# Project for school help

For a school project I decided to try and find the power efficiency of a stepper motor. I had envisioned setting up a stepper motor to a pulley system and recording the time it took for it to raise a certain mass. I had planned on comparing the potential energy of the now raised mass to the power input of the stepper motor which I would use P = V * I. Although I'm a bit confused about how I would go about finding both V and I. I currently have a Nema 17 Bipolar stepper motor rated at 2.8V and 2.0A which is hooked up to an Arduino motor shield connected to an Arduino Uno Rev3. I saw that someone said that stepper motors draw a constant max current so would that mean that the power input of the stepper motor is always 2.8V * 2.0A? Or does the voltage vary depending on the speed I have the motor rotating? Should I use a different kind of motor? I am very new to this so please excuse me if these are obvious questions. Thanks in advance

Nema17 tells about the dimensions of the mechanical mount of the stepper.
Forget about the 2.8 volt. 2 Amp tells this stepper needs a current controlled stepper driver. A DC motor driver will no do.
Current limiting drivers, as I got it, switches the current on an of during the time the coil is energized. Hook up an oscilloscope and look! It will not be that easy to measure the energy being used. Also note that steppers consume current also at a stand still.

AS Railroader pointed out, the efficiency of a stepper motor being held in position is exactly ZERO. Lots of power applied and no work being done. Holding in place is not work.

Paul

So said the school teacher, standing, having 200 lbs on the shoulder is no work.... but for steppers it is.

Work = force * displacement, no displacement = no work, however the teacher's metabolic processes are functioning, so there IS energy being consumed.

Thanks for the responses, seems this was more than I bargained for. Maybe I'll try and find the holding torque of the stepper motor rather than its power efficiency.

That sounds much more obtainable.

trumanyardley:
Thanks for the responses, seems this was more than I bargained for. Maybe I'll try and find the holding torque of the stepper motor rather than its power efficiency.

That's very sensible.

If you want a slightly tougher challenge you could measure the torque when the motor is moving. Stepper motor torque falls off rapidly as the speed increases.

Your idea of lifting a weight will work well to measure the power efficiency of a brushed DC motor (and the gear train if used).

Measure the voltage input and current draw of the motor using a multimeter.

Robin2:
That's very sensible.

If you want a slightly tougher challenge you could measure the torque when the motor is moving. Stepper motor torque falls off rapidly as the speed increases.

Maye a torque - RPM curve?

jremington:
Your idea of lifting a weight will work well to measure the power efficiency of a brushed DC motor (and the gear train if used).

Measure the voltage input and current draw of the motor using a multimeter.

Ehh. Will that work well? The wave form of voltage and current will likely not be sinusoidal. Many (most?) multimeters assume a sinus curve to make a correct measurement.
There are multimeters showing true RMS for other wave forms but OP need to verify that. Else measuring the efficiency of a stepper will not be worth much.
What do You think? I had a one year univercity course in electrical mearuements a long, long time ago. How much more capable the modern multimeters are is beyond my knowledge.

A brushed DC motor does not work with AC.

jremington:
Measure the voltage input and current draw of the motor using a multimeter.

With a stepper motor the power draw is part of the specification - most of them give details for the coil current and nominal voltage or coil resistance.

If you want to measure in more detail I reckon you would need an oscilloscope that could follow the current limiting process of the stepper driver. And I reckon it would be a pointless exercise.

The OP's decision (in Reply #5) to give up on efficiency and just measure torque seems very sensible to me.

...R

With a stepper motor the power draw is part of the specification - most of them give details for the coil current and nominal voltage or coil resistance.

It was about a BRUSHED DC MOTOR, for those of you who have trouble reading.

The OP's decision (in Reply #5) to give up on efficiency and just measure torque seems very sensible to me.

The torque is part of the motor specification, at the rated current.

jremington:

I missed that.

I guess I gave too much attention to the Title of the Thread

...R

Is it interesting to measure performace in a few different aspects? Efficience is not soo easy....

real world applications is really all we care about although we do love to talk about theory.

consider a pulley on top of a door
your stepper with a take up reel. a take-up spool with something thin like a pencil is much better than something larger in diameter.

use fishing line and a cup to hold weights
raise the cup while ramping up the speed
you will have to figure the rate change.
Assume 1st test is by rate of 1 additional step per second
Then 1 step every 1/10th second, then 1/100 th… and so on

At some point your weight will cause missed steps at some RPM,
You can double the weight and repeat,
Then half the weight and repeat.
The stepper will start to miss steps once the weight of the cup is greater than the motor output.

I would suggest trying it at the lowest possible voltage that will work with the motor and the driver. but at or lower than nameplete voltage. The current should be set once for all tests.
this will give you a base line.

Then increment voltage to the driver. increase in steps of 50% of nameplate to get a graph.

You will get curves and since most ratings like horsepower are ‘work over time’.
Using the above, you will have a way to determine weight over time.

Horsepower is a unit of measurement of power, or the rate at which work is done. A unit of power equal to 550 foot-pounds per second

Hello,

As the title says I'm doing a project for school in which I'm going to examine the relationship between the rpm of a stepper motor and the weight it is able to lift. Basically, my setup is a lever that is attached to the shaft of a NEMA 17 stepper motor which is controlled by an Arduino motor shield. 20 centimeters out from the pivot point is where a mass will be hanging. Upon my first trial, the motor couldn't even lift 50 grams even after I lowered the RPMs so I was hoping I could get some clarification on some things. First off my motor is rated for 0.59 NM and I was wondering how that would translate to how much my motor could lift and from what distance. Secondly, I've seen mentions of static torque and dynamic torque and possibly accelerating the step speed of the motor, is this something I should try rather than just running at a constant step speed? Anything helps as I'm still very new to all this.

What school gives You a task You are not ready to handle?
Or.. is this an easy way to awoid working Yourself?
I did my graduate work mote than 40 years ago, long time before both Internet and Arduino forum, and managed. How? By reading specs, documentation etc.
Who will employ a guy that needs this kind of help?

When you have an Arduino question, there we’re here to help.