There wouldnt be a problem if I used some kind of 2-part ways of measuring revs, but I would rather stick to something like gyroscope, as I want to make it easy to attach to a wheel. Later I will worry how to send the data for processing (BT or WiFi).
Could you give me any tips on which way should I go?
So, tldr: how to measure wheel revs just by attaching one HW to it?
Put a white sticker on the wheel and detect it optically. I assume the car is on rollers, can you not measure the roller speed the same way? Otherwise wheel RPM is directly related to vehicle speed, you just need to look at MPH or KPH.
Yeah, I had the same idea with sticker, but I think its not gonna be efficient. I need to update the wheel speed few times per second. For rollers I was using optical encoder, but now I wonder how to do it with just one thing attached to wheel (tests should be done on the road). See the picture attached in the first post.
Accelerometer + Arduino + Bluetooth? The Nano33BLE has all of those on a small PCB. Sketch to take the accel readings (if the sensor is fast enough) and compute the average rpm. Powering it could be fun, maybe a pendulum arrangement to keep a magnet in a constant orientation with coils moving past it to generate power and recharge a battery.
But on a modern car, especially if it has ABS, it will have a wheel tick sensor on each wheel and you might be able to get those, or a proxy for them, off the CAN bus at the OBD2 connector.
I was once parked next to a Rolls Royce which had big "RR" badges on the hubs - I was impressed when it moved off and the RR logo stayed upright!
Reluctor (magnetic) sensor with toothed gear with one tooth missing as index pulse. Measure period between pulses and compute inverse. Pulse stream is as rapid as you need (bigger = faster pulses, more often.) Standard bicycle drive gear with one tooth ground off should work well.
Apply calibrated braking pressure and see how much RPM is lost ... A friction clutch also works. Standing start acelleration (time to known speed) is easily measurable and gives you friction if you know mass,
The easiest way to do this is to take an ignition pulse signal and use that - very simple .
Do your power runs in one gear , accelerating through rpm range .
The maths to get anything sensible is tricky , (weight air restistance, flywheel intertia etc ) but for comparison purposes it’s okish , must use same bit of road
I have a commercial one , there is just one clip onto the ignition coil and that’s it - never tried it tho .
