The good news is we are hearing stories that Toyota has a fix for the intermittent "brake problem" that is being applied at the factories since January. The bad news is I'd bought two, three axis accelerometers from
Gulf Coast Data Concepts to study a problem I've never been able to reproduce.
Gulf Coast Data Concepts makes a USB interfaced, accelerometer and I bought the X6-2, Li-Poly powered, and X6-1A, AA powered units:
The don't include a 3-axis yaw but with two, located as far apart as possible, differential acceleration should give angular measurements, pick two of three:
Regardless, this is my first, unpolished measurement of our Prius hitting a speed bump while braking and hitting a speed bump:
The salient data points:
- linear acceleration blue line - a positive acceleration values are braking, zero is no braking, and a negative value is acceleration. Obviously, I had the wrong end pointing forward.
- Two light taps are evident in the Ax line as I approached the bump trying to time brake application relative to the bump. I'll need to figure out a fixed object to initate braking.
- Hitting the speed bump, the brake system really has to do some modulations including a few excursions to zero but braking continues.
- The unit was configured for 80 samples per second and I'd experimented with "dead band" but I may have misinterpreted the timestamp. More work to do here.
- After leaving the bump, normal braking returns and evens out. This is normal braking behavior.
- Red line, verticle acceleration - intially a significant increase in 'gravity' as the car accelerates up.
- The first initial upward acceleration shows a slackening followed by a second upward impulse.
- There is a slight reduction in G as the car 'floats' past the peak and then back to another slight impulse. Then a final float before reaching the pavement with compressed struts and springs.
- The last bit shows the suspension extending up, gradually, and back to normal gravity.
I'm one of the 50% who have never experienced the 'brake problem,' reports of an intermittent fading after hitting a road surface anomaly ... railroad tracks, manhole covers, patched roads, potholes, ice/snow/leaf patches and even a rippled road. Understand that for the past month, I've tried to replicate the problem. Regardless, there are reports that there is a fix that is being applied at the factory and suddenly the interest in the 'brake problem' has faded.
Any new tool takes a little time to master. Issues like drift, calibration, timestamps, and data handling can be investigated with Excel. But for operational use, I'll write some software to handle the mass of data. The device can sample 320 per second so the data can grow quite fast and Excel is so ... limited.
Bob Wilson