Well the gimbal controller finally showed up, it spent a week in New York, presumably making its way through customs, it was shipped from Latvia. It seems to be working pretty good, The one thing that I would definitely recommend are gimbal motors with hollow axel shafts, this would make wiring the gimbals and IMU much easier and clean. I’m now ready to mount it on the hex copter and see what happens, stay tuned…
360 degree panorama of the End of the Ash River Trail: (click on it for a larger image)
If you have been following me at all concerning my adventures into multi-rotor platforms for photography you may already know that I was pursuing a rock steady stable platform from which to take aerial photography shots from. Videography is definitely a back burner issue with me, my main interest is with still photography.
My initial disappointment was with the DJI Phantom 2 Vision in that the camera was rather poor quality, at least when measured against professional photographic equipment. The dynamic range was low, the lens was too wide an angle, the fisheye aspects were unacceptable, and worse the images from this camera were difficult at best to correct for image distortion.
I almost immediately sought out alternatives, the Go-Pro was also unacceptable to me since it also has a pronounced fisheye look to its images. Initially I adapted my Nikon J1 camera to the Phantom but found that it was simply too heavy to be safely flown with the Phantom. After exploring other avenues I found that I would have to spend over five grand to get a decent platform that could safely lift my Nikon J1, let alone my intended camera, my Nikon D800.
I was searching for a cost friendly alternative so I first built a quad using DJI’s E800 motor/ESC combination but found that these motors don’t come close to their advertised thrust in their “Tuned Propulsion System” it should, in all honesty, be called the Detuned Propulsion System. So I set out to build my hexacopter.
I was having troubles tuning the necessary vibration isolators to prevent the inevitable resolution robbing vibrations away from the camera. I was even looking to scrap my drone program entirely in favor of a balloon based system which has very little or no vibrations at all.
Then it dawned on me after a test flight. I have used tie cord as a safety backup in case the vibration isolators would become separated from the camera platform and after a previous hard landing all four indeed became detached. The next flight I forgot to reattach the isolators so the platform was hanging by the tie cord loops. The four tie cord loops were not all equal in length so the camera was flown at a ten degree, or so, tilt angle. After landing and giving my self a Homer Simpson DUH! I decided to download the flashcard and see what I got.
To my surprise the sharpest images that I have taken to this day from any aerial platform! That was the key! For the first time I was able to stitch a decent ten image panorama together! The problem with fisheye lenses is that they don’t stitch into decent quality images very well. Even though the camera was tilted and the copter wavered around due to both the normal GPS wondering and well as the ten to twenty MPH gusty breezes my stitching program, PtGui Pro, was able to easily stitch the ten images together. The other main problem with this particular panorama is that I did not take the images with enough overlap. While there are some areas of the image that certainly need improvement it is the IMAGE RESOLUTION that beats all previous images taken from any ariel platform, at least by myself!
Next to stabilize it even more I will be looking into a downward facing stabilization camera to supplement the GPS for position hold as well as an ultrasonic range finder to supplement the altitude hold function. Using vibration isolators between the camera platform and then suspending the gimbal from the airframe with tie cord is a perfect answer for total vibration isolation for still imagery, while this is obviously not a very good solution for videography – well I really don’t care that much about moving pictures anyway 😉
Update: I may have spoken too soon when suggesting that tie cord may not work for video, here is a video taken with the exact same setup as was used for my stitched pano:
You can clearly see the difficulties in taking a series of still images to stitch together for a pano, the copter is flailing around in the wind. Most of the jitteriness seen in the above video would be minimized when a two axis stabilizing gimbal is utilized. Note that the video from the Nikon J1 is not very good to begin with, compared to the D800, slow panning on a stationary tripod results in marked loss of resolution, not seen at all in this video. I am becoming convinced that a third axis gimbal motor may be necessary due to the unreliably unstable rotation control of the hexacopter is around the z-axis, especially when windy. Yup, retractable landing gear and a third axis gimbal motor may ultimately be necessary.
