Dear members,

I like to inquire info on the use of the P4P at open sea.

We intend to use a drone at sea, launching and retrieving from a small inflatable boat (6.5m).

What are, if any, the limitations for launching at sea?
Is this necessary to do a full calibration each time you start-up (fly) the drone? or can this be by-passed (e.g. done on land)?

For our (research) purposes, the exact flying height is required. Reading from many other posts, this is unlikely to be achievable using dji installed GPS/barometric values.
Does anybody have experience installing/using extra devices to measure more exact height?

Thanks for your input

Hi Oceandrone,

Normally the only calibration required at launch site is the compass calibration when you are taking off from a new place that could have a different magnetic declination value.

Re height measurements, your question is a bit too broad.

Are you talking about devices to be installled on the drone ? Handheld? Requiring a baseline? Optical? Laser? Ultrasound? etc. etc.

What precision do you look for in your measurement? +/- 1 cm per 100 meters of height? +/- 1 cm per 10 meters of height? 1 meter per 10 meters of height?

How far from the small boat would the drone be when you need an exact height measurement?

"I like to inquire info on the use of the P4P at open sea."
Note that the warrantee does not include water damage, and salt spray does not go well with electronics over time, also it does not float which means that you can't return it for warrantee issues to be fixed.  You should consider it a disposable item when used at sea!

"We intend to use a drone at sea, launching and retrieving from a small inflatable boat (6.5m)."
This is a bit dangerous without plenty of practice, you need to launch it from your hands, held above head height and catch it on return.  Do not try it unless there is good lighting conditions for the Vision Positioning System to be able to hold it steady above you, and only do it in calm conditions, do not take off from the boat itself as it is likely to either hit you or hit the water.

" What are, if any, the limitations for launching at sea?
Is this necessary to do a full calibration each time you start-up (fly) the drone? or can this be by-passed (e.g. done on land)?"
Never do a calibration on a boat, you should only be doing a calibration once or twice a year anyway and 100m away from any metal for the compass calibration.

"For our (research) purposes, the exact flying height is required. Reading from many other posts, this is unlikely to be achievable using dji installed GPS/barometric values.
Does anybody have experience installing/using extra devices to measure more exact height?"
The ultrasonic sensors will give an accurate height up to 15m, they don't work beyond that.  The barometer is fairly accurate, and at sea where there will not be big temperature variations I would expect it to be plenty accurate enough.  Of course I don't know what accuracy you need, but if you check the take off height (which will be 0) and the landing height (which may be a few meters out) then you pretty much know the accuracy of the rest of the readings on a short flight.  I think on most flights over sea you will find take off and landing well within 10m and probably within 5m.
If you are adding extra equipment such as data loggers then beware of blocking the ultrasonic and vision sensors, there is not much room where it is safe to put stuff. If you block the ultrasonics then it can fall out of the sky unexpectedly and if you block the vision sensors then it will become very hard to hand catch at sea in even a light breeze.

" Thanks for your input"
Please post your results and experiences in return...

Aloha Oceandrone,

     Antonio and Nigel have most of it covered for you.  As noted, you will be doing hand releases and catches.  This will require relatively calm seas and good boat handling.  The flight crew will also have to include the operator and the handler (Launch and Catch).  The two of you will have to practice on land before attempting to operate off of a boat.  There are a number of YouTube videos about release and catch of the DJI Phantom.  The most important point is that you have to hold the Phantom by the vertical struts of the landing gear with one or both hands.  Both hands is always better on a boat.

     The best practice will be to use a pick-up truck and a large parking lot so you can align to the wind.  The handler will stand in the back of the pick-up truck facing the tailgate with your butt against the cab.  Spread your legs to a stable position and lean backward into the cab.  If you can tie-in to the truck it will be safer but the truck will not even get up to 3 miles per hour and will travel straight down-wind.  Practicing should start on near windless days.

     The operator will sit in one corner or the other back by the tailgate.  The handler will face the tailgate and watch the Phantom approach from behind the truck.  The operator will practice approaching the handler from behind the truck with the Phantom at just above head level.  The truck will travel at a very slow speed less than 3 miles per hour depending on the wind.  Preferably, the truck is driven by the boat operator for better teamwork.

     The launches and catches will be the same.  The operator should not start the Phantom until it is held above the handlers head.  Then when catching, the operator has to completely shut down the Phantom to complete the catch.  The handler does not bring the Phantom down to head level until the blades stop spinning.  This should be practiced first just standing on solid ground.

     The most stable part of the boat is aft and the most maneuverable part of the boat is the bow, therefore you will want to keep the aft part of the boat clear for releases and catches.  Look into getting a bos'n's belt (or a lineman's belt) so you can clip into lines secured to the sides of the boat.  There should be at least three lines in a stable triangulation to secure the handler.  Four lines should be used if the padeyes are not available for a triangulation.  The bos'n's belt (or a lineman's belt) usually has padeyes on the sides as well as front and back middle.  This will allow you to clip in to the boat for stability, yet the lines are removable.  This belt can also be used for the land drills practice with the truck.

     Depending on where the control console is on the boat, you will want to locate the handler away from the transom of the boat and the console but laterally in the middle of the boat.  The way most boats are designed, this will be the most stable part of the boat.  With the handler's belt tied in to the boat, the handler should be very secure and stable facing aft toward the transom.  The belt should not be tight, nor should it be loose.  The handler will be able to move their upper torso to handle the catch with both hands and over head.

