SOMEONE WAKE SCUDLEY UP! Lol.

Ok, I looked up the specs on my Delorme PN-20 gps. For what it's worth, the specs state

WAAS-enabled, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position

GPS accuracy:
» Position: < 15 meters, 95% typical*
» Velocity: 0.05 meter/sec steady state (translates to about .11 mph)

WAAS accuracy:
» Position: < 3 meters, 95% typical*

So what can we glean from this?

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means to measure buggy speed which is reasonable and acceptable to us all.

I think if we took a vote, GPS would indeed by a 'reasonable and acceptable' measure of buggy speed to 99 odd percent of us.

Would I trust one to save my life if I got lost....absolutely.

Do I believe the speed shown on the GPS is completely accurate? No, of course not. But most of the time, it's close enough.

Will it affect the size of my grin while buggying? HELL NO!!

And the size of my grin when buggying is THE most important thing

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Originally posted by Scudley You did not read the paper, or if you did you did not understand any of it, as it was a suggestion as to how to fix the problem using available technology. Bike computer is a quarter the price and can be 10x as accurate so GPS is not smartest or cheapest- but GPS is so sexy. Well if you want to know if one guy is really faster than another, GPS does not rule the day unless one guy is going less than half the speed of the other. The guy who wrote the paper was concerned about measuring boat speeds, so hopefully the much larger marine market will come up something soon. I am really sorry the news has upset you so much. Please do not be pissed off with me cause I told you about the problem, take it up with Garmin or whoever it was that sold you something that does not do what you thought it did. I really look forward to seeing my critics provide the accuracy of their GPS so we can go over the numbers together and see whether the numbers are any better than I say they are. Afterward maybe the group can come up with a means to measure buggy speed which is reasonable and acceptable to us all. S

Okay, you win. I'm an illiterate, silly, Red Nek. GPS is a sham and I am lying to myself in believing it is anything more than a gross indication of relative movement. Thanks so much for setting me straight on the folly of my ways. I feel enriched and enlightened for it.

Right, now, off ya go...

I started thinking about this a bit more after reading the article Scudley references. It appears the author, Tom J. Chalko, has a a Masters of Science and PhD in engineering. The article makes sense to me. Unfortunately his credentials aren't helped by the rest of the new-age, quasi-science on his website: http://nujournal.net/

But the order-of-magnitude difference in accuracy for speed measurements using Doppler Shift GPS vs trackpoint calculations seems obvious, and has apparently been of interest for verifying high speed sailing and speedsurfing records. See for instance http://www.gps-results.com/GPS_Speed.pdf and the other artciles referenced therein.

GPS receivers record position, time, and other NMEA data depending on brand and model. The sampling rate for the data depends on brand and model, but 1Hz and 5Hz are typical rates (1x or 5x per second). Velocity calculations are performed within the receiver, using brand-specific algorithms. Standard GPS position fixes are accurate within 10-15 meters (33-49 feet). DGPS can increase accuracy to 3-5 meters (10-16 feet). WAAS should enable sub-3 meter accuracy. My guess is most of the buggy or kite skiing fixes we are discussing are standard GPS accuracy. Say your GPS receiver samples position fixes at 1 Hz. At a true 70 mph, you will have covered 103 feet in a second. If your fix is accurate to 15 meters, or 49 feet, an 'instantaneous' speed calculation based on only those two waypoints could theoretically be as low as 54 fps, or 37 mph; and as high as 152 fps, or 103 mph. Interestingly, since velocity is deduced from position fixes, the slower you are going the more error there can be in an instantaneous velocity calculation.

BeamerBob's last post mentioned his DeLorme pn-20 specs as:

WAAS-enabled, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position

GPS accuracy:
» Position: < 15 meters, 95% typical*
» Velocity: 0.05 meter/sec steady state (translates to about .11 mph)

WAAS accuracy:
» Position: < 3 meters, 95% typical*

What can we glean from this? Firstly, WAAS enabled doesn't guarantee WAAS accuracy. WAAS works only in North America, and I've spent plenty of time in Northern MN and WI where it isn't working on my Etex Vista. Secondly, there is no confidence interval for the claimed margin of error for velocity measurement. A 95% confidence interval is a generally accepted statistical standard of certainty. It could be anything here. Lastly, the claim for velocity accuracy is for 'steady-state' conditions - not instantaneous, which is what where I'd bet a number of speed bursts displayed on GPS receiver displays fall.

