Hey all.
Currently designing an autonomous submersible for a university engineering project. Was considering using the Ardupilot Mega with a magnetometer and gps installed for navigation via dead reckoning with intermittent surfacing for position checks using the gps. Has this autopilot system ever been used in an underwater vehicle? Are there any possible reasons why this system wouldn't be suitable? The control systems will be set up in a similar manner to a manned submarine, with foreplanes for depth control and a crossplane for pitch and roll, but these should be somewhat analogous to the control surfaces of a UAV. It will also need to control the main ballast tank.
thanks
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We have already deisigned the three loop contrllor and undergone a PIL simulation. Now we begin to design the navigation code for the IMU. I am learning about the strawp down inertial navigation and kalman fiter, which might be used in the navigtion code design.
In my view, there is no difference between the UAV control and AUV control for they both need a three stabilization loop (pithc,roll,yaw). In fact our AUV control board is prviously used in the unmanned helicopter and works well, all you need is change the height sensor in the air to depth sensor is the water to control the depth of the AUV.
Hoping that will hlep you, my mailbox: fdybit@126.com
Hello Gerry, good to hear there are other people attemping something similar with Ardupilot! Though I myself am using the ardupilot mega setup and imu shield. I am currently in the process of figuring out how everything works in the code, as well as getting my hardware sorted. Unfortunately, the current priority is designing components and systems so they can be manufactured or purchased (2m-long steel hull, crossplane servo linkages, ballast etc), then once all that is sorted I can get to coding.
I will keep researching this though, and keep you updated if I make any breakthroughs. I'll look more into the HIL setup and see if there's anything useful.
Today I learned the difference between an IMU, an AHRS, and an INS.
The OpenPilot project project seems promising. http://wiki.openpilot.org/display/Doc/OpenPilot+INS
Personally, I think that the ArduIMU + compass is accurate enough to get the job done. Use of a differential pressure sensor in the nose can infer forward velocity, and a second pressure sensor can be used to read depth.
Thinking about the problem, I'm wondering if the refresh rate on the GPS can be slowed to a crawl with more IMU samples in between. If you were to set your destination at the surface while you had GPS, and then locked in your attitude, you may be able to get to your destination before the GPS refreshes and then surface for a saw tooth profile.
To start from scratch, http://diydrones.ning.com/forum/topics/how-to-extract-angular
Still trying to understand the difference between a Kalman filter and a DCM
http://diydrones.ning.com/profiles/blogs/dcm-imu-theory-first-draft
Euler angles have gimbal lock but for a submersible that doesn't seem to be a huge problem. ArduIMU can be configured to ouput data in several formats. "output.ide"
The whole project seems pretty doable if you lower your accuracy standards far enough. If you plan on operating in shallow water a Doppler Velocity Logger is a popular way to go. Laser scanners are popular, but I don't know if the Kinect laser is close enough to visible light to cut through water very well.
As no-one has responded I shall.
APM has never been used in an underwater vehicle although it has been used on water very successfully (see Harald Molle's epic blog of his adventures). The limitation is on guidance as the APM is inherently GPS based but I'm sure some dead reckoning will help out that (although I'm unsure how you will measure speed). As for control surfaces I'd assume the standard code would be pretty good although your PID values will have to be changed. As for ballast I would even know where to start but you have 4 spare PWM channels to deal with that so you should be ok.