Determing maximum load, knowing the torque of the motor.

[Huomenta]

Hi,

Could someone help me with determing the max weight of the cylinder in light blue?

Motor has a torque of 0,025Nm,
Gear 1 has a diameter of 4 mm,
Gear 2 is not yet defined. For this exercise, we could say 8 mm.

The dark blue parts in the drawing are shafts.

Is it correct if I'll use the formule T=F*d (T=torque, F=force, and d is distance)?
So the force in gear 1 will be 12,5N? Does it mean that the maximum weight of the cylinder will be 1,27 kg?

Thanks for feedback!

 

[desertfox]

Hi Huomenta

Yes the force at the tip of gear 1 will be 12.5N which means the torque on gear 2 if its 8mm in diameter would be

12.5N * 8/2 = 50Nmm or 0.05Nm

Not sure why you think the max weight of the cylinder would be 1.27kg.
From your diagram the cylinder sits central on the shaft and I think what you need to do is consider the inertia of the shafts and cylinder as they rotate from standstill upto final rev/min.

desertfox

 

[desertfox]

Hi Huomenta

I should have asked what is the application of such small gears?
Whats the power,speed and type of motor your using?

desertfox

 

[Huomenta]

Because F=12,5N, I calculated it to mass (12,5N/9,81) and thought the max mass was 1,27kg.
But, I guess I overlooked the inertia.

The motor I start from, is this one:

http://www.eminebea.com/content/html/en/motor_list/pm_motor/pm35s048.shtml

The motor has to rotate 1,25 rotations per minute (1 step per second). I know it isn't the perfect motor for this application, but I've only got this one at home.

From the chart, I saw for a rotation of 100 pulses per second, the output is 0,025Nm (chart of uni-const, the green line).


So, T=J*a (J=inertia, a = acceleration in radians/sec²)

a = 1step/sec *2*pi = 6,28 radians/sec²

=> J = 3,98 gm²

So, J = MR²/2
If R of the light blue cilinder is 0,05meter, the max weight will be 3,2 kg.

Please, correct me if I'm wrong.

I didn't calculate the inertia of the gears. Is it negligible?
If not, is it correct if I say: Jtot = JG1 + JG2 + JGload? And Jtot = 3,98 gm²?

 

[desertfox]

Hi Huomenta

According to this link:-

http://www.eminebea.com/content/html/en/engineering/motors/pm_motor/selection_pm/torque.shtml

your motor is only capable of a torque 0.01 to 0.02Nm your going to overload it.
What you need to do is find out what your mechanical load is in terms of torque and then see if the motor you have is capable of driving it.
Also multiplying radians by 1step/sec does not give angular acceleration.
Sorry I have to ask are you an engineer?

desertfox

 

[drawoh]

Huomenta,

Is this thing rotating at steady speed, or is it a servo-system of some kind?

Stepper motors normally are sized by rotor inertia. Your load should not exceed ten times the motor inertia, and you should try very hard to keep the ratio below five. The lower the better.

JHG