Wingsail Controller Evolution

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

Self Trimming Wingsail Design 101 (or What I should have known already)

 Self Trimming Wingsail Design - 101

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.

Reference: Center of Pressure (nasa.gov)

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

Voyager 3.0 - First On-water Trial

Its November 2021 and most lockdown restrictions are gone now.
Today was the first opportunity to get on the local lake for the maiden voyage of Voyager 3.0.
It was good to get the boat in the water for the firs time,  but it was inconclusive due to turbulent winds coming through the nearby trees making course keeping difficult.

I need to pick a day on the lake with north-westerly winds to get the cleanest winds for testing.

Voyager 3.0 Approaches First Sailing Trial

September 2021 in Melbourne is still a time of lockdown with restricted travel.

This has allowed time on the weekends to move forward with Voyager 3.0.

The first sail for Voyager 3 is almost complete and almost ready for the water. 

This is the Lake sail, which is intended to be a fairly large sail for lake use, not in the ocean.

It is expected that the Ocean sail will be about 75% of the size of the Lake sail.

The structure of the Lake Sail is complete, awaiting the plastic covering.

 Voyager 2.0 Last Voyage. What happened ?

Voyager 2.0 was at sea for 32 hours before the failures occurred, leaving the boat adrift for a further 44 hours.

The mast was broken off , and the electronic controller was lost.

Voyager 2.0 shortly after recovery

The mast suffered a brittle fracture at deck level.

The image below shows the fracture.

Remainder of Mast showing the brittle fracture at deck level

A test bend was performed on the remaining part of the aluminium mast.

It displayed the typical ductile bend expected of aluminium tubing.

The aluminium mast had been in use for around 3 years. 

The brittle fracture was probably due to work hardening or a fatigue failure.

This failure was avoidable.

Testing of the remainder of the mast showing ductile failure.

The Electronic Voyager Controller was lost when the lashing failed. The lashing was fixed to the hull using a simple 25mm screw through the fibre glass and into the foam. 

This was fine for trials on a lake, but clearly not suitable for ocean conditions.

Failed Lashing intended to restrain the Equipment Compartment 

The Spot GPS and the controller are housed in a Sistema Brilliance 920ml container. After 76 hours at sea, about 5ml of water had entered the container.

This implies that additional sealing will be required if these containers are used at sea. The containers are watertight for short durations, such as lake trials.

Tests will need to be performed to establish the reason for the water ingress. This could include diurnal heating and cooling, improperly seated seal, possibly due to dirt particles, or simple leaking through the seal.

Brilliance 920ml Container with the 5ml water acquired during the 76 hours at sea.

 First and Last Ocean Voyage of Voyager 2.0

May Day 2021, a Saturday, at 6am, Voyager 2.0 commenced its first ocean voyage from a beach at Torquay in western Victoria. The course consisted of seven waypoints covering 55nm through to a beach in Western Port, in eastern Victoria.

The course from Torquay to Pt Leo.

Pre-Launch

Sunrise on May Day with Voyager a few kilometres into the voyage, still in range of the LoRa telemetry.

The winds were light to moderate from the north for the majority of the journey.

She sailed well for 32 hours to the waypoint south of Cape Schanck, a distance of approximately 30nm. Voyager successfully round the waypoint at about 1:40pm on Sunday May 2nd.

Voyager 2.0 sailed well for 32 hours in Bass Strait.

The boat successfully rounded the waypoint, and commenced the beat in the north easterly wind, but within about half an hour there was a catastrophic failure of some type which meant the boat was no longer sailing. 

With good fortune, the winds turned to the south east later that night, at around 20 to 25 knots.

The slow rate of drifting, in strong winds implied that wingsail was not present.

Eventually Voyager drifted with the tides and the south easterly winds into Western Port.

It ultimately drifted in to a beach at Shoreham, where I was able to retrieve it, 44 hours after the failure.

It was an extraordinary coincidence that the beach at Shoreham where the boat drifted ashore was just 3km from the intended destination at Pt Leo. 

Once Voyager was retrieved the nature of the failure became apparent.

The wingsail was missing as expected, but also the main controller was missing. 

This contained the electronics including the SD card recording the sailing data.

It was lucky that the GPS satellite tracking  was not lost, and allowed the remainder of the boat to be retrieved.

The remnants of Voyager on the beach at Shoreham.

Voyager 3.0 Emerges

Voyager 3.0 Design Goals

Voyager 3.0 is next in the series of the Voyager sailing drones.

The main aim for Voyager 3.0 is to be able to operate at sea for about 14 days or longer.

