Raising a mass at constant velocity

[engineeringstudent90]

I want to be able to calculate the force required by a hydraulic cylinder to lift a 3500kg load vertically to a height of 1.2 meters in a time of approximately 3-4 seconds. Can someone help. All comments will be hugely appreciated.

[swansont]

Technically, if you're raising it at constant v (of ~1.2m/3 sec = 0.4 m/s), the force needed is mg = 3500kg*9.8m/s = 34300 N. But if you start from rest, you need an additional force, because there is an acceleration involved in getting from v=0 to the final speed. So it depends on how quickly you want to get up to your constant speed.

[lesolee]

I want to be able to calculate the force required by a hydraulic cylinder to lift a 3500kg load vertically to a height of 1.2 meters in a time of approximately 3-4 seconds. Can someone help. All comments will be hugely appreciated.

 

Following on from swantsont's response, let's look at the acceleration.

Remember your maths from when you were 16 years old?

SUVAT

S=ut +(1/2)a*t*t

S= distance travelled

t= time taken

a= acceleration

We start from stationary so u=0

 

S= (1/2)a*t*t

a= 2S/(t*t)

 

Accelerate 0.6m in 2 seconds. I get 0.3m/s/s

The required acceleration is so much lower than the gravitational acceleration you can pretty much ignore it in this case.

 

Of course re-reading the post title

you want "constant velocity".

Well you might

want to moderate this and allow plenty of time to accelerate and decelerate, otherwise the inertial load will require infinite force!

Edited December 3, 2012 by lesolee

[InigoMontoya]

I want to be able to calculate the force required by a hydraulic cylinder to lift a 3500kg load vertically to a height of 1.2 meters in a time of approximately 3-4 seconds. Can someone help. All comments will be hugely appreciated.

 

Work = mgh = 3500*9.8*1.2 = 41.16 kJ

 

Time = 3.5 s.

 

41.16 kJ/ 3.5 s = 11.76 kW.

 

Nothing's ever perfect without losses and such so I'd buy a 15 kW hydraulic pump.

 

 

I know, not what you asked for, but it's what the real world wants to know.

[alpha2cen]

I want to be able to calculate the force required by a hydraulic cylinder to lift a 3500kg load vertically to a height of 1.2 meters in a time of approximately 3-4 seconds. Can someone help. All comments will be hugely appreciated.

Minimum force calculation method.

Constant velocity movement is impossible said before.

[latex]L=\int_{0}^{t_{L}}Vdt[/latex]

 

Teoretical maximum power calculation

P=F(0.5L)/0.5t_L=(36000N)(0.5x1.2m)/(0.5x3.5s)(w.s / N.m)=12.3kw

Edited December 5, 2012 by alpha2cen