I don't know how each GPS receiver is calculating and displaying velocity information, but it seems to me if you really want to be concerned with accuracy and record setting, then you need to level the playing field with consistent data gathering and agreement on a common equipment set-up. It appears that using GPS receivers with a high sample rate that record NMEA Doppler-shift time data in their sample streams, and post-processing the data through a common software method would guarantee this accuracy. Some of this post processing software was pointed out in PetriL's thread 'Speed results from Finland, some new records?' (http://www.powerkiteforum.com/viewthread.php?tid=17292). Picking a GPS receiver that does this internally and displays the speed might be a solution, but it would be wrong to assume the majority of units do this.

Bragging rights using a photo of a GPS display works for me. Just don't expect it to hold up in court, or the Guiness Book if that's where you want to see it.

krumly

If I increase my personal best, all that matters to me is my personal achievement and recognition among my peers. This has me thinking of moving my bike computer over to the buggy for verification. If someday it all came together and I broke Arie's record (don't laugh! ) , I would want my peers and I to have confidence that I really did it. Using 2 technologies might be just the verification to have confidence in the numbers. As stated above, I think my gps does a fantastic job, since I would scrutinize any number that didn't "feel" correct. I've never had a number that wasn't legitimate based on the feel of the run. If anything, I've had runs that felt faster than the reading gave me. This is interesting to talk about for sure.

Do the papers indicate any software that the gps' use to subtract the average additional zigzag distance and thus arrive at a more accurate speed guestimate. I dont mind getting up to 50.11mph to brag about doing 50 but if I have to crank it up to 52mph I'm getting out of the game!
PB 47.8 on ice, snowspider kitesled, 5m HQ apexII. See if you can beat that you other kitesleders! + or - 0.11mph

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Originally posted by snowspider Do the papers indicate any software that the gps' use to subtract the average additional zigzag distance and thus arrive at a more accurate speed guestimate. I dont mind getting up to 50.11mph to brag about doing 50 but if I have to crank it up to 52mph I'm getting out of the game! PB 47.8 on ice, snowspider kitesled, 5m HQ apexII. See if you can beat that you other kitesleders! + or - 0.11mph

Based on the purported accuracy of my gps, you would only be off by .055 mph (at 50 mph) worst case so you don't have to sell all your equipment!

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Originally posted by BeamerBob Quote: Originally posted by snowspider Do the papers indicate any software that the gps' use to subtract the average additional zigzag distance and thus arrive at a more accurate speed guestimate. I dont mind getting up to 50.11mph to brag about doing 50 but if I have to crank it up to 52mph I'm getting out of the game! PB 47.8 on ice, snowspider kitesled, 5m HQ apexII. See if you can beat that you other kitesleders! + or - 0.11mph Based on the purported accuracy of my gps, you would only be off by .055 mph (at 50 mph) worst case so you don't have to sell all your equipment!

Thanks Bob, that's my point exactly. Although I was not aware that WAAS was not available world wide (because I lead a sheltered life these days) and in spite of the fact I can see where that alone might raise an eyebrow here or there, the question is purely academic. One would have to have something far greater at stake than bragging rights to invest in emerging technology for the sole purpose of recording top speed on a freakin' kite buggy. Guinness is one thing. A community of solid people, many of whom I would routinely stick my hand in fire for... I would expect better of them for no other reason than personal integrity. "Gear" ain't gonna make that happen.

If you can't trust yourself, who are ya gonna trust, a pile of silicon and solder ? Really ?

I've owned several GPS's since I started using them back in 1996
2 X Magellans were like house bricks and very slow but always good to navigate even though back then the accuracy was good to within 70 to 100 metres. (frequently better than my navigating with a compass) That was due to the US government back then having a random screw up (security) system on the satellites to prevent accurate readings. Paranoia on terrorrism was prevalent even 20 years ago & not without good reason as we susbesquently learned..

