GPS timing the mile, continuation...

[Fubar]

Mile Timing Thread

I don't understand why timing is even an issue. We have radar that can track objects traveling in excess of 4000mph and do so accurately enough to collide with said "object" from miles away. Why are there issues confirming a large metal car traveling in a predetermined straight line? It seems like two lasers across the 6inch finish stripe could be accurate to within cm/sec.

 

[HHGT]

Accurate readings can be fairly easy

I am curious how the field technicians decide on what GPS accuracy truly means.

On military basis and for less than $8,000 we used to strike two ground monuments and GPS calibrate them for what is known as Ground Truth. Once the beginning and end point is established and corrected for earth curvature your distance (in this case 1 mile) is set in stone. The only thing that changes is Time "t". We know that "t=0" at launch so now we measure the for the final "t" at the point where the vehicle crosses the final monument. An accurate reading can come from a differential GPS which is accurate to approx 1 Ft. but if you want to remove any uncertanties, RTK (Real-Time Kinematic GPS is more appropriately used. We have found that RTK GPS is accurate to a Nano second. We used to measure munition speed with RTK GPS technology.

More info here...http://pro.magellangps.com/en/products/aboutgps/rtk.asp

 

[Mullet]

What did he just say?

 

[HHGT]

Hmmmmmm

This could throw many scientific gadgets off calibration.

 

[Fast Freddy]

hate to burst your bubble guys but a GPS loses its accuracy when you are still under acceleration. the way a gps calculates speed creates a delay in calculations. therefore if you cross the finish line and you are still accelerating a GPS will not give you an accurate reading. it will read slower than you are actually going. now if you cross the finish line at your max speed and you are not still accelerating then you will get a more accurate figure.

and even that does not tell the entire story with a GPS. there is at least one second of delay after you hit max speed before a GPS can accurately calculate your true speed. therefore a GPS is irrelevant in a speed contest such as a 1 mile top speed shootout. anything less than timing equipment like the Mojave Mile uses or the NHRA or the Bonneville salt flats will not give you accurate info.

if you don't believe me then mount your gps (configured for real time data and not max speed) right next to your speedo and have a passenger compare the two under acceleration in 4th gear with a TT GT and you will understand what i am talking about.

in fact video tape the two under acceleration and post it here on this site and i will bet anybody $100 that i am right :wink

 

[Paul Vincent]

That would only yield average speed. Wait, I can't make technical arguments... I'm just a glorified babysitter. I still don't know why this can't be fixed for cheap cheap money. I will consult with the magic 8 ball for sound advice later.

Well, what I am asking for is how much time it took Ray to travel the standing mile. We know that in the past few years top fuel and Funny Cars got elapsed time for the quarter mile of less than 4.5 seconds at speeds of ~ 330 mph, so my question is asking for the elapsed time for Ray's standing mile at 266.938 mph. If my math were any good, I'd likely be able to figure it out accurately, but it isn't, so the best I could do would be an approximate elapsed time, but I'd like an accurate figure if possible (just to be able to say, "Ray Hoffman driving his Ford GT did the standing mile on April 25th, 2010 in X seconds)." Thanks again.

 

[Fast Freddy]

Well, what I am asking for is how much time it took Ray to travel the standing mile. We know that in the past few years top fuel and Funny Cars got elapsed time for the quarter mile of less than 4.5 seconds at speeds of ~ 330 mph, so my question is asking for the elapsed time for Ray's standing mile at 266.938 mph. If my math were any good, I'd likely be able to figure it out accurately, but it isn't, so the best I could do would be an approximate elapsed time, but I'd like an accurate figure if possible (just to be able to say, "Ray Hoffman driving his Ford GT did the standing mile on April 25th, 2010 in X seconds)." Thanks again.

it is impossible to calculate finish line speed based on ET.

for instance a top fuel dragster can go wide open throttle for the first 300 feet and blow the motor and cross the 1/4 mile finish line with the following time slip > 8.99 @ 120 mph as just one of many possible scenarios......

 

[BlackICE]

hate to burst your bubble guys but a GPS loses its accuracy when you are still under acceleration. the way a gps calculates speed creates a delay in calculations. therefore if you cross the finish line and you are still accelerating a GPS will not give you an accurate reading. it will read slower than you are actually going. now if you cross the finish line at your max speed and you are not still accelerating then you will get a more accurate figure.

