mm thick. The end OD is 185mm.

Whilst velocity increases as it goes up, this is more than matched by reduction in weight being lifted per revolution.

So for one minute, you need an RPM of your roll of 13. That's a lot of gear reduction going on there for a motor doing say 3000 or 1500 rpm

For potential energy alone you need 680W (~1hp).

With starting friction and the friction of the gears, support rollers etc, a factor of 3 or 4 maybe needed. Once it starts moving it all gets easier and faster if you keep a constant RPM.

At the start you're doing about 7cm/sec rising to 12.5 cm/sec at the end. Slowing it down before the end would be a good idea as you will have a fair bit of inertia by then.

So at least a 2kW (3HP) motor I would say, but maybe more if you can get it. 3kw / 5hp should eat it.

A drawing, photo or sketch would be good to see.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

But as mentioned earlier, no one will be happy with 60sec, they will want something like 10-15 sec is my guess.

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P.E. Metallurgy, consulting work welcomed