How to add a motor to the database
You can add a motor to the database by using the motor_finder and Io_finder sheets.
First, you have to do some measurements (or find some measurements on the web or somewhere else):
Take your motor and set it on a bench.
Choose several propellers of different size, not to small, not to large (be sure you're not going to burn the motor !).
It should be OK if you only have one batteries pack to make the measurements, the important thing is too have a somewhat "large" range of RPM, but the best is too have the choice between several voltages (by using 2S, 3S and 4S for example).
Measure volts, amps and RPM at full throttle.
Take care to make short measurements in order to keep the motor's temperature almost the same.
You should finaly obtain something like that (here it's with a 1000 Kv motor):
|APC 9x6S||6,04 V||4,44 A||4969|
|7,42 V||5,97 A||5917|
|11,39 V||10,95 A||8354|
|APC 10x7E||6,21 V||6,70 A||4699|
|7,46 V||8,64 A||5430|
|11,10 V||14,57 A||7307|
|APC 7x6E||6,15 V||2,74 A||5404|
|7,48 V||3,59 A||6431|
|11,17 V||6,45 A||9161|
|14,79 V||10,05 A||11551|
|APC 8x6E||6,15 V||4,02 A||5145|
|7,35 V||5,24 A||6009|
|11,15 V||9,80 A||8419|
Then, do the same but without propeller to have some "no-load" data:
|No Load||6,06 V||0,60 A||5719 rpm|
|7,97 V||0,71 A||7481 rpm|
|10,10 V||0,79 A||9413 rpm|
|12,04 V||0,91 A||11197 rpm|
|14,05 V||0,97 A||13038 rpm|
Then, go to the motor_finder sheet in Tetacalc and enter the data (not the no-load data!!) here:
Only the volts, amps and rpm are really needed. Be carefull not to move any of the cells !
Then enter the theoretical Kv of the motor here:
You should obtain this graph:
It shows the calculated resistance of the system according to the measurements and the theoretical Kv.
And this graph:
It shows the error between the true amps and the calculated amps at this time of the process.
Also you should see this:
It means that, for the moment, the model matches the true amps measurements with an average error of 4.19 % and a max of 11.41 %.
Now, the game is to reduce this !
You can do it by playing with the "+" and the "-" below the theoretical Kv (they increase or decrease the Kv by steps of 1, 10 or 100). Click on either a "+" or a "-" and see what happens to the average error.
After some time, you should find a Kv where the error is the smallest. In this case you should have:
Here, the resistance of the system is almost in linear relation with the RPM, and R² is close to 1.
Here the red line should to the horizontal.
For the moment, you should have found the effective Kv of the motor, and the relation between the "apparent" resistance of the system and the revolution speed:
You also have a value that is (should be!) close to the real armature resistance of the motor:
(I've measured the armature resistance of this motor at 0.140 ohms at 23°C !)
Now you need to find the no-load current.
If you only have one value of the no-load current, it's very simple, just enter it here:
If you have several values, leave it blank and go to the Io_finder sheet.
Then, enter the no-load run values here:
Tetacalc should find an appropriate formula that matches the measured data. But you can manualy enter the exponent if you want:
Now that you have found the no-load current relation with rpm, you can go back to the motor_finder sheet, and enter the missing informations:
The name and weight of the motor, the temperature during the test runs (you can also leave this one blank), and eventualy the source of the data (it can be a web page).
Finaly, when everything is done, you can just click here:
This will send the data to the database...