Originally Posted by michaelk
Yes, look into using Inertial Measurement Units (IMUs) using a fibre optic gyro. They are small and used in drones etc. I think you will find that using acceleration as a sole means for determining position very crude. Also IMUs have a drift factor, if you do not use some external input for speed and depth make sure to take it into account.
This is the other sensor I found intresting: http://www.allthingsmicro.com/produc...accelmag-board
is has all 3 in one neat pcb ... the only snag is that they are not oriented in the same axis which will require software coordinate rearranging. But am an absolure nubi in this field so any suggestions are welcome.
Yeah ... I was guessing that the deceleration caused by drag (and fluid current) would be unmeasurable so I'd haveto account for that somehow, maybe have a small propeller up front attached to an undriven DC motor and measure the tension produced. If I remember correctly the voltage produced is close to linear with angular velocity of the prop, and that should be linear with the speed too.
Water is really dense compared to air so I cal assume any lateral drift is dew to fluid movement, or at worse, the sub changing immersion depth ... so I guess doing full auto might need a means of measuring depth too. How about an accelerometer placed on a tilting surface that is moved by pressure differential between outside and inside ?
Really coarse if fine for a first attempt at a drone ... if I like it I'll look into better accuracy but GPS will not work under water so I'll haveto figure out something else.
Update on the sensors: A friend of mine has a 10DOF left over from is multi-rotor drone chopper ... he's gonna give it to me for some reasonable price so I think I'll go for that.