This blog documents the ongoing development of low cost autonomous ocean going sailing drones, utilising a self-trimming wing sail. The sailing drones are currently controlled using Teensy microcontrollers, using C++. This is the Voyager series of sailing drones.
100 days on a Beach and a broken leg - 6th Bass Strait Voyage The 6th voyage on Bass strait for Voyager 2.7, commenced from Torquay Fisherm...
Sunday, 25 September 2022
Design and Construction Changes after Voyager 2.5 - Part 2 - Voyager 2.6
September 2022.
Voyager 2.5 has been rebuilt since ending up on the rocks in May.
She's been rebuilt to directly address the issues encountered in the last voyage, and is now designated Voyager 2.6.
Most of the issues addressed are related to hardening against water and preventing water ingress.,
Voyager 2.6 ready for the water
Most of the water leaked in through the Wing Angle Sensor housing and ran down the silicone tubing cable duct into the main equipment housing to the main controller board.
The Wing Angle Sensor housing was 3D Printed in ABS plastic.
It leaked a small amount of water over the period of two days.
The sensor housing is still 3D Printed, but it is now filled with epoxy resin.
No water should get into the silicone tubing cable duct, but just in case, it has been partially filled with silicone sealant to ensure no water can pass.
Sensor housing potted in epoxy, and the silicone tube cable duct sealed with silicone sealant
The aim is keep water out of the main equipment housing, but if water does get in, the next aim is to reduce the chance of water causing problems.
The two PCBs for the wing sail controller and main controller have be redesigned to be potted in epoxy resin to improve resistance to water.
This has been been done by reducing the number of onboard connectors, and moving them off-board as in-line connectors. When connectors are placed in-line within the wiring, they can more easily be sealed. The onboard connectors in the previous design corroded dramatically, are a difficult to seal.
More components have been placed on the PCB to allow the overall height of the assembly to be reduced. This allows the whole controller assembly to lifted higher within the equipment housing to reduce that chance of coming in contact with any water.
New controller boards; potted in epoxy and designed to minimise onboard connectors.
Controller Boards
The previous build of Voyager 2.5 included the use of Plasti Dip aerosol spray as a rubberised sealer for some components such as the wing sail battery assembly.
Water leached through the Plasti Dip applied using the aerosol spray. so this was not to be used again.
Plasti Dip no longer supplies non-aerosol products in Australia, but there are competing rubberised paints that can be used as a dip.
Battery Assembly (light blue) dipped in rubber sealant paint.
Fully assembled Voyager Controller for Voyager 2.6 ready for installation
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:
Ensure no water can get into the electronic compartments
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.
This article aims to provide a detailed representation and interpretation of each piece of evidence obtained from the voyage and subsequent failure of the Voyager 2.5 within the entrance to Western Port.
Voyager 2.5 was approaching the entrance to Western Port, but stopped sailing near 12th July, 11pm and drifted back out to sea with the tide. This was against the South Westerly wind of around 15 to 20 knots. Rather than drift back into Western Port with the change of tide, she drifted east toward Cape Woolamai, for about 19 hours.
Then she spontaneously turned left and drift north straight on the rocks near Pyramid Rock.
The whole time she was drifting, the winds remained fairly constant from the South and South West. Despite this, she suddenly changed course and headed for the rocks.
Voyager 2.5 as found at low tide, the next morning
View of Voyager showing the equipment containers still intact
The equipment compartments were intact, but about 50ml of water had leaked in to the main compartment.
The smaller forward compartment containing the satellite tracking equipment remined dry and fully operational.
The electronic components in the main compartment suffered significant electrolytic corrosion around the power circuitry.
The computer includes an SD Card for logging many of the vessels sailing parameters.
Fortunately, the SD card is intact and all log files are accessible.
Path of Voyager after failing to enter Western Port, through to the rocks
Each time the computer boots up, it increments a Boot number.
The mission commenced with Boot #501.
The log files showed that the computer stopped logging data about 18 minutes after the failure occurred.
About 19 hours later, the computer started again with Boot #502 and ran for about 5 minutes.
This coincided with the vessel commencing to drift in shore.
Then the computer rebooted again with Boot #503 and ran for 12 minutes.
It then washed on to a rocky beach. The computer did briefly restart with Boot #504 for a few seconds about 3 hours later.
Detail of movement of Voyager near the time of failure.
Detail of movement of Voyager near the time turn to run ashore
View Log Analyser visualising the vessel state after the failure.
