PX4FLOW minimum focus distance (speed detection on car)

I would like to use PX4FLOW to get X/Y speed of my ground vehicle with much higher rate and precision than what GPS can offer, as I want to control maximum allowable steering angle based on it (and possibly detect wheel spin and/or tire slip).

However, I’m not sure if it is possible to use it this way, as ideally I would need to mount it just couple of centimetres above the ground (up to 10cm), and unfortunately I can’t find any information about minimum focusable distance for the sensor. Has anyone tried this, please?

Hey @haplm, I have never used a PX4FLOW myself, but I did some digging, and it looks like you can tune the lens focus, and there seems to be quite a lot of extensibility and configuration options you leverage. Have you had a chance to read our docs on the PX4FLOW yet?


Thanks, Ramón, yes, I did read the doc. Minimum focus distance is not mentioned there, and being also a photographer, I know that each lens has a minimum focus distance (which typically increases with focal length of the lens). So I’m pretty sure that there’ll be a lower limit under which the lens can’t be focused any more.

So I have realised that the answer is not the PX4FLOW module, but the sensor, and more precisely the lens it uses. Turns out that the sensor is MT9V034, and it is using M12 lenses. Therefore it is “just” a matter of finding the right M12 lens that can focus on the chosen distance…

Well, thank you for forcing me to think a bit more than I did before :slight_smile:

I’m glad I was able to help, even though my link didn’t accomplish anything, at least I got you thinking.

There’s something about saying things out loud that makes your brain process what you are saying and puts it through a different lens (no pun intended) and sometimes yields better results, AKA Rubber Duck debugging.

I’m glad I was your duck for today. Good luck!

Hehe, exactly.

Anyone who would be interested in the further reading, here are more details about the chip:

Some lenses:

Please note that you need lens bigger than 1/3", lens sizes here:

And this looks like an ideal lens for my needs: