Power consumption of electric motor

[TOONCES]

Hi everybody,

I'm building a board game right now.

The game consists of a train of gears that I would like to drive with an electric motor.
The gear train can be many different sizes (# of gears) and patterns (size of gears).

What I would like to do with the motor is measure the load on the motor (when driving the gear train) relative to the max power output of the motor or maybe the free-spinning power output.
Basically I want to measure the efficiency of the gear train and compare that to theoretical values of the efficiency.

End all, I would like the measurement of the efficiency to be done at the board with a display showing the efficiency measured.

a little direction would be great,
thanks everybody

 

[edgepflow]

You could purchase an "ampmeter" and measure the motor's current draw. With the motor current and motor voltage you can calculate the motor power and efficiency of your system.

 

[TOONCES]

Thanks for the reply

I'm worried this may not compensate for the internal power losses of the motor or the losses in the ammeter.

If I were to do this would I have to have an ammeter in series with the positive and negative terminals on the motor in order to measure the current in and current out?

How would I take the actual number value readings from the ammeter to be used in a computer?

 

[Unrest]

What I would like to do with the motor is measure the load on the motor (when driving the gear train) relative to the max power output of the motor or maybe the free-spinning power output.

Is there are load at the end of the gear train? If not then the gear train will have zero efficiency since (power out) / (power in) = 0/x.

Similarly, there's no power output by a free spinning motor.

Basically I want to measure the efficiency of the gear train and compare that to theoretical values of the efficiency.

You could measure the torque at each end of the gear train, and the speed anywhere in it. Then you can calculate the input and output power of the gear train alone. Torque measurement shouldn't be too hard with an barely-moving arm applying force to a stationary force sensor. You can do the same with the motor. Regardless of losses in the motor, all the torque it generates will be transmitted through the body which can be mounted on a similar sensor thing.

If the load is high enough you could measure motor torque from the current as Edgep suggested. That may be pretty accurate because it wouldn't be affected (I don't think) by resistive losses in the windings.

 

[TOONCES]

I have been running under the consideration that the frictional losses of the gears in the train would be the load on the motor. I essentially need to quantify these frictional losses through measurement.
With that said, I think what I meant by "free-spinning power output" is the power output by the motor with a gear on it, or the motor with a gear on it turning another (equally sized) gear. So, I want to take the 'free-spinning output', FS, and then measure the frictional losses through the motor, FL. the "efficiency" I've been thinking of is (FS-FL)/FS. Or reversing the FS and FL...I'm not sure which is greater. That is the efficiency that I wanted to compare to my calculations.

Measuring torque and speed seems like it could be difficult/expensive on a board game. I'm not sure what you mean by "a barely moving arm applying force to a stationary force sensor". Also, do you have any suggestions for measuring the speed?

I'm still considering the measuring the current draw of the motor.

Thanks again for the responses

 

[Unrest]

losses through the motor, FL. the "efficiency" I've been thinking of is (FS-FL)/FS. Or reversing the FS and FL...I'm not sure which is greater. That is the efficiency that I wanted to compare to my calculations.

Your quantities confuse me. What's the gist of your calculations? That would make it clear what you're trying to measure. Is it:
1) The torque lost in the gear train or
2) the decrease in motor speed due to the gear train being connected or
3) the efficiency of the gear train (output power / input power)

For 1) I think you can just find the current-torque relationship for the motor, already adjusted for internal losses. Then the current measurement will tell you the torque according to that relationship.

For 2) there maybe be a way to measure speed from motor voltage and current, but not sure how accurate it would be.

3) is what I was talking about before. If you don't want to directly measure efficiency you can perhaps use the game to predict what it would be if there was a load. That might be possible using 1) or 2) and making some assumptions about how friction will increase with load - I guess linearly.

Bear in mind that 'efficiency', however you define it, will vary with both speed and torque. That may or may not be negligible.