10/23/12 flight

Record of flight 10-23-2012

Batteries; QPA and B were fully charged and only used about 2700 mAhr each with internal resistances still 1.6-1.9 mOhm.  Tx was fully charged at 11.4 v.  Throttle curve is working very good.  We saw a noticeable increase in copter stability after balancing motor cans, props and replacing a motor (#8) with a bad bearing.  The power distribution board and all esc's were replaced due to sporadic serial communication errors.

Copter Black Box files: GPS00003.gpx and GPS00004.gpx  Note: It looks like the copter's clock is fast by about 4 hours.  Both flights were 221 sec (3.68 min) and 205 sec (3.41 min).  Four transients 75 m long separated by about 20m,  Defined by 6 way points.  We are rotating the camera to horizontal after take off and before landing to help with ground clearance.  Typical parameter download: (note good elevation and speed curves.

Camera: Cannon T2i
We flew twice, once with f-stop of 18 and once at 22 (maxed out) with fixed focus (taped down). These are simply way too high and drop the shutter speed to nothing. Next time we should fly once with 1/500 shutter and once at 1/1000 shutter and see what we get. We also need to keep in mind that we may need to raise the ISO some (from 200) to make the higher shutter speed work.

Pirate Eyes

We have tried to shoot some video from the copter and found piloting Line of Sight (LOS) is very difficult.  One needs to keep LOS to comply with current regulation for sUAV in US air space FPV guidelines  Currently most people use goggles with small LCD screens which precludes LOS flying.  A new product called Pirate Eyes has a small monocle that allows one to see video transmitted from the platform but also to have LOS on the copter.  Below is a review I found for RCGroups: 
Hello all,
I ordered a Pirate Eye in a desperate attempt to make our pilot's life a bit easier and to get better aerial shots in return. The main problem for the pilot was that he was at no point able to judge distances adequately and framing shots perfectly flying line of sight only. Our camera operator's ground station wasn't helping, as the pilot had to stand close by and look him over the shoulder every now an then to see the live-footage. 

So here's our two cents wrapped up in a little review:

We ordered the "hobby version", as the pro version wasn't available. Not a big deal, as the only difference is that the pro version has both the smokey and the clear glasses and comes in a case. 

In detail, our version came with the smokey glasses with the display and video adaptor attached, a nylon pouch, a cleaning cloth and a small goody bag containing an allen wrench,
distance pieces for the monocular, a neck strap and spare rubber rings for attaching the video cable to the glasses.

The overall quality of the set is great and IMHO justifies the price of around 400 Euros. If I look at the overall price of our aerial platform, this is peanuts... but as I said, that's just my personal opinion.

On to the important stuff: We only had the chance to try the Eye twice over the weekend for a couple of hours, but were initially pleased with the results. Setup is hassle free, the glasses fit perfectly and the display gave us crispy live-video out of a Canon 650D. Our initial worries that the tiny monitor
might fog-up as it frequently happens with closed systems like the Fatshark due to a lack of venting fortunately weren't confirmed. However, we have yet to try it under warm and humid conditions...

Flying was a breeze and we could see that the pilot's confidence got a boost. While maintaining a steady line of sight at most times looking straight ahead, he could easily 
look down at the display and frame shots precisely. For us that's a huge plus, as we are currently flying a no-pan-gimbal and all pans have to be done by the pilot...

I know this might sound a bit over-enthusiastic, but if a product caters perfectly to my needs, I'm more than happy to help promote it a bit. Especially when it's coming from a small niche company.

Just a final note to finish this up: The pirate eye is not made for FPV-flying. If you want to immerse yourself, buy a Fatshark or similar. If you are, however, into aerial video and photography, give the Eye a chance and try it out.

Hope that helps!

