JP GleyzesFeatures
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
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 here : BoM
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: PCBWay shared project. 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
Power considerations
5V can be delivered either by the DC/DC converter or directly by the ESC of your plane (prefered solution)
power with DC/DC converter :
- first tune the trim pot value in order to get less than 5V (4.8V) output (do not power anything else before...)
- when this 5V is achieved, you can paint the trim pot with a drop of nail varnish to fix the potentiometer
- then (and only then) solder the SJ solder pad on the bottom side of the PCB. The 5V will now flow to the DFPlayer and the ESP32 (via the battery connector)
- Do not solder the SJ1 solder pad
Power with the ESC :
If your ESC is equiped with a strong enough BEC (1A for the ESP32) you can power the board and the ESP32 directly with the ESC connector :
- do not solder the SJ solder pad (nor the DCDC module if you want)
- solder the SJ1 solder pad
- connect the ESC servo pin header to the ESC connector on the board and power your ESC
I recommend this second option (power with the ESC) as the ESP32 can eat up to 700mA (max) this will not stress the ESC which is able to drive all the servos of a plane...
If you choose this option, then you can avoid to solder the DC/DC converter and save its price!
sensors
Five sensors are there to measure the parameters of your motor and propeller:
- ADC to measure battery voltage
- current sensor to measure current flowing into the motor
- IR sensor to measure rotation speed of the propeller
- temperature sensor to prevent over heating of the controller
- load cell sensor to measure the "weight" of the propeller (converted to thrust !)
Links for these sensors are provided into the bill of material
ADC
Voltage of the battery is directly measured by one of the ESP32 ADCs
R1/R2 are a voltage divider needed to decrease the battery voltage to the ESP32 range (3V)
V_IN = R1 x Vbat / (R1 +R2)
So you have to be careful when selecting these resistors depending on the maximum voltage you plan to use for your battery.
Here are the values for a lipo 3s battery (my prefered setup!)
With R1 = 20k and R2 = 6.8k you will get max 3.3V with a fully charged lipo at 13V (3x 4.3V = 13V)
current sensor
To safely measure high current motors I have selected a powerful 100A current sensor : ACS758_100B
This sensor module is equiped with an operationnal amplifier on its OUT2 pin. So that you can input this pin safely on a micro controller ADC.
This sensor is "bidirectionnal" meaning that it can measure positive and negative currents. The zero value is at mid range of the ADC thus at 2.5V when the sensor is powered at 5V. This is totally withing the range of the ESP32 ADC specifications. (no need to change this OUT2 value if you measure values between 0 and 2.5V !)
LoadCell
A loadcell will measure the thrust of the propeller.
I have choosen a 10kg loadcell. This device need an amplifier HX711 to adapt its value.
Connection between load cell and amplifier follows this schematics:
Propeller RPM
To measure the propeller speed we need to setup a tachometer. It will be made with an IR sensor. The reflection of the IR beam on the arms of the propeller will trigger interupts on the ESP32, and we will compute the rotation speed.
Temperature
A DS1820 chip will take care of measuring the temperature of the ESC.
Software
To be written