Not my tutorial, but I thought it was worth posting a link here because I've seen the question asked a few times on the forum. This is a very nice demo and some very useful information from Pawel, as per usual...




Other methods are also described in Oscars article at the link below...

https://oscarliang.com/current-sensor-calibration

I've always done the number batteries, write down MAH used each flight, and write down mah put back in by charger.

Then average about 10 flights together and use a formula to adjust the settings (cant remember what it was).

That method works well enough for me

Whats your favourite method?

I prefer the clamp current/amp meter method but this depends on how well calibrated your multimeter is.

As long as I get the current reading within a reasonable ball park to know when my battery runs out.

I think ph2t's procedure from one of his posts HERE is also a good method, re-quoted below...

ph2t Wrote:I use this method to calibrate an FC's current sensor.

1. Connect a multimeter in-line (series) between the battery and quad.
   
2. Set multimeter to current measurement (10A scale)
   
3. Connect power to quad
   
4. Connect FC to betaflight
   
5. Spin all motors up and aim for 1A on the meter, note the current value BF reports.
   
6. adjust current gain value in BF
   
7. repeat steps 5&6 until the value is a close as possible between BF and the multimeter
   
8. use offset value to get idle current draw correct
   
9. spin all motors up to 2A on the meter, confirm accuracy of BF value
   
10. repeat steps 6 and 9 till ok
    
11. spin all motors up to 3A on the meter, confirm accuracy of BF value
    

Maybe a stupid question but... why can't I use the method of the clamp but spinning motors without props ? Like the method of ph2t i mean.

(22-Apr-2021, 01:04 PM)Zanna83 Wrote: Maybe a stupid question but... why can't I use the method of the clamp but spinning motors without props ? Like the method of ph2t i mean.

I believe the scientific answer is probably because doing the calibration with props on provides a more realistic "load" on the motors. The same load as you would get when flying with the same props you used to do the calibration with. Obviously there are also some risks and dangers involved when doing it that way.

(22-Apr-2021, 01:27 PM)SnowLeopardFPV Wrote: I believe the scientific answer is probably because doing the calibration with props on provides a more realistic "load" on the motors. The same load as you would get when flying with the same props you used to do the calibration with. Obviously there are also some risks and dangers involved when doing it that way.

I agree with you but reverting the props gives you a different "inertial" load on motors I think it's still not realistic. Do you think the result may be altered by performing the test without props ?

(22-Apr-2021, 01:36 PM)Zanna83 Wrote: I agree with you but reverting the props gives you a different "inertial" load on motors I think it's still not realistic. Do you think the result may be altered by performing the test without props ?

But you're not ramping the motors up to full power. You're just giving the motors a bit of downward force load at low RPM. I don't know the answer to your second question. There is only one way to find out which is to do some further testing on top of what Pawel already demonstrated. Do a calibration with the props off and another calibration with the props on to see if there is any (or much) difference in the end result.

(22-Apr-2021, 01:36 PM)Zanna83 Wrote: I agree with you but reverting the props gives you a different "inertial" load on motors I think it's still not realistic. Do you think the result may be altered by performing the test without props ?

It shouldn't make any difference, Most FC's Use a shunt resistor style current sensor which simply measures the current flowing through a trace on the PCB, the same as your multimeter is measuring the current flowing through the wires in the circuit using these testing methods.

It doesn't matter is the load on the motors is real or not, the amount of current flowing at the shunt resistor and at the multimeter is the same because they create a circuit. If you have a PDB style FC you could leave all of your ESC's and motors disconnected and hook a lightbulb to the ESC power pads and calibrate the current sensor if you really wanted to, it works exactly the same.

TLDR; doesn't matter what the load is, all you are doing is making sure that the current sensor reads it correctly.

Might be comparing mAh used to mAh charged is not the absolute exact calibration but for me it is definitely the most useful. I think about it like that: if I have a say 2000 mAh battery and discharge it to 3.5v per cell which I consider safe and then put back 1800 mAh measured by my charger then I want my OSD to show me the exact same 1800 mAh used, including internal resistance heating of the battery etc.

This way I don't care how precise is my FC or charger measurement are, I just want them to be the same. I just need my FC voltage sensor to be accurate which is much simpler to calibrate.

Formula from TMacFPV

So today I used Pawel's method to calibrate my current sensor. I can tell you now that it felt horribly dangerous to be running the motors on the bench at such high speed with props on even though they were fitted upside down with the quad just trying to suck itself to my desk meaning that it couldn't really go anywhere. I didn't even want to think about the consequences if something had gone wrong either electrically or mechanically. Wearing a suit of armour would probably be sensible move I don't have one so I just used the cross my fingers and pray method instead. I do however strongly advise that you at least wear safety glasses / goggles if you do it this way.

Anyway, I can see why this procedure seems to work better with props fitted. Without props I was getting readings in Betaflight which were fluctuating all over the place making it difficult to determine a mean average by eye. With props fitted there was still some fluctuation in the figures but not as erratic as without props fitted. I can say I was very happy when the procedure was complete and I could stop the motors and unplug my quad. It's certainly not a procedure for the faint-hearted

Late response but just saw this thread. Humble to see Snow posting my method. The reason I take three readings to to see if the current meter is consistent in taking it's mV/A reading. As bffigjam said, it's a series circuit that will always read the current going through it. Whilst I haven't looked at the props on method above what I believe it would achieve is a higher load current to test an increased range on the current sensor. One would see that this could result in a more accurate meter rating for the current sensor.