Design and Construction Changes after Voyager 2.5

Design and Construction Changes after Voyager 2.5 - Part 1

The key points learnt from the voyage of Voyager 2.5 in July 2022 were:

1. Ensure no water can get into the electronic compartments
2. Assume water will get in, but ensure that it won't cause any damage.

Step 1. Ensure no water can get into the electronic compartments

Water leaked into the main electronic compartment.

The equipment compartments (excluding the Wing Angle Sensor housing) were tested by placing under water with a covering depth of about 20mm for 12 hours. 

There was no measurable water leak during this time.

Watertight Components

The Wing Angle Sensor housing was tested separately by placing it under water for 12 hours.

A significant amount of water leaked in.

Leak Testing of the Wing Angle Sensor Housing

It became apparent that the majority of water entering the watertight compartments, entered via the Wing Angle sensor housing, and flowed down the silicone tube to the main compartment.

It is not clear whether the water leaked through the walls of the 3D printed component, or beside the brass tube.

The Wing Angle Sensor did fail whilst at sea, due to water damage.

Design changes:

• Add silicone sealant into the silicone tube to form a plug approximately 10mm from brass tube.
• Pot the Wing Angle Sensor housing with epoxy, and allow the epoxy to flow into the silicone tube, up to the silicone sealant plug.

These steps should ensure that the assembly is completely watertight, and that the Wing Angle Sensor is protected from water.

Telemetry Antenna with Breather Cap could extend down further.

The Telemetry Antenna projects up a tube fitted with a cap to acts as a breather for the main compartment. 

The breather allows the electronics to be exposed to atmospheric pressure. This allows an atmospheric pressure sensor to operate.

It also protects the compartments from over or under pressure during the diurnal heating and cooling cycle. If the compartments were sealed, then water on contact with the compartment seals may be sucked in as the internal temperature drops.

 

There is a risk that some water may have entered the compartments by splashing up the vent cap and then down the antenna tube.

This risk should be mitigated by making a vent cap that extends down, almost the full length of the antenna tube.

Step 2. Assume water will get in, but ensure that it won't cause any damage

All assembled PCBs were finished with spray on lacquer Conformal Coating. Multiple coats were applied.

This was completely ineffective when exposed to salt water.

There was considerable damage and corrosion around power pins on all PCBs.

Voyager Controller showing corrosion damage

Wing Sail Controller showing corrosion damage, but not on the epoxy coated board connector wiring

The power connector and servo connector for the Wing Sail Controller were implemented as in-line cable connectors. They were sealed on the board using epoxy resin with cable tie strain relief.

This was successful. Theses connections did not suffer corrosion damage.

The in-line cable connections can be sealed using self-amalgamating silicone tape. This was successful, but care needs to taken to ensure that the tape seals correctly.

Wing Sail Servo controller showing corrosion

Design changes:

• All PCBs will be dipped or brushed with epoxy resin to completely seal them.
• Where practical, all connectors need to be moved off -board and implemented as in-line cable connectors. This is to allow the entire PCB to be sealed with epoxy.

The in-line cable connectors will be sealed using self-amalgamating silicone tape. This has proven to be effective.