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Old Jan 03, 2015, 02:19 PM
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Quad Otter, another VTOL joins the fleet, flight video added

This ship is based on the venerable Twin Otter STOL by de Havilland.

I had my first transitions flights this AM. It went very well. We had an unanticipated break in the winter weather this morning with very little wind so I grabbed my gear and headed outdoors for some test flying. Here are my observations from this testing in point form:

1) Hover is rock solid and hands off
2) Hybrid mode (motors tilted about 40 degrees) is also very solid with a slight nose up tendency as the flight speed picks up
3) Forward flight was perfect and control was great. Rolls are very fast, loops easy, dead stick gliding smooth with a decent glide ratio.
4) Top speed in forward flight is excellent. The model is fairly clean aerodynamically and I chose higher kV motors to allow good forward flight speed.
5) Low speed/high alpha flying was surprisingly good. The plane was able to fly much slower than I expected with good control.
6) Transition back to hover is a non event

I was able to make several transitions. What actually worked the best was when I skipped flying in hybrid mode and flipped the tilt switch all the way at once which gives about a 4 second tilt time. Based on these tests, the transition can probably easily be reduced to about 2 seconds.

No video today. I'll get some flying video with transitions as soon as I can...weather permitting.

Maiden hovering video:
VTOL Quad Otter, first test hovering (3 min 13 sec)


More testing:
Quad Otter Testing (3 min 34 sec)
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Last edited by leadfeather; Feb 11, 2015 at 07:04 AM. Reason: added second video
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Old Jan 03, 2015, 02:20 PM
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Construction details

The airframe is constructed of epp covered in 3 mil laminating film. This is a light yet tough combination. During the early flight trials I was glad about the toughness. The wing is a hot wired epp airfoil . It is the wing from a product called a Quick Stick made by Fancy foam. The rest of the airframe is made from 9mm, 1.3 lb. density epp.

I chose to support the motors from the fuselage. I think this is a simple arrangement and adds minimal weight. It also allows me to use a single servo for the til mechanism. The carbon tube motor support spars rotate in aluminum tubes that are glued to the fuse. I adapted a plastic motor mount stick for mounting the motors. Normally the motor would slide in the end of the plastic stick, but I used this mount to slide on to the spars. This allows me to adjust the angle of each motor independently. It also allows the motors twist in a crash and prevent damage.

The components I used were:

KK 2.1 Flight Control Board
Spektrum Receivers
1 of 13 gram metal gear servo for motor tilt
3 of 9 gram servo for ailerons and elevator
Mystery 12 amp ESC flashed with SimonK firmware
SunnySky x2412s brushless motor... a current favorite with the 250 size quadcopters
HQ 6030 carbon filled plastic props
2200 mAh 3s battery
A servo slower for the tilt servo
A 5V 3A BEC for the servos
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Old Jan 03, 2015, 02:20 PM
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Tirals and tribulations along the way

One of my goals with this project was to see if I could build a good vtol craft without having to interface with a computer whatsoever. I am using the KK flight control board (fcb) with the factory code.

To make this work I did the following:

At first, I used Y connectors at the Rx to go to the fcb and to the servos. I could have run the servos through fcb but in the factory code you are stuck with gyro input to the servos. Gyros on flight control servos usually flutter at higher speed. The Y connectors turned out t be a bad idea; they caused a feedback to the fcb and made the hovering controls less stable. It wasn't horrible with the wing off, but with the wing on (and more y connectors hooked up) things got unflyable and I had my first bad crash...not much damage at all. Quick repairs and I sent the Otter back up with the aileron servos disconnected.
Better hovering then the next disaster. One of the esc's; rear left; melted down, and by the time I saw the smoke and disconnected the battery it destroyed the fcb and another esc. This delayed the pproject as I had to wait for a new fcb.

Next I removed the Y connectors and installed a second Rx for the servos. Yes it works; one Tx bound to two Rx's; first time I've tried this. This way the KK is only operating the 4 motors; and in fact as far as the KK fcb thinks it is operating a quad and nothing else. So far this is working great.

The next issue I had was with the propellers. I had started with GemFan 630 props. These are very flexible props; the flexibility effects the hovering stability and limits the power. Too much power and the blades vibrate badly. They are also weak; I had one break while in hover and this caused a crash...no real damage fortunately. I then installed HQ 6030 props. They tested great on my test stand, and the difference in hovering stability was very noticeable when I swapped in these props. The combination of the 20 gram Sunnysky motor and the HQ props can provide over 500 grams of thrust...more than double what I need to hover ... remarkable for such a light weight package.

Today with all the issue fixed I had my first flights out of doors. So far the Otter seems to work very, very well as a VTOL craft and this is with the stock K firmware. I just wanted to see if this was possible ( I hate all of the tedious computer stuff). After I do some more flying and testing I plan to upload the OpenAeroVTOL firmware. It should make the Otter even better.
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Old Jan 03, 2015, 02:24 PM
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Further work

Here is my list to complete this project:

1) More "transition testing" to forward flight to fine tune the transition time/servo slower
2) Install some landing gear; mostly for looks.
3) Finish decorating
4) Get more flight time with factory firmware, get some video.
5) Install the OpenAerovtol code
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Old Jan 03, 2015, 07:15 PM
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Very nice. It's hard to imagine why Y cables would confuse the KK2 board. I did it that way on the first VTOL trainer with no difficulty. I never knew you could bind two receivers to one TX at the same time. I will watch out for the props on my build.
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Old Jan 06, 2015, 08:14 PM
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Quote:
Originally Posted by Ran D. St. Clair View Post
Very nice. It's hard to imagine why Y cables would confuse the KK2 board. I did it that way on the first VTOL trainer with no difficulty. I never knew you could bind two receivers to one TX at the same time. I will watch out for the props on my build.
The Y cable thing surprised me too. With just the tilt servo Y and the elevator Y active the stability was only effected a little, but when I put the wing on and hooked up the ailerons servos (a Y at the Rx and then another Y for the aileron servos) it got really bad, particularly pitch stability.

