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I think the Cayman may be a bit of a mudrunner, as I was a couple of seconds faster than the rest of my group at the end of the morning run, which included 911s, Boxsters & 914s. The first group managed to squeeze in 5 or 6 runs before the rains, but they weren't posting times, so I'm not sure how I faired against them.
I also tried out a MaxQData GPS data-acquisition system I just got. It's about $300 and captures stuff like track map, lat & long Gs, speed, etc. Here's a chart overlaying a couple of runs (second and sixth):
The line graph at the bottom shows speed over time, the red line is the faster second run (by about 4 seconds). The track map shows acceleration in blues (darker = harder) and braking in red and the width of boxes along the track are proportional to lateral Gs (course is running counter-clockwise).
The track map also shows up the limitations of a GPS-based system. The courses are inaccurate by up to 2 meters, run-to-run, the apparent line differences were not so great. Second, as the car moves around you get different numbers of satellites in view and the readings can drop off for a series of samples, showing up as unrealistic discontinuities as, for example, in the red track around the bottom-right left-hander.
Still, it definitely showed how & where I was improving run-to-run. Here's some stats from those two runs:
I'm a little surprised at the 0.94 lateral Gs in the rain, though the car did feeld very solid. The Mich PS2s are pretty good in the weather, it seems. There was clearly head-room in the braking, I was not quite brave enough to really push threshold in those 6 runs. Interesting stuff, will report more as I continue to experiment with it.
Cheers,
John.
PCA - Porsche Club Of America
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I was running with PASM, SC and PSM all on, though I can't say I specifically noticed PSM taking over, except the braking into the tight hairpin which is offscreen on the track map I posted. I was pretty carefully squeezing on the throttle most of the time (doing my PSMing), even on launch. I think having SC on does modulate the PSM activity, but the real answer would have been to try with PSM off.
I think if I'd run in the afternoon I would definitely have tried PSM off, but the times kept going down so I was happy to have it there for safety. Actually, I hope it rains again for one of the local AX's, I really enjoyed the challenge, and I will try turning PSM off for sure.
About that hangar, in the drivers meeting they said we'd have to hold operations if a helicopter came out until it took off!
PASM - Porsche Active Suspension Management
This active damping system offers continuous adjustment of individual damping forces based on current road conditions and driving style.
The driver can choose from two setup modes, ‘Normal’ and ‘Sport’, using a separate ‘damper’ button on the center console. ‘Normal’ mode is designed for general road driving and circuits with uneven tarmac. ‘Sport’ mode is intended for smoother track surfaces, where the harder settings help eliminate pitch and roll.
In either mode, PASM continuously evaluates the current conditions while automatically selecting the corresponding damper rates from the respective set of mapped values.
A range of sensors are used to monitor the movement of the body under acceleration, braking and cornering maneuvers, as well as on poor road surfaces. The PASM control unit then evaluates this data and modifies the damping force on each individual wheel in accordance with the selected mode. The result is a significant reduction in body movement as well as a better grip on the road.
For example: if ‘Sport’ mode is selected, the suspension is automatically set to a harder damper rating. If the quality of the track surface falls below a certain threshold, the system immediately changes to a softer rating within the ‘Sport’ setup range. When the quality of the tarmac improves once more, PASM automatically returns to the original, harder rating.
Need more information about PASM? Click this link: FAQ for PASM
PSM - Porsche Stability Management
While it can’t overcome the laws of physics, the revolutionary Porsche Stability Management (PSM) system does lend an added degree of balance and control to the Cayman’s mid-engine driving dynamics, inspiring surefooted confidence in corners and extreme situations.
A standard feature on the Cayman and Cayman S, PSM continuously monitors steering input, road speed, yaw velocity and lateral acceleration to calculate the actual direction of travel. If the car begins to steer off line, PSM instantly intervenes with precision brake inputs on individual wheels to help bring the car back onto the driver’s intended path.
If braking alone isn’t enough to correct the vehicle’s cornering line, PSM then calls on the Cayman’s engine management system, adjusting engine output as needed to help stabilize handling. PSM can also compensate in an instant for mid-corner changes in load resulting from deceleration or braking. When Sport mode is selected with the optional Sport Chrono Package, PSM’s threshold for intervention is raised, allowing for greater driver involvement. If you prefer driving without automatic PSM assistance, the system can be set to standby at any time. In this case, it will only intervene under heavy braking, where both front wheels exceed the ABS threshold.
For all of its technical ability, PSM goes virtually unnoticed in everyday driving situations, preserving the Cayman’s natural agility.
One thing to keep in mind is MaxQData's internal sensors are depending on chassis motion, meaning its readings need to be normalized against chassis lean on all four directions. Under hard braking, for example, let's say that the car dives 5 deg, you have to subtract 5 deg from MaxQData calculation to get to the true G loading under braking. There couple of equations use for that and need to know how much the car the car dives under 1G braking, or leans at 1G lateral loading, etc.
However, that is way to much work unless you are trying to do instrumented absolute comparison between cars or some similar situation. Best way to use MaxQData is not to take the reading as absolute, but use reference points between runs/lap to determine if you can improve your braking, cornering or throttle application. Also, another great way to use it if you modify your car is to determine when understeer/oversteer situations are induced to make corrections to chassis points. Although I never used it in that capacity, it is useful to tune engine parameters as well.
Looks like you quite of bit of fun. I think autocross in the rain is tremendously valuable and teaching [img]/fckeditor/editor/images/smiley/MWPX/regular_smile.gif[/img]
FT, a 5 degree dip or roll will only bias the readings by about 0.4% (1-cos(dip)), so the 0.94 lat Gs would become 0.936; still pretty good on street tires in the rain. But, you are right, the best way to use this gear is for run-to-run comparisons.
As it happens, the particular MaxQData system I'm using is GPS-only, so it doesn't have any accelerometers or gyros. It uses doppler-shift analysis to compute vertical, northing & easting velocity components & derives speed and heading from those. These turn out to be relatively much more accurate than positioning, around+-0.056 mph, +-0.4 degrees at 25mph or +-0.2 degrees at 50mph, and deltas in these are used to reckon lateral and longitudinal G-forces. Depending on where the GPS unit is in the car, the dip & roll angles will have different effects, unlike an accelerometer whose axes pitch with the car. I have mine sitting on the engine cover, so not far from the COG.
Anyway, it's lot's of fun for a geek like me, maybe it'll help with my driving. And, yes, I heartily recommend AX in the rain for improving your driving!
And I was trying to explain.... [img]/fckeditor/editor/images/smiley/MWPX/teeth_smile.gif[/img] Let me guess, amatuer or pro pilot?
Looking forward to more autox reports and graphs. My MaxQData does not have the GPS, but new version of the software seem quite improved, so might get a Garmin unit.
Yes, sorry about going on a bit. I'm a computer scientist and a bit of a math geek, actually, so the GPS-based stuff has caught my interest. Of course, I'm just starting at competing with the Cayman, so I have to be careful not to over-analyze and continue to work on getting the butt calibrated.
I'm writing my own track analyser and will post some screen shots of it when it's worthy.
As to the Garmin unit, you probably want to make sure it can sample at a reasonable rate, at least 4Hz, particularly if you are going to use it for track speeds (as opposed to AX speeds). The GPS unit that MaxQData sells is actually just a rebranded unit from Socket Communications (http://www.socketcom.com/) and it can do 5Hz.
Linear Mode