Freddy it depends on the GPS used. Most GPS units used for navigation sample at only 1Hz. These are not very good for speed measurements as you stated. But other devices sample at much higher frequencies and are more accurate when you are accelerating. I use a Driftbox from Racelogic. It samples data at 10 Hz and my results match my time slips very closely. Racelogic has other higher performance boxes that sample at even a higher rate for even better results. Many car companies and magazines uses these boxes and get good results. Is it as good as a properly setup timing device, NO. But it is pretty damn close! My results varied less than 0.1 MPH from the time slips I got during the TX mile.

 

[Fast Freddy]

Freddy it depends on the GPS used. Most GPS units used for navigation sample at only 1Hz. These are not very good for speed measurements as you stated. But other devices sample at much higher frequencies and are more accurate when you are accelerating. I use a Driftbox from Racelogic. It samples data at 10 Hz and my results match my time slips very closely. Racelogic has other higher performance boxes that sample at even a higher rate for even better results. Many car companies and magazines uses these boxes and get good results. Is it as good as a properly setup timing device, NO. But it is pretty damn close! My results varied less than 0.1 MPH from the time slips I got during the TX mile.

you will lost $100 if you bet me :willy

a gps is more than just Hz. it depends on how many satellites you are tracking and even then there is a limit to how many you can collect data from due to orbital positioning. and not only that there is a delay in transmission between your GPS and the satellites no matter how much Hz your gps operates at :wink

 

[Fubar]

hate to burst your bubble guys but a GPS loses its accuracy when you are still under acceleration. the way a gps calculates speed creates a delay in calculations. therefore if you cross the finish line and you are still accelerating a GPS will not give you an accurate reading. it will read slower than you are actually going. now if you cross the finish line at your max speed and you are not still accelerating then you will get a more accurate figure.

and even that does not tell the entire story with a GPS. there is at least one second of delay after you hit max speed before a GPS can accurately calculate your true speed. therefore a GPS is irrelevant in a speed contest such as a 1 mile top speed shootout. anything less than timing equipment like the Mojave Mile uses or the NHRA or the Bonneville salt flats will not give you accurate info.

if you don't believe me then mount your gps (configured for real time data and not max speed) right next to your speedo and have a passenger compare the two under acceleration in 4th gear with a TT GT and you will understand what i am talking about.

in fact video tape the two under acceleration and post it here on this site and i will bet anybody $100 that i am right :wink

True but if you measured with a laser unit (say 12 inches off the ground) shooting two beams (around 6 inches apart) you could accurately calculate the average speed traveled between the two lasers. This seems like it would be a simple, cheap device were the calculation are easy to understand, replicate and be fair to all. You could even stack 10 of these lasers on top of each other for failsafe purposes and verification.

copyright 2010 - FUBAR'd productions, please send me your check as soon as you finish reading this.

Well, what I am asking for is how much time it took Ray to travel the standing mile. We know that in the past few years top fuel and Funny Cars got elapsed time for the quarter mile of less than 4.5 seconds at speeds of ~ 330 mph, so my question is asking for the elapsed time for Ray's standing mile at 266.938 mph. If my math were any good, I'd likely be able to figure it out accurately, but it isn't, so the best I could do would be an approximate elapsed time, but I'd like an accurate figure if possible (just to be able to say, "Ray Hoffman driving his Ford GT did the standing mile on April 25th, 2010 in X seconds)." Thanks again.

For the purpose of comparison, I agree the number would be fun to have but traction is such a huge issue that it's not that relevant. The guys who run the mile a lot would just ignore the comment.

 

[Fubar]

you will lost $100 if you bet me :willy

a gps is more than just Hz. it depends on how many satellites you are tracking and even then there is a limit to how many you can collect data from due to orbital positioning. and not only that there is a delay in transmission between your GPS and the satellites :wink

Why are vBox's considered such a good device for measuring 60-130 and track lap times?