Voyager 2.0 can only operate for about 4 days on battery. Voyager 3.0 will include solar charging with the aim of allowing continuous operation. An endurance of 14 days at sea should allow for a rounding of King Island from the Victorian coast and back.

Tests of solar charging rigs have suggested that around 20 solar cells as a minimum are needed for reasonable charging levels for a 2S battery powering Voyager.

The dimensions of Voyager 3.0 have been entirely dictated by the compromise of minimum size for ease of handling, versus adequate deck space to accommodate enough half-size solar cells to support reasonable charging levels.

Overall dimensions of 1800mm length and 350mm beam were chosen to allow possibly up to 23 half-size solar cells to be accommodated.

Proposed Deck Layout with 23 Cells 

Proposed Layout for Voyager 3.0 along side Voyager 2.0 for comparison

Commence Construction of Voyager 3.0 with the Stringer, shown partially completed here

Preparing to glue the first foam sheet on the stringer.

Part way through cutting the foam sheets using a hotwire cutter.

Commence shaping the laminated foam hull.

Part way through shaping of the foam core hull

Voyager 3.0 with glassing finished, ready for fit-out, along side Voyager 2.0

Note: This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.

Another Port Phillip Crossing Attempt - Post COVID Lockdown

Melbourne, Australia has come out of the second lockdown recently, so on December 10 2020, I commenced another run across Port Phillip.

In the months since the last run we've been in lock down for weeks at a time and not permitted to either leave home or leave our local area without good reason.

During this time Voyager 2.0 has had some hardware and software updates based on lessons learnt during the last crossing attempt.

The main software issue being addressed was the method of correcting the course as the vessel is steering toward a distant waypoint.

Checks done. Ready to go again.

 Steering to a Waypoint

When waypoints are only a few hundred metres away, it is simple to steer a course representing the Bearing to Waypoint (BTW) and you will typically arrive there, having followed closely along the rhumb line.

When the waypoint is many miles away, and the steering method is to steer the BTW, then it is quite likely that the vessel will deviate great distances from the rhumb line over a period of time.

This was one of the problems encountered during the last voyage across Port Phillip in March 2020.

The main software design change since then was to continual measure the Cross Track Error  (CTE) and use this to add a proportional course correction to the BTW to encourage the vessel to return to the rhumb line. The amount of course correction to apply is calculated as the ratio of CTE to CTEMax (where CTEMax is defined in the mission as half width of the corridor to the next waypoint), multiplied by gain constant.

Hence the simple course to be steered is: BTW - CTE/CTEMax x Kc

Note: This is all assuming that a course can be laid directly to the waypoint without tacking. If tacking is required, then a whole set of different rules apply which are beyond the scope of this article.

The first 10 hours were good

The vessel sailed from east to west, and for the first 10 hours was perfectly on course, staying very close to the rhumb line.

Unfortunately, at 6am the next morning, it was once again picked up be a fishing boat. A commercial fishing vessel this time.

This can be seen in satellite tracking plots shown in the image below. It was picked up in the middle of Port Phillip, as it was heading eastward, and carried on the remainder of their fishing trip, before the fishing vessel returned to her home port of Port Arlington.  I arranged to meet them there for the handover.

Satellite Tracking Plot 

Shared View: Voyager 2.0 December 2020 - SPOT Tracking (findmespot.com)

Mission in Yellow and actual course in Green. You can hardly separate them

Conclusions

The new method of steering using CTE combined with BTW appears to work well.

I've tried to sail across Port Phillip twice now, and failed both times due to human intervention.

I'll need to add signage suggesting to "KEEP CLEAR" or head out to the open ocean where there's less chance of meeting other vessels.

Port Arlington - Home Port for the last vessel to "rescue" Voyager

This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.

Solar Charging Trials during COVID19

Solar Charging Trials - in COVID Times.

It is August 2020 in Melbourne, Australia. We haven't been allowed to travel any distance for many weeks now, so there's no sailing trials permitted for hobbyists. So no chance to test the new sail, or the new LoRa telemetry system now installed on Voyager 2.0.

This allows time to start looking ahead to Voyager 3.0, which will be a scaled up version of Voyager 2.0 at 2m LOA, and about 0.5m in beam.

The intention of Voyager 3.0 is that it has a large enough deck space to accommodate enough solar cells to allow for missions of indefinite duration. Currently the battery capacity of Voyager 2.0 is about 80 to 120 hours (4 or 5 days). The Wingsail battery life is about 200 hours (8 days).

