This one got off to a rocky start. With all the modifications to the tail, just levelling the control surfaces was not quite enough to get the plane to fly straight. Look out for unintentional barrel rolls in the video :D
Launching the plane for the first time, it tented to pitch the nose down, taking almost half nose up input to fly it straight. This resulted in a "roller coaster" flight, where some altitude was gained, then controls centred and trimmed little by little. Business as usual.
After landing and physically adjusting the trim settings the second flight was a lot smoother.
Combined flight took around 10 minutes with 10.63km travelled at around 50km/h:
The plan was simple. Utilize the battery (3 minutes full throttle or 9 minutes half throttle) to the fullest.
Start with 1 minute of full throttle to get some altitude, 66% or 6 minutes half throttle left. Flay a couple of overpasses for 4 minutes, 2 minutes left at half throttle. Land with remaining battery.
Sadly the plan didn't go quite as planned:
First take off attempt was aborted because one of the wheels snagged on the grass and turned off the runway (here were 10 seconds of full throttle lost). Then the plane didn't get as high as intended, so flying by the visible size, the plane was flown farther then intended (here it took longer to fly back). Add some wind higher up, so when trying to hold the plane as still as possible for the photos produced larger turns.
Long story short, 5 minutes and 33 seconds later the plane landed 3 meters from the runway because it ran out of power to run the motor 20 centimetres off the ground approaching the runway. But the new landing gear held. No pivot over this time, just some torn duct tape.
Much was learned today and if the pictures turn out useful, it was worth it.
With only the control circuit between the autopilot program on the phone and the plane for autonomous flights missing, the weight of the plane is now just below 1.9 Kg. Not bad for all the equipment.
But is it better? Yes!
First, the vibrations are almost gone:
Left picture, previous flight, fully loaded with the stock motor at full throttle.
Right picture, this flight, fully loaded with the new motor at full throttle.
The difference is enormous:
And that's not al. With the new engine, the plane now climbs effortlessly:
In this test, with no one around on the ground or in the air, altitude difference of around 300 m was achieved.
And with no problems with telemetry this time, we learned that the cruising speed at which the altitude can be maintained is around 45 Km/h, which takes about half throttle.
Unfortunately, but not unexpectedly due to all the extra equipment, the gliding profile is somewhat disappointing. With the engine off, the plane glides, but the vertical speed necessary to maintain the cruising speed is around -35 Km/h, peeking at -50 Km/h. In short, it flies but it eats up altitude like crazy as can be seen on the video above at 3:00 mark (yes, the propeller keeps spinning due to resistance).
But, smoother and more powerful motor means better images and video from the cameras, and that's what we want!
And that's not all it did. The camera system works! It successfully takes pictures and video:
Stereo pictures! Might be uncomfortable to look at since the lens distance is not optimized for human viewing, but the depth data is there.
Still taken, synchronized and aligned by hand. There is one more part missing from the plane, and that is the circuit that will relay the data from the autopilot running on the phone to the servos. And part of that will also be automatic synchronised picture taking. As for the alignment, that will be the fun part once we have some real data.
And yes, there is also stereo video. Slightly easier for humans to watch, since distance between lenses is offset by the distance to the object in focus.
But unfortunately the video taken is slightly blurry. Fault of the stock engine, which is not of the best quality and is causing much vibrations, which are also noticeable on the panoramic video. Not much can be done here but to replace the engine with something better.
And while we're at it, replace it with something more powerful, since while the plane flew, and it flew quite stable, it had horrible climb rate and required full throttle to maintain altitude.
Now with three cameras on board, there is one more flight video:
The landing could be better :P Not used to the extra weight, the runway was missed by 30cm, touching down on high grass and flipping over. So nothing but pride was broken.
And what would a report be without the visualization of the whole flight:
Unfortunately there was problem with the SD card in the phone, so not all the data was captured hence the lack of attitude visualization and force graphs.
All in all a very successful test flight. What works and what doesn't is known, so the next logical step is to work out the kinks and try again!
Some more flying experience, this time in the wind.
And just so, it won't always be the same, this time the panorama render was shifter for 90° (left side is the view to the front and right side is the view to the back):
And visualization of course:
And what would be a training session without bloopers? Not so educational. :P
Turns out, that you can do loops and rolls with this plane on purpose too, but you better have everything mounted on with enough strength to withstand the extra forces!
Or on your next flight, right after levelling from a loop, the battery decide to fly away in a different direction. But luckily, with no control, the plane managed to find the only bush near and far and landed "softly":
Couple drops of glue is a bargain for telemetry data:
As the title describes, second time in the sky, trying out the new modifications.
Getting ready in the sun:
And let's jump right in to the fist flight of the day:
Pretty pictures, right? Only getting better! By the way, did anyone catch the barrel roll near the end?
The plane was quite nose heavy, which made it difficult to keep it the air, so right after take off it was decided to land at the end of first circle. Would you know, right at the end there was some more wind and for a second I didn't know if it was flying up or down, away or not. Yes, that's when the barrel roll happened.
Luckily the plane landed and after some weight redistribution and some elevator trimming was ready to try again:
Still a bit nose heavy, but much more manageable this time around.
Three laps for fun and science. And for fun, attention should be given to the last lap before landing. It takes "ages" to fly far away enough, but only seconds to fly back, causing quite a speedy landing. The answerer to this mystery is wind (flying against the wind = slow, flying with the wind = fast).
