Setting the current sensor in iNav

Published by Mr. D on

Flight controller current sensors historically were not very accurate. They used to have around a 10% variation, but now it is more like 1%. So the suggested scale factor by Matek, for example, is reasonably accurate. This makes setting the current sensor in iNav is much simpler; starting from a good initial scale.

How the current sensor works

The current sensor on our flight controllers works by measuring the voltage drop over a shunt resistor. The voltage that is measured through the shunt is linear to the current. Therefore, the scale factor is based on the exact resistance of the shunt resistor. So if we know the voltage and scale factor, we can calculate the current.

So we have an exact scale, surely that means we have the exact current? Unfortunately not. Due to imperfect component, there can be current creep in the system as a whole. So what we need to do is tune the scale and add an offset to get the reading by the sensor as accurate as possible.

What do we need to do this

We will need:

  • A model set up with iNav installed and connected to your computer
  • A multimeter, RC model power meter, or other tool to measure the amps. The more accurate this tool, the better. This must be connected so that it measures the same current as the flight controller. In most cases it will be between the battery and the flight controller/PDB. I would recommend the ToolkitRC Power Meter.

Getting ready to take the readings

This procedure needs to be performed with the propeller on. Please take all precautions possible to do this safely. This is dangerous, and all possible care must be take; preferably with a physical barrier between you and the propeller.
I will not be held responsible or liable for any injuries that occur. You do this at your own risk.

Firstly, go to the manufacturer of your flight controller or PDB and find the correct current sensor scale. Companies like Matek have this information easily available on their website. For example, less than a minute finds the scale of 250 for the F765-WING.

Then, in iNav, go to the Configuration page. In the main area of the screen you will see two columns. In the right column, there is a section for Current Sensor. Make sure that the scale value is set to the number on the manufacturer’s website. If you can’t find a scale from your board’s manufacturer, use 400. Then, set the offset to 0; this is important. Finally check that battery current monitoring is enabled. Save and reboot. While the flight controller is rebooting, put the current sensor scale in the form lower down on this page.

Setting up the tool for taking the readings

Now you will need to set up your multimeter or power meter between the battery and flight controller. When you read amps, all the current needs to go through the meter, it cannot be measured in parallel like voltage.

Using a Clamp Meter

The simplest device would be a clamp meter. Simply attach this around the positive lead of the battery.

Using an RC Power Meter

Plug your battery in to the IN or Source side of your power meter. The lead you normally plug your battery in to, goes to the OUT or load side of the power meter.

Using a Multimeter

For a standard multimeter, you would need to make up a special lead with a power connector at each end. The negative wire can go between the connectors as usual. But the positive leads would need to be able to plug in to your multimeter. The other thing to remember with multimeters is that most of them have a maximum current rating of 10A; so do not exceed this. There is a video that shows how to make a lead up here.

Remember if you’re using a multimeter, it may be limited to 10A.

Finally, plug in the battery and reconnect to iNav. Go to the Outputs page. There is a current display on the Outputs page, which is handy for this task. Now, enable the motors, now we are ready.

Taking the readings

Now that we are all set up, we can start recording the readings. To do this, we will be taking two measurements during each reading. The first reading will be at idle, or low throttle. The prop should be spinning, slowly. Both iNav and the power meter must be displaying a reading. Increase the throttle to get a reading if necessary.

  1. Record the Battery Current displayed in iNav
  2. Record the reading on your power meter/multimeter

There are spaces in the calculator below to enter these readings.

Next we need a to take more readings. We will be doing the same process as before, only at a different throttle levels. I recommend taking at least five readings, to get a more accurate calculation for your current sensor. The more readings you take the better. Be sure to spread the readings over all different throttle levels. Though, take a few more readings around the throttle level you normally fly at.

Remember if you’re using a multimeter, it may be limited to 10A.

Raise the throttle to the decided level. Then record the current displayed in iNav and on the power meter in the calculator below. The more readings you make, the more accurate the results will be. Shut the power off on and disable the motor. Then click the calculate button.

The Calculator

Current Sensor Scale
Flight Controller readingPower meter reading
Idle current
Throttle level 2
Throttle level 3
Throttle level 4
Full Throttle

Go back to the Configuration page and the Current Sensor area. Enter the results from the above calculator in to the scale and offset boxes. Then save and reboot.

I hope this was helpful

Thank you for reading this article. I hope you found it useful. There are more articles on this site that may answer more questions. I also have a YouTube channel at www.youtube.com/c/MrDFallingwithstyle with content like this. A like and subscribe on there would be greatly appreciated.

This article has helped 140 people. For more useful things, please check out my YouTube Channel.

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Categories: iNav Flight