The previous image is taken from the Voyager Log Analyser software. This is part of the Voyager suite of software that is used to visualise the vessel state and sailing parameters.
The wind is coming from the South West, and is confirmed by the AWA in the image.
The vessel is drifting out to sea, as confirmed by the COG in the image.
The vessel is lying beam on to the wind.
The rudder command is trying to turn to port, but the vessel is not responding.
This implies that the steering is ineffective.
This could be due to mechanical damage or electrical damage.
On balance, it is most likely electrical damage, due to water ingress around the Wing Angle Sensor housing.
The following video is a screen recording of the Voyager Log File Analyser.
It shows the first minutes of Boot #502. It shows the moments after the computer has started up and establishes its location. the boat id lying broadside to the wind on the starboard tack. As soon as location is established, then it tries to turn the vessel, and it responds in seconds.
This transition can be seen in the first 20 seconds of this recording.
It is unclear if the vessel can steer properly, but it appears that the vessel does have an intact steering mechanism, and it was responsive to the computer.
The recording also shows that the Wing Angle sensor is probably faulty, constantly showing an apparent wind of -6 degrees, off the bow. If the vessel could steer, it would be constantly trying to bear away from what appears to be a head-on wind.
Detailed log of events
Note: Temperature is measured by the Wing Angle sensor, located within the sensor housing at the base of the mast.
11/7/2022 07:27:04 Switch on at Torquay Boot #501
12/7/2022 14:53:21 Turn at the Cape Schanck waypoint
12/7/2022 16:52:44Temperature reading drops from 15 to 14 degrees C.
12/7/2022 22:50:46 Temperature reading increases from 14 to 15 degrees C, after about 6 hours.
12/7/2022 22:52 Approximate time of failure
12/7/2022 22:52:09 Steering command is trying turn hard to port, the vessel is not responding.
12/7/2022 22:56:46Temperature reading increases from 15 to 22 degrees C, after about 6 minutes.
12/7/2022 23:09:46 Temperature reading increases to 82 degrees C.
12/7/2022 23:10:12 End of logging Boot #501
13/7/2022 18:04:49 Start logging with Boot #502 Note: The Steering servo would be commanded to centre as part of boot up.
13/7/2022 18:05:13 The rudder is commanded to steer to port.
13/7/2022 18:05:16 The vessel has responded and turned 90 degrees to port. No longer lying beam on to the wind. No longer held in hove-to state.
13/7/2022 18:10:24 End of logging Boot #502
13/7/2022 18:10:35 Start logging with Boot #503
13/7/2022 18:23:16 End of logging Boot #503
13/7/2022 21:05:39 Boot #504, a few seconds only.
Link for plot of positions reported via satellite:
This could be due to mechanical damage or electrical damage.
On balance, it is most likely electrical damage, due to water ingress around the Wing Angle Sensor housing.
It appears that the temperature sensor within the Wing Angle Sensor started to return faulty data in the minute or two prior to the failure.
The implication is that the sensor was suffering water damage, in the minute or two prior to failure occurring.
The boat drifted in a hove-to situation for 19 hours after the failure.
For this to occur, the rudder would be turning the vessel to starboard, trying to steer too high to the wind.
It seems likely that the steering failed when the rudder was steering to starboard, and then didn't return.
The vessel left the hove-to position at 6:05pm the next day, at the same time that the computer booted up a second time.
When the computer boots up it initially commands the steering servo to centre the rudder.
It appears the steering may have been partially working, to allow the rudder to move and release the vessel from a hove-to state. She then drifted ashore.
This further reinforces the point that the rudder was mechanically operational while at sea, and the failure was due to electrical faults, due to water ingress.
Further Leak Testing
Water was found in the equipment compartments, and it must be understood how it got in.
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 measure water leak during this time.
The Wing Angle Sensor housing was tested separately by placing it under water for 12 hours.
This article will summarize some the key real world statistics established after 39 hours at sea.
This information is only available because we are able to retrieve the vessel from rocks and read the on-board SD Card.
Voyager sailed well for about 39 hours until she stopped sailing due to water ingress.
Power Consumption
The Battery was a pack of 14 x 18650 Cells, made up as 7P x 2S.
One of the cells had been tested and verified as having better than 3000mAhr in the voltage range of 4.2Vdc down to 3.0Vdc.
The main battery dropped from 8.30V to 8.12V over the mission.
This corresponds to 0.18Vdc drop over 39hours, or 0.11Vdc drop per day
Assuming a constant rate voltage drop, this would yield 20 days expect life, allowing for a 2.2Vdc drop, from 8.3Vdc to 6.1Vdc . The actual rate of voltage drop would increase as voltage drops.
The Voyage Controller employs switching regulators to drop the 2S voltage down to 5Vdc for the servo, and 3.3Vdc for the electronics. As the supply voltage drops, the supply current increases to maintain a constant power consumption.
The Wing Sail battery voltage dropped from 4.16V to 4.08V over the mission.
This corresponded to 0.08Vdc drop over 39hours, which is 0.05Vdc drop per day.
This yields 20 days expect life
The Battery consists of 2 x 3Ahr 18650 Cells x 1S
Steering Servo Usage
The steering servo made 67k movements over the mission in 39hours
This corresponds to 1.8k movements per hour.
The Wing Sail Trim Tab made 9,895 movements over the mission, 39hours.
This average out at 250 movements per hour over the mission.
The rate of movement was 10 movements per hours over the first 6 hours.
Pitch
The variation of Pitch over mission was not extreme. The largest value of pitch was 10 degrees, at the start, while on land. The next largest was 9 degrees down, but typical values were less than 4 degrees.
Roll
The variation of roll over mission was not extreme. The largest value of roll occurred on land. The next largest was 40 degrees, but generally under 20 degrees.
Temperature
The temperature is measured in Wing Angle Sensor located in the Wing Angle Senor housing located at the base of the mast.
The measured temperature varied in accordance with the diurnal cycle over the 39 hours of the voyage, except for the last half hour where the measured temperature increased dramatically.
This was most likely due to water damage.
Atmospheric Pressure
The barometric pressure sensor is collocated with the compass sensor.
Link for plot of positions reported via satellite:
Dawn on Monday morning July 11, 2022, Voyager 2.5 was launched from Torquay Beach for a mission through to Western Port, on the eastern side of Melbourne, Victoria.
It is a journey into Bass Strait with distance of around 50nm or around 80km. The mission was made up of around 8 waypoints, expect to take just under 48 hours.
Voyager 2.5 undergoing lake trials in 15 to 20 knots.
Planned course from Torquay heading east to Cape Schanck and into Western Port
Voyager 2.5 on Torquay beach just prior to launch 7:30am 11/7/2022
She sailed well for the first day and a half, but near the 39th hour Voyager stopped sailing. She drifted back out to sea with the tide, and then drifted along the coast of Philip Island for about 20 hours, and drifted ashore on the rocks.
Sailing well past the Cape Schanck waypoint heading into Western Port at 6:30pm 12/7/2022 - 35 hours
Voyager stopped sailing just before reaching the the West Head waypoint 10:59pm 12/7/2022 - 39 hours, then drifted back out to sea.
Voyager drifted east for another day coming ashore on rocks at Redcliff Head, Philip Island at 9pm 13/7/2022
Fortunately we were able to recover the boat from the rocks the next day. This was valuable, and has helped us work out what went wrong.
The onboard SD Card that logs many of the boats operating parameters is intact and can be analysed.
View from Pyramid Rock looking west toward Flinders, showing Redcliff Head, at around the time of coming ashore.
Voyager 2.5 as found on Thursday morning at low tide, perched on a rock.
The preliminary review of the evidence suggests that the boat stopped sailing because water leaked into the main equipment compartment and damaged the controller.
The evidence suggests that the water leaked through the Wing Angle Sensor housing. This is a 3D printed component. It appears to be watertight, but over a period of two days, a small amount of water can leak through the walls of the printed component. In future, this component will be assembled using different methods to avoid the leaking problem.
Voyager 2.5 suffered a lot of damage on the rocks. It is likely that she will patched up yo be able make another ocean voyage to further test the systems.
The next article will discuss some of the overall results from the voyage.
A further detailed article will cover the evidence and events surrounding the failure.
Link for plot of positions reported via satellite:
After Voyager made an ocean voyage in May 2021, she was retired, and focus shifted to Voyager 3.0. But after some thought it was decided to refurbish and upgrade Voyager 2.0 to become Voyager 2.5 with aim of completing an ocean voyage.
The main features of the upgrade of Voyager 2.5 are:
Aluminium mast replaced with Carbon fibre.
Aluminium fin increased in thickness from 3mm to 5mm, to increase stiffness and strength.
Sail Plan reduced in height by 100mm to reduce heeling moment, but increased length cord low down. The overall sail area was increased, but heling moment was reduced. Overall, its a much better sail plan.
