Saturday, January 24, 2015

UAS Excelsior Alpha - Vectored Thrust Tricopter

I was doing some fast, straight line FPV flying with one of my quadcopters and a few things struck me about how multicopters fly in a straight (horizontal) line;

  • The more you pitch forward (to go faster) the less aerodynamic you are
  • The angle of the pitch actually serves to reduce lift, effectively fighting the motors
  • Finding the maximum forward speed is a risky, manual process.

So what if you wanted to build a multicopter optimized for forward flight?  I've seen some 250mm FPV racers that actually had the front two motors angled forward to increase the forward speed at a lower pitch angle.  I found myself asking - what if you could dynamically actuate the front motors forward instead of pitching the whole aircraft?  (Similar to the motors on an Osprey, but sans wings.)

Vectored thrust on multirotors is uncommon, but not new.  Still, this idea has a singular purpose which makes working out the details and controls a bit easier.

So, I decided to build one.  I give you Excelsior Alpha - my proof of concept Vectored Thrust Tricopter:

And here it is in flight:

I settled on a tricopter design because I liked the idea of yaw (rotation around the Z axis) control being completely independent of the individual motor speeds.  Otherwise, vectoring the front motors forward is going to have some weird roll/yaw side effects.  Tricopters don't alter the motor speeds for yaw. Instead, they vector the tail motor on the Y axis to rotate the aircraft around the Z axis.

For the thrust vectoring, I decided the simplest design would be to mount the front motors on a single shaft running along the X axis at the front, and then couple that shaft to the airframe in a way that allowed a servo to rotate it - effectively pitching the front motors fore and aft.

Here's a video of the drive actuator mechanism: (Note the frame plates have changed a bit since this was taken.)


Build One Yourself!

DISCLAIMER I:  This is a largely unproven design.  It needs some improvement. I hacked it together in a couple of weeks as a proof-of-concept.  I'm only sharing it because in spite of these facts it worked better than I expected, and I've had lots of people ask me for the build details.

DISCLAIMER II:  This is not a beginner project.  I do not recommend undertaking this if you aren't already familiar with RC TX/RX hardware, flight controllers, ESCs, and the like.   I'll list the parts, but I unfortunately I don't have time to write a walkthrough or answer questions about the basics of multirotor construction / configuration / flight / &etc.


Purchased parts: 

(Links go to items I used from hobbyking.com, feel free to substitute / experiment!)

Main components
498x12mm Carbon Fiber Tube (drive motor arm, cut to ~290mm length)
OrangeRX R100 DSM Satellite Receiver (or use a traditional R/C receiver)
ZIPPY Compact 1800mAh 3S 25C Lipo  (3S 1300mAh - 2200mAh seem to work well.)
2 x 7x4.5 3-blade counter rotating props

Misc assembly hardware  (May be incomplete!)
M3 screws (~14mm?) & nuts
heat shrink tubing (for solder-on bullet connectors)
4" zip ties
velcro strap (hold the battery)

3D Printed Parts 

(main frame plates and various mounts)
I've uploaded all the parts to Thingiverse:

I printed them from PLA at .2mm layer height on my Printrbot Simple Metal.  (~25% infill I think)

You'll need to print:
1 x excelsior_top_plate
1 x excelsior_bottom_plate
2 x 12mm_collar (used to hold the motor arm in position)
1 x 12mm_sleeve_servo_arm 
1 x servo_arm
1 x 12mm-to-14mm-tube-adapter (to mount the Talon Tricopter Tail Mount to the 12mm tube)
4 x 12mm_tube_clip (optional - I use 3 for the ESCs and one to hold the XT60 battery clip)

Miscellaneous Construction Notes:

I drilled a 3mm hole through the CF tubes to mount:
 - The motor mounts
 - The collars left & right of the main plate
 - The sleeve servo arm
 - The tail servo assembly & adapter

In each case I positioned the part first, then drilled the hole (in each side separately if necessary), then threaded the screw through the part and tube together.

The main motor arm is 290mm long because that was the longest length of a broken 500mm tube leftover from a crash that I happened to have on my bench.  It seems to work well, but that size is fairly arbitrary as it was determined by chaos theory, not computation.

Flight Controller Setup

MORE TO WRITE ON THIS SOON!

