ESMOTOR 1/4 mile record - 9.59 @ 146 mph
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Maybe this was already covered, but you know that the way the VBOX and the tracks measure trap speed is totally different, right?
The VBOX interpolates (or integrates or whatever, you guys discussed it) the actual speed the car is doing at exactly 1320 ft from the position of movement start.
A 1/4 mile (or 1/8) has a pair of lights approximately 60ft apart, in the 60ft prior to the distance thats 1320 or 660 feet from the first staging lights, that measure deltaT between the lights, which tells you the average speed over that 60ft.
Depending on how deep you stage, the VBOX 1/4mile time should be slightly greater but the trap slightly higher.
Perhaps the difference in measurement of different things would explain the variability? Just another rabbit hole.
The VBOX interpolates (or integrates or whatever, you guys discussed it) the actual speed the car is doing at exactly 1320 ft from the position of movement start.
A 1/4 mile (or 1/8) has a pair of lights approximately 60ft apart, in the 60ft prior to the distance thats 1320 or 660 feet from the first staging lights, that measure deltaT between the lights, which tells you the average speed over that 60ft.
Depending on how deep you stage, the VBOX 1/4mile time should be slightly greater but the trap slightly higher.
Perhaps the difference in measurement of different things would explain the variability? Just another rabbit hole.
Maybe this was already covered, but you know that the way the VBOX and the tracks measure trap speed is totally different, right? The VBOX interpolates (or integrates or whatever, you guys discussed it) the actual speed the car is doing at exactly 1320 ft from the position of movement start. A 1/4 mile (or 1/8) has a pair of lights approximately 60ft apart, in the 60ft prior to the distance thats 1320 or 660 feet from the first staging lights, that measure deltaT between the lights, which tells you the average speed over that 60ft. Depending on how deep you stage, the VBOX 1/4mile time should be slightly greater but the trap slightly higher. Perhaps the difference in measurement of different things would explain the variability? Just another rabbit hole.
Last edited by longboarder; Nov 2, 2015 at 06:51 AM.
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The vBox software from Pencilgeek takes the velocity data from the file and can calculate any acceleration data points including 1/4 mile terminal speed AND 1/4 mile trap speed just like a track. So the vBox gives you the same data from your track (plus a lot more) See below screenshot pic:
I guess I have to go buy one of those and find an abandoned runway.
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The vBox software from Pencilgeek takes the velocity data from the file and can calculate any acceleration data points including 1/4 mile terminal speed AND 1/4 mile trap speed just like a track. So the vBox gives you the same data from your track (plus a lot more) See below screenshot pic:
That is pretty direct and not particularly subject to guessing or any significant inaccuracy other than clock jitter and misplacement of sensors.
Last edited by wrs; Nov 2, 2015 at 12:46 PM.
He described his methodology and it's not just like a track. It's an estimate based on unknown data values. So it's a guess and subject to the limitations of the approximation method and the data used. The track makes real timing measurements at 1320 ft and 1254 ft and uses a difference quotient to produce a trap speed, i.e. the average speed between the two points. The same is true of 60ft time and ET at the track.
That is pretty direct and not particularly subject to guessing or any significant inaccuracy other than clock jitter and misplacement of sensors.
That is pretty direct and not particularly subject to guessing or any significant inaccuracy other than clock jitter and misplacement of sensors.
The vBox used in conjunction with Robert's website is correct. I don't care what else you say on the subject.
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I have no doubt that wrs's 135? trap speed with the Fab setup was not accurate.
It's simply not possible.
It's like where I got a slip saying my 1/8 mi trap was 119mph.
I just ignored it because it's obviously wrong.
It's simply not possible.
It's like where I got a slip saying my 1/8 mi trap was 119mph.
I just ignored it because it's obviously wrong.
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I posted the data, Vbox doesn't match at Ennis or SAR in most of the cases it's off by 2% or more, longboarder needs to post the timeslips and the vbox results to prove his point. As far as I am concerned, the SAR slip was correct, you or anyone else would have to prove otherwise and the 1/8 time on those three slips was reasonable. You have a problem with it, prove it's wrong.
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lmao. then i'll call it Robert's wild *** guess if you want. His wild *** guess ties out almost exactly to every 1/8 mile and 1/4 mile I have ever run at multiple tracks on the west coast. So his wild *** guess is pretty damn good. It also ties out to a number of other tracks back east like Atco and Englishtown from my friends' data. If it doesn't tie out to a particular track like it didn't at Sacramento, then is the vBox is wrong? lol guess what...the vBox was right and Sacramento quietly changed their timing system and now it ties out.
That's your opinion, I have data that says otherwise and if you don't care, why do you keep responding? LMAO.
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I don't think clock jitter would be an issue for 200hz sampling and anyway, your timing is probably run off an interrupt from an external clock. You could be affected by interrupt latency inside the Android or IOS low level interrupt processing anyway. I am talking about a pure electronic circuit in the case of what we had developed.
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My performance box results are often 3-5mph different on trap speed than what the track measures and these are NHRA certified tracks. I kind of think I would rely more on fixed sensors a few feet from the car than I would a radio signal broadcast from 22,000 miles up with a 95% CEP of +- 10ft. A car moving at 145mph is covering 212ft/s. The trap measurement is the last 66ft and on a 10hz Vbox that would give three samples about 21ft apart with a 10ft position error per sample to make a trap speed estimate from. First problem is where do the three samples fall with respect to the final 66ft? The second is the position error in the samples. The samples are spaced evenly in time but not distance and with the track, it's just the opposite. Thus, using a numeric differentiation technique to produce velocity from distance will produce different results due to this variation in data used. The real trap speed can only be gotten from the track, the Vbox information is only at best a rough estimate. With respect to ET's, it's a lot less probable that the Vbox sampling error will be noticed due to the distances and time involved. I trust the Performance Box on ET and 60 ft times but not trap speed at such high velocity. Obviously the 20hz version of the Vbox would suffer less error but the problem is the same with respect to where the samples fall and the error in them. In fact, at 20hz, the samples should be about 10ft apart at that speed but that is within the margin of error in the tool itself so the data is useless.
