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### Author Topic: Lift weight motor calculation  (Read 15256 times)

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#### felltery

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##### Lift weight motor calculation
« on: August 26, 2008, 11:48:08 AM »
Hello forumers

I live on the fourth and last floor of a building. There i have my hobby room. On one side of the building there is an empty space. I want from this side to make an elevator (not for people of course) to elevate heavy things for my projects. Not more than 100 kilos.

I would not go into more details for this crane as i think are not important but if you want i can analyse you all the construction.

The thing is that i want to choose drum and motor. I already have a torque converter that will reduve the input rpm with a ratio of 1/30 (approximately).

Here are my calculations:
I want to have a lifting speed about 20 meters per minute (the carriage will make about 30 sec to come to the 3rd floor).
The motor i will choose may have 1500 or 3000 rpm. Suppose i get the one with the 1500rpm
After the torque converter the rpm will be 50rpm
In order to get a speed of 20mt//min, the drum must be calculated:
Every minute we have 50 turns, so every 50 turns there must be 20 meters. This means that every turn of the drum, it must pull 20/50 = 0,4 meters. The peripherial of the drum must be 0.4 meters. This means that the diameter of it must be:
per=pi * Diam = > Diam = per/pi = 127.38cm. The drum must be about 130cm diameter.

Up to here i can handle. Now what should be the power of the motor to lift with this drum 100 kilos?

Any help will be apreciated
Thank you

#### spic0m

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##### Re: Lift weight motor calculation
« Reply #1 on: August 26, 2008, 14:49:11 PM »

#### felltery

• Guest
##### Re: Lift weight motor calculation
« Reply #2 on: August 26, 2008, 15:46:11 PM »

A ready made what? A ready made crane? I told you in my post that i already have the equipment, i need only the drum motor. Will the ready made crane be chaper than a drum and motor? You are not talking about chinese cranes are you?

And why much safer?

And after all, why not build it my self?

#### serafino

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##### Re: Lift weight motor calculation
« Reply #3 on: August 26, 2008, 23:17:32 PM »

#### spic0m

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##### Re: Lift weight motor calculation
« Reply #4 on: August 26, 2008, 23:25:44 PM »
With 200 euro you can buy a non chinese crane wich is already passed a test that it works with safety and it has not a meter and 30 cm diameter, which is to big i think. Maybe it work, or i'm sure it'll work but IMO sometimes is better not to rediscover the wheel. Nevertheless if you wana go and build it, fine by me and glad to help anyway i can but still that is my opinion  .

#### felltery

• Guest
##### Re: Lift weight motor calculation
« Reply #5 on: August 26, 2008, 23:34:08 PM »
Every minute we have 50 turns, so every 50 turns there must be 20 meters. This means that every turn of the drum, it must pull 20/50 = 0,4 meters. The peripherial of the drum must be 0.4 meters. This means that the diameter of it must be:
per=pi * Diam = > Diam = per/pi = 127.38cm. The drum must be about 130cm diameter.

There is an error here. The diameter is not 1 meter and 30 cm. it is:

0.4/3.14 = 0.127mt = 12.7cm

Quote from: spic0m
With 200 euro you can buy a non chinese crane wich .......
With 200 euro you can buy 5 motors and drums...

Quote from: spic0m
Maybe it work, or i'm sure it'll work but IMO sometimes is better not to rediscover the wheel........
No i do not rediscover the wheel. I am building something with common knowledge. I will not try to discover magnetism, then electromagnetism, then the coil, then the effect of electromagnetism over two coils, then the rotor and stator, then the ball bearings and casting methods to discover the motor. I consider all these given and proceed directly to purchase one
« Last Edit: August 26, 2008, 23:38:37 PM by felltery »

#### spic0m

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##### Re: Lift weight motor calculation
« Reply #6 on: August 26, 2008, 23:34:51 PM »
That makes more sense.

#### felltery

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##### Re: Lift weight motor calculation
« Reply #7 on: August 28, 2008, 16:17:51 PM »
Well? Any help anyone?

#### spic0m

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##### Re: Lift weight motor calculation
« Reply #8 on: August 28, 2008, 16:28:33 PM »
There might be some charts out there that give the details you want, i'll check out and tell you.

#### Supernova

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##### Re: Lift weight motor calculation
« Reply #9 on: August 28, 2008, 19:04:35 PM »

The torque M (in Nmt) is the force applied (N) x the lever arm(mt). You must first convert kilos to Newtons:

1Nt = 0.1019Kilos => 100 Kilos = 981.3Nt

Not the lever arm. Actually, the lever arm is the radious (NOT DIAMETER) of the drum. You have already calculate the drum to be 12.7cm so the radious = 6.35cm. To convert it to meters we divide it by 100 and this makes the radious of the drum 0.0635mt.
The torque is:

M = F X L = 981.3 X 0.0635 = 62.31 Ntm

Now, to calculate the mechanical power required to achive this torque, we use the folowing formula:

Pmech = M X w (it is not w, it is the greek letter "omega")

"w" is the angular velocity of the drum. The units are red sec. You provided the angular velocity to be 50rpm. To convert rpm to rad sec, multiply by (2pi/60) so:

w=50rpm x (2pi/60) =  50 x 0,1047 = 5.235 rad sec.

Pmech = M x w => Prot = 62.31 x 5.235 = 326.25 Watts.

This is the mechanical power that the motor must have to lift this weight in that speed. In ideal world, the electrical power should be the same, but calculate a motor efficiency of n = 0.8, and now:

Pel = Pmech / n = 326.25 / 0.8 = 407,81 Watts.

So, choose half a kilowatt motor and you are perfect.

The current (for 1 phase motor of course) will be:
P=U x I x cosf

P = U x I x cosf = 220 x I x 0.85 = 187 x I => I = P/187 = 2.1amps

Is that ok for you?

#### felltery

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##### Re: Lift weight motor calculation
« Reply #10 on: September 01, 2008, 22:04:04 PM »
I KNEW IT!! I knew someone would help. Where have you been all those years? Be sure, i will com back for more info...

Thankx alot

#### spic0m

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##### Re: Lift weight motor calculation
« Reply #11 on: September 01, 2008, 22:17:01 PM »
Better late than never!

#### Supernova

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##### Re: Lift weight motor calculation
« Reply #12 on: September 02, 2008, 17:45:37 PM »
Better late than never!

I suppose that for 100 kilos, felltery do not want to calculate all these staff like the boom angle and rope stress, neither the stall motor torque...
Half a kilowatt motor will lift 100kilos (with the pulley of course near to 90 degrees angle from weight to motor) like feather...

Anyway, these calculations are very nice spicom.

#### spic0m

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##### Re: Lift weight motor calculation
« Reply #13 on: September 02, 2008, 18:59:10 PM »
Where i digg it they didn't have "building an electric winch for amateurs" and since i'm not familiar with those subjects that's what i had to contribute.
Anyway you never know, after he builds the first maybe he likes to build a more pro one!

#### Supernova

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##### Re: Lift weight motor calculation
« Reply #14 on: September 03, 2008, 10:24:17 AM »
Where i digg it they didn't have "building an electric winch for amateurs" and since i'm not familiar with those subjects that's what i had to contribute.
Anyway you never know, after he builds the first maybe he likes to build a more pro one!
Yes, and maybe he will make a mega lift for constructing the bridge over atlantic