Basic setup:
  • I reflashed the FC with Cleanflight and the modified it (provide patch?) to allow me to control an additional servo on S2 using the AUX3 channel input
  • I changed the channel map put AUX3 on the elevator (pitch) stick, and pitch on the AUX3 channel.
  • I put the FC in 'ANGLE' mode at all times so it will hold the craft level when I actuate the thrust vectoring.  This allows me to adjust the pitch with the AUX3 knob (as a result of the remapping above) and control the forward/reverse vector with the elevator stick.

You could accomplish something similar without modifying the FC software by using a traditional R/C receiver and connecting "ELEV" from the RX to the vector servo instead of the FC.  Just be sure to put the FC in "Angle" mode since you won't have any pitch control unless you connect an analog AUX channel to the FC Elev input.


If you undertake this, let me know what happens and GOOD LUCK!  ;)


Sunday, January 4, 2015

Phoenix (Nebula Class) UAS - Status: LOST

Class: Nebula (F330)
Date Built: 2014.04.22
Date Lost: 2015.01.02

Today we declare Phoenix - my primary FPV quadcopter - LOST.  Its final flight was Friday, 2 Jan 2015 in the large private dirt field that I like to fly at.  I was performing some aggressive acrobatics when something on the quad failed, sending it into the infamous quadcopter death spiral.

Despite knowing where it failed and roughly where it went down - the quad was not located at the crash site.  I had a colleague join me in the search, and we gave up after an hour.  Two subsequent returns to the area and I have concluded that we can't find it because it is in fact no longer at the crash site.  My current working theory is that someone from the neighboring park saw it go down and took it in the few minutes between the crash and my going to retrieve it. :(
This was the aircraft that I learned FPV flying on. It will be missed.

Phoenix final specifications:


  • Frame: F330 Quadcopter Frame
  • Motors:  Turnigy D2822/17 1100kv 100W
  • ESCs: Turnigy Plush 10A
  • FC: MultiWii Pro (Mega2560) running MultiWii 2.3
  • RX: OrangeRX R100 DSM2
  • VTX: Boscam TS-351 200mw 5.8GHz
  • OSD:  MinimOSD running MWOSD
  • Camera:  GoPro Hero 2
  • Props:  7" x 4.5" x 3 blade orange
  • Battery:  Turnigy 3S 3000mAh 20C


Some memorable videos taken with this particular quad:





Friday, December 26, 2014

Beginner's Guide to Flying a Quadcopter

So you got a quadcopter or other multirotor aircraft recently. Welcome to the hobby! Here's some notes about getting started, learning to fly, and what to watch out for.

This is not an all-inclusive list, and I highly recommend also reading / watching some other guides. Above all else, be safe and be mindful of where you fly. Don't fly over unwitting crowds or people, over other people's property without their permission, or any place that might pose a hazard to aircraft, automobiles, or people.

I highly recommend learning to fly with an inexpensive "nano" quadcopter such as the Blade Nano QX or the Hubsan X4 (Amazon).  If your first quad is a DJI Phantom 2 or something of similar size and weight, please consider buying an inexpensive nano quad like the ones mentioned here and learning on that first. There are a few reasons for this:
  1. You will crash. Crashing a $60 quad is a lot easier to deal with than crashing a $600+ quad.
  2. Small, lightweight nano quads survive lots of crashes. 330mm, 450mm, and larger quads almost never survive a crash without some damage.
  3. Small, lightweight nano quads don't hurt when they hit people, animals, or things. Larger quads can.
  4. Small, lightweight quads require you to learn flying and orientation skills that are necessary to fly larger quads. Larger quads are more stable and have more advanced features, which can dangerously mask your lack of skill until it's too late. By learning on the smaller, more agile, less advanced quads you are actually becoming a competent enough pilot to handle the larger ones. 
Don't be the guy flying the larger ones who doesn't have the competence to handle it.
{end rant}

Basics

Always power on the quad with it sitting still and level. All quads need a few seconds sitting level to calibrate the MEMS gyro / accelerometer each time they power on. If you apply throttle and the quad tries to go off in one direction violently: Land, unplug the power, plug it back in and let it sit level for 10 seconds again.

Keep the "trim" settings on your controller centered. If the quad "drifts", it's not because your trim is wrong. That's not how quads work. There's something else going on.