2 X Garmin II+ these were the first GPS's that I could easily upload & download on the PC. I used the first Fugawi software for that. These were accurate on speed etc. Their triangular shaped body made for more complicated fixing on the buggy downtube.

1 X Garmin Geko.
Neat mini GPS that gave good readings but the display actually died from being shaken around too much in the buggy.

3 X Garmin Etrexes. These have been excellent except for one that I think has developed a problem. I buggied just a few hundred metres & it read 475 kms (definitely suitable for dropping dead in the desert). The speed looked to be working accurately though.
One of them has had a tough time with the black rubber band around it peeling and a button fell off. I fixed that by trimming a small pencil eraser, poking it in the hole and then sticking the thing together with contact glue, additional bits of old inner tube rubber, electrical & Scotch tape. It's my favourite GPS & still use it today although my kiting buddies look at me in disgust when I fix this tatty looking GPS to my buggy.

They are all accurate on speed, as they all read the same in the car and the same as the Satnav that I keep permanently in the car. My car speedo reads 5 kph more when I'm driving at 100 kph. l checked several cars and noticed that all car speedos run faster than the true ground speed.

The only thing that I don't depend on are the altitude readings. I find these are way out. I have a separate altimeter that is good to about +/- 2 metres. This works on an atmospheric pressure, so it is important to always adjust it at a known height or known pressure to be confident of its accuracy.

WTF is this about GPS.
Basically anyone that has their GPS ranking on PTW is all false? hard to believe.

so what if the accuracy is out by a few, you look at the top 10 buggy speed pilots and speed pilots from other sections of kiting (snow/ice). we didn't get here by looking at our GPS to figure out how fast we went. the world record was done with 4 GPS, and two different models from Garmin.
we went out at the perfect time, in the highest of winds, and went for it. not many can say that.

so when you're passing cars on the highway at NABX its a whole new experience and feeling.

SCREW the technical talk ... just ride.

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SCREW the technical talk ... just ride.

Best advise yet - /End of thread

I'm am completely new to this sport and I'm not even thinking about speed records but here is my 2 cents....

There may be only 10 top buggy riders now but when there are a hundred and the top two are only seperated by a couple 10ths of a mph, you will want to know your exact speed. At least I would. Who cares if it's Guinness or any other record book that it might be in, if it's the top speed in the sport it should be exact, in my opinion.

If you're not going for a world speed record then who cares if it's off a little bit, it's just for your own records and those, for me anyway, don't have to be exact. It's just a general idea of how fast I'm going, that's all I need to know for now.

Just my .02, please don't be angered by my opinion.

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Originally posted by BeamerBob SOMEONE WAKE SCUDLEY UP! Lol. Ok, I looked up the specs on my Delorme PN-20 gps. For what it's worth, the specs state WAAS-enabled, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position GPS accuracy: » Position: < 15 meters, 95% typical* » Velocity: 0.05 meter/sec steady state (translates to about .11 mph) WAAS accuracy: » Position: < 3 meters, 95% typical* So what can we glean from this?

If you are taking readings every 1 second, a 95% confidence means on average 3 readings every minute have are off by more than 3m.
We are not making a steady state measurement.
I would have more confidence in these reads if people used the data logger functions and recorded their track. At least that way we could see that in the seconds before and after their record max speeds were reasonably consistant. No kind of official record keeping body would accept records consisting of photos of the digital readout.
They would probably want to see some kind proof the equipment was calibrated and working properly. It might be nice to have a half hour of stationary data readings logged at 1 s intervals to ensure that the velocity reads zero when it is not moving taken before and after the
the record. It would also be nice to see that your readings were taking place where you were buggying.
Rather than putting multiple gps on the buggy it would probably be wiser to put two on the buggy and have the others stationary at locations on the perimeter of the flying to ensure that all signals are good over the area.

A pictures of the gps max speed display are cute but leave little to confirm the data is valid.

In most other sailing speed records the use a trap for speed they are not concerned about the alignment of the trap except the tack should be relatively perpendicular to wind. I think their attitude is that if you can't steer your boat so you go through trap straight, you're not much of a sailor.
The other possibility is that for a long time in sailing, speed only counted if it was in the direction you wanted to go.

