Bridge crane motor calculation

In my opinion the following proceeding may be considered:
If the maximum weight it is 2500 kg [=9.8 *2500 N] ascends by 0.3 m/s then P=8.9*2500*0.3=6.68 kW netto. If the motor eff.=0.8 and reducer eff.=0.9 then motor required power will be 6.68/.9/.8=9.28 kW.
If the wheel diameter is 0.132 m then the time required for one turn is:
length/speed= time
0.132*pi()/0.3=1.38 sec or 60/1.38=43.4 rpm.
Let’s say the reduction ratio will be 34.5. Then the motor rpm will be: 43.4*34.5 =1497.3
[1500 rpm rated]. [minimum motor 9.28 kW/1500 rpm.].
However, since the motor works and stops you may reduce the required power according the duty type-see for instance IEC 60064-1 for duty type.

lukin - do you need a motor for travel? Or for lifting? Or do you need two motors? One for travel and one for lifting? Or, perhaps three motors? One for lifting, one for bridge travel and one for trolley travel?

If it is only for travel, then the weight doesn't enter the power calculation directly and if it is for lifting, then the wheel diameters etcetera are not important.

And speed - is it lifting speed or is it travel speed?

Can you, please, make your question a little bit more complete?

Gunnar Englund
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Half full - Half empty? I don't mind. It's what in it that counts.

My mistake: the lifting “wheel” it is call “drum”[I think] and compared with 50 ton bridge crane- the smallest bridge crane I ever saw- has to be about 25 cm diameter. Now it seems to me the 4 wheels are the entire bridge “legs” indeed and they are not form a 4 stages [rope pulley] reducer as I suspected .
The bridge has to be “one shaft” that means a single beam on which the trolley moves.
Since the total bridge weight it is mentioned I think this has to be the bridge moving drive motor about .

I can't figure it out either.
I don't think anyone can until we get to know what motor(s) it is about.

Gunnar Englund
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Half full - Half empty? I don't mind. It's what in it that counts.

Sorry for my late reply

The motor is for travel only

The wheel are for travel. Speed is traveling speed.

The brigde crane as I said is small

It travels on two railways. Distance between rails is 5m aprox

2 of the 4 wheels are motorized and are coupled to a common shaft that has a sprocket in the middle. The sprocket will be driven by the motor and speed recucer that I need to calculate

Load = 2500+500 = 3000 kgf = 29419,95 N
wheel rpm = v/r = 0,3x2/0,132 = 4,54 rad/s = 43,14 rpm

i= motor rpm/wheel rpm = 1745/43.14 = 40,2

Friction force = Load x Us
Us = static friction coeff. For steel = 0,4
Torque = Friction force x wheel diam /2 = Load x Us x wheel diam/ 2
Torque = 29419,95 x 0,4 x 0,132/ 2= 776,68 N.m

motor torque = 776,68 / 40,2 = 19,32 N.m

motor Power = 19,32 x 1745 x 0,1047 = 3529,89 W

3,5 kW seems too big to me

what am I missing?

Is the crane sliding? If not, you shall not bother about friction coefficient for steel. Steel wheels on steel rail would be more like 0.05 - 0.1

Gunnar Englund
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Half full - Half empty? I don't mind. It's what in it that counts.

the wheels are not sliding

using Us=0,05 the motor`s power is 661,38 W
using Us=0,1 the motor`s power is 882,44 W

I will install a 1,5 HP to compensate for losses
thanks for the correct friction coefficient Skogsgurra