Speaking of hovering: "Level" flight and "stationary" flight are not the same thing. Most quads have an auto-level mode. This does not mean they will hover in a stationary point without assistance. In fact, almost no quad will do that. (Certainly no nano quads will.) When you see a quad hovering in place and not drifting in any direction, there's a pilot who's moving the controls fairly constantly to correct for drift. That is normal. It actually takes a fair amount of practice. (When you see a quad hovering in place, do a flip, and then continuing to hover in that same place, you're looking at a pilot who's had hours of practice doing that. cough, cough.)

LiPo batteries:


Once you get a feel for how long the battery lasts, try and stop flying at about 80% drain instead of 100% (e.g. when the copter gets weak instead of when it just won't fly anymore.) This will more than double the lifetime of your batteries.

If you can, resist the temptation to immediately put the battery on the charger after you've drained it. (That also shortens the life of the battery.) Let it "rest" for a while before charging it again. 15 minutes is probably long enough for those little 1S batteries. 30-60m is more appropriate when you move up to larger quads with 3S & 4S batteries.

Yes, given the above two points you'll definitely want some more batteries.

Here's a good LiPo battery guide, if you're interested in knowing more about them.

Throttle & Orientation

The hardest skill to master when learning to fly a quadcopter is maintaining orientation. The second hardest skill is controlling throttle while you're also controlling other maneuvers. (This is why early on you always either suddenly hit the ceiling or the floor when you're surprised.)

Fly it "tail in" (tail facing towards you) for a while until you get comfortable with maintaining a stable altitude throughout. Tail in is the easiest way to fly, because you and the quad are facing the same direction. In this orientation, the controls are natural feeling. For a while, it will feel like that's the only way you can fly, and if the quad gets yawed (rotated around the Z axis) more than 50° to either side you'll quickly lose control. Patience!

Once you've mastered "tail in" flying and start to get bored with it, it's time to learn to fly at different orientations! (I don't recommend trying this before you have some experience and don't have to think about the throttle controls anymore. Stick to "tail in" flying until you're comfortable.)

Here's what worked for me when learning orientation:

Left / Right Passes:

Start with the quad in front of you and facing to your left. (Its left side is towards you.) Take off. Practice hovering. Remember that LEFT is towards you and RIGHT is away from you. Make a 180 turn by yawing to the right. Now it's facing right and the RIGHT side is towards you. Practice hovering like that. Repeat until you can make the turns and then maintain control without having to think about it so much.

Once you get that down, do the same thing but have the quad move forward before the 180° turn. Fly it by you with the LEFT side towards you, have it turn 180°, then fly it back by you with the RIGHT side towards you, turn 180°, &etc.

Boxes

Once those maneuvers seem easy, add a straight out leg and straight in leg to each side so you're actually flying a large square in front of you (with the quad always flying forward.) Remember that on the "inbound" leg the quad is facing you so left and right will seem reversed. The same is true for the Left/Right passes though, so you should already start to have a feel for that.

Figure Eights

Now, try flying a figure eight in front of you. (With the quad flying forward throughout the maneuver.) If you can do it, congratulations. You have a solid handle on flying in all orientations.

Completing all of the above comfortably took me months. Feel free not to tackle any of it for a while. ;)

Outdoor flying

It's inevitable. You've been flying indoors a while, and you're tired of hitting walls and ceilings. So you think "It's nice out, let's go OUTSIDE!"  DANGER WILL ROBINSON.

These things are incredibly small, incredibly fast, and there is no documented service ceiling. They're often capable of flying higher than you can see them at!

You will lose control of the quadcopter.  How you fly and how you react when things go wrong are the difference between having to repair the quad or having to spend two hours in vein looking for it, giving up, and then sheepishly buying a new one.  I have lost three quadcopters so far.  Lost ... as in, they flew away and I never found them again.  It's easier to do than you think.  Here's some advice to try and prevent that.

  • Get low.  Don't fly above rooftops, treetops, or other nearby obstacles. (Certainly not if you haven't mastered ALL of the orientation lessons above.) A funny thing happens five feet above the immediate obstacle line: WIND. There's probably a steady breeze 20 feet up that doesn't exist at ground level. A steady breeze can carry your nano quad away faster than you can bring it back to you. The turbulence between the ground level and that steady breeze can also cause your quad to make unexpected turns, which can throw off your orientation.
  • Be willing to DROP.  At some point you will find yourself higher and/or farther away than you intended. Your instincts will be to add throttle and fly it back. BE WILLING TO ABORT and just cut throttle and let it crash. It's better to have to repair a quad than to not know where it ended up.