And to top it off, another pivot at the end. Turns out the landing gear takes a bit more force then expected. The first landing bent the gear in to the foam of the plane where the home made plastic mount ended and the second landing flipped over on loose gear.
Still some kinks to work out, so back to work then.
Today's challenge, visualize sensor data and find out what's wrong and how to fix it.
Step one, visualization (partial for now, other sensors and animated map in next iteration):
Well, looking at the attitude meter at the bottom left, one could see that the orientation data from the sensor is useless.
Looking at it even closer, one could see that the orientation data starts to drift as soon as the engine is turned on. Even before it's set to full power, where there are visible vibrations.
Could it be that the motor itself if distorting the magnetic field enough to skew the sensors? Do the vibrations from the motor play a part? Is there something else?
And here she is, officially know as AVI@TOR MK4 (Aerial Vehicle Intended @(Academic Testing) Or Research), taxing on the runway, ready for take off.
And she flew happy ever after, right? Well, let's call this one a learning experiment :P
First take off attempt:
So, what went wrong?
* Underspecified battery - not enough power for the motor to accelerate quickly and take off on a short stretch.
* Undercarriage designed for smooth surfaces - having one wheel in front and two in the back is good for maneuvering on the ground, but not so much when trying to accelerate on a grassy field.
Front wheel snagged on the grass, causing the plane to flip over. In the process breaking the steering wheel/rudder servo.
All of that was quickly resolved with a servo replacement and a beefier battery.
Or so it was thought, but the flip must have made some more damage, since on the next try the plane was vibrating a lot more, which was unnoticed until the video was revived.
First flight (but with shaky video from the first crash, the ending is still good though):
So, what went wrong this time?
Just as the plane was lining up to land, it started to loose altitude. Even with the engine set to full and elevator pushed to maximum. So last few meters off of the ground, the engine was cut off, which tilted the plane downwards, accumulating some speed and land hard short of the runway.
It felt as though the engine was loosing power again, which might mean the battery is still undersized. And the tilting downwards after the engine was cut off means the plane is nose heavy for this configuration.
But it also might be, that the (unseen) heavy vibration from the motor dislodged the battery, causing it to shift position, making the plane nose heavy and causing it to loose altitude.
All of that caused it to land hard, still almost horizontal, which would be perfect, but as with the first take off attempt, the front wheel got snagged. And with a much greater force this time, causing the front wheel to break off.
This would all be tragic if there was no data to make pretty graphs and pictures. But there is, so it's all good:
GPS data; realistic altitude estimation and position, speed & altitude from the autopilot.
Altitude and speed in graph form. It looks like the take off speed was around 40 Km/h.
Orientation data: yaw, pitch and roll. Black represents raw data and color represents data filtered with a Kalman filter. The vibrations from the engine make are too strong, so the readings are mostly noise.
What to do now? Well, we're wiser so we're going to improve it!
First redesign will be for the undercarriage. The two wheels on the back will be replaced with sturdier ones and be placed on the front. So the plane will be tail heavy is the weight of the plane is on the wheels. And the front wheel will be reused and placed on the tail, enabling it to steer the plane on the ground.
Also the engine mount, shaft and propeller (which will have to be replaced) will be expected to reduce vibrations, as will the mount for the phone/panoramic camera/autopilot module.
But before all that, some effort in to visualizing all the data with the panoramic video, since you can't post graphs on You Tube :P
Unwrapped pictures from the 360° panorama lens, treated with b-splines, looked pretty. But they weren't right.
How do we know? We checked:
And for that a 360° panoramic calibration checker board was created.
Confused yet? Pay attention to the height of the squares. Still confused?
Unwrapping the picture with Polar to Cartesian transformation, we can
see that the squares aren't square. In fact they get less and less
square.
It turns out that the correct transformation would be from Log-Polar to
Cartesian coordinate system. And even then with a calibration parameter
for the lens, since the real world is not perfect and the log base != e.
While used to describe continuous surfaces in 3D models, their
ability to produce a value at sub pixel resolutions con be abused here
to unfold the 360° panorama more smoothly.
Panorama when unfolding with the nearest pixel to the calculated value:
Panorama when unfolding with the sub pixel value:
The down side is that using brute force to calculate every pixel amounts to couple of hours per full resolution image.
Next step, use science & math to speed things up!
And to finally fix the aspect ration (now that the images are smooth).
Sorting out the aspect ration issue (should the
width and height be determined by the difference of surfaces from inner
our outer circle or be set by the radius & circumference), still
needs some work.
But the next big challenge is to antialise the image.
It was not, as
previously thought, a problem with the lens distortion or pixel shape.
Or any other mythical unexplained reason. No, just a simple mix up with
with the normalisation of the vectors.
If the image is not equal in height and width, then 1 X != 1 Y.
Yes, it's true. The 360° panorama lens is half a sphere coated in reflective material suspended above the camera.
Well,
in this case, half a sphere coated in reflective material with a hole
at the top, suspended above the camera with a mirror on top of it. But
it makes pictures like this (mounted on the plane):
Now it needs some processing before it's something you can look at
without getting a headache. So after relearning some of high school's
math (if you ever wondered why do you need to know something in
Cartesian and Polar coordinate systems, this is why) this is the result:
