GPS Data tracker, w/accelerometers

[nickfrey 0]

http://www.ripxx.com/home.php


Anybody got any experiance with one of these... 10 data points per second. Sounds promising for flight tracking. And the G force info could be pretty interesting.

[Hellis 0]

G-forces is only a messure of speeddifference.
So if you know your speed you can calculate the G-force.

If you connect your audioble to your computer you can get speeddata.

[bofh 0]

I don't know anything about this device more than a quick reading of their site, but...

Quote

G-forces is only a messure of speeddifference.

the device has both accelerometers and gyroscopes in it, so it may provide better acceleration information than a plain GPS receiver.

With 10Hz logging it is better than most GPS receivers too.

Quote

If you connect your audioble to your computer you can get speeddata.

Not in 3D.

[SethInMI 174]

Accelerometers would give better performance, rather than double differentiating position.

The nice thing about a sensor like this is the full inertial reference frame (3 accelerometers and 3 gyros). I doubt the quality of either sensor type is good enough for an true inertial solution for any length of time (double integrating accelerometer data requires high quality stuff), but the GPS provides position.

The accelerometers and gyros will provide an instantaneous attitude solution, which would be nice to have. This would show you things like:

1. How head low or head high you were at at any point on the jump (was it a steep dive or shallow dive).
2. How fast that flat spin was rotating.
3. What happened on that funky opening. You could see speed, pitch, and rotation of the body during the opening sequence.

I don't know how this would work for skydiving. Probably depends on how well the software can take out the gyro bias, and the quality of the gyros and accelerometers.

[ramble]
Usually the bias is taken out standing still, and for some extreme sports like a short downhill run (skiing, snowboarding, mnt biking etc) this would be easy, stop at the top of the run, zero gyros and get an initial orientation set, then do your run for a few minutes. Skydiving has the whole plane ride thing that would make keeping a known orientation valid more difficult, but if you set a button on jump run that would set a known orientation, it would help. Either way, rotations like flat spins and barrel rolls would be easy to determine, but orientation (pitch, etc) would be harder. Also when traveling at a constant velocity the accelerometers will give some orientation info (basically which direction the ground is), which would be very useful. Blah, blah, blah, Kalman filter, blah, blah, blah.
[/ramble]

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[base851 0]

Great, I just plunked down money on a QStarz Q100eX and this comes along. FML...

[Hellis 0]

The Ripxx has been around for a few months.

What i noticed from the jumps that i have made with GPS is that the altitude data is very unreliable in freefall.
On one of my jumps the data shows me as ~3000 feet lower than i was, and when i was under canopy it noticed the misstake and bumped me up to the correct altitude.
Usually i have very good reception inside the plane, so im really clueless on why it happens.

The jump i made this wednsday was horrible, just as i exit the plane 1.5 minute is missing

I think a GPS with barometer is the way to go.

[shropshire 0]

Quote

I think a GPS with barometer is the way to go.

Yeap. My old Garmin Vista does and seems a lot more accurate.

GPS is not so good in the Z-axis

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[Hellis 0]

The odd thing is that if you look at the first file (ends with 1409.xls) the numbers are "perfect".
All numbers look good.

The second file (1446.xls), it shows i hit the ground at 140 km/h.
The numbers "flow" but looking at the vertical speed it seems to be way to high for a trackjump.
I can understand that the GPS might missread the altitude once or twice, but to get the wrong altitude every time for almost one minute. Thats just odd.

All numbers are in meters and km/h

[crwper 7]

Quote

I can understand that the GPS might missread the altitude once or twice, but to get the wrong altitude every time for almost one minute. Thats just odd.

Could be related to the model the GPS is using. Most GPS units use a Kalman filter with an associated model which basically describes the kind of motion you're expecting. This allows the GPS to be much more accurate than it otherwise could be, provided your motion is described well by the model.

With my old Garmin GPS-10, I noticed that the results it returned in freefall sometimes looked uncannily like a series of parabolas, which led me to believe that the GPS had lost satellites, and was now extrapolating data.

In your case, I wonder if the values for the second jump are dominated by extrapolation, rather than actual data.

Michael

Edit: What GPS are you using?

