# Back up recovery device **URL:** \ **Category:** DIY AUVs\ **Tags:** vehicle-design\ **Created:** [June 17, 2026, 11:49am UTC](https://discuss.bluerobotics.com/t/back-up-recovery-device/23183 "2026-06-17T11:49:16Z")\ **Posts on this page:** 1\ **Showing post:** 10
**Author:** ![EliotBR](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.bluerobotics.com/eliotbr/32/6937_2.png) [@EliotBR](https://discuss.bluerobotics.com/u/EliotBR)\ **Post date:** [June 18, 2026, 3:53pm UTC](https://discuss.bluerobotics.com/t/back-up-recovery-device/23183/10 "2026-06-18T15:53:06Z")
> [@brad\_smith](#): > > If I clamp the ribbon with stainless screws, the galvanic corrosion should eventually dissolve the magnesium and release the weight. Some testing would be needed to dial in the timing and reliability. Fair enough. I imagine that’s quite reliant on the salinity of the water you’re operating in. Another option to consider is > [@Building the world's first consumer deep-sea dropcam](https://discuss.bluerobotics.com/t/building-the-worlds-first-consumer-deep-sea-dropcam/3618/8): > > … a dissolving PVA release … e.g. using 3D-printed PVA filament as structural elements to hold the weight. The biggest challenge with chemical processes is likely the variability of release time, particularly since it may be difficult to control exposure to water flow/agitation. That said, assuming the emergency recovery time can be “set” to a fair amount longer than the intended dive time, that’s perhaps not a huge concern if the range of timings is well-established beforehand. > [@brad\_smith](#): > > Would it be possible to determine the direction of an underwater beacon without specialized equipment, or would that require something like a hydrophone array? There’s generally a tradeoff between sensors, time, and spatial resolution/knowledge: 1. If you have multiple sensors you can quickly determine directionality by the time delta between the sound wave reaching each one 2. If you have just one sensor then moving the vehicle can give a sense of whether you’re going towards or away from the beacon, either by the intensity of the received pulses (provided the signal is not saturating), and/or by their frequency (e.g. moving towards a source incurs a doppler shift, and pulses are received at both higher carrier frequency, and closer together in time) 3. An omni-directional receiver can receive all pulses but without knowing immediately where it came from, whereas 4. A highly directional receiver knows more about where a received signal came from, but may miss signals that are received while the receiver is not facing the source - This does not have to be binary, i.e. a receiver could be _more_ sensitive in a particular direction, but still receive signals from other directions Depending on whether you expect a vehicle failure to result in a stationary vehicle or one that’s drifting with a strong current, the speed with which you can update directional knowledge may be low priority or critical. Then of course there are variations of the signal, vs the reliability you expect to receive it with. @AndrewMI’s suggestion of a sophisticated signal that communicates exact position can allow recovery with very few received transmissions, but is then reliant on a high enough signal to noise ratio over the period the signal is being received that that position is actually decodable/interpretable by the receiver. It’s also reliant on both the beacon and the recoverer actually knowing where they are, which may work fine, but could also cause problems if one of those positions aren’t well-aligned. --- _[View the full topic](https://discuss.bluerobotics.com/t/back-up-recovery-device/23183)._