Brigde Crane calculation

[lukin1977]

I posted this thread in the electric motor forum but got none replies so I am posting it again here. Thanks!

I need to calculate the electric motor and speed reducer for a small bridge crane. Its been very long since I have done this type of work and I not sure how to do it

Max crane load will be 2500 kg
Bridge crane weight 500 kg aprox

Number of wheels 4
Wheel diameter 132 mm

Speed 0,3 m/s

The motor and reducer will move with a chain drive a long shaft (5 meters) that connects 2 of the wheels

Any help please?

lukin1977

 

[drawoh]

lukin1977,

This is not a clear question. What does the motor do? What allows the motor to lift stuff?

--
JHG

 

[MikeHalloran]

He's clearly talking about the motor that drives the crane bridge along the runway. There is a separate motor for lifting.

I think basically you have to decide how big a piece of dirt the wheels have to ride over.
... or just look in anyone's catalog and use that number.



Mike Halloran
Pembroke Pines, FL, USA

 

[lukin1977]

The motor is for driving the crane on the railway.

Mike: I dont understand your comment about the piece of dirt. Could you explain?

 

[Occupant]

Maybe something like this --->

 

[Occupant]

Screwed up, I hope this makes more sense --->

 

[lukin1977]

Occupant: Why didn´t you add the crane´s weight to the load?

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
Torque = Friction force x wheel diam /2 = Load x Us x wheel diam/ 2 Us = static friction coeff for steel = 0,4
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?

 

[Occupant]

I overlooked it, that's way, but I had to do it over again anyway - I (or my program) got confused by the units.
The difference, however, is that I put a 50mm dia. bushing in the wheels and that's what generates the friction opposing the motion.

 

[lukin1977]

Thanks,
the two motorized wheels do not have a bearing of 50 mm. They have a keyed shaft
the remaining two wheels have a bronze bearing diameter 30 mm

 

[Occupant]

Then the keyed shaft has bearings. I just selected 50mm bronze bushings because you didn't specify and if they are ball bearings, you'll have to adjust the coefficient of friction.