Measuring Efficiency with Arduino Motor Shield

:slight_smile:

Before I state my question, let me describe my project setup first. What I want to do is measure the efficiency of an electric motor powered by a battery. I want to see how long it will last on its own. Then I am going to use a system of gears and attach that same electric motor in series with another motor to create a "generator". The purpose is to see if the system with the "generator" will last longer on the same amount of power as the system that was just motor and battery. Theoretically it will work but that is why I want to test it. Technically I could just use the motors and batteries and leave the Arduino out entirely but I want to measure the speed, direction, and power usage to get a graphical representation.

So here are my questions:

  1. I want to power the motor and the Arduino separately. Is there a way to have the motor plugged into the Arduino without getting power from it? All I want the Arduino to do is measure the efficiency. I don't want it to have any effect on the power of the system. Basically I want the motor to get power from a 9v battery only and I want the Arduino to be powered by the usb only without them having any effect on each other.

  2. Most of the motor shields say that they measure speed and direction. Do I need a separate shield to measure voltage/amperage?

This is the Arduino I plan on using:
http://Arduino Uno R3- https://www.sparkfun.com/products/11021/
Motor Shield:
Seeed Motor Shield- http://www.radioshack.com/product/index.jsp?productId=37846196/

If you have any suggestions or anything I'll take them. This is my first Forum Post about anything ever and it is also my first time every building anything electrical so bear with me. Thanks for your help.

The Seeed Motor Shield does have separate logic and motor-power inputs, so, yes, you can operate the Arduino and motor board on separate supplies. They do have to have a common ground, though, which is taken care of by the shield.

The L298 does not have a current measurement output. You would need to incorporate a separate current shunt resistor to measure the current drawn by the motor controller and motors. To measure the motor supply voltage, which is higher than the Arduino supply, will require a voltage divider.

tylerdillehay95:
Is there a way to have the motor plugged into the Arduino without getting power from it?

What exactly do you mean by "plugged into" ?
And are you referring to the motor that is acting as a generator or the motor that is driving the generator?

You can use the Arduino analog inputs to measure the motor voltage (on either motor) as long you use a voltage divider to ensure that the voltage cannot ever exceed 5v or fall below 0v. You will need to connect the Arduino GND to the motor GND - but that connection may happen within the motor shield.

To measure power you need to measure amps at the same time as volts and measuring amps is not nearly so simple.

The usual way is to feed the motor current (I will measure the generator in a moment) through a very low Ohm resistance - maybe 0.1 Ohms or 0.01 Ohms - and measure the tiny voltage across the resistance, The current can then be calculated using Ohms law. The PROBLEM is that the Arduino ADC in a Uno cannot measure those small voltages and you will need an external precision amplifier. The Arduino Mega and Leonardo do include amplifiers for this purpose.

For the generator you need to have a load resistance - at a guess 10 Ohms might be suitable. Again, measuring the voltage drop across the resistance will allow you to calculate the current. The ADC in the Uno may be able to measure the voltage across that resistor. For any given generator and test conditions there is probably an ideal load resistance that allows the generator to create maximum power but I don't know how to figure that out apart from trial and error. Others here may know.

...R

Please do not cross-post. This wastes time and resources as people attempt to answer your question on multiple threads.

Threads merged.

  • Moderator

tylerdillehay95:
Theoretically it will work

No it won't...basic law of physics.

Thanks a lot for the info!
Switching to an Arduino Mega won't be a problem at all as I haven't bought anything yet.

Let me make sure I understand this correctly:
In order to measure actual power usage and production I need to measure voltage AND amps. So I can use an analog voltage divider to measure the voltage. Then, using Ohm's Law, I can measure the voltage through a resistor to get amps? So in order to do this I will have to buy a breadboard and set up resistors and stuff right? Forgive me if my questions make me sound like an idiot.

I found this. I don't even know if it exists but I think it might be what I need.

All of my other questions were answered perfectly by the way. Thank you. I'm not sure what cross posting is thought. Sorry. I didn't see anything like this anywhere else...

tylerdillehay95:
. I'm not sure what cross posting is thought. Sorry. I didn't see anything like this anywhere else...

First page of this section there is a heading...."How to use this forum-Please read"

tylerdillehay95:
Let me make sure I understand this correctly:
In order to measure actual power usage and production I need to measure voltage AND amps. So I can use an analog voltage divider to measure the voltage. Then, using Ohm's Law, I can measure the voltage through a resistor to get amps? So in order to do this I will have to buy a breadboard and set up resistors and stuff right? Forgive me if my questions make me sound like an idiot.

This is pretty much correct but I'm not entirely sure if you know how to put it into practice. I suggest you draw a diagram of the electrical circuit that you plan to use and post a photo of your drawing. Show where the current flows and where the different voltages will be measured.

The board you linked to is the right sort of thing but I suspect that particular board would not be sensitive enough to measure the small currents you will be generating.

By the way, I had intended to say that your assumption

The purpose is to see if the system with the "generator" will last longer on the same amount of power as the system that was just motor and battery. Theoretically it will work ...

is fundamentally wrong. When you put a load on any motor it requires MORE energy to maintain the same speed. And the output of the generator will ALWAYS be less than the input to the motor driving it due to many inefficiencies in the process. If you have any doubts about this get yourself a Physics text book.

...R

The situation is actually a bit worse than Robin2 suggested. The power output by the generator is always less than the power input to the generator. Both the motor and the generator are inefficient and lose energy as heat and noise in each electrical/mechanical conversion.

You should not be fooled by the YouTube videos showing perpetual motion machines; they are always faked! Here is a lovely one: Evolution of Perpetual Motion, WORKING Free Energy Generator - YouTube

jremington:
The power output by the generator is always less than the power input to the generator.

I thought that is what I said. It is certainly what I intended.

I like the YouTube videos about magnet motors (and in case anyone belives them - they are all fakes).

...R