 

[Fast Freddy]

True but if you measured with a laser unit (say 12 inches off the ground) shooting two beams (around 6 inches apart) you could accurately calculate the average speed traveled between the two lasers. This seems like it would be a simple, cheap device were the calculation are easy to understand, replicate and be fair to all. You could even stack 10 of these lasers on top of each other for failsafe purposes and verification.

copyright 2010 - FUBAR'd productions, please send me your check as soon as you finish reading this.



For the purpose of comparison, I agree the number would be fun to have but traction is such a huge issue that it's not that relevant. The guys who run the mile a lot would just ignore the comment.

YOU FAIL

go back to physics class and then go talk to the Chief tech of timing and scoring at Bonneville and mail your check to me overnight :lol

 

[dbk]

Hey fellas, let's start a new thread in the racing section or something. Thanks.

I hate posting from my iPhone. Can't wait to get back to real Internet.

 

[Fast Freddy]

Why are vBox's considered such a good device for measuring 60-130 and track lap times?

this cars speed was not measured with a V-BOX :wink

http://www.youtube.com/watch?v=LKQ-xj5C2m8

 

[BlackICE]

Freddy, you bring up relevant points where a GPS timing unit may not produce great results, but that doesn't preclude it working pretty damn well under good conditions. It you have a good antennae location and are in a favorable position on earth whereby a large number of satellites can be locked on to, the results can, and do, match up very well with the standard timing equipment. I have such results both at the TX mile and at Hennessey's track. The numbers match much less than 0.5% difference. Will that happen all of the time, NO. Can it yes. Worst case a GPS device won't work at all since you cannot lock to enough satellites. I haven't run into that problem yet with my Driftbox mounted low on the center of the windshield. I do get a loss of signal error "beep" whenever going under a bridge for example on a track. Some cars like Sam's favorite, BMWs, have windshield that block out GPS signals.

This said, a GPS unit is not a great solution for a mile event, since it would be nearly impossible for all of the cars to get a good lock on enough satellites and the timing in not unbiased, not hackproof and inconsistent amongst all of the cars.

 

[Fast Freddy]

^^^^^^

.5% error is not the same as 0.0% error :wink

oh yeah and one more thing. i will be going 200+ mph at the Mojave mile in the future with a whipple and nitrous. and i don't need traction control either :driving:

and i also bet that somebody will wreck at the Texas mile and die as a result of their lack of safety.

i don't need turbos or Texas to join the 200 mph club :beer2:

 

[BlackICE]

^^^^^^

.5% error is not the same as 0.0% error......

oh yeah and one more thing. i will be going 200+ mph at the Mojave mile in the future with a whipple and nitrous too. and i don't need traction control either :driving:

and i also bet that somebody will wreck at the Texas mile and die as a result of their lack of safety.

i don't need turbos or Texas to join the 200 mph club :beer2:

Freddy from what I read from the Mojave rule book if you run nitrous and a Whipple that is 2 power adders that put you into the unlimited class. That requires a roll cage and fuel cell! I don't believe you are going to add those items. So maybe a stealth installation.

I agree than nitrous is the best way to goes to get 200+ at Mojave without a TT.

 

[Fast Freddy]

Freddy from what I read from the Mojave rule book if you run nitrous and a Whipple that is 2 power adders that put you into the unlimited class. That requires a roll cage and fuel cell! I don't believe you are going to add those items. So maybe a stealth installation.

I agree than nitrous is the best way to goes to get 200+ at Mojave without a TT.

i went 182.3 mph at the Mojave Mile with nothing more than a 2.87" pulley (14.5 psi) + tune and a catback exhaust on the stock blower and stock tires. the DA on my run was 4000 above sea level according to my weather station and i had a 10 mph crosswind :wink

how fast did you go? as i recall you have a whipple supercharger + accufab throttle body with how much boost? do you have headers or a catback exhaust? what kind of tires were you running? have you ever dyno'd your GT and if so how much horsepower did it make?

i have never even dyno'd my GT. i am guessing that it only makes 625 rwhp at the most......

 

[skyrex]

Put down the TT deposit on Saturday. My mile for September just got much more interesting!! :banana

Looks like we all want a little more after our March experience. :thumbsup :cheers

 

[Fast Freddy]

Put down the TT deposit on Saturday. My mile for September just got much more interesting!! :banana

Looks like we all want a little more after our March experience. :thumbsup :cheers

:cheers