Flyaway Recovery

This is by far one of the hardest skills in outdoor quadcopter flying, so it's going to get the longest treatment. I don't think this applies as much to other R/C aircraft, because most R/C aircraft won't keep flying if you become disoriented to begin with. They just crash. But many quads will obediently keep themselves level and in the air even if you and the quad are on completely different pages about which way it's facing and/or moving... and this is how quads get lost.

In my (contentious) opinion you should master flyaway recovery with nano quads before you ever fly anything larger. Dropping a nano quad over the visible horizon is annoying, and possibly a slightly expensive ($100) lesson. Dropping a 4+ pound quadcopter with a 3S lipo battery over the visible horizon could cause serious injury or property damage. Better to learn the safe and cheap(er) way!

The set-up is this:

You're flying outdoors, a little higher than you're used to, maybe doing some fast maneuvers or trying something new, when suddenly you realize the quad is doing something other than you expect. It takes a few seconds to register this discord in your head and by the time you do the quad is a hard to see speck over the top of your neighboring horizon / obstacles. E.g.: It's either over and beyond a nearby treeline or rooftop. You're scared to cut throttle, because you don't actually know where it will come down. To not lose sight, you've had to add power, so it's now higher up (and further away). What do you do?!?!

This is a terrifying situation. Here's the reality:  Without experience, you are about to lose your quad and there's probably nothing you can do about it.  If it were a larger, advanced aircraft this is where many hit the "Return To Home" switch and pray. (Whether that's the Right Thing To Do™ is a subject for another day.) If it's a nano quad you really only have two options: A: Try and regain orientation at the risk of it going even further away, or B: Just give up, cut the throttle, and go searching for it.

Everyone tries option A first. Sometimes for too long. Two of my three aforementioned lost quads were this exact situation. I fought and fought to get it back and eventually watched in vein as it disappeared and was just.... gone. (The third was actually an equipment malfunction that I couldn't do anything about.)

When this happens to you (cough, cough) my one remaining piece of advice is this: DON'T TURN OFF THE TRANSMITTER. Pull the throttle to idle, run to wherever you think it may have came down. Stand still for a second, take in the surroundings, then "goose" the throttle a few times and listen. You may be able to hear it whining and trying to spin up the motors. This may be how you locate it. If not, well, how long you spend looking (and to what extent) is between you and your deity of choice. Good luck. :-P One hint, though, NANO QUADS are never as far away as they look. In fact, it's probably only half the distance away that you think it is, so start there.

Lost Orientation Recovery During a Flyaway

Let's go back to the point just before you lost it. You can see it, it's a speck on the horizon, and you don't know which way its facing.

Here's what you do:

Regardless of orientation:
  • Calm down. You're going to panic. Try not to "panic fly" though. 
  • Avoid any YAW inputs. (It will only make things worse) 
  • Avoid abrupt control inputs. You can lose control easily. 
  • Avoid full deflection of the controls. (Don't push any sticks all the way to the edge!) 
  • Turn on auto-level (if it's not on already.) 
IF you think the quad is facing TOWARD or AWAY from you:
  • Very gingerly try "LEFT ROLL" first. Try moving it left for a second or two. 
    • If it moves LEFT: Center the stick, pitch it back gingerly and hold it and just patiently wait. 
    • If it moves RIGHT: okay, it's actually facing you. pitch it forward gingerly and hold it, and just patiently wait. 
IF you think the quad is facing LEFT or RIGHT respective to you:
  • Very gingerly try to PITCH FORWARD first, for a second or two. 
    • If it moves LEFT: It's facing left. Center the stick, roll it left gingerly, hold it, and just patiently wait. 
    • If it moves RIGHT: It's facing right. Center the stick, roll it right gingerly, hold it, and just patiently wait. 
If you don't know which way it is facing (or the above maneuvers don't result it it moving left or right respective to you):

This is the most dangerous situation, because your attempt to determine orientation might actually send it out of sight. The good (?) news is, there's only a 1:4 chance that a direction you pick will be directly away from you. So ask yourself, do you feel lucky, punk?

