Current Behaviour
Despite having calibrated the Voltage "scale" and the Current "scale" and "Offset" using calibrated instruments (up to 20Amps for the current), when I flew my model using iNav 8.0.1 there was a significant error in the OSD voltage display. Simple Ohms Law showed that at maximum throttle (fixed wing plane) there was a 0.34 Volt difference between the OSD voltage and the actual LiPo balance connector voltage with the system drawing 29.25 Amps which is a system resistance of 11.6 milliOhms. Using the manufacturers specifications for the XT60 pin resistance, 14AWG 300 wire resistance per metre with the measured wiring lengths, and the Matek PDB current sense resistor gave a theoretical resistance of 12 milliOhms (the same as measured).
Desired Behaviour
Add a new adjustable value under the voltage calibration scale (with a default value of zero e.g. no compensation) where users can enter the wiring system resistance in milliOhms. The voltage correction can then be applied as detailed in the Suggested Solution below.
You can easily calculate the resistance as I did by using the OSD current and a LiPo tester (or better, a calibrated voltmeter).
Suggested Solution
I resolved the issue in the Programming Tab by multiplying the Current by 12 and dividing that result by 1000. That answer is then added to the measured voltage and stored in a Global variable. In the OSD menu I then set the Custom OSD element to display the corrected voltage.
I also went one stage further by programming a Global Variable to "store" the battery state Icon after checking the corrected voltage. That allowed me to have a battery Icon that follows what a LiPo tester would show. Now when I fly I have an accurate display of the LiPo balance port voltage and a battery indicator that tracks the LiPo balance port percentage in the same way that a LiPo tester does e.g. it may drop to amber of even red when I use full throttle but it recovers back to green when I ease off the power.
Who does this impact? Who is this for?
In my case a fixed wing FPV flier, but I shall be using the solution on all of my models that have wiring longer than that of a typical "drone".
Additional context
My only comment is that it is a simple revision that adds a feature that can easily be ignored if the default zero resistance is retained, but the modification allows a flier to see OSD that relates to the traditional LiPo tester behaviour.
Current Behaviour
Despite having calibrated the Voltage "scale" and the Current "scale" and "Offset" using calibrated instruments (up to 20Amps for the current), when I flew my model using iNav 8.0.1 there was a significant error in the OSD voltage display. Simple Ohms Law showed that at maximum throttle (fixed wing plane) there was a 0.34 Volt difference between the OSD voltage and the actual LiPo balance connector voltage with the system drawing 29.25 Amps which is a system resistance of 11.6 milliOhms. Using the manufacturers specifications for the XT60 pin resistance, 14AWG 300 wire resistance per metre with the measured wiring lengths, and the Matek PDB current sense resistor gave a theoretical resistance of 12 milliOhms (the same as measured).
Desired Behaviour
Add a new adjustable value under the voltage calibration scale (with a default value of zero e.g. no compensation) where users can enter the wiring system resistance in milliOhms. The voltage correction can then be applied as detailed in the Suggested Solution below.
You can easily calculate the resistance as I did by using the OSD current and a LiPo tester (or better, a calibrated voltmeter).
Suggested Solution
I resolved the issue in the Programming Tab by multiplying the Current by 12 and dividing that result by 1000. That answer is then added to the measured voltage and stored in a Global variable. In the OSD menu I then set the Custom OSD element to display the corrected voltage.
I also went one stage further by programming a Global Variable to "store" the battery state Icon after checking the corrected voltage. That allowed me to have a battery Icon that follows what a LiPo tester would show. Now when I fly I have an accurate display of the LiPo balance port voltage and a battery indicator that tracks the LiPo balance port percentage in the same way that a LiPo tester does e.g. it may drop to amber of even red when I use full throttle but it recovers back to green when I ease off the power.
Who does this impact? Who is this for?
In my case a fixed wing FPV flier, but I shall be using the solution on all of my models that have wiring longer than that of a typical "drone".
Additional context
My only comment is that it is a simple revision that adds a feature that can easily be ignored if the default zero resistance is retained, but the modification allows a flier to see OSD that relates to the traditional LiPo tester behaviour.