Quatos Thrust curve measurement

Introduction

Quatos needs to know the relationship between thrust and RPM for your propeller. So you need to perform a set of measurements to

Before doing these measurements, make sure you have performed the R2V calibration on ESC32 and placed it into closed RPM operation mode so that you can give an rpm set point.

Mount the motor and prop on a thrust measuring rig, like the one shown below:

Then run the motor using the ARM, START and RPM command in the ESC32 CLI. Connect using Putty or ECU.

You then run the motor in increments of 300-500 rpm, measuring the thrust at each step until you reach max RPM of your motor and prop combination.

Note down these numbers and copy them into the Value and Thrust columns of this spreadsheet. When your values are entered, it will automatically generate the parameters A1 and A2 at the bottom of the sheet.

You must now add it to your parameter list as follows

MOT_VALUE2T_A1         1.067689
MOT_VALUE2T_A2         0.003965

RPM Scale

To make sure that AQ and ESC32 is keeping in sync, we need to state a RPM scaling parameter on both ESC32 and AQ main controller. For example if max attained RPM was 7800 so that needs to be set on both sides.

Add the following to your ESC32 configuration:

PWM_RPM_SCALE 7800.0

And on the AQ side you add the following into your param file or set it via QGC.

MOT_VALUE_SCAL         7800

Remember to write to flash and restart for changes to take effect.

#define DEFAULT_MOT_VALUE_SCAL         3.7

Put these 3 defines into your Quatos profile and you are now done with setting up Quatos thrust and moment of inertia settings. You are almost done.

Thrust – RPM Relationship using OSX Grapher (instead of Excel spreadsheet method)

Ok, now over to the thust – rpm relationship calculations. In this example the Mac OSx grapher tool is used, please inform the team if a similar tool  for other platforms is discovered. The table created in the thrust measurement is now needed. Start the grapher tool, the default is display and select the default.

Now press on ‘+’ and select new point set. That is where you need to enter the rpm and thrust values that are measured. After the default point set is presented, click on edit to enter your values.

.

By default the pointset is populated with 3 columns and some sample data. We only need 2 columns. In the first column the rpm value and the 2nd column the measured thrust in grams. How many rows is depending on how many samples you’ve taken.

Time to enter the relationship formula. Once the points are displayed click on interpolation. We need the custom interpolation. The formula is: y = a * x + b * x^2. Once entered click on display.

Windows users can use this tool: http://www.padowan.dk/download

1. Run the program and set the appropriate ranges for X and Y axis

2. Enter a series of data: RPM – X, thrust – Y

3. Now we need to add a function. Click the icon and add “model” and type a function: ($a*x)+($b*sqr(x))

After confirmation (OK) the curve will be drawn.

4. Click 2 times on the function displayed in the window on the left. You can see function etit window with 2 interesting parameters (A and B).

The values you need from this exercise are the ‘a’ and ‘b’. Those need to be transferred to your param configuration file in the Quatos section. set DEFAULT_MOT_VALUE2T_A1  to ‘a’ value set DEFAULT_MOT_VALUE2T_A2  to ‘b’ value

//Quatos controller specifics
#define DEFAULT_QUATOS_AM1 -8.0f
#define DEFAULT_QUATOS_AM2 -14.0f
#define DEFAULT_QUATOS_PROP_K1 14.62f
#define DEFAULT_QUATOS_L1_ASP -10.0f
#define DEFAULT_QUATOS_L1_K1 18.6f

#define DEFAULT_MOT_VALUE2T_A1 -0.0199f
#define DEFAULT_MOT_VALUE2T_A2 1.9638e-05f
//A1 & A2 are from your thrust to rpm graph (the calculated a & b coefficients.)

#define DEFAULT_MOT_VALUE_SCAL 8300
//MOT_VALUE_SCAL has to match PWM_RPM_SCALE in the ESC32.