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Author Topic: Dynamic Positioning  (Read 2905 times)

Brian60

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Dynamic Positioning
« on: June 04, 2016, 05:47:33 PM »

Jonathon I mentioned this in answer to you on my topic however......

Well I guess it's going to be a 9 DOF IMU with a seperate GPS chip. I cannot find an IMU that combines the accelerometer, magnetometer, gyroscope and the gps on one board.

I've searched interweb till I am blue, adafruit etc all have the 9 DOF IMU or even 10/11DOF, but the extra sensors are for barometric pressure etc. None of them seem to incorporate a gps. Have you come across one at all? Or do I really have to use seperate units?

g6swj

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Re: Dynamic Positioning
« Reply #1 on: June 04, 2016, 06:04:01 PM »

Brian,

I use separates:

  • IMU Adafruit 10-DOF IMU Breakout - L3GD20 + LSM303 + BMP180
  • Adafruit Ultimate GPS Breakout - 66 channel w/10 Hz updates - Version 3

You will probably want external antenna with GPS - although it does get a half decent signal on a windowsill so perhaps suck it and see and buy one only if required.

Your Arduino program will get pretty busy as there are lots a libraries required - I am currently pushing the UNO memory to it's limit but I am also firing the RFM69CW radio as well.

Merging all the code together GPS & IMU took a while with lots of errors along the way caused by yours truly!

Not sure exactly what your project scope is but you may not need GPS (it may be useless) if you just want to hold position - GPS states 3m accuracy - I have been focusing on telemetry bit and yet to get to the real world use of the IMU/GPS data. The only reason ( apart from some fun) of the telemetry bit was so I could see raw sensor data on shore to get my head around the position correction code

I have learnt so much playing with this stuff so even if it doesn't work as desired it was a worth while investment of time and effort.

Regards
Jonathan
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Brian60

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Re: Dynamic Positioning
« Reply #2 on: June 04, 2016, 06:12:20 PM »

Graham take a look at this explanation video....

https://www.youtube.com/watch?v=7DELJMW2ZW0


You will that although we are all wanting to control different things, ie Jonathon with telemetry, me with dynamic positioning, yourself with stability. They all more or less rely on one of these wonderful small add on circuit boards - the IMU. Its just that the data will be interpreted and used in different ways.

For instance mine is quite complicated, turning and applying varying thrust in the opposite direction to wind or current. However for yours the data would be used to apply an up motion on one side and a down motion on the opposite side of the hull. So whereas I need to read 9 (10 if you count the gps) pieces of info, your chip would only need to utilise 4, pitch, roll and yaw and forward motion (reverse is counted as forward motion ok2 ) so you could get away with a 6DOF IMU.

Its the work of connecting them via Arduino and having all that electronic data actually do 'something' which is the hard part :-))


Here's a disclaimer :} if I have mis explained any of this, Jonathon can jump in and correct it!

Brian60

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Re: Dynamic Positioning
« Reply #3 on: June 04, 2016, 06:17:40 PM »

Jonathon I've done a lot of reading and watching Youtube this week {:-{ the reason for the gps really is to correlate its data with the gyro data, it seems in robotics this is done to cancel out any error that may creep in. Until I get the hardware together I'm not even sure on what sketches I am going to have to start chopping adding and editing to get it all to work %% I frazzled my brain when I got to a page talking about Kalman Filtering with the gps and 9DOF IMU on a robotics site {-) All good learning experience.

g6swj

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Re: Dynamic Positioning
« Reply #4 on: June 04, 2016, 07:45:36 PM »

Brian - snap !
Quote
I frazzled my brain when I got to a page talking about Kalman Filtering with the gps and 9DOF IMU

Hence the reason for wanting to see the numbers on shore so the fog may clear and I can "SEE" what is happening.

Funny thing is other people have already done this but it's fun burning your own trail.

Jonathan
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Vts99

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Re: Dynamic Positioning
« Reply #5 on: June 04, 2016, 08:23:08 PM »

Thanks Brian yeah I was hoping to start with something simple to try on my little patrol boat and maybe a similar setup to u later as I'm building the fairmount alpine tug and can see the gps side of it coming in handy for the realism side of it 
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Re: Dynamic Positioning
« Reply #6 on: June 06, 2016, 08:36:57 PM »

Split and renamed!  :embarrassed:
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Brian60

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Re: Dynamic Positioning
« Reply #7 on: June 07, 2016, 11:51:39 AM »

Cheers Martin, Lets hope I can add some worthwhile info in coming weeks.

g6swj

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Re: Dynamic Positioning
« Reply #8 on: June 12, 2016, 05:19:24 PM »

Hi Brian - replied here as I think it makes more sense under this subject

Re your question
Quote

Jonathon I'd like to get a second opinion here.