The Solar Cells in use are the Sunpower C60 cells. These are a light weight and flexible (within limits) and can be sliced up. They can provide over 3A at around 0.5V in direct sun. I'm currently slicing them into thirds, which can yield around 1A at 0.5V per cell in direct sun, and of course when connected in series, the three cells can yield 1.5V at 0.5A.

The image below shows a typically test set up for working out the basic parameters of the charging setup.

Preliminary Test Set up for assessing Cell Quantity and Charging Circuits

In order to evaluate different Solar Charging arrangements in the real world, I commenced with the Wingsail by pressing into service the failed (overweight) WingSail #2. This was kitted out with 4 third size slices of Sunpower C60 Cells in conjunction with the LTC3015 Step up DC-DC converter charging a single 18650 Li-ion cell. The load is the current Wingsail Controller board, but without the Bluetooth module, which was replaced with an Ebyte LoRa module instead. The Wingsail Controller was programmed with software primarily intended to read 3 sets of Voltages and currents and transmit them to a monitoring station.

Mock up of the Voyager Wingsail and electronics for trialing Solar Charging

It will be necessary to place cells on both sides of the sail.

The current Wingsail (without Solar Charging) has two 18650 cells. It is expected that only one cell will be required once solar charging is used. This will partially offset the increased weight due to solar cells (but not by much).

The test rig charging circuits and the the test rig software  are still being adjusted, but the aim is to monitor the operation of the solar charged Wingsail over a period of a month or so.

During this time, we'll start on a mock up of the deck of  the future Voyager 3.0 and set up a solar charging test rig for her.

This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.

Change Over to LoRa for Telemetry

Change Over to LoRa Radio for Telemetry

The Telemetry Radio used onboard Voyager 2.0 for the past few years has been the standard 433Mhz APM Telemetry Radio.

It operates well over short distances of a few hundred metres, as a transparent full duplex serial link, with a default transmission rate of 57600 Baud.

Traditional APM Telemetry Radio

The design of the telemetry system was that the vessel would constantly broadcast telemetry messages, whether they were being received or not.

The specific messages being broadcast are enabled by bit mask.

The mission definition does support power control where the telemetry radio can be powered off or on during specific mission steps.

The problem with the standard low cost telemetry radio is that distance is very limited. More efficient antennas were used to extend the range to a few hundred metres, but the link was always marginal at that distance.

LoRa Radio

LoRa (Long Range) Radio offers long range communications up to several kilometers with line of sight. 

LoRa is proprietary technology developed by Semtech, who provide a range of transceiver chips, primarily the SX1278. Many PCB modules are available from multiple suppliers using the SX1278 device.

The module used here is the Ebyte 433MHz E32-433T20DT 100mW.

Ebyte 433MHz LoRa Radio

The Ebyte module incorporates additional microprocessing components in order to provide a serial interface, making it reasonably simple to incorporate into the existing Voyager Controller design.

Ebyte Modules mounted for use with USB for the Voyager Base Station and a Serial Connection for use onboard.

The Ebyte LoRa module uses an effective transmission rate of approximately 2400 Baud. It can be increased, but that is at the cost of reduced range. The default rates are being used here.

The design of the telemetry system has been changed to a "request" system, rather than a broadcast system. This means that the vessel remains mostly silent and only transmits telemetry messages in response to specific requests from the Voyager Base Station.

Hence the scheduling of telemetry messages is dictated by the Base Station.

This alleviates the need to consider power control for the Telemetry Radio on board the vessel, because it will only transmit on demand.

The main aim of changing to LoRa Radio is to gain increased range for telemetry and control of the vessel. This should allow faster reconfiguration and testing of the Wingsail and the vessel, without the need to keep returning to shore.

Note: This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.

Wingsail Development

Wingsail Development 

All sailing testing so far has been performed using the one sail. It was originally designed and made as a very conservative prototype, not trying to push the boundaries far.
Its been a tough and reliable sail, with its longest voyage being across Port Phillip over a couple of days.

Wingsail #1

Dimensions:

• Height 1000mm
• Chord Length 150mm
• Area 0.15 sq metres
• NACA 0015 (15% Chord)
• Weight 820g

Wingsail #1

Wingsail #2

This Wingsail was short lived. Not enough thought was put into its weight and the stability of the boat. I thought the stability margin was quite high and didn't need to be considered much.

That was very wrong !

Dimensions:

• Height 1100mm
• Chord Length 330mm max, tapering down to 165mm.
• Area 0.32 sq metres
• NACA 0018 (18% Chord)
• Weight 1298g

Wingsail #2 - too heavy

When Wingsail #2 was trialed in the water in a mild 10 knot wind, the boat simply laid over and wouldn't right itself. A big failure.