Pick one of the above and try it. If you've already tried LEFT, then try FORWARD (or vice versa). I like to try "LEFT ROLL" first but that's just me. The main point is be deliberate and methodical in your attempts, don't just haphazardly try things. Try LEFT ROLL for a couple of seconds and if it doesn't move LEFT or RIGHT clearly, then counter with the same amount of RIGHT ROLL for just a second to freeze it and then move on to trying PITCH FORWARD instead. If you're slow and deliberate you, with practice, will be able to determine which side is facing you.

In all of the above situations:

Once you figure out which side is towards you:

  • Go ahead and bring it directly towards you by pitching / rolling it towards you. Do not attempt to "turn" or yaw it back into a more comfortable orientation. You might under/overshoot the turn and then you'll have to start all over again.
  • Be patient. You're panicked, your heart is racing, and "time dilation" is in full effect. Resist the temptation to yank the controls, and be willing to trust that the quad is coming towards you based on a small (25%?) control input even though you won't be able to tell for the first several seconds. If you direct it towards you and nothing seems to happen, then IT'S PROBABLY WORKING. Just hold it and count to five and you should suddenly see that it's getting bigger as it comes home. This is the most satisfying feeling in the world, btw.
  • Once you get it back: Land, sit down, breathe. You're more panicked than you realize. Losing control of a flying thing and then regaining it is a lot more mentally taxing than you imagine, and you probably need a minute to collect yourself. 
Read all of the above and visualize having to do it a few times, and you might just pull it off the first time it happens to you! ;)

Happy flying!

Tuesday, November 18, 2014

Grand Canyon flight / Magneto Failure

So last week my wife and I left the kids with the grandparents and headed for the hills in my '67 Skyhawk for my 40th birthday.  Our plan was to fly from Palo Alto to the Grand Canyon by way of Las Vegas.

Day 1
Flight One: Palo Alto (KPAO) -> Shafter / Minter (KMIT) Mohave (KMHV)


Route on Skyvector.com

Departed as planned, but the haze in the south central valley was terrible. Bakersfield reported "Skies clear, visibility 2 1/2 miles" (That's not haze, it's fog!) So, I amended my destination and went over the hill to Mojave (KMHV) instead. While having lunch I double checked the rest of the route and decided since we were already in the Mohave desert to go ahead and continue via the Trona, CA corridor instead of going South to Palmdale.

Flight Two: Mohave,CA (KMHV) to Henderson, NV (KHND) via Trona Corridor

Route on Skyvector.com

I've done this route a few times now. This was the first time into HND that LAS approach refused to clear me into the Class B when coming east through the Columbia Pass... which means I had to descend under the shelf, continue east until I was due S of HND and then descend to within about 1000' of those hills to fly towards HND. No big deal (it was a very clear day) just not what I was expecting.


Day 3: KHND to KGCN (Grand Canyon Airport)

Route on Skyvector.com





- Flawless. Got radar service from HND and LAS on the way out, and was handed to LA Center for the rest of the flight. I had planned the flight to go over the Hoover Dam and BLD VOR, but Vegas Approach wanted us further south than that for arriving traffic. No big deal.

LA Center confirmed that I was familiar with the Grand Canyon special VFR rules (I was) and had no further questions after that. Winds were 20G30 on the ground, so it's probably good that the special VFR rules kept us 3K+ above it anyway. At 11,500 it was smooth.

GCN: You're advised to remain with your aircraft upon landing until the FBO comes to get you, since there's a TSA area between the ramp and the FBO. Yay for security theater. (Taxiing my aircraft around is safe, but walking isn't!) Other than that oddity, and the $7.20/gal avgas, it's just like any other GA airport.


Day 4: KGCN -> "Dragon Corridor" (N) -> "Fossil Canyon Corridor" (S) -> KHND

Route on Skyvector.com







Scenic flight over the canyon tour corridors before departing west. We donned our O₂ cannulas again and took off into the same 20+ knot winds we landed in yesterday. GCN tower was very friendly and continued to provide traffic alerts as we did circling climbs south of the Supai sector to get to the required 11,500 feet for flying the corridors to the North. It was turbulent near the ground but smoothed out nicely once we were over 2k AGL.
Man, that is a big canyon! We continued north past the Dragon Corridor to the edge of Marble Canyon before turning back west and south. There was snow on the ground in the shadows north of the canyon. Monitoring the tour operator frequencies made us aware of the constant stream of helicopters criss-crossing the canyon beneath us. It's hard to imagine how they manage those beasts over those ridge lines at 8500 MSL in gusty 20-30kt winds, but they didn't seem fazed by it.