     The operator will locate themselves in a stable area near the back of the boat.  They need to sit or otherwise be secure so they can see and concentrate on bringing the Phantom in to the handler.  The Phantom approaches the handler from behind the boat at above head level.  The operator then brings the Phantom down into the hands of the handler.  Once the Phantom is secure, the operator stops the propellers.  

     Hope this helps!

Aloha and Drone On!

Note that if you take off or land from a moving platform, the vision positioning system will have a conflict between holding position relative to the platform or holding position relative to the ground/sea which can result in unpredictable and potentially dangerous movements.  Thus always release and catch above head height, try to keep the boat moving as slow as is practical and manoeuvre the aircraft to the boat rather than the boat to the aircraft, and don't hang around at low altitude when you take off = immediately go vertically upwards to a decent height.  

Probably worth the person with the controller practicing cutting the motors, once caught, with the emergency stop (CSC) rather than using the normal throttle down motor stop as it can be a lot quicker and can avoid a fight for the person trying to hold the aircraft while the boat is moving.  The aircraft is quite strong and can damage humans - don't try to fight it over position. Just support it vertically - this is the biggest danger on a moving boat.

It can be done safely with practice, people do use them for research from boats and they are much safer than larger drones, but do take safety and training seriously.  A boat is not the place for a beginner pilot and catcher to practice.


Other issues:  

• When the battery runs low it will return to the place it took off from even if the boat is no longer there - learn to deal with RTH and how to cancel it.
• If you take off at mid day in calm conditions in hot weather, by the time you land there may be a strong onshore wind - understand the weather.
• Maximum wind speed is around 30mph, but at that speed it will have great difficulty returning against the wind, again learn to understand the weather and make sure the return flight is downwind whenever it is not calm weather.
• Always charge the batteries to full on the day they will be used, especially when flying over water.  A battery that has not be charged for a week must not be used over water.
• Make sure that the boat does not contain one of those large, very powerful, recovery magnets - it will affect the aircraft compasses which could be dangerous.
  

Also, invest a good pair of two ways radio headphones so the handler and the pilot can communicate during takeoff and landing.

Aloha Oceandrone,

     Again Nigel, and this time Maxi, are giving you more good advice.  Print it out and you have a manual!

Aloha and Drone On!

Ignore what the others have said about compass calibration.
The manual for the P4 pro (p57) tells you not to calibrate  the compass.
It's completely unnecessary and messing with it is more likely to cause problems.

The indicated altitude will be reasonably accurate (and it doesn't come from GPS or it would be +/- 200 ft)

Labroides Posted at 2017-4-8 03:44
Ignore what the others have said about compass calibration.
The manual for the P4 pro (p57) tells you not to calibrate  the compass.
It's completely unnecessary and messing with it is more likely to cause problems.

Presumably if you take it from the northern hemisphere to the southern hemisphere then it needs a calibration, otherwise it will be trying to fly upside down?

Thanks for all your great advice and input,  this forum is really valuable.

I understand it wont be an easy job, and practise on land will be surely high on the agenda before taking it out to sea.

We have a platform on the bow of the boat, providing an extra meter height above the vessel.
I think, the catch and release events with the vessel facing with the weather and waves, with the person holding the drone on the platform will be the best setup in our case, as the stern of the boat is small and full with other research equipment and has an A frame sticking out.

Regarding the height measurements, we prefer to have it as accurately as possible in order to make precise calculations from photo and video collected

@Antonio76 1 cm /100m is great but we wont be able to use RTK stations, if we can get 1cm / 10m accuracy that would be excellent.
Other research teams use custom (larger) drones, (the one i know of) which have extra barometric devices  installed onto the electrical circuit. for instance Motorola's MPXAZ4115A
They are not very expensive to buy, but I guess manupulating with the hardwear is asking for trouble.
The fact that these consumer drones are so advanced in their flight and optical quality, I prefer to use these if suitable, than getting a 20k drone, (and loose it at sea)
Its a pity the VSP doesnt work up to a little more height say 25m.

I will inquire about having a barometric device installed one way or another, ( i am not an electronic expert ..) and post the experience once its works and tested.

Again, thanks for all you input and advice

Oceandrone Posted at 2017-4-9 01:29
Thanks for all your great advice and input,  this forum is really valuable.

I understand it wont be an easy job, and practise on land will be surely high on the agenda before taking it out to sea.

"We have a platform on the bow of the boat, providing an extra meter height above the vessel.
I think, the catch and release events with the vessel facing with the weather and waves, with the person holding the drone on the platform will be the best setup in our case, as the stern of the boat is small and full with other research equipment and has an A frame sticking out."

Paint a big "H" in the centre of the platform to make it a proper landing pad

Then make sure that you don't stand on the "H" - it's purpose is to make it easy for the vision positioning system to lock on to the boat and thus make it easy to catch.

The extra meter of height will be useful in windy conditions as it will take it up into more steady air than will be found down nearer the surface.


"I will inquire about having a barometric device installed one way or another, ( i am not an electronic expert ..) and post the experience once its works and tested."

I'm not sure that will help much over the aircraft's twin barometers.  The propellers are producing 1.5Kg of lift which obviously affects what a barometer will see, plus any wind will produce a pressure differential across the aircraft and lift over some surfaces, including when just hovering.   There isn't anywhere on a Phantom that you can mount it where it wont be affected by the propellers.

Over water I would think that a sonic measure would be best if you can get enough range.  

Possibly you could calibrate the aircraft barometer by hovering 10,15,20,25m above the boat, looking straight down and measuring the length of the boat in pixels on a 4K video frame.  Not sure what accuracy that would give you at the heights you are interested in?  Let us know if you work it out...