The 9DOF IMU board from Adafruit (the one you are using) I thought about sourcing this in the UK, however most wanted 3 times the US price and the official importer want over 50 :o So I'll be ordering direct. But I came across on one english site that it is no longer available as out of production.

Going to the Adafruit site it is still available so I reckon they are telling porkies. Now this is where I'd like advice. On the Adafruit site there is also this 9DOF IMU,....  https://www.adafruit.com/products/2472

OK its twice the price but as it says most of the math is done onboard rather than having to collect algorithms and code it. It seems a much simpler way to go if half the work is already done.

What do you think? Is it worth the extra cash or go with the original?

There a several IMU units by Adafruit, Sparkfun and Pololu as well as others. I am using the Adafruit 10DOF - I got this for no other reason than it was a recent release item.

I think going back to basics you need the compass and accelerometers and gyroscopes sensor functionality. I am no expert on this an very much on the vertical learning curve. Have a look at the Pololu ( MinIMU-9 v3 Gyro, Accelerometer, and Compass (L3GD20H and LSM303D Carrier) ) it has some of the same sensors as the Adafruit 10DOF but costs 15

Maybe a PM to forum members tsenecal or dreadnought72 who are far more knowledgeable than me on this issue.

Hope that helps
Jonathan
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Brian60

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Re: Dynamic Positioning
« Reply #9 on: June 12, 2016, 06:14:52 PM »

 :-))

I still think I'll go for the one I documented. If they have done some of the coding work and embedded it to the chip it can only help.

g6swj

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Re: Dynamic Positioning
« Reply #10 on: June 12, 2016, 06:47:42 PM »

Brian,

How much have you found them being sold for? Looks like Amazon has them @30

Adafruit 9-DOF Absolute Orientation IMU Fusion Breakout - BNO055

Jonathan
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Brian60

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Re: Dynamic Positioning
« Reply #11 on: June 28, 2016, 07:05:15 PM »

Well after my sister in law turned up yesterday without my grp matting, the build of my new hull is on hold until August now {:-{

On a brighter note she did bring the electronic stuff I have been waiting for, among which is this little beauty.
 So all is not lost I can start to meddle with the dynamic positioning side of the electronics..

This is a 9DOF IMU, or in other words its an Inertial Measurement Unit with 9 degrees of freedom. To capture these nine distinct types of motion or orientation related data: 3 degrees each of acceleration, magnetic orientation, and angular velocity. the pcb has these individual chips on board...

    3-axis accelerometer
    3-axis magnetometer
    3-axis gyroscope

So each of these little wonders measures movement as forward/reverse, up/down, side/side. Very useful information if you can interpret the readings and send the relevant commands to motors etc.

So I will say its going to be a few weeks worth of headaches until I can get something worthwhile to put in print again, but check back from time to time.

The photo shows the whole pcb not much bigger than a postage stamp.

essex2visuvesi

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Re: Dynamic Positioning
« Reply #12 on: June 28, 2016, 11:02:36 PM »

My son is playing with one of these as well
He's working on a "learning" RC car that will learn the fastest route around a track
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Brian60

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Re: Dynamic Positioning
« Reply #13 on: June 29, 2016, 09:28:50 AM »

That will be interesting - maybe he could teach Lewis Hamilton a thing or two!

There is a Youtube (or maybe I read many pages of it someplace) video by a german I think, about doing the same with a boat on a lake.  However you also need the gps board, the way he tackled it was to plot the entire lake with waypoints every few feet and combined with the IMU he followed a course of 'sorts' Last time I looked at it, the results were not encouraging, the boat seemed to wander all over the place between plotted points.

If I can find the link again I'll send you it, if anything it can show what you lad will be up against.

david48

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Re: Dynamic Positioning
« Reply #14 on: June 29, 2016, 11:16:27 AM »

take a look here it might be of interest to you . gamesontrack.com     , sorry I can not get it to link,,
I have some sort of recollection at being at a model railway show and the set up had a road system built in to the lay out and there was three satellite over the layout trains and vehicles  were taking control from there .
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Brian60

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Re: Dynamic Positioning
« Reply #15 on: June 29, 2016, 06:03:19 PM »

Sorry can't find the actual link E2V but there is this one related to cars...

http://diydrones.com/profiles/blogs/apmrover-1280-a-fun-ugv-project-for-in-full-autonomous-reco

The big problem is your car will need to know where all corners are - it can't learn this like a boat holding posiiton can. Then each track through each corner can alter on each lap as it has to avoid other slower cars, so no two laps will be the same. Good luck mate.

Brian60

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Re: Dynamic Positioning
« Reply #16 on: June 29, 2016, 07:49:59 PM »

Found it.....

http://diydrones.com/profiles/blogs/ardupilot-goes-into-the-water-3

A lot of pages to work through, but take a look at some of the maps and how poorly the boat transcribes the course. It is worth reading the text because it will outline what you are up against.
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