Position hold mode with waterlinked dvl not working correctly

I’m having another issue with the waterlinked DVL this time on a different system. This system is running into some issues with the DVL which wasn’t previously happening with a different system. I should mention in comparison to the last system, this system is going DVL → separate fathom x → Topside fathom → PC. Now i have managed to get it all working in the sense that i am able to connect to it and get into position hold mode, however it seems to only work for a bit before it starts to spit out errors like “imu stopped aiding” (despite it being safely off the bottom, but overall despite it saying these errors it can still work fine). However, usually about 5-10 seconds of arming while in position hold, the DVL reading starts to shoot out in multiple different direction (the little triangle), causing position hold to thrust wildly in whatever direction is opposite.

this is an example where after activating position hold mode it thinks its going off to the north west despite it actually being held in place.

Any ideas on what might be causing this?

Hi @Qlowe,

Given you’re showing the DVL’s own position estimate here, it’s likely the DVL is giving faulty readings to ArduSub, which is then failing to maintain the position because the information it’s receiving doesn’t make sense.

The main reasons I can think of for a DVL giving faulty readings are:

  • usage in an unsuitable environment, where it can’t get a good lock
    • if you’ve used the same DVL (or another of the same type) in that location before then that’s unlikely to be the issue
  • insufficient/noisy power supply
  • faulty/damaged DVL
    • you’ll likely need to contact Water Linked support if this is the case

As an extra possibility, if you’re also seeing errors about no depth sensor connected then this thread should help, but I wouldn’t expect that to be relevant given you’re seeing the issues in the DVL’s own estimates, which shouldn’t be related to ArduSub’s depth sensing.

Just to clarify, do you have two Fathom-X boards in the vehicle, going over the same tether pair, to a single Fathom-X at the surface? That should work, but if instead you have two sets of Fathom-X boards using independent tether pairs there will likely be issues with cross-talk between the pairs that messes up the communication of one or both lines.

We would generally recommend using an Ethernet Switch in the vehicle, rather than an additional Fathom-X board.