Hi all,
I am interested in long-distance ocean-going drones.
To date, I am aware of only 2 craft that have made it across the Pacific; both WaveGliders. They are the Papa Mau and the Benjamin. Both released at the same time from San Francisco, it took 1 year for the Papa Mau and another 3 months for the Benjamin. They were both solely under wave-power using the SV2 version.
However, 2 more WaveGliders released at the same time failed to make it from SF to Japan.
Another boat, the Honey Badger, is a sailboat and made it from SF to Hawaii in 34 days. This design is different to a regular sailboat, but clearly it works.
Scout was an attempt to go across the Atlantic using solar power and a propeller but got lost about half way across.
The new SV3 version of the WaveGlider is now more of a boat-hull design than a surfboard and now possesses a solar-powered propeller pushing the underwater glider.
BlueRobotics are beginning to produce the T100 and soon the T200 thrusters, with 5lb and 10lb thrust respectively. Two T100s were used to power their SolarSurfer in an attempt to travel up the Californian coast but some weed fouled one of the thrusters (possibly a prop spur would be the right solution?). Plus, when the sun went down, there appeared to be just as much drift during the night than forward motion during the day.
An underwater torpedo glider like SLOCUM or Seaglider needs very little energy, but working at depths complicates things immensely.
And here is my question:
"If you wanted to go from one side of the ocean to the other, which design would you choose? And which route would you choose?"
If I wanted to go westwards across the Pacific, I could potentially use the equatorial currents and use OSCAR (Ocean Surface Current Analyses - Real time) to help catch the best currents but then a couple of days ago I saw a beautiful map at Global Fishing Watch (something Google are involved in) and saw that those same currents are highly fished, and so probably best avoided due to the danger of nets.
I like the SailDrone idea as there is less underneath to catch upon compared with the SolarSurfer and WaveGliders, but the guidance tech on the SailDrone is probably harder to master. Other sailboats don't appear to have much success.
To date, thrusters and props for this size of boat have not proven themselves of this type of endurance. I would like to see how well the T200s fair out at sea.
A good design might include:
- A hull that cuts through the water like the SV3 rather than gets bumped around like a surfboard.
- A glider with a thruster on the glider like the SV3, but with a tether that can be detached in case of emergencies e.g. fishing net entanglement which seems to be the biggest risk.
- A self-righting hull.
- Two or three T200 thrusters attached to the hull of the boat, but with only one in operation at a time as the other two are redundant until one thruster fails (problem: the glider below should be in front of the boat and pulling it along)
Thoughts?
Replies
Here-s my current status on wing that will be 1000x260mm.
There are three 5x10x1000mm wood sticks for longerons (two lateral + one at trailing edge), XPS foam & 3mm lexan (flutted polycarbonate) for ribs, 3mm lexan for trailing edge, bamboo skewers for trailing edge conection with ribs.
two 5x10x700mm sticks for tail-to-nose boom.
The "mast" is just for show, its half height, so it will connect with the wing with a small bolt exactly in the center of effort of the wing.
The reason for that is if the wing is rigid enough, the wing's thrust will be centered in that point, that could have a small sliding bearing. The second bearing - at the base of the wing will be larger but its friction should be low, since (almost) all effort is applied at the center of the wing - top of the mast bearing.
---------------
I find fluted polycarbonate quite interesting, light, flexible, unlike styrofoam it rather flexes than breaks on impact. I wonder if it could be used for the hull.
DSCN1329.JPG
DSCN1331.JPG
here-s a study on wing sails https://www.google.com/url?sa=t&rct=j&q=&esrc=s&sou...
the chosen configuration was tested on a big autonomous catamaran
I'm not sure editing works as it should.
Just wanted to add this link, a much thorough document about this autonomous boat: http://waas.stanford.edu/papers/Thesis/GabrielElkaimThesis01.pdf
Good find. I briefly read through the documents but will take a proper look tonight.
I have been trying to pin down what actuator is needed, and then based on this what the power requirements would be (to then find the right solar panels and batteries)
I wrote to Firgelli Automations to see how long they last. The reply was that all the actuators have a life of 30,000 cycles.
I can't find a consistent answer of what this means. Is it total distance traveled? For example, if it is 15 inches with 30,000 cycles does that equate to 450,000 inches? Is this regardless of how many actuations it takes to get to that distance?