Stability Measurements

It was clearly important to stop assuming the stability margin would be ok, and actually take measurements.

A setup was established to measure the mast tip loading required to hold the boat flat at 90 degrees of heel.

With Wingsail#1, the mast tip loading was measured at 475g at a distance of 1210mm from the deck.

This sail has demonstrated good performance in strong winds.

With Wingsail#2, the mast tip loading was only 250g at the same height off the deck, and boat laid over in mild wind.

Wingsail #3

Wingsail #3 is the same size as Wingsail #2, but it has been designed to minimize weight and heeling moment while retaining as much strength as possible.

Dimensions:

• Height 1100mm
• Chord Length 330mm max, tapering down to 165mm.
• Area 0.32 sq metres
• NACA 0018 (18% Chord)
• Weight 980g

Changes:

• The printed components were all redesigned to reduce weight. Previously, the printed pieces were designed as mostly solid pieces, and printed with infill of about 10% to reduce weight, as well as incorporating large circular holes. The components were all redesign by shelling them to about 1.5mm.
  Continuous checks were made on the design of each component by performing the slicing operation and noting the length of filament that would be consumed, in order to estimate the weight of the finished item.
  The weight of the finished component was determined to be 7g per metre of filament, as reported by the slicer.
  The end result was a reduction of mass of the printed components by almost 50%.
• The film previously used was 250 micron A4 sized clear acetate film, used for binding documents. I'm now using 200 micron A3 sized film.
  This has plenty of stiffness for a sail of this size, and the larger A3 size allows for less overlapping seems, and hence a neater result with reduced weight.
• Lower the centre of mass.
  The electronics and the battery with its switch, were lifted on Wingsail#2 in an effort to ensure it was high out of the water. This was a mistake because of the significant cost in loss of stability.
  The battery and electronics are now as low as possible, while remaining forward of the mast.
• Lower the centre of mass.
  The tail section and the forward counterweight have been dropped by 200mm, so that they are as low on the deck as practical.
  This has a significant effect on stability.
• The 12mm aluminium mast has been replaced with carbon fibre.
  The carbon fibre mast now consists of  three sections:
• 500mm by 12mm OD and 10mm ID
• 500mm by 10mm OD and  8mm ID
• 1000mm by 8mm OD and 6mm ID
• The Carbon Fibre tubing fits nicely together as a press-fit, to form a tapered mast.
  The aluminium mast weighed 125g. The carbon fibre tapered mast weighed 76g.

Result

The new Wingsail #3 has a mass of 980g (roughly 320g less than #2).

It requires a tip loading of 500g to hold the boat flat a 90 degrees of heel. This is a great improvement, and is slightly higher than 475g of Wingsail #1.

Wingsail #3

Next Steps

The next step is to get the boat in the water for trials.
There is still room for improvement in reducing the heeling moment due to mass, by reducing the mass of the tail. This causes a second-order problem, because the counter-weight is unnecessarily large to balance the tail. Hence, any improvement in the weight of the tail should see almost a double improvement in overall weight.

Resolutions from the First Long Voyage - March 2020

This post covers each of the issues identified after the March 2020 Voyage across Port Phillip, and the resolution.

Cross Track Error Resolution

The Cross Track Error (CTE) calculation has poor resolution when the waypoint is many miles away (e.g. 20 miles).
The reason for the poor resolution is that the CTE is calculated using Sine(CDA) x DTW. But the CDA is represented as an integer value. (CDA is Course Deviation Angle).

Illustration of  CTE Resolution

This has been corrected by ensuring that the calculation and relevant values are all floating point.

Course To Steer

The Course To Steer (CTS) for the simple case of sailing directly to a waypoint, is simply the Bearing To Waypoint (BTW). This is ok for short distances, but when the distance to waypoint is large, and maximum CTE is small by comparison, then the vessel can easily reach or exceed the boundary for the leg. This in turn may cause the vessel to take drastic corrective action and tack on to an inappropriate course to address the excursion beyond the course boundary.

The CTS needs to use CTE as part of the steering algorithm.

The design change has been to add a CTS Correction offset.

CTS Offset  = CTE/Max CTE x K

Where K is constant representing the CTE gain.
The constant K should be stored in the EEPROM as an adjustable parameter.
Possible values for K may be 10° or 20°.

This course correction is added to the BTW. The correction is proportional to the CTE, and hence should greatly improve course keeping.


This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.