Accuracy of the Integrated IMU

[KillaBoDilla]

I am looking at purchasing the RaceCapture/Pro MK2 Lap timer, data logger, telemetry system for the sole use of capturing and logging the position data (roll, pitch, yaw and accelerations x,y,z). This is a research project for a program at my school which is going to be used to validate a simulated model of the vehicle we are testing. I don't have any experience with this module and before we commit on the purchase I would like to hear from a few folks that have experience with retrieving this data and the accuracy and precision there of. Also I would like to hear if the position data is good enough to be used in real time as an input to an active suspension, ie hydraulic or pneumatic shock absorbers or something of that sort. Just throwing Ideas out there.. Thanks in advanced!!

[stieg]

Hi KillaBoDilla,

Some accuracy improvements to the gyro will be coming in the 2.8.6 firmware release. Its faily accurate with a bias less than .1 deg/s in any direction. It is possible to get a live telemetry stream over the USB port of the device. It has extremely low latency (hard to say how low... never measured) but its obvious when you have the device plugged into your computer via USB and look at the dash refresh rate.

RE suspension... what exactly are you trying to do?

[KillaBoDilla]

So for an update we have just received the RaceCapture Pro within this last week or so. So after not much time looking at we have developed a few questions concerning the unit and the way it captures data.

Before we mount the device to the vehicle we were looking to do some bench testing to validate the current accuracy of the unit. Is there any standard simple tests we can perform to confirm accuracy? I would like to just be sure we are getting valid data to move forward.

Also we have noticed that when running the unit on a bench to get familiar with the program interface we statically measured roll angles and the unit appears to capture the change in roll angle but doesn’t hold that value after the angle is reached for a period of time. For example the unit sees a change from 0deg to 10deg but once at 10deg for any period of time the graph flat lines to read 0deg. I haven had much time to investigate if a setting needs to be changed or if there is any programming that needs to be done but It is a current issue I need to take a look at and would love some feedback on this. We have just scratched the surface looking into the unit but we are trying to speed up the process of integrating this into the vehicle as fast as possible.

As for the suspension project we were looking to take roll and yaw info and using that to drive a dynamic suspension however I believe that project is going to be held off till another date. At least till we get comfortable using the data logger and manipulating the data.

[stieg]

Before we mount the device to the vehicle we were looking to do some bench testing to validate the current accuracy of the unit. Is there any standard simple tests we can perform to confirm accuracy? I would like to just be sure we are getting valid data to move forward.

Once you have configured the correct X, Y, and Z channels based on orientation of the Unit, next calibrate it. Once done you can easily test accelerators by rotating the unit 90 degrees on an axis. This should cause that axis's accelerator to go to 1 G or -1G in force. For the gyro, you need to turn the device at a known rate. I usually test this at 90 degrees per second. If you turn it at that rate along an axis, the value should be about 90 or -90 for that Axis (Pitch = X axis, Roll = Y axis, Yaw = Z axis). Do note that there is a bug in the 2.8.5 firmware and the gyro values read high. This is a know issue and a fix is coming in the 2.8.6 firmware.

Also we have noticed that when running the unit on a bench to get familiar with the program interface we statically measured roll angles and the unit appears to capture the change in roll angle but doesn’t hold that value after the angle is reached for a period of time. For example the unit sees a change from 0deg to 10deg but once at 10deg for any period of time the graph flat lines to read 0deg. I haven had much time to investigate if a setting needs to be changed or if there is any programming that needs to be done but It is a current issue I need to take a look at and would love some feedback on this. We have just scratched the surface looking into the unit but we are trying to speed up the process of integrating this into the vehicle as fast as possible.

Gyroscopes measure angular velocity, not angle. Units of a gyroscope are in degrees/second. What you are looking for is something like a compass perhaps, which gives you an absolute heading relative to magnetic north (assuming ideal conditions of course). You can achieve this somewhat by integrating the angular velocity to get an offset angle relative to where the unit was initially pointed. Hope that helps.