TwistedGray
Contributor
On a side note, you can order directly from the vendor
I am still quite excited to see how this project is going though! Sounds quite interesting...
Underwater Navigation Device
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On a side note, you can order directly from the vendor
I am still quite excited to see how this project is going though! Sounds quite interesting...
Kacem,
Just noticed this thread. I had spent a couple of days looking at the feasibility of building one of these from a 6-axis mems a year or so ago, I've mentioned it here on scubaboard in response to some threads on "what should we invent for scuba".
My conclusion was that the drift error using available devices I was looking at made it impractical. I think I came up with something like 1/4 mile max error for a 1-hour dive.
It sounds like you're
1) Identifying newer, intrinsically more accurate mems devices.
2) Doing a cleverer job of filtering the noise in s/w.
3) The idea of remotely mounting the sensor itself on the tank where it's less likely to be rotating/moving relative to diver position. I was imagining a hand-held or wrist-mounted unit and resolving the rotational attitude of the device by integrating rotational accelerations, in order to know how to interpret the translational accelerations in real space, causes a lot of the drift error.
I'm mentioning this because I had one idea for minimizing drift error that you haven't mentioned here, that I thought I'd pass on: A button the diver can press that says "Right now I'm not moving and not rotating. Any linear or angular velocities derived from integrating accelerations can now be set to zero.".
Of course, if the diver lies about that the errors are worse, but the potential for reducing error if used correctly seems worthwhile. If used once at the turnaround point, the total drift error at the end of the dive might be halved.
I'd be really interested in one of these in the < $500 range, please keep working on it, and also keep us salivating with occasional progress reports.
Just noticed this thread. I had spent a couple of days looking at the feasibility of building one of these from a 6-axis mems a year or so ago, I've mentioned it here on scubaboard in response to some threads on "what should we invent for scuba".
My conclusion was that the drift error using available devices I was looking at made it impractical. I think I came up with something like 1/4 mile max error for a 1-hour dive.
It sounds like you're
1) Identifying newer, intrinsically more accurate mems devices.
2) Doing a cleverer job of filtering the noise in s/w.
3) The idea of remotely mounting the sensor itself on the tank where it's less likely to be rotating/moving relative to diver position. I was imagining a hand-held or wrist-mounted unit and resolving the rotational attitude of the device by integrating rotational accelerations, in order to know how to interpret the translational accelerations in real space, causes a lot of the drift error.
I'm mentioning this because I had one idea for minimizing drift error that you haven't mentioned here, that I thought I'd pass on: A button the diver can press that says "Right now I'm not moving and not rotating. Any linear or angular velocities derived from integrating accelerations can now be set to zero.".
Of course, if the diver lies about that the errors are worse, but the potential for reducing error if used correctly seems worthwhile. If used once at the turnaround point, the total drift error at the end of the dive might be halved.
I'd be really interested in one of these in the < $500 range, please keep working on it, and also keep us salivating with occasional progress reports.
rstofer
Contributor
This is pretty neat technology. I did a few minutes worth of Google and there has been quite a bit of work done on positioning.
I wonder how USBL will work out with multiple divers? It's pretty clear that the diver can't emit the ping.
But I wonder if a system with multiple buoys couldn't work a lot like the current GPS system. We know depth so all we would have to do is receive pulses from 3 synchronized transmitters at known locations and we should be able to tell from the time delay between the pulses how far we were from each. We would have 3 circles of position and the common intersection is our location.
We'd need a little keypad to enter the coordinates of each buoy (which we could drop off our boat) and the rest is just arithmetic. I suppose we would want all the other capabilities like track, waypoints and all that. Probably an automatic return to the boat - like the Man Overboard (MOB) function of marine GPS systems.
LORAN did (does?) a similar thing with time delays and very high power transmitters.
Richard
TwistedGray
Contributor
Richard, there are such devices already out there; however, they may be costly (relatively). I know of a few different types of positioning: [-]USBL[/-], SBL, LBL, and Tracking Ranges. We build the other three...
There is essentially two different types of devices that can go on the diver. The diver can have a pinger or a transponder. The pinger simply pings whereas the transponder is interogated by a single ping then replies with its own (three) pings. You can see which is "better".
It is possible to track multiple divers in SBL or any of the other three (I would guess USBL, too). The only downside with that is that you can only track one diver at a time. Each position is going to take 1-3 seconds (potentially longer) so if you are tracking two divers you would get a position update rate of only 6 seconds. That's not too bad though; however, when you get up to five divers, you're update rate gets quite long: 30 seconds.
Even the most basic SBL still is going to run about $5k.
Picture Below: The yellow squares represent the transducers. The colored circles represent the 'targets'. As you can see, we are tracking six right now. This isn't really a track; we were just testing out another function to the software (in case you were wondering why they are all just sitting there).
lmorin
Contributor
rstofer
Contributor
Very cool!
As you might imagine, I'm an old EE. Retired and diving away my Social Security but still interested in 'magic'.
Richard
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reefduffer
good hearing from you. Many ways to reduce the drift, mainly on the Gyro, by software mainly.
basically the idea is to bring it back to zero after some sampling; you can also do it automatically without pressing any button.
make sure also the MEMS are not correlated, that why i suggested some of them in this thread.
this will help the Magneto to be corrected by the ACC (tilt) , and the ACC to be corrected by the Gyro and vice versa.
but the most important is the velocity of the diver, the application it self doesn't deal with high speed, so you can easily with a smart software guess if the data you are getting are accurate or not.
i mean, a diver cannot rotate 90° in 1 millisecond
all those hints helps to reduce the drift, so far i'm in the range of 1-meter drift after 50mn DIve
kacem
good hearing from you. Many ways to reduce the drift, mainly on the Gyro, by software mainly.
basically the idea is to bring it back to zero after some sampling; you can also do it automatically without pressing any button.
make sure also the MEMS are not correlated, that why i suggested some of them in this thread.
this will help the Magneto to be corrected by the ACC (tilt) , and the ACC to be corrected by the Gyro and vice versa.
but the most important is the velocity of the diver, the application it self doesn't deal with high speed, so you can easily with a smart software guess if the data you are getting are accurate or not.
i mean, a diver cannot rotate 90° in 1 millisecond
all those hints helps to reduce the drift, so far i'm in the range of 1-meter drift after 50mn DIve
kacem
Hi everybody,
I new at this forum, I came across it when researching for a very similar device as kacem78 are building.
Kacem78, have you considered the ADIS16354. This sensor is calibrated for a much wider temperature range than the ADIS16350.
It sounds like you're done quite a bit of work on the device. Have you come as far as to implementing the mathematics needed to do the sensor fusion (between the magnetometer and accl/gyro)?
I've just ordered the parts, so I'm lagging behind a bit there but I was hoping to get a handle on the math while I'm waiting for the parts. If you have any models or data you wouldn't mind sharing, I'd be gratefull :-D
This is only a hobby project for me, but it would be great if we could share experiences.
regards,
Oivind
I new at this forum, I came across it when researching for a very similar device as kacem78 are building.
Kacem78, have you considered the ADIS16354. This sensor is calibrated for a much wider temperature range than the ADIS16350.
It sounds like you're done quite a bit of work on the device. Have you come as far as to implementing the mathematics needed to do the sensor fusion (between the magnetometer and accl/gyro)?
I've just ordered the parts, so I'm lagging behind a bit there but I was hoping to get a handle on the math while I'm waiting for the parts. If you have any models or data you wouldn't mind sharing, I'd be gratefull :-D
This is only a hobby project for me, but it would be great if we could share experiences.
regards,
Oivind
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