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910 and skydiving
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http://connect.garmin.com/modern/activity/547532283


So the 910 actually worked quite well for sky diving in terms of altitude and speed. It was a little off on altitude while in the plane, due to a difference in pressure, but was pretty darn close!
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Re: 910 and skydiving [spire] [ In reply to ]
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The 910 should do a good job of tracking your speed and altitude right up until the VFR FLIB not listening to ATC plows right through the jump zone and takes you out.

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Brian

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Re: 910 and skydiving [spire] [ In reply to ]
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That's really cool.
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Re: 910 and skydiving [gienopes] [ In reply to ]
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Did you wear an aero helmet?

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Re: 910 and skydiving [spire] [ In reply to ]
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Like the HR spike

jaretj
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Re: 910 and skydiving [jaretj] [ In reply to ]
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jaretj wrote:
Like the HR spike

jaretj

+1 that's awesome!
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Re: 910 and skydiving [J_R] [ In reply to ]
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The speed track is interesting. Initially your speed slows as you jump out of the plane, then increases again as you accelerate, then drops, of course, when you deploy the chute.

Like the HR spike before you jump out. Is that when you got up out of your seat and it hit you that this shit just got "real".


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Re: 910 and skydiving [spire] [ In reply to ]
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That's pretty cool. I've actually been curious about how the Garmin computes speed when there is a large vertical component of the velocity. It looks like it ignores it entirely (i.e zero speed as elevation plummets from 11000+ft to 3600ft between 18:42 and 19:28.

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Re: 910 and skydiving [motoguy128] [ In reply to ]
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Looking at the "player" it spikes right when elevation drops so probably as soon we jumped out of the plane. Was pretty intense in a small plane, had to put your legs outside of the plane before actually "jumping".
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Re: 910 and skydiving [tribritre] [ In reply to ]
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Actually, that very thing happened when we went to watch our friends jump. Any idea where that was?
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Re: 910 and skydiving [ZackCapets] [ In reply to ]
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Yeah, gps-based speed is solely off of 2 dimensional position (latitude and longitude) divided by time between the data points. I wonder how far off a GPS device's calculated speed would be if you're biking up or down a (very) steep incline. I guess it would be a pretty easy test if you set up 2 head units: one that measures speed from GPS and another that uses a wheel-based magnet to measure speed and then compare the results. Unfortunately for me, living in Chicago pretty much prevents me from doing any sort of test like that. I wonder if Ray from DC Rainmaker has done or could do a similar test (hint, hint).

EDIT:

Okay, I got bored and did the math. The steepest road in the world is apparently Baldwin Street in Dunedin, New Zealand. The average slope is 19 degrees or 35%, which corresponds to 1 meter up for every 2.86 meters across. This puts the ratio of the horizontal (GPS) distance to slope (real) distance at 2.86:3.03, which gives an average difference of 5.6%. I.e., if you were going 30 mph as measured by a wheel based sensor (your "real" speed), your GPS device would display 28.32 mph, which is a calculated displacement.

Sorry to sidetrack this thread. Really cool skydiving data, by the way. Too bad you broke some serious FAA regulations by having a GPS device turned on in a plane :) Hope no one reports you!
Last edited by: Anando: Jul 23, 14 9:57
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Re: 910 and skydiving [spire] [ In reply to ]
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And you burned 200 calories doing it! Thanks for posting, thats pretty cool.

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Re: 910 and skydiving [Anando] [ In reply to ]
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if a GPS had a reliable altimiter, a smart algorithm should be able to account for the effect of road slope when determining over the ground speed and distance.
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Re: 910 and skydiving [spire] [ In reply to ]
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I don't know why, but this is my favorite part:

"Activity Type: Other | Event Type: Uncategorized"

Cracked me up for some reason.
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Re: 910 and skydiving [npage148] [ In reply to ]
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But as he just calculated, the difference is negligible on all but the steepest roads in the world, and even then it is barely large enough to be measurable.

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Re: 910 and skydiving [ZackCapets] [ In reply to ]
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ah, the stealth edit. I didn't really want to get all soh-cah-toa on it so I was hoping someone would do some quick math to see how large the error it would be
Last edited by: npage148: Jul 23, 14 10:54
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Re: 910 and skydiving [Iron Buckeye] [ In reply to ]
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My favorite part is the minimum altitude of -87m. Doesn't sound like a good end result on a skydive.
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Re: 910 and skydiving [npage148] [ In reply to ]
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as a function of grade, the error is cos(arctan(grade/100))*100

here's what is looks like graphically with a few notable climbs plotted (Westernport Wall is the hill in Savage Man)


Here's my math if anyone wants to check it because I haven't had to do trigonometry in a very, very long time

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