[kallend 2,027]

Quote

Quote

I think a GPS with barometer is the way to go.

Yeap. My old Garmin Vista does and seems a lot more accurate.

GPS is not so good in the Z-axis

Which is why planes need DGPS or LAAS to autoland using GPS to drive the autopilot.

...

The only sure way to survive a canopy collision is not to have one.

[Hellis 0]

So does that mean its good to have the Kalman filter or not?
I dont think they made a filter for track/wingsut jumps, or?

Im using a Royaltek, because it was free
I got it with my phone a few years ago and never used it untill now.

I have been looking around for other GPS devices.
This one looks good on specs but im unsure about the size and the fact that it has a screen (bad landing or bumping it the plane).
http://www.wintec.com.tw/en/product_detail.php?pro_id=78

[crwper 7]

Quote

So does that mean its good to have the Kalman filter or not?

I would think they all have a Kalman filter, since it would be hard to get usable GPS data at a decent rate without making some assumptions about the kind of movement you expect. I'd say there are two major factors that contribute to good/poor GPS data quality:

• An appropriate filter model. If the model assumes your motion will look like driving a car, and then suddenly you're in freefall, it may not give very accurate results.
• Good signal-to-noise. This is partly a function of hardware design, and partly a function of GPS placement. Where are you mounting the GPS?

The best way to figure out if the model is good, I think, is to see what kind of results others have had with the same GPS and similar mounting.

Michael

[Hellis 0]

Then maybe i should mail the manufactor and ask what kind of filter it has.

My GPS is mounted on the outside of my helmet. Its placed on the backside of my head and has a clear view of the sky.
When i sit inside the plane it has almost full reception even though im sitting below the wings and the plane only have smal windows.

[LouDiamond 1]

Quote

http://www.ripxx.com/home.php


Anybody got any experiance with one of these... 10 data points per second. Sounds promising for flight tracking. And the G force info could be pretty interesting.

That reminds me a lot of the FRWD that came out circa 2004ish. They had the 200 and the 400 models and then they went to a B model and a W model at some point. If you are interested in the history, there are several threads in the forum on it. As far as I know, FRWD isn't sold anymore. The Ripxx looks very similar to the 200/400 FRWD in many ways, to include being over priced ($330.00). It would be easy to do the same things that the Ripxx does for about half the price with a simple Wintec-201 logger and a copy of Paralog if you're looking to save some money. Plus the Paralog software is written for skydiving and not skiing.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[kallend 2,027]

Quote

Quote

I can understand that the GPS might missread the altitude once or twice, but to get the wrong altitude every time for almost one minute. Thats just odd.

Could be related to the model the GPS is using. Most GPS units use a Kalman filter with an associated model which basically describes the kind of motion you're expecting. This allows the GPS to be much more accurate than it otherwise could be, provided your motion is described well by the model.

With my old Garmin GPS-10, I noticed that the results it returned in freefall sometimes looked uncannily like a series of parabolas, which led me to believe that the GPS had lost satellites, and was now extrapolating data.

Not that anyone would spend $2000 for a skydiving GPS, but my Garmin AERA560 aviation GPS clearly has a new technology receiver or antenna or both; it will lock on the the satellites when it is sitting on my kitchen table indoors. None of my previous GPSs would do this.

...

The only sure way to survive a canopy collision is not to have one.

[crwper 7]

Quote

Then maybe i should mail the manufactor and ask what kind of filter it has.

Alas, I think that would only tell you why it has issues. Really, what you're looking for is a solution, and I think the best solution is probably to find out what works for others, and go with that. Sounds like you've got it mounted well, so I guess there is something with the unit itself that's causing problems.

Michael

[crwper 7]

Quote

It would be easy to do the same things that the Ripxx does for about half the price with a simple Wintec-201 logger and a copy of Paralog if you're looking to save some money.

To be fair, the Ripxx offers information that cannot be inferred from a GPS log, namely, accurate rate of turn and acceleration information. However, I'm not sure this information is useful for wingsuit pilots, except in real-time applications.

Michael

[LouDiamond 1]

HERE is some good news that will eventually be a benefit to all of us.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING