s200 G Sensor
The Hondata G Sensor manual
is available online.
What is the G Sensor?
The Hondata G Sensor is a module containing a two axis accelerometer
which plugs into the s200 Interface Box. It allows you to datalog lateral
and longitudinal acceleration simultaneously.
What do I need?
To use the G Sensor you need:
||G Sensor module for s200
How accurate is the G Sensor?
The base accuracy of the accelerometer used in the G Sensor is 5 mG, or
0.005 G. For comparison typical acceleration is 0.25 - 0.50 G in second
gear, braking and cornering generate 0.80 - 1.20 G. Vibration and
mechanical isolation of the sensor from the chassis has an influence on
accuracy, but this is in part offset by software smoothing. Under
typical conditions it appears that the G Sensor is accurate to 0.01 G.
How do I use the G Sensor?
The G Sensor allows you to datalog acceleration, cornering and braking
forces simultaneously while the car is on the move. Below is an
image of the real time G Force display, showing the traction circle and
the G Force as a vehicle brakes then corners.
The acceleration information can be used in conjunction with other
datalogging sensor information for analysis. The image below is from the
same recording as above, showing the manifold pressure as well as the
lateral and longitudinal acceleration.
Since vehicle acceleration is directly related to engine output, given
the vehicle mass and gearing it is possible to calculate the engine output
to the wheels by recording an acceleration run. Below is a sample
dyno plot from G Sensor data (click to enlarge). We apologize for the car
used in testing failing to reach 100 hp (stock D16, 140,000 miles).
The blue line to measured wheel torque, red is power and the green line
is calculated aerodynamic loss, which is used to compensate measured
torque to that as measured by a dyno.
How does the G Sensor compare to a Dyno?
Typical repeatability of the G Sensor dyno plot with back to back runs
is plus or minus 1% engine output. Runs performed under different
conditions (e.g. weather, tire pressure, wheels) will be different, but
the repeatability of the G Sensor is generally good. In the future
correction for temperature and pressure might be added to HondaLogger.
The resolution of the G Sensor in determining a change in engine output
is about 2 hp. We will update this figure as we conduct further testing.
Comparing the results of the G Sensor with a conventional dyno shows a
difference between the Dyno and the G Sensor. Initially is appears
that the G Sensor reads less power than the Dyno by about 10%, but we will
have to test more vehicles to refine this figure. Real world engine
output as measured at the wheels varies with the gear used during the
acceleration run, as the engine will use more energy to overcome engine
inertia in lower gears. A lower gear will give less output and will raise
the peak power and torque rpm. In our testing we found that 2nd gear gives
about 5% more power at 300 rpm lower than 1st gear, while 3rd gear gives
5% more power again than 2nd gear at about 100 rpm lower than 2nd gear.
This inertial effect accounts for some of the difference between the G
Sensor and Dyno.