We picked up LA Center again south of the Fossil Canyon Corridor and flew back to Henderson without issue.


Day 5: KHND -> KMHV -> KPAO (Returning home)

Departed back the way we came, across Death Valley and through the Trona corridor. Stopped in Mojave for lunch and gas, only to discover upon my pre-flight check that my left magneto was no longer functioning at all. (It worked fine prior to departing Henderson.)

Returned to ramp, aborted flight, arranged a rental car from the neighboring Ford dealership. :(

Thankfully, Kenneth Hetge in Tehachapi, CA was available to do a field repair. It turns out both mags were due for an overhaul. The coil on the left one had cracked and finally died. Aero Services in Van Nuys overhauled both, replaced the coils, and Ken reinstalled them on the aircraft. Two days and two AMUs later I returned to Mojave with the rental car to retrieve my aircraft without further incident.


Some other airplane GoPro shots

Tuesday, June 24, 2014

FPV Flying, The FAA, and the rules.


This morning my inbox exploded with articles about the FAA's recent Interpretation of the rules for R/C flying. Specifically with their consideration for "First Person View" (FPV) flying. (Flying by reference to a video transmitter on board the model aircraft.)

http://motherboard.vice.com/read/the-faa-is-trying-to-ban-first-person-view-drone-flights


http://www.faa.gov/news/press_releases/news_story.cfm?newsId=16474&cid=TW223


http://www.faa.gov/about/initiatives/uas/media/model_aircraft_spec_rule.pdf

Summary: According to the FAA, FPV flying in the US is not legal, even with a spotter.

Details:  [14 CFR Part 91 , Docket No. FAA-2014-0396, "Interpretation of the Special Rule for Model Aircraft"]:
Under the criteria above, visual line of sight would mean that the operator has an unobstructed view of the model aircraft. To ensure that the operator has the best view of the aircraft, the statutory requirement would preclude the use of vision-enhancing devices, such as binoculars, night vision goggles, powered vision magnifying devices, and goggles designed to provide a “first-person view” from the model.
Such devices would limit the operator’s field of view thereby reducing his or her ability to see-and-avoid other aircraft in the area. Additionally, some of these devices could dramatically increase the distance at which an operator could see the aircraft, rendering the statutory visual-line-of-sight requirements meaningless. Finally, based on the plain language of the statute, which says that aircraft must be “flown within the visual line of sight of the person operating the aircraft,” an operator could not rely on another person to satisfy the visual line of sight requirement. [...] While the statute would not preclude using an observer to augment the safety of the operation, the operator must be able to view the aircraft at all times.

My reaction:
On the surface, that seems rational. Where it falls apart is that FPV flying doesn't necessarily have to be done in locations or at altitude where such oversight makes any sense at all. I am 100% on board with the idea of preventing people from operating R/C aircraft without LOS at high altitudes in places where I might be in my Cessna. 

But does that mean it should be illegal to wear FPV goggles and fly around a field, away from any airports, at < 200 feet elevation? If my Cessna is ever there, it's because I'm doing an emergency landing. Randomly encountering an R/C aircraft (or bird, or baseball) is fine with me.

Does that mean it should be illegal to fly aircraft using FPV equipment under tree canopies (where there can't possibly be other aircraft?)

The FAA rule is draconian. FPV flying is becoming not just a hobby, but a sport. And by passing draconian rules like this the FAA is taking rational conversation off the table and ensuring that thousands of people will just disregard them and break the rules.

And that puts me at greater risk. Thanks a lot.   

FAA , if you are listening - let's have a conversation about this.  Blanket restrictions on very popular, widespread, and largely safe activities are not a good idea.  Let's discuss where FPV flying does and doesn't make sense.  Let's discuss where interference with aviation operations may and may not happen.  And let's discuss how to properly educate the FAA, pilot, and R/C communities about each other's activities, so we can coexist in a safe and harmonious way.  

Today it's a battleground, and each side is largely misrepresented by misinformation to the others.  This isn't the way forward.