If you want to be known as the "World Record" holder, I think you have to at least provide the documentation that would satisfy the requirements of high school science lab.

S

Agreed.
A proper world record attempt as in speed sailing a need for a strict set of guidelines would be called for. Otherwise anyone could get in their car and record a record breaking speed on their handheld GPS, but for us buggiers it's just a bit of fun. Highly addictive fun! :D

In my experience, if the surface you're riding on is hard and smooth, the wind consistent and you're using a performance kite in a well sorted buggy AND you're going absolutely flat out, then you can expect no more than 2.2 x wind speed.

I've yet to achieve 2.2.

I'd say 2.1 x wind speed is a safe bet in ideal conditions + setup and 2.2 as a maximum when everything comes together at once.

I went out in 54mph gusting to 69mph winds and failed to even get close to 1.3 x wind speed. 69mph should have seen me doing 140mph. lol

A dedicated GPS is more than accurate enough for what we do IMO.

I know smooth wet ice will produce 30+ mph in winds under 10mph and yet I had to have 30mph winds to get my PB of 47 mph. I think the boys from Belgium got some pretty efficient runs on ice , 3x wind speed. There were some discussions about what speeds you can get out of what winds but there is no doubt ice and wide open spaces certainly make it all possible.

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Originally posted by Scudley Validity is up to the sporting body. S

You see this is a major problem with being "official" regarding speed records...

Guiness records are done over a certain distance in opposite directions within a given time...

Our sport is so unpredictable it can never be set up, how can you say right get to Ivanpah on 16th Feb 2012 we'll go for the record....and on the day there's a lovely 8mph breeze. Not only that, we do not travel the whole run in a straight line, but more of an "S" shape, so again....validating an "official" speed record is nigh on impossible....

So with that in mind, buggiers as a community are not too fussed about the official side of things, mostly we are all using the same equipment, and if a guy is jumping up and down with a huge grin because he has just broken his personl best at 28mph, then we are all pleased for him and accept his GPS reading. When we are getting up to our world fastes speeds, then extra GPS's are added, just to be sure...and when 3-4 GPS devices all read within a few 10ths, then, quite frankly that is more than plenty good enough.

I haven't read the paper nor intend to waste my time on it....I am just more than happy to go with the flow.

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Originally posted by popeyethewelder You see this is a major problem with being "official" regarding speed records... Guiness records are done over a certain distance in opposite directions within a given time... Our sport is so unpredictable it can never be set up, how can you say right get to Ivanpah on 16th Feb 2012 we'll go for the record....and on the day there's a lovely 8mph breeze. Not only that, we do not travel the whole run in a straight line, but more of an "S" shape, so again....validating an "official" speed record is nigh on impossible.... So with that in mind, buggiers as a community are not too fussed about the official side of things, mostly we are all using the same equipment, and if a guy is jumping up and down with a huge grin because he has just broken his personl best at 28mph, then we are all pleased for him and accept his GPS reading. When we are getting up to our world fastes speeds, then extra GPS's are added, just to be sure...and when 3-4 GPS devices all read within a few 10ths, then, quite frankly that is more than plenty good enough. I haven't read the paper nor intend to waste my time on it....I am just more than happy to go with the flow.

It is funny that all other sailing sports have the same problems and are able to deal with them.
I do not have a problem with reporting PB's with GPS, but I think the "world record" needs a little better documentation than a picture of gps units with a max speed displayed.

S

It is there has to be witnesses,

I tried to mount my bike computer on the buggy and without epoxying the pickup unit to the fork, I can't get it on there. I guess if the wind is high enough to make it a "special" day, I'll strap on a second gps.

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Originally posted by Scudley Quote: Originally posted by popeyethewelder I do not have a problem with reporting PB's with GPS, but I think the "world record" needs a little better documentation than a picture of gps units with a max speed displayed. S

If somebody was making or losing big $$ over portions of a mile per hour I could understand you having a "problem " with how it was established . Fact is it isn't the America's Cup, just a bunch of buggy nuts chasing after bragging rights and maybe some sponsorship. Mostly a bunch of Euro's who could care less if you have a problem with their numbers. Fact is they don't care if you have a problem with their methods and neither do the greatest majority of the rest of the buggy world.