Or is a cycle simply turning on and turning off? In which case, this kind of actuator won't cut it and a hydraulic system may be more appropriate..
You might also want to look into windwane actuated steering, there are several wind-driven devices that steer the boat in a way to keep constand wind direction.
An actuator that moves the steering wind-vane instead of the rudder will require not only less power but also much fewer corrections/updates.
However it adds complexity and fragility.
Here I found a good description if you-re not familiar with them http://www.selfsteer.com/windvanes101/classification.php
They also provide ideas about how to steer with less force. (smaller actuators)
(for some reason I cannot save this message)
I recall seeing an actuator - mechanical part, without motor - they claimed a life of something like 2000 or 4000 km total movement. That-s enough for many million cycles. It makes me think it is not a mechanical issue. I did not saved the link.
I'm entirely not sure but I think the DC motor's brushes/connector make the weakest point in the actuator. Some messages ago I think I touched the subject. Every start and stop affects them.
Running too, but a motor like in car radiator fan works several thousand hours and may survive the car itself.
They should live alot more cycles at lower voltage and lower forces than their nominal values, but I don't know any study on this matter.
An option, not comfortable, is to make rudder actuators yourself. Using either brushless or stepper motors. Reliable mechanics could be scavenged from windshield wiper motors. These can handle a couple milion cycles or so.
the weight of the wing, at this stage, is 164 grams, of which 33 grams for tail boom. It could be little lighter and stiffer if I would use a carbon rod for boom, but this way - with two wood sticks - it was simpler to cross it around trailing and leading edge spars.
The holes for the mast, made in the styrofoam ribs, were reinforced with rings cut from 20mm pvc pipe
Sorry for the late reply.
I like the APM power module. I hadn't seen it before.
A water pump should also be self-priming and not mind sucking air. Something like tihs may be OK:
https://www.sparkfun.com/products/10455
An example of a water detector, although I wonder how it stands up to salt.
http://www.emartee.com/product/42285/Water%20Level%20or%20Salinity%...
You are right about sending photos. I hit send before thinking it through. It would be very expensive to send even a small photo. There are less expensive satellite alternatives but they only work close to large land masses (because of where the satellites are positioned) and not way out in the ocean.
The position of the linear actuator was more about keeping it as dry as possible in addition to any width limitations. The wire looped around a small pulley and attached to the horns only needs to the two small holes at the back of the boat to operate it, while keeping the electro-mechanical stuff out of the weather. This fitted well with an sea kayak as the holes were often already there.
Is LiPo the best choice for a battery? LiPo are light, and thus suitable for aircraft, but other types are available. Maybe Absorbent Glass Mat batteries?
I agree that more than one solar panel is necessary. They will get encrusted with salt and possibly with bird droppings. I'm not convinced 2 batteries and controllers would be necessary. That said, if it goes down then the boat is dead in the water (or rather is sailing without any control).
Here is a great graphic showing the parts and connections for a multi-copter:
http://diydrones.com/profiles/blogs/pixhawk-infographic?xg_source=a...
These are two related links by the same person demonstrating porting Ardupilot to Linux on a BeagleBone BlacK
https://www.youtube.com/watch?v=ealH3qP_pBE
http://diydrones.com/profiles/blogs/first-flight-of-ardupilot-on-linux
One of the reasons to do this is to add redundancy for the sensors on an aircraft but also to add more processing power. A BeagleBone Black plus the PXF cape expands the possibilities so things like image processing and better diagnostics are available. Plus, it should also make things like talking to the wind-vane, linear actuators, water pump, batteries and satellite easier to do. However, I don't think it is quite ready for prime-time. Maybe in a few months.
Maybe an additional board is necessary to be able to receive course updates and it may as well be the BeagleBone. Other options include the Arduino (less capable) and Raspberry Pi (more capable), but the BeagleBone has more capability. I'm not discounting a setup like Jack Edward's which does many things but not yet the satellite communication.
