andrew7 Posted January 25, 2007 Share Posted January 25, 2007 I was thinking it be nice to test acceleration, braking and cornering g's on the 7. Does anyone have any experience with testing computers like a Beltronic or a G-tech or are they useless school boy toys? Do you have to spend a thousand to get something accurate or has technology improved enough to become affordable? It might even be fun for an autocross run, cheap DAS. Link to comment Share on other sites More sharing options...
scannon Posted January 25, 2007 Share Posted January 25, 2007 I had the use of a G-tech a few years ago. I couldn't get anywhere near consistant results from it. One time it told me my Miata engine was generating 520 hp. I was laughing so hard I nearly drove off the road. I think you need one that uses GPS rather than acceleromters. Skip Link to comment Share on other sites More sharing options...
slngsht Posted January 25, 2007 Share Posted January 25, 2007 I don't think GPS refreshes fast enough, nor is super accurate. I have an accelerometer hooked up to the PC in my car, but haven't used it for anything other than peak g's. Best way is a 5th wheel. Link to comment Share on other sites More sharing options...
scannon Posted January 25, 2007 Share Posted January 25, 2007 Most all the car magazines test using a GPS system. A friend has one and it shows g forces, corner speeds and a lot more info. Showing it against an outline drawing of the track is really helpful for getting each corner worked out. I plan to get one once the Caterham project is finished. Skip Link to comment Share on other sites More sharing options...
slngsht Posted January 25, 2007 Share Posted January 25, 2007 what's the sample rate? It's great for road racing, but if you're trying to measure 0-60, it's gotta have a high sample rate.slngsht2007-01-25 17:41:50 Link to comment Share on other sites More sharing options...
Al N. Posted January 25, 2007 Share Posted January 25, 2007 I have a G-Tech and it's amusing. There is this more sophisticated one (Trak-Mate?) that seems to be much more accurate/useful...I'll have to look it up. Link to comment Share on other sites More sharing options...
andrew7 Posted January 25, 2007 Author Share Posted January 25, 2007 Thanks everyone, That is what I thought, mostly smoke and mirrors or is it leds and graphs. I never seen one in person or heard if they worked but was sceptical and thought I'd ask. Link to comment Share on other sites More sharing options...
slomove Posted January 26, 2007 Share Posted January 26, 2007 Thanks everyone, That is what I thought, mostly smoke and mirrors or is it leds and graphs. I never seen one in person or heard if they worked but was sceptical and thought I'd ask. Well, I would not say it that harsh....I found the accelerometer function of the G-Tech Pro functioning quite well, that means for 0-60 or 1/4 mile comparisons it seems to be pretty accurate. It allows for roll-out setting to compare with published tests (I believe most car manufacturers use a 12" roll-out which makes a huge difference). The horsepower calculation is a different story...You need not only to plug in the (honest) car weight including load but additionally the linear equivalent of the moment of inertia of rotating masses which can be significant for a Seven as a percentage and difficult to estimate. I am using 250 pounds as wild-ass guestimate for wheels, driveshafts, diff, gearbox, clutch, flywheel, crank and pistons. That gets me somewhat close to what is probably the power. Another error source is the RPM pickup. The G-Tech does not connect to the ECU or crank sensor but measures the ripple noise on the 12V power with the idea that the alternator spins proportially to the engine. Very clever but if this noise is filtered too much or if the RPM are not calibrated correctly the HP result can be anything. But, in my car the RPM reading is pretty good. Finally, I am trying to do a coast-down deduction. When you get to e.g. 60 mph the air drag, tire and drive train friction are quite high. Therefore I look at the positive acceleration at the moment just before I take the foot off the pedal and the negative acceleration (without braking) just after. I use the ratio of negative/positive accelaration to correct the calculated HP figure After all, I like the G-Tech as a comparative measurement tool to asses e.g. engine improvements and knowing the limits it does a reasonable job for the money. Can it measure engine power precisely? No way, but even on any given dyno the numbers can vary wildly. Gert P.S.: I use a low cost bicycle GPS gadget with automatic lap trigger for track timing which is kind of O.K. but only accurate to 1 sec. I believe the more expensive data loggers with GPS can do 100 updates per second. Link to comment Share on other sites More sharing options...
