# Stepper Motor Sizing

#### mioumitsou

Apr 26, 2016
2
Hello Forum,

Im relativaly new to the world of electronics...
recently I started my own project, that being a solar array drive mechanism. I have sized my stepper motor to be in the range of 0.07 - 0.1 Nm but I am lacking a feel for this number. Could sombody please point me to some applications for such motors so I can get a feel for the possibilities of this type of motors?

Also, I would like to ask the same uestion regarding a stepper motor of mNm.

THank you!!!

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,062
Welcome to electronicspoint.

1 Nm can exert a force of 1 N on a 1 m long lever (or a drum with a 1 m radius). 1N is roughly eqivalent to the force a mass of 0.1 kg receives by earth's gravitation.
A torque of 1 Nm allows you, for example, to lift a 100 g bar of chocolade at the end of a 1 m long stick mounted to the motor.
If you need to apply more force (aka lift or move heavier weights) you'll need a motor with higher torque or some gears to increase torque at the cost of rotational speed.

#### mioumitsou

Apr 26, 2016
2

So i have further continued my calculations and still lack confidence in my numbers. Reading through literature I came to understand that step motors along with other motors follow a type of trapezoid profile (acceleration -> ct velocity -> deceleration). The maximum torque required from the motor is found in the acceleration/deceleration range where it must overcome the bodies inertia. The problem that I am facing is that in my design I am not facing an acceleration range.

For an example of what I mean, I need to rotate a solar array 300 deg within 23min. Hence there will be no continuous rotation of the step motor but rather a rotation of 0.217 deg/sec. How would I go about to calculate the torque required by my motor?

#### duke37

Jan 9, 2011
5,364
Unless your array was in existance since the beginning of time, there will be an acceleration phase.
The torque required will probably be due to unbalanced mass and wind and snow loading loading, also bearing friction. You should measure these.
At the rates you need, it would be better to run your motor at a much higher speed and gear it down to suit. This will give more torque and so enable a smaller motor to be used.

0.217 deg/sec = 13 deg/min = 0.036 rpm
A 1000:1 gearbox needs the motor to run at 36 rpm, still very slow.

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