Autosport Labs

Posting this in the General Q&A since it's more of a general usage question rather than a sensor component question.

I'm curious to know, how are people using the yaw rate sensor information?

I was under the mistaken impression that the data coming out of the yaw rate sensor was something on the order of -10 to +10 deg/s and would directly indicate of the car was under or oversteering. After the last autocross I realized it doesn’t work like this. Absolute yaw rate values of -45 to +45deg/s don’t tell me much by itself.

It sounds like a differential yaw rate signal is required to indicate if the car is under or oversteering. But how to get this with the RCPro?

One option I found was to calculate lateral acceleration from yaw and vehicle speed with a formula like this:
Vehicle speed in kph * Yaw * (( PI / 180) / 3.6 / 9.81)
So if this value is lower than the measured lateral acceleration then the car is understeering??? And if higher then oversteering?

Alternately, this equation could be turned around to calculate a virtual yaw signal like this:
Lateral acceleration in g / ( vehicle speed in kph *(( PI /180) / 3.6 / 9.81))
So if the measured yaw is higher than this calculated yaw then the car is oversteering? Though I’m struggling to understand the converse, how if this calculated yaw is higher than measured yaw the car could be understeering.

So I’m really interested to know how other people are using the yaw rate sensor information, what equations you’re using, how you’re integrating it with other sensors, what kind of conclusions you can make, etc.

Hi,

Additional sensors are helpful, like steering angle. Once you have that then you can compare yaw with commanded steering input. You'll be able to tell with your car what is normal rotation based on turning and what is actual understeer and oversteer.

I did something similar to what you mentioned with the math by creating an overlay of the expected yaw vs lat g lines at various speeds. Its interesting to look at but I think the steering wheel angle or steered angle would help a lot more. This graph was from an autocross and I felt that the car was mostly balanced but I am still learning how to drive faster. The graph didn't really show me anything new. Good luck, I am curious what you will come up with!

I'm not at all sure that yaw rate will tell you if you're understeering or oversteering. My experience is that if I caclulate lateral acceleration from speed and yaw rate, it closely tracks the measured lateral acceleration. If you want to know the yaw angle relative to the direction of travel, you need to compare GPS direction with magnetometer direction. Unfortunately, neither of those channels are available. You can calculate GPS direction from the fix data in post processing, but you still don't know the vehicle orientation. At high slip angles, you can have significant yaw and still be understeering.

Comparing steering angle to speed and yaw rate would be a better approach.

Steering angle is a relatively easy sensor to add, so that would be a quick indicator. But yes, oversteer cannot be reliably determined from Yaw alone.