Updated Wing Sail Controller PCB. Improved design and an improved software increased battery life of Wing Sail from around 8 days to 20 days. The radio link was changed from Bluetooth 4 to Bluetooth 5 (with other methods in between).
Updated Voyager Controller PCB, with new Teensy 3.6 microprocessor, rather than the Arduino Mega2560. Improved design and an improved software increased battery life of main controller from around 8 days to 20 days.
Improved fastening of the equipment cases to the hull to prevent them being lost.
Voyager 2.0, with a similar setup used for the ocean voyage in May 2021
Voyager 2.0 refurbished as 2.5, under-going final lake trials prior to going to sea, June 2022.
Voyager 2.5 on Torquay beach, preparing to go to sea
The wingsail is mounted on ball bearing races, and must be able to freely rotate. It also has a trim tab that must be controlled.
My solution to this has been to develop a controller to operate a trim tab servo under the command of a radio signal of some type.
The Voyager Sail Controller is visible in the image of Voyager 2.0 sailing, as the green PCB in wingsail.
Voyager 2.0 with Sail Controller V1 fitted in the Wingsail
The first designs used Bluetooth 4 as the communications link. The Voyager Sail Controller was set up as a Slave Bluetooth 4 device, connecting to the main Voyager Controller which was the Bluetooth Master.
This worked well but the Bluetooth 4 modules had a continuous current drain of about 9mA while connected.
Prototype Wingsail Controller using Bluetooth 4
Voyager Sail Controller V0 using Bluetooth 4 - August 2018
Voyager Sail Controller V1 using Bluetooth 4 - March 2019
During 2019 we changed the main telemetry link to the vessel to be LoRa radio using the Ebyte devices.
The Ebyte LoRa devices can be operated in a low power mode, where they wake up at predetermined intervals and check for a signal and then return to sleep. In practice, this yields an average current drain of around 6mA.
It also yielded the benefit that there are less components required on the Main Voyager controller, because the radio link to the wingsail is the same as the telemetry link to shore.
The only problem is the slow data rata rate and high latency. This yielded delays of around 1 to 2 seconds from when the wingsail should be responding.
Voyager Sail Controller V2 using LoRa Radio - May 2019
In 2022 the Bluetooth 5 module JDY-25M became available, and new Wingsail controller V4 was developed.
The JDY-25M Bluetooth 5 module has an idle current of around 1mA.
The low current consumption, combined with high data rate and low latency make a good option.
As of mid-2022, this is best version of the Wingsail controller yet.
When the wingsail is fitted with 2 x 2200mAHour 18650 cells, the wingsail has a projected battery life of at least 2 months.
This compares very well with the original Bluetooth 4 Wingsail controller having a battery life of around 8 days.
Voyager Sail Controller V4 using Bluetooth 5 - February 2022
The first sailing trials for Voyager 3 in late 2021 were disappointing.
The boat could not sail a straight course and was uncontrollable.
At first, I thought it was due to turbulent winds caused by the nearby trees, but eventually it became apparent that there was a basic design flaw in the new sail.
The issue relates to the location of Centre of Pressure for a foil.
The Centre of Pressure must be behind the axis of rotation to ensure that the self trimming wingsail will operate correctly and "feather", pointing into the wind.
Various refences indicate that the Centre of Pressure (CP), or Aerodynamic Centre of a foil with established circulation is around 25% back from the leading edge.
Before the circulation is established, the CP will be located close to the centroid of the foil.
My sail design has the axis of rotation located 37.5% back from the leading edge. This was chosen, because it seemed reasonable
The image below shows the calculated location of the line of the CP (25%) and the line of the Centroid (50%).
First Wingsail Design for Voyager 3 - CP is too far forward.
The calculated CP is forward of the axis of rotation by about 18mm. That is bad.
The effect of this is that initially the CP will be close to the 50% line (behind the mast), causing the wingsail to feather and commence operating.
Then as the circulation builds, the CP moves forward to the 25% line (forward of the mast). This causes the leading edge to fall away, and foil stalls, and CP moves back to the 50%.
So with these conditions, the wingsail may oscillate back and forth, yielding an uncontrollable boat.
The video below provides examples of unstable behaviour of the sail.
In future, I plan on placing the mast at the 25% line within the foil. Then a tail of almost any size will ensure that the CP is drawn behind the mast, yielding a stable design.
Once the issue of CP being located at the 25% line was understood, a new larger tail could be designed which would draw the CP aft.
The image below shows the new locations of the CP and centroid with the new tail fitted, which is just over 3 times the size of the original tail.
Updated Wingsail Design - CP remains aft of the axis