Once I went to the separate Rx's for the motors and for the servos the Otter stayed super stable ... probably the most stable hovering VTOL I've done to date.

Running two Rx's was a first for me. I'm glad it seems to work well. The weight of the 2nd Rx is less than the Y connectors it replaced.

I've got the landing gear made. It is going to be removable since ti is easy to damage and it is not needed for this craft...but it does look good and a little more scale with the gear in place.

I can't wait for the weather to improve a lot. It is really cold at this time. I'm anxious to fly some more. The maiden transitions to forward flight went so well that with a little tweaking I think they may become "hands off".
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Old Jan 07, 2015, 10:07 AM
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[QUOTE=leadfeather;30401704]The Y cable thing surprised me too. With just the tilt servo Y and the elevator Y active the stability was only effected a little, but when I put the wing on and hooked up the ailerons servos (a Y at the Rx and then another Y for the aileron servos) it got really bad, particularly pitch stability.

Once I went to the separate Rx's for the motors and for the servos the Otter stayed super stable ... probably the most stable hovering VTOL I've done to date.

Running two Rx's was a first for me. I'm glad it seems to work well. The weight of the 2nd Rx is less than the Y connectors it replaced.

QUOTE]

I am glad you found a solution with the 2 RX's, but there is something going on that we don't understand, and that worries me. There may be something marginal about the DC power distribution, or perhaps the signal grounding. Whatever it is, I hope you didn't just temporarily make it better so it comes back to bite you later.
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Old Jan 09, 2015, 06:00 PM
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I did some more finishing touches. All of the decals for the Otter came from an Easy Glider built years ago but decals were never applied.

Now I just need some nice weather to move in so I can fly.
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Old Jan 09, 2015, 06:06 PM
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Did you ever install the OpenAero-VTOL code, or are you still running the stock code?
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Old Jan 09, 2015, 06:21 PM
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Quote:
Originally Posted by Ran D. St. Clair View Post
Did you ever install the OpenAero-VTOL code, or are you still running the stock code?
Still the stock firmware. OpenAero-VTOL will be coming on board before long. For my own personal experience I wanted to see if it was possible to make a good VTOL without interfacing with a computer.

I should mention the KK is far easier to use than the Wii based control system I've used on my other VTOLs.
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Old Jan 09, 2015, 08:27 PM
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My first VTOL (of the modern era) was the predecessor to the VTOL-Trainer (Bixler) with a similar layout as the Quad-Otter. It flew on the Stock KK2.0 firmware of the time and flew fine. This configuration just happens to perform very well even with the motor stability enabled in forward flight. All I did was turn off AutoLevel when in FFF so it wouldn't go crazy when doing loops and rolls. That and I did not use any I feedback, just P.

I am interested in hearing what you think of OpenAero-VTOL once you get into it. It is certainly more complex to set up than the stock firmware because it has so much more power. I look forward to hearing how logical (or not) you think it is.
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Old Jan 10, 2015, 05:04 AM
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Quote:
Originally Posted by Ran D. St. Clair View Post
My first VTOL (of the modern era) was the predecessor to the VTOL-Trainer (Bixler) with a similar layout as the Quad-Otter. It flew on the Stock KK2.0 firmware of the time and flew fine. This configuration just happens to perform very well even with the motor stability enabled in forward flight. All I did was turn off AutoLevel when in FFF so it wouldn't go crazy when doing loops and rolls. That and I did not use any I feedback, just P.

I am interested in hearing what you think of OpenAero-VTOL once you get into it. It is certainly more complex to set up than the stock firmware because it has so much more power. I look forward to hearing how logical (or not) you think it is.
We think along the same lines. I also used the same quad configuration (for the same reason) on my Jump Jet project (over two years ago already) with very good results. The Wii controller was left in "hovering quad" mode all the time and I used a tilt servo and servo slower hooked up directly to the Rx. One of the more interesting aspects of the Jump Jet project was how well it flew without control surfaces. With just a little up tilt of the fans in forward flight I had good enough flight control to perform loops and rolls without control surfaces on the wing or tail.
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Old Jan 29, 2015, 09:53 AM
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I had a lucky break in the weather last evening; warm very low wind; unusual here this time of year. I ran out right at sunset to fly; I was hoping to get some nice video to show the Otter off. Had some great flying; multiple transitions in a single flight and some aerobatics. Rushed home only to find out the camera was badly out of focus the whole time; grrrrrrrr!

Oh well, maybe time to buy a new camera while I wait for the next break in the weather.
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Old Feb 09, 2015, 07:28 PM
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Here is some video from this evening, just after the sun had set. Hovering is easy with the auto level. For the transitions to forward flight, I skip the hybrid mode and flip the switch all the way forward. So easy, and hands off. Transitions back to hover is also very easy. This is really fun.

Quad Otter Testing (3 min 34 sec)
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Old Feb 10, 2015, 07:15 AM
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Very nice...what was wind speed that eve?...H
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