rv-4mike Posted January 26, 2007 Share Posted January 26, 2007 No personal experience, but I have seen a lot of data captured by a Trak-Mate system and it's pretty impressive. I dont know about using something like this for computing HP but its good for performance measurement - especially relative performance. Like before - after a mod to see if you made it better or worse. Also car to car. If you take a look at the Ariel Atom forum archive one of the guys has a thread with a bunch of performance testing in his car and someone elses. Its pretty cool. You can run the two traces simultaneously. Its like watching a race in real time. You can see which car/driver was faster on which part of the track. I think to get truly useful data any system would need both accelerometers and GPS. Link to comment Share on other sites More sharing options...
slomove Posted March 30, 2007 Share Posted March 30, 2007 After a demonstration at the last track day I have been playing a somewhat with the MaxQData >GPS-only data acquisition system . Actually it is very nice for logging driving performance data on the race track or for autox, especially the comparison option for consecutive runs or between different racers with the graphical/color representation of lateral and longitudinal acceleration. Obviously it can not log any car parameters but if you are just looking for pretty precise lap times and hints where you lost some seconds this is it. The user interface is a little clunky and getting the Pocket PC to connect with the Bluetooth GPS was a challenge but that is maybe because I have not done it before. It also claims to be usable and quite accurate for drag runs but at 5 Hz GPS update rate I don't know. The software can be downloaded free for unlimited number of computers and it has no use restriction or registration but the price for the GPS module is a little steep at $299. Now as it happens, >Semsons is selling a device that looks extremely similar for $99. I got one but right now it seems to be out of stock. I guess MaxQdata needs to think about the feasibility of their business model http://www.usa7s.com/aspnetforum/images/emoticons/eek6.gif Gert Another one >here slomove2007-03-29 22:07:59 Link to comment Share on other sites More sharing options...
Keith Posted March 30, 2007 Share Posted March 30, 2007 The car magazines use GPS systems exclusively. GRM uses the Traqmate, although when my car was at the track with the Atom we didn't get a single good datalog out of the bloody thing. Car and Driver seems to get much better results out of theirs - I think it's a V-Box. Link to comment Share on other sites More sharing options...
slngsht Posted March 30, 2007 Share Posted March 30, 2007 Their sample rate must be really high... how can they tell the difference between 4 seconds and 4.1 seconds 0-60 time at 5Hz? Link to comment Share on other sites More sharing options...
Keith Posted March 30, 2007 Share Posted March 30, 2007 According to the documentation, the VBox can use either 20 Hz or 100 Hz. Link to comment Share on other sites More sharing options...
slomove Posted March 30, 2007 Share Posted March 30, 2007 Their sample rate must be really high... how can they tell the difference between 4 seconds and 4.1 seconds 0-60 time at 5Hz? As they transmit time, position and precise speed (0,05 m/s), the speed between time stamps could be interpolated with pretty good accuracy. It might be at least good to 1/10 sec, possibly better. I am not sure however, what the time window for the speed measurement in the GPS chipset is for every transmission, i.e. if it is almost spontaneously or over a certain period within the 1/5 sec. This Bluetooth GPS standalone solution is not going to compete with high-end 100Hz GPS data acquisition systems. The beauty is in the comparably low cost and unobtrusive size at reasonable accuracy. You don't even need to install it in the car but can carry it in your pockets. Gertslomove2007-03-30 15:29:19 Link to comment Share on other sites More sharing options...
Boxologist Posted August 27, 2007 Share Posted August 27, 2007 anyone gone any further with any of the setups? i found a few items, some i'm quite interetsed in. I'd like to find out what Evolution School is using. before making a sizable purchase. http://www.trackpedia.com/forums/showthread.php?t=2490 http://www.mr2oc.com/showthread.php?p=2767518#post2767518 Link to comment Share on other sites More sharing options...
Cherik Posted August 28, 2007 Share Posted August 28, 2007 I've used both the G-tech and the AP22 from Race-Technology. The G-tech is primitive and I had a difficult time getting reliable readings from it. The AP22 on the other hand, is very good. two axis accelerometer and impressive PC analysis software. A bit more expensive than the G-tech, but.. you get what you pay for :-) Check out the website and go to the car section - products - AP22 etc. http://www.race-technology.com/ap22_10_1529.html http://www.race-technology.com/software_10_1095.html Link to comment Share on other sites More sharing options...
tnttim Posted August 31, 2007 Share Posted August 31, 2007 Campbell Scientific makes an older 21X that I have seen on Ebay once in a while for a few hundred dollars. It is a Datalogging computer that I have seen dropped from a shelf and still worked. Then you just get some Accelerometers, tc, or monitor the TPS and tach, They arent to complex. Just hooking up the stuff correctly and getting it al to work is a bit much but if you do it is a good starter. Will hook to a laptop. Tim Link to comment Share on other sites More sharing options...
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