Monday, June 16, 2014

Donkey Quad


Update:  Have one?  Building one?   Click Here: Donkey Quad Manual

A while ago I bought an inexpensive HobbyKing F330 frame, thinking I would use it with some SunnySky X2212-9 1400KV motors and 8" props I had.  Unfortunately, that turned out to be a very unstable combination.  It was fast as hell, and good at aerobatics, but I couldn't tune the shakes out of it.  I decided those motors were just too big for that small 330mm frame.

On a whim, I was looking at the cheapest 3S capable outrunners that HobbyKing sells when I ran across these ugly duckings here:

The Donkey ST2004-1550kv, "When pulling power matters and looks.. well.. just don't."

HobbyKing Donkey ST2004-1550kv
The mounts are nonstandard ugly aluminum tangs with holes in them.  The sticker oddly says "ST2204-1550kv" whereas the website part number os "ST2004-1550kv".  They have 3mm shafts, but don't include any collets or prop adapters.

But, they're dirt cheap, they work as advertised, and they're seemingly a lot more crash resistant than the similar-rated Park300 1400kv motors I used to use on a similar sized quad.

I had to use 4" zip-ties to attach them to the F330 frame.  I did it by threading the tie down through one hole, under the frame, up through the opposing tang, and then putting a cut off zip-tie "head" on the other end.  Repeat for the other set of tangs and you have a solid mount with no screws.  ;)
Mounted w/zip ties

Paired with some disused Afro 12A ESCs, a MultiWii MicroWii FC, OrangeRX R100 receiver, and some 7x4.5 props and I have a small, super light, fairly agile quad.  It's not the fastest one I own, but it's light and agile enough to do in-place flips or double-descending-rolls.

It turns out to be a joy to fly, and I've been spending more time with it than my more expensive quads.

Several people have asked me for a parts list, so here it is:
QtyItem
1F330 Frame
4Donkey ST2004-1550kv Brushless Motor
4Turnigy Plush 9g 10A ESC
1MultiWii MicroWii ATmega32U4 Flight Controller
1OrangeRX R100 DSM2 Satellite Receiver
1XT60 Male power connector
4Props: 7045, 7060, or 8038 (2 CW & 2 CCW)
43mm prop adapter
1ZIPPY Compact 2200mAh 3S 25C Lipo

A few build notes:

  • Use 4-inch zip-ties to attach the motors (described above)
  • You can use an XT60 to 3.5mm bullets power distribution cable instead, especially if you choose 10/12A ESCs that have 3.5mm bullets.  I built one this way, and one with directly soldered leads.
  • You'll have to bind the R100 to your transmitter with a separate receiver (or by flashing special Spektrum Satellite Bind Code to the FC first.)
  • This quad can actually carry a 2600mAh battery for 10+ minutes of flight time!
  • Add a lipo alarm to warn you when the battery is low.
I have two built right now.

One with 7060 phosphorescent props, UV LED strips on the arms, and a 4W spotlight:




The other with 8038 props, a GoPro Hero 2, Minim OSD board, and video transmitter on it:


Saturday, March 8, 2014

Ducky EDF Quad - Motor Mounts and Second Test

I had the EDFs mounted to the frame with zip ties for the first test.  That proved a bit unstable.  I also had the problem of the motor housings sticking down lower than the rest of the quad, which posted a threat to them on landing.

Talon motor mount
So, I decided to kill two birds with one stone by making some EDF mount brackets that extended vertically below the bottom of the motor housings.  The Turnigy Talon frame I used included these aluminum "T" mounts, intended to be mounted horizontally at the end of the tubular arms to allow you to mount the motor on top.  I simply turned them 90 degrees so that the flat face was vertical to align them with one of the two flanges protruding from the side of the EDF housings.

To mount the EDF flanges to them, I fabricated a mounting bracket to use as a clamp.  I used an old license plate frame that I cut into four equal length parts and drilled matching holes in:

Four mounts cut from a discarded license plate frame

Drilled and mounted to EDF with motor bracket

Mounted to quadcopter frame

I filmed a new test flight with the modifications.  I wasn't really thinking about the fact that I was filming during the flight, or I would have put more effort into keeping it closer to me.  Overall, it flies really well.  It has a slight left yawing tendency, but I suspect that is because I haven't really done anything to precision align the EDFs.  (I just eyeballed them and clamped them down.) 

I avoided using 100% power to see how it did on flight time.  With the flying you see it used about 70% of the battery life in just over 5 minutes.  So, not bad!