Features

On an RC plane, propeller performance depends on pitch, diameter, profile, and material.

Testing your propellers will allow you to measure and improve their efficiency.

This motor + propeller test equipment will measure:

• Thrust
• RPM
• Current
• Voltage
• Electrical power
• Temperature

This project is an improved version of https://hackaday.io/project/202213-rc-motor-propeller-test-bench

Compared to V1 version we can now access to :

• torque
• mecanical power
• motor efficiency
• propeller efficiency
• 
  

It can be controlled either manually via a servo tester or your radio transmitter/receiver or automatically via your Android phone.

Schematics

The heart of the system is based on a Lolin32 lite ESP32 microcontroler.

Then a bunch of sensors are added to measure all the parameters.

An Oled dispaly is (optionnaly) there to help debug or usage without smartphone

Bill of material can be found at the bottom of this page

This schematics is pretty much identical to the V1, simply 2 more load cells have been added . One is for torque measurement and the other one is for spare !

PCB

I have designed a nice and compact PCB allowing to fit the ESP32 and to connect all the sensors

The PCB was kindly sponsored by PCBWay and is as usual of excellent quality.

You can order it here directly from this page. It's cheap, delivered very fast and so professional looking!

And if you are new to PCBWay please use this affiliated link : https://pcbway.com/g/o35z4O

Soldering this board is quite easy and result is a mezzanine board with three floors !

How to measure motor and propeller efficiency and torque and power

Compared to V1 version we will now access to more parameters to characterize your system. But these parameters are not "directly" measured by sensors...

Electrical power 

ePow is simply the product of Voltage by Current

ePow = Vin x Iin

​

Mechanical power

In an electric motor, the mechanical power is defined as the speed times the torque. 

• Speed expressed in rd/s
• torque expressed in N.m​

​As we measure RPM (Rotation Per Minute) we can get Speed wiyh this simple conversion

rad/s = RPM/60 × 2π

mPow = RPM/60 x 2π x Torque (in W)

Torque

​Our first load cell will measure the strength (F) applied by the lever attached to the body of the motor. When the propeller rotates the torque is applied on the motor body but in the opposite direction. The lever has a L = 0.0605 m length. 

If F is expressed into Newton then

Torque = F x L (in N.m)

​Motor efficiency

​motor effciciency is the ratio of mechanical power by electrical power

motEff = mPw / ePow

​

propeller efficiency

Finally the mechanical power output by the motor is directly transmited to the propeller (direct attachement of the propeller on the motor shaft)

And the propeller produces thrust which is measured by the first loadCell

Propeller effciciency is said to be the ratio between Thrust and mechanical power

propEff = Thrust / mPow

However this definition found into tytorobotics blog, is not valid... An efficiency should be "dimensionless"...

A real estimate of propeller efficiency would need to have a wind tunnel to measure air speed "v".

propEff = (Thrust x v)/mPow

​

​All these formula are handled into the android application when exporting the sensors values. (See below)​

​Torque mechanical housing

We know now how to measure motor and propeller parameters but how to physically measure the torque ?

One way to do this, while allowing the motor shaft to spin, is to mount the entire motor housing on good bearings concentric with the shaft axis so it would freely spin backwards if there were any torque on the shaft. Then you can use the same arm and scale setup to measure the torque required to keep the motor housing from rotating.

This is exactly what I did when attaching the motor housing on a rotating axis while its motion will be blocked by the lever "pushing" on the torque load cell. 

A picture is better than a lot of words...

This CAD model has been 3D printed and all the stl files are accessible on thingiverse