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IMU For AUV


(Chetan Soni) #1

Hi all,

In AUV, IMU is crucial and selection of right IMU is very important there are many open source IMU’s available nowadays like RAZOR from Sparkfun with AHRS and many from ADAFRUIT…etc

But using them for inertial navigation is bit complex and erroneous as well.

I need some suggestions about selection as well as placement of IMU in blue robotics ROV/AUV frame…?

 

Chetan Soni

IIITDM, India


(Jacob) #2

If you want to get started quickly with an IMU, there are many libraries for the MPU6000 and MPU6050 (gyro+accel), and the MPU9150 and MPU9250 (gyro+accel+magnetometer). I don’t think you will be able to do inertial navigation with these sensors without a localization system. The IMUs on the pixhawk in my bluerov are slightly forward of the center, and it doesn’t seem to make a difference when pitching/yawing.

-Jacob


(Chetan Soni) #3

Thank you, Jacob, for your reply

Can I use RAZOR IMU for inertial navigation ?

With RAZOR, we can use AHRS algorithm…any suggestions///?

 

Which IMU you would recommend me for a Stand alone Inertial Navigation. so many people use Vector Nav IMU but it is costly business…

Chetan

IIITDM Chennai, India


(Jacob) #4

If you are referring to the board sold by adafruit, these sensors are in the same league as the ones I mentioned. You can implement an AHRS with these, but if you try to integrate the measurements provided by these sensors to obtain absolute position, the error will accumulate very quickly. An external source of position information will be needed in addition to the IMU.
-Jacob


(Chetan Soni) #5

Thank you, Jacob,

I am using GPS on surface and depth sensor for altitude underwater in addition with IMU will it help to get some positional info inside water?

 

Chetan

IIITDM, India


(Jacob) #6

When you dive and loose your gps lock, your horizontal position estimate will be unusable within a matter of seconds. At least this has been my experience experimenting with the ArduSub firmware on the pixhawk, which has dual IMUs and uses an EKF.

-Jacob


(Kevin) #7

Thanks for trying it Jacob. Any idea what the “circle of error” is with the current setup?


(Jacob) #8

I couldn’t even guess right now, and I didn’t take a look at the position error while it was running. It grows faster than the BlueROV can move.


(Kevin) #9

If that’s the case with the Pixhawk IMU’s, any thoughts on maybe how to integrate a better external IMU, such as a Sparton Nav EX IMU-10? Expensive, I know, but there aren’t many options out there.

In checking out another company for GPS for Divers, I found this: Project Ariadna. They’re using IMU’s for their navigation system as well, instead of acoustic beacons.



(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.


#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.