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IMU For AUV

(Jim N.) #10

Hi Kevin,

Thanks for the links. The sparton is quality. If you really want to do things right, spend the money on a good INS. As for project ariadna…i question anyone making big claims and offering no technical specifics. Also, the website seems to be owned and run through UAE, which not a red flag on it’s own, but a finland based company with a site owned by the UAE…seems fishy, lol. anyway. awesome if it’s legit…but, awfully over produced videos.

now as far as dead reckoning with the pixhawk…i wouldn’t. you are double integrating inducing horrible drift…the ekf isn’t going to do much for you without another sensor giving you position estimates. dvl, vision, something, lol. second everything Jacob wrote.

(Kevin) #11

In continuing my research, I found this https://inertialsense.com/download/uins-2-datasheet/ maybe the EVB-1 with the INS-2 when it becomes available?

Finding a GPS aided INS is pretty difficult and I haven’t seen any for the RPi let alone the Pixhawk.

(Pierson) #12

In the AUV world we generally say that IMU are exclusively for orientation of the vehicle underwater. Localization is done by combining the IMU’s orientation information with a DVL or USBL.

For reference our vehicle runs 3 IMUs including a Sparton AHRS-8, and other similar quality IMUs and our positional drift from IMU double integration is generally places us on one of nearest celestial bodies.

For localizing an AUV I would recommend either the Nortek DVL or a Teledyne DVL These units are not cheap, so I would closely examine if your application truly needs localization. Many if not most AUV applications, especially on the hobbyist level, do not need localization.

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#13

Yes. DVL and USBL can be integrated with IMU and depth sensor to obtain more precise estimation of vehicle. We have implemented this in deep ocean work-class ROV in pool and sea. DVL can measure status accurately, especially in pool. In the sea, Phins that is very expensive is used. Has DVL been integrated into ArduSub now? Thx.

(Kevin) #14

@Hughhugh We haven’t been able to find any affordable DVLs, so no work has been done in ArduSub.

#15

@kevinkThe DVL used is ADCP from WorkHorse Monitor Teledyne RD Instruments(TRDI)Acoustic Doppler Current Profiler(ADCP). Maybe u can have a try. Thank u.

(Jacob) #16

Hi @Hughhugh, do you have the price tag or datasheet/documentation info on the Phins or DVL? We could integrate DVL as we have integrated USBL, but no one has stepped forward with a candidate unit yet.

#17

@jwalser Hi.Phins from IXSEA costs too much. As I know, it is about 100W RMB including tax(the tax is very high). The DVL is much cheepercompared with PHINS, and the performance using DVL is very good too because the positioning is very accurate. Only the IMU estimation for attitude will decrease during the control test when yaw rate is too big. In the deep ocean experiment, PHINS will be used to keep vehicle safe. I can send the DVL manual to u. Plz leave your email. Thx.

#18

Hi @jwalser, I have watch bluerov with USBL mission video in the pool. The positioning performance will decreases when rotating in the water. I think it is brought by wave and current near surface. Also the estimations of position are not obtained timely. So the DP controller does not work.

(Jacob) #19

Which video are you talking about? The positioning controller can be made to work in a wide range of systems/circumstances by informing the controller of things like delay and noise in individual measurements, adjusting trust in IMU measurements vs external position measurements, etc. The results will of course improve if the timing and accuracy of the external measurements is improved.

You can shoot the manual to jacob@bluerobotics.com, or upload it here so everyone else can see :).

Also, what is 100W RMB in USD?

#20

Hi @jwalser, it is the link https://m.youtube.com/watch?v=L4_yZWwPSqA

Compensator for controller may work , and I am working on it. Besides ADCP from WorkHorse Monitor Teledyne RD Instruments, NavQuest 600 Micro DVL http://www.link-quest.com/html/models_nq.htm has been employed in AUV. The manual is pdf , can not be authorized to upload. The price of PHINS is about 180,000 in USD.

(Jacob) #21

I updated the forum settings. PDF is allowed now.

#22

@jwalser The MANUAL for ADCP can be accessed here. WorkHorse Technical Manual_Nov07-dvl.pdf (5.4 MB)
And there is explanation for ADCP in Japanese. <a class=“attachment”
manual_B.pdf (2.0 MB)

(Jacob) #23

You are now a basic user; you may upload now.

(Kevin) #24

Sparton updated their portfolio with the INS-20. The company says its for GPS degraded or denied environments, so maybe short hops for us underwater until a DVL is available. No idea on pricing and the output data isn’t very specific.
INS-20-800x800-300x300

(James Jackson) #25

Hey, just wanted to pitch in here (not really a part of the community, but found this page via google search - seems pretty awesome!) I’ve just integrated the INS output of the inertialsense EVB as a GPS sensor to the Pixhawk https://github.com/inertialsense/Firmware/tree/inertialsense. I haven’t done the IMU or replaced the internal estimator yet, though the inertialsense’s ins output is superior to the pixhawk.

It’s a really cool sensor (statically and thermally calibrated dual IMUs), and the dual magnetometers are robust to magnetic interference, so it might do okay while under water for short periods. I set it up so we could do RTK via QGroundControl, but I’m wondering if the integration would help you guys out at all.

3 Likes
External IMU with pixhawk
(Jacob) #26

Thanks dawg.

(Kevin) #27

@superjax08 Good stuff with your integration work! I saw on your docs that you have the uINS up and running with the PX4 Firmware. Do you have a time-frame or a roadmap of when it would be integrated into the main ArduPilot repository? I’d be interested in buying a unit and trying it once supported.

(James Jackson) #28

Probably not for at least another month or two here, but when I do I’ll definitely let you know!

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(Milos Seskar) #29

@jwalser you mentioned using an EKF through pixhawk, i’ve been trying to figure this out for some time but I am not quite sure how it works. Is there any chance you have some sample script I could test on the BlueROV2 or strong documentation I could try to follow? All the sources online are very vague in regards to implementation, and I’m essentially a half-step above clueless at control theory. Thanks