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Hi and an at sea IMU question

MKL

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Apr 21, 2017
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Hi - I live in the North East US and have an Inspire 1 which we are using for marine mammal research off various boats. We also fly a custom built hex that has Mikrokopter software and we use their Boat Mode very successfully. It recalls the calibrations from when last ashore and does really well. I have had some good Inspire flights off one of the same boats (an aluminum sailboat), but twice now after 3 or 4 good flights on each occasion, I have turned things on and got no error messages, but then when ready to launch, (we do an auto takeoff hand launch), as you slide the ribbon to confirm, it gives an IMU error. A couple of times rebooting everything fixes it and it then flies fine, but then it wont fix with a reboot. Maybe I need to keep trying till it is happy? When I came back to land it turned on just fine and did not ask for an IMU recalibration. There was only 8 knots of wind and no appreciable sea state. My guess there is enough motion that the IMU cant lock on at sea at times, but is fine once on terra firma again, but would appreciate any thoughts. And no, I will never attempt to calibrate IMU or compass at sea. And yes I have the necessary permits to fly over marine mammals for research.
 
You are correct in that the MK stack (and the Freefly Alta) both have either boat mode or motion booting that skips the IMU check. Unfortunately we do not have that with DJI yet (at least not as a direct feature that can be turned on by the user). I suspect you are encountering just a little too much motion at start up when you are at sea. The part of your post that caught my attention was that you were able to power on a few times before getting this error. Maybe its just luck, but I was just talking to an Inspire 2 client of our who is having the same issue. They were on a boat and successfully powered on and launched a few times before starting to get the error as well. I wonder if an IMU check is actually good for a few readings if it can not get a successful check at start up. This is completely a guess and only based on a few people's stories like this so it could be everyone just having the same luck for a while before not being able to boot up. Our inspire 2 client tried booting on land before going on a boat last time and they hot swapped their batteries while they were out there in order to never turn the copter off until they were done shooting...not sure that is recommended, but it worked for them.

If you don't have these Hand Catch handles yet, they are a great little accessory. They fit the Inspire 1 and Inspire 2.
Secraft Hand Catch for DJI Inspire

If I hear any more info about the motion booting feature I will post again on this thread so you get notified about it.

Thanks!

Michael
www.FloridaDroneSupply.com
 
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You are correct in that the MK stack (and the Freefly Alta) both have either boat mode or motion booting that skips the IMU check. Unfortunately we do not have that with DJI yet (at least not as a direct feature that can be turned on by the user). I suspect you are encountering just a little too much motion at start up when you are at sea. The part of your post that caught my attention was that you were able to power on a few times before getting this error. Maybe its just luck, but I was just talking to an Inspire 2 client of our who is having the same issue. They were on a boat and successfully powered on and launched a few times before starting to get the error as well. I wonder if an IMU check is actually good for a few readings if it can not get a successful check at start up. This is completely a guess and only based on a few people's stories like this so it could be everyone just having the same luck for a while before not being able to boot up. Our inspire 2 client tried booting on land before going on a boat last time and they hot swapped their batteries while they were out there in order to never turn the copter off until they were done shooting...not sure that is recommended, but it worked for them.

If you don't have these Hand Catch handles yet, they are a great little accessory. They fit the Inspire 1 and Inspire 2.
Secraft Hand Catch for DJI Inspire

If I hear any more info about the motion booting feature I will post again on this thread so you get notified about it.

Thanks!

Michael
www.FloridaDroneSupply.com

Thanks for the reply. This sounds right. We often do close to 20 flights a day at sea and this is thus a major Inspire obstacle for us. Interestingly this has not been a problem for folks using an Inspire 1 at sea last year, at least in the small survey of two users I am aware of. Maybe this is an upgrade induced issue.

I have a set of carbon fiber catch rails that I bought on line. I have fat pool noodle sections on each which has the buoyancy to float the bird in case of a ditch to at least retrieve the parts and data. A few years ago we ditched another bird, and at least it's some solace to know that SD cards are dunkable.....
 
Yes, motion booting or boat mode would be a very useful feature to have built into the GoApp...and glad to hear you have something to make the hand launch and catch a little safer. Good idea on the pool noodles - I have seen that on other large copters as well.

How do you like the MK stack?
 
Yes, motion booting or boat mode would be a very useful feature to have built into the GoApp...and glad to hear you have something to make the hand launch and catch a little safer. Good idea on the pool noodles - I have seen that on other large copters as well.

How do you like the MK stack?
Its very stable and the Boat mode upgrade was a game changer.

Can you give a sense of how you hot swap an Inspire 1. I imagine some kind of dongle to an external battery in parallel?
 
The hot swap was an Inspire 2 client. They ejected the batteries but kept one pushed in while they added a fresh battery to one side and then did the same to the other side. Not sure how you could do it with an Inspire 1. Although, possibly you could do it with the battery mod device that people have used to add additional battery capacity to the Inspire 1. I would be a little concerned about the battery voltage differences between an external Lipo and the Inspire 1 batteries during the exchange.
 
The hot swap was an Inspire 2 client. They ejected the batteries but kept one pushed in while they added a fresh battery to one side and then did the same to the other side. Not sure how you could do it with an Inspire 1. Although, possibly you could do it with the battery mod device that people have used to add additional battery capacity to the Inspire 1. I would be a little concerned about the battery voltage differences between an external Lipo and the Inspire 1 batteries during the exchange.
Thanks - I need to check back with friends who have apparently not had this problem and see what their solution is.
 
Hi - After talking to 3 buddies who also fly an I1 at sea a lot, the summary is that they have occasionally had the same IMU not happy problem, but never insurmountable. I guess I was being too cautious. It seems that the IMU can take a while to settle down. So waiting a while with the bird, RC and ap all on lets it fix itself. Putting it back on the deck for a bit before trying to start the motors helps. None of them use auto takeoff, which I was doing exclusively. So for at sea use: manual take off, hand launch and hand catch (with helmet, gloves and eye protection for launcher/catcher) and with all the following off: auto landing gear, visual sensor, and smart return home. Since learning that patience is a virtue re IMU stabilization at sea, I have not yet been unable to fly. Did 8 consecutive flights the day before yesterday. It may just a take a bit of time to get the bird to agree to turn the motors on. The easiest mistake to make with a hand launch is to not have the bird facing out when you take off, especially on a boat with mast and rigging..... Critical part of the preflight checklist.

The other thing I have found is that if you are manually updating the home point to the RC to follow the boat's position, it helps to elevate the tablet about 6 inches above the RC to give the RC GPS a better view of the sky. To do this I just made a 6" aluminum strut between the tablet clamp and IMG_3626.JPG the bracket on the RC - see attached photo. Trouble is, taking the time to update RTH position is a PITA. So much of DJI software and hardware is great, but lack of an auto RTH update to RC position, the cryptic file structure for the RAW video requiring Cinelight, with a command R reboot on a mac to see the RAW drive at all, and lack of a transparent complete off line flight data download makes it less than stellar in those regards.
 

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