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Tuesday, 24 July 2012
XoomSpeed datalogger/traction control
Since our first event back in 2006, we always wanted to know more about what the car was doing and why one run was faster than another. We had a look around at what was commercially available but felt everything was either not powerful enough, or too expensive for our budget. Since the team includes a lot of expertise in harder and software development, the obvious solution seemed to be to build our own..
Development of the system started in the second half of 2007. Testing of the datalogging was completed in time for the last event of the season in October.
2008 saw the continuing development of the firmware, and the launch and traction control functions were added and tested at the events through the season.. Writing the documentation also started in August '08, and the latest version of that can be viewed and/or downloaded here.
For the 2009 season, 4 more XoomBoxes were built and supplied to other competitors on the Scottish sprint/hillclimb circuit. GPS logging was added, and the functionality of the analysis software, XoomCentre, evolved to provide power display and analysis tools.
At the end of the 2009 season, a new board was produced, slightly smaller and incorporating a no. of modifications we wanted in the light of experience gained with the original.
Anyway, here's the spec.
Analogue inputs - 8 x 10bit inputs range selectable 0..2.5V or 0..10V. 6 of the inputs are available on external connectors, the other 2 are internally connected to +/- 2g xy accelerometers.
Frequency inputs - 6 available. This gives us the ability to record all 4 wheel speeds, the engine speed (via the tacho output from the ecu) and also injector frequency and duration.
GPS recording. The RS232 port enables logging from any GPS receiver with standard NMEA output. GPS time, latitude, longitude, altitude, velocity and heading are decoded and recorded from the NMEA output
Shift light - 7 LED segments lit in sequence as the engine rpm approaches the red line. These LEDs are also used to indicate status such as "launch control armed', memory card invalid or read only and so on.
Rev limiter - programmable soft and hard engine cut.
Data Recording - SDRAM card, 1GByte as standard, FAT16 or FAT32 filing system, so can share data with PC and camera or even mp3 players. Importing recorded data to a PC is as simple as copying a file. Logging rate is fixed at one record every 40ms, ie a record is written to the SDRAM card 25 times/second. Each record contains the current value of all 8 analogue channels and the most recently acquired frequency from each of the 6 frequency channels.
Launch control/traction control/flat shift
Having decided to put that lot into the design, it seemed rather obvious that enough info was available to perform launch control and traction control as well. Accordingly outputs were added to the design to permit individual switching of 4 fuel injectors. The circuitry has been designed to permit individual injector pulses to be suppressed and give fine control of the engine's output.
Launch control has two distinct functions.
Traction control is easier to describe, but just as complicated to implement.
For the V2 XoomBox, we've added the ability to fit an extension module inside the case. The design of the X10ders means that they can provide additional data channels, included both in the datalog files, and also visible on the PC's live data display. X10der modules already available include
Being able to view the collected data in helpful ways is critical to the success of the project. Development of the data analysis package (PC based) is essentially complete. Key features are be
It was an ambitious project, but as of June 2008, all of the above functions have been tested and verified. More info and results are available from the links at the side of this page. The download of the XoomCentre software includes real data files collected from our car in competition. The photos below show the first batch of boards for the original 2007/8 prototypes.
The first batch of boards arrives
One has been partially populated to check the mechanical assembly and fit to the case
This site was last updated 06/19/12