# arduino Uno as a measurement of efficiency

i don’t know if its the right place for this, sorry in advance.

i want to find the efficiency of a brushless motor using arduino uno. i don’t know how to approach this, but i have some rough ideas.

you can see in the attachment a clear picture on what is going on inside my head. the questions i have are:

what is the best way to find the power that the motor consumes (as a function of throttle %). i don’t want a live monitoring of the power, instead i want it to take a sample every second and fill a table in excel for the voltage, current, and electrical power.

what is the best way to get readings of torque and RPM so i can get the mechanical power and do the same thing in arduino where it will fill a table of several points in time and then get the motor efficiency.

thrust from a prop will be measured using a load cell and an amplifier.

i may change the esc with servo tester and the battery with a power supply.

thank you

P=IV

So you need a measurement of current and voltage to know what the motor is using. There are commercial and consumer units available to calculate electric power used by devices. "A wall socket power meter".

Power in a mechanical sense is harder to measure...

P = Work / time

Work = (Force x distance)

Mechanical Power = (Force x Distance) / Time

So you need to know the force and the distance of a mechanical system over time to know its power.

Torque is a measure of force over distance...https://en.wikipedia.org/wiki/Torque

Some maths (I never did mechanics...so you are on your own/need others for that) will yield what you want.

Are you trying to figure out this efficiency when the motor is installed in a machine or are you figuring it out with a lab setup? To see how much work is provided, try pulling weights vertically.

liudr: Are you trying to figure out this efficiency when the motor is installed in a machine or are you figuring it out with a lab setup? To see how much work is provided, try pulling weights vertically.

I have to design a machine that tests the efficiency of a brushless RC motor and a propeller.

Motor efficiency = Mech Power / elec Power Mech Power = torque(Nm) × RPM (rad/s) Elec Power = I × V = I²×R =V²÷R

Prop efficiency= [ Thrust (N) × Speed (m/s) ] ÷ Mechanical power of the motor

The math is not the problem, i just want to know how to set up the arduino with a bunch of sensors that can give the readings of all the parameters listed above, where can i find these sensors and do they need some calibration? Is there a sensor that i attach between the battery and ESC and give me electrical power readings? Can i make the arduino out puts these readings into matlab or excel? These kind of question that bugs me :(

Thank you.

The hard bit will be measuring the thrust and the wind speed. The wind speed needs a calibrated anemometer, but the thrust will need some kind of strain guage to which the motor and the prop are attached. This will need some clever mechanical engineering.

I think you want to measure torque and rpm by pulling a fixed amount of weight vertically up and adding more weights until your weight is pulled up at a constant speed. This way your motor torque equals gravitational torque and rpm can be calculated with speed of the weight or an encoder on the shaft.

I don't know about thrust etc. maybe a wind tunnel.

2 x pi x torque x rps == power ( mechanical). 'rps' is revs per second.

Answer in watts if you measure torque in newton-meters. If you want it in horsepower, measure in ft-lbs, multiply by 32.2 and divide by 550. I prefer the SI approach!

the hard bit is measuring the torque.

A dynamometer does this by flexibly mounting the motor or loading device , and measuring it's torque as a force with a lever of known length and a spring balance or load cell.

CE Parsons, the inventor of the steam turbine, had a calibrated spring-loaded flexible section in his propshaft in 'Turbinia', and measured the amount of twist in that section at speed . Hence the phrase 'shaft horsepower' . Very ingenious.

Some electric power steering systems in cars use a similiar idea with a flexible bit in the steering column.

Allan