Well I finally attached my Nikon J1 onto my quad, actually I first attached it a few weeks back but the jello effect prevented decent video. Actually the jello effect was not that bad but it still was there. I used the vibration isolation platform from my Phantom Vision 2 so it is a bit overloaded. I must shop around for some heavier duty isolators.
You will notice that when pointed into the wind everything is fine, however, when pointing away from the wind the copter had to point nose high in order to offset the wind. This caused the isolator platform to rest on the battery causing a slight jello effect which then caused the camera difficulties auto focusing. Also note the tilt of the horizon when pointing perpendicular to the wind.
The battery tested well, with out any wind, the battery flight time for simply hovering was 30 minutes from full charge to 22.2 Volts, where I have programmed the PixHawk to Return To Launch (RTL) mode, providing ample reserves. But in todays wind the flight time was limited to about eighteen minutes, Remember while stationary hovering in one position it was actually fighting the wind and actually flying at an airspeed of 15-20 MPH+.
I am now ready to design and build a two axis gimbal for it as well. Here is a short video, note that I was testing this beast in a 15-20 MPH wind that was gusting to well over 30 MPH. While the video may cause air sickness I think the PixHawk handled it quite well, at least after it decided on a point on which to hold its position. I had to provide some inputs initially to prevent it from blowing into a tree.
Well I didn’t wait for DJI to finish my customer service order to finish their process and purchased a new motor and ESC. The PixHawk open source project has turned out to be ultimately successful, but a very fragmented and frustrating path since the documentation is weak and scattered across several web pages. It actually does not help that the PixHawk has two separate competing branches. I think it would actually be beneficial if both branches worked together to produce a reliable and bug free platform from which to program the PixHawk autopilot.
Instead we have two very buggy and unreliable software paths, called flight stacks, that are necessary in order to properly program the PixHawk hardware. WARNING going the open source route is plagued with numerous updates that may, or may not, be steps forward. This is especially true since the two sides are competing for additional features instead of competing for reliability and robustness.
Well that being said, my first flight using the PixHawk and QGoundControl default settings using the DJI 350 model as a starting point was successful. The default settings use very conservative low values for the PID feedback settings and this shows in the video. The aircraft controls were very sluggish and slow to respond from error input such as the effects from strong wind gusts. Obviously more tuning is in order.
One of the things that I noticed with the PixHawk’s GPS is that it is much more sensitive. While I could get a GPS lock with my DJI Phantom placed near a window or patio door the PixHawk can lock on to five satellites a full twenty feet from any window inside of my apartment! I’m very impressed! Also note that while I had some trouble reliably controlling the aircraft, due to weak default PID input values, the aircraft still acted in a positive manner, even at the end of the video when the battery became detached and ultimately unplugged it still landed upright and unscathed! The first flight for the PixHawk were decidedly superior to my first flights using the Phantom autopilot, which all ended up with uncontrollable crashes and in the destruction of several propellers:-(
Here is an image showing My new creation with the DJI Phantom. Note the huge 10AH 6S battery that obviously needs a more robust mount than velcro and a single bungee strap to secure can provide.
I’m actually thinking that I will use this prototypes acquired knowledge into making a hex-copter, since the extra weight of the battery eats up most of the extra power supplied by the motor-ESC combination. It was obvious from this first flight test that the hover power was actually at about 50% when adding additional weight of a camera/gimbal system will probably overload this setup, especially when used with this huge 10AH battery. DJI is actually sending me a new ESC, I’m still not sure if they are sending me a new motor and props, but I will find out Monday when the shipment should arrive.
Oh ya, I also have been spending a lot of time learning how to use and program my new radio transmitter and receiver, the FrSky Taranis Plus sixteen channel transmitter and the X8R SBUS receiver. Also an open source steep learning curve quagmire of fragmented sources of software ind information. Ultimately I am very happy with my choice, just be forewarned a lot of time surfing the web for weak and fragmented documentation should be expected.
Sounds like to me another trip to Home depot…