I will make contact with this guy who looks to be doing something very similar and is further ahead:
http://diydrones.com/profiles/blogs/pacific-bot-project-rockhawk
He is using Arduino. Note that he is using this linear actuator:
https://www.servocity.com/html/heavy_duty_linear_servo__115__.html
Personally, I prefer this one as at $150 it is half the price, has a better IP rating (Ingress Protection) and has feedback to determine the position:
http://www.firgelliauto.com/products/feedback-rod-actuator
The LAC control board is $40 extra but it can connect to an Arduino, and presumably other boards.
I did write to a trimaran designer who thought that his Ninja Spider would be a good model, although with a smaller wing as unmanned means it lacks the weight of a body to keep it upright.
I have studied the proa design and was aware of the Bionic Broomstick. The reason I am wary of it is because it's a niche design, but I also have my reservations that I could sail it well. The algorithms for sailing a regular boat would have to be altered for the proa and I am not certain that the benefits are worth it. However, I have no problem is someone demonstrates that it works perfectly and proves me wrong! :)
I'm not sure about the usefulness of a pump. The instrument/batteries compartment should be self draining, above water level. The hull can be made glassing over a solid block of foam, or with bulkheads that seal many comparments, in this case what compartment will the pump drain? A pump for each compartment? How about amas, should they have drain pumps too?
------------------------------
Batteries - If the boat needs weight, for ballast, then lead acid batteries might provide just that. UPS batteries, are resonably cheap and have a good working life. Solar chargers are built for lead-acid voltages, they will hurt a LiPo that is less forgiving with both over charge and discharge. So for LiPo, the battery charge should be managed with controller logic. It is not too difficult, but it's extra work. Solar chargers for lead-acids are cheap and small, it's not such a penalty in cost or weight to use two, just to be safe when one of them breaks.
--------------------------
I was also thinking about using a second more powerfull board, for more complicated tasks than an arduino can manage. But I dont really know what an arduino can do above basic navigation, so I feel it's better to postpone an extra board to the moment when I'm certain it is needed. Existing APM pilots provide for comands via radio for changing course during flight. Yes it could need some extra logic for a satelite modem but not much. A satelite modem has an interface not much different from old telephone line modems that worked fine with Comodore 64, Sinclair spectrums computers back in the eighties, when they had much less processing power that an arduino has today.
--------------------
It is nice to have builtin feedback from the actuator, but I would worry about the potentiometer lifetime. A potentiometer has a sliding friction based contact, and most common have lifes around 10000 cycles, some, special built, can do more. A rudder actuator needs much more. That's my worry, the same potentiometer based feedback comes with a $5 servo, "control board" included.
---------------------
Retrofiting a manned boat has the problem that with less weight not only the sail needs to be smaller, but with 80kg less payload, it is also possible to have a different position of CLR, in relation to wingsail's center of effort. That might affect its helm, and require adjustment of amas or daggerboard/keel position.
A basic, rectangular section hull like bionic broomstick's (and many others) could not only be cheaper, but easier to change mast/amas position.
Yeah, a proa has its complications and could be more difficult to sail autonomously. I mentioned it mostly because of the hull style - it can be cheap, easy to make and efficient, and work as well for a trimaran configuration too.
Hi,
I'll begin to make a 1m catamaran model boat, for tests. There are a few reasons for catamaran choice.
- I found a lot of information about designing sailing catamarans, regarding both stability and sailing performance.
- with a main body between the floats it's easyer to move both wing mast and a central daggerboard back and forth and tweak for an optimum placement of center of wind pressure of the sail in relation with the center of hydrodynamic lateral resistance to achieve a configuration that sails "well", in the sense of being able to maintain head with only small rudder adjustments.
- regarding stability I have an idea to make a kind of elastic mast support. That, on strong wind, instead of capsizing the whole catamaran will rather have only the mast heel, when a treshold bending moment is passed as result of either wind force or mass inertia (on heavy waves) . I know that reduction of the power with wing tail should avoid capsizing forces, but this will provide a passive, mechanical-only means to avoid capsizing,
This flexing support should also reduce the need for a very strong mast and/or wing since any excess lateral forces will result in bending the mast from its base rather than breaking it.
- the capsize prevention mechanism can be upgraded for capsize-recovery with the help from a single extra mast-tilting servo-motor and from flotation of the wing that will avoid the (unlikely) capsized catamaran to get into turtle situation.
-
2
-
3
-
4
-
5
-
6
of 8 Next