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Trying to make sure that calculations are correct. Motor calculation.

Trying to make sure that calculations are correct. Motor calculation.

Trying to make sure that calculations are correct. Motor calculation.

(OP)
Hello I want to make sure that the calculations I am doing are correct.

I am trying to move a refrigerator wirelessly (I know, please don´t ask why).
This refrigerator weighs 70Kg and I´m trying to figure out if I use 2 or 4 motors.
Asumming I will use 4 motors, those 70Kg will be distributed for the 4 motors.
The static friction coefficient is 1. I have attached an image

https://drive.google.com/file/d/0BwBiiNcJ8DICQS13T...

With wheels with 4cm radius I have calculated about 7Nm of torque.
Also the RPM is about 500.

Are my calculations ok? Thank you in advance

RE: Trying to make sure that calculations are correct. Motor calculation.

Are the wheels turning at that rate or is it the refrigerator? Which axis is the refrigerator rotating about? Did you include wind resistance in your power calculations?

I cannot open the attachment.

RE: Trying to make sure that calculations are correct. Motor calculation.

The 500 RPM speed to fast to move object!

RE: Trying to make sure that calculations are correct. Motor calculation.

Are your wheels locked up? Assuming they're free to spin you wouldn't be using the coefficient of friction in your calculations. You'd need the rolling resistance (quite a bit lower than 1.0)

RE: Trying to make sure that calculations are correct. Motor calculation.

The refrigerator (no, I won't ask, but I AM CURIOUS!!!!!) is on top of the roller-radio-gadget, right?

If so, you will be much, much more stable if the wheel are not UNDER the refrigerator platform, but are outside of the platform so they have a larger moment arm against acceleration and turning over.

Figure walking speed.
1/2 meter/sec horizontal speed = 50 cm/sec.
From a 4 cm radius wheel = 24 cm circumference = only want a 2 rev/sec or 120 rpm

RE: Trying to make sure that calculations are correct. Motor calculation.

You did not describe how the motors drive the wheels, so it's hard to say whether 2 motors are better than 4 motors. If you are driving all 4 wheels, then 1 or 4 motors would likely present the least complexity. One motor with some sort of power distributing mechanical drivetrain would ensure equal and reliable drive torque at each of the 4 wheels. But 4 motors with each driving its own wheel would allow precise speed and torque control using electronics.

Another consideration is how you intend to steer and/or brake the vehicle. 7N-m at each of 4 wheels at 500 rpm is a bit less than 2hp. But the 8cm dia wheels turning at 500 rpm is 410 ft/min, which is a pretty good pace.

RE: Trying to make sure that calculations are correct. Motor calculation.

If the wheels are turning, rolling friction mentioned above is the number to use, then tack on an additional 10% for bearing friction.

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