Cheers,
Danj

Caps and Cans

Since taking pictures we have been experiencing focusing problems with the Cannon T2i.  We are moving at 3 m/s at 60 m AGL and take pics every 1.5 seconds.  Other will need to chime in and fill in camera settings and transect information.  Somethings we have well focused pictures and other times not.  To eliminate copter vibration as a cause we balanced the props with a magnetic prop balancer:

 The light tip had drops of CA glue added to bring it into balance.  Next, we went to balancing the motor cans (without prop).  Right now we are just going by sound, feel and the copter ACC display in MKTools.  When we tried adding tape to motor #7 it made an awful screaming sound and the change in rpm goes in huge steps.  We soldered in another motor and we know the esc was bad.  This was our second esc to fail.  Each esc has a deformed area on the MOFSET closest to the inboard capacitor.  It looks as thought the cap has overheated and melted into the component.  The esc was ordered as well as new 355 uF/25V caps.  We will also inspect and replace all aftermarket caps and then silicon glue each down.

Update 10/2/12
I changed out esc #7 and #2.  Esc #2 had tp be change out because I tried to take out the capacitors and had to really heat up the board.  I did not want to risk a motor failure in flight so I changed it out.  I consider it $70 buck of insurance.  I also solder in one of the capacitor backwards.... all the anodes go on the outside of the board and are clearly marked.  I also used silicon to support the capacitors since this can be a source of vibration.  I made a table of motor wire and their connections to make assembly easier:

Motor       Color sequence (looking down on copter and going clockwise)
1               BPG
2               PGB
3               BPG
4               PGB
5               PBG
6               PGB
7               BPG
8               PGB
P-purple, G-grey, B-blue

I will continue balancing but this time I will use a laser and mirror like this:  http://www.youtube.com/watch?v=QnjflLDxQQU

What is he doing out there?

I flew a quad for while but always lost orientation.  When I was flying a tricopter I could tell front and back much better. So I built a V-tail quad.  I have best of both worlds.  Excellent yaw authority but no mechanical linkages.  I also get the added stability of a quad but with better orientation from a distance.  Got it finish and programmed a multiwii board (Quadrino Zoom - 9 degrees of freedom, Acc, gyro, compass and barometer) a friend loaned me.  Did a late night flight with the LED's blazing in the neighborhood.  Heard my neighbors say, "What is he doing out there?"

Got the idea from here: http://www.rcgroups.com/forums/showthread.php?t=1622447

Used Arduino 1.0 sketch with V-tail and Quadrino Zoom commented.  Used the Multiwii 2.0 configuarator to setup board.  Powered board with a single bec from motor 3.  

Got to tune the PID's since I have some twitching.  Will update when/if I get it dialed in.

ArduCopter 2.7.3

There is a new release from ArduCopter that looks to have made major improvements.  It might be time to grow the copter fleet.  One of the things that was most impressive to me was how tight they have been able to make the waypoint tracking, even at speed.  For turns less than 60 deg, the copter doesn't even slow down. Look at version 2.6 waypoint tracking (top) vs. 2.7.3 (bottom):

LiPo Objective Figure of Merit

There's a lot of marketing hype in the "C" rating of LiPo's.  The C-rating is the highest recommended discharge current from a cell.  Manufactures have been over estimating their C ratings for awhile.  So people have created tools addressing this issue.  One that I like normalizes the C rating using the internal resistance (IR) and cell capacity.   This tool is called the LiPo Objective Performance Calculator: LIPo Tool One wants cells that have the highest capacity with the lowest internal resistance.  Our Quadropower 4s 6200 mAhr have an average IR of 1.5 milli-ohms (really good value).  So from the web site we see:

Figure of Merit - 1.21 (the higher the better)
Max Current = 152 A or ~20 amps per motor
True C rating = 25

As the cells are cycled their IR's will increase.  When the IR = 5 they will only be able to deliver 85 amps comfortably.  This is only ~10.5 amps per motor!!!  At this point the voltage of the cells will sag very low (V = IR, right?) and we will see the low voltage warning.  We have learned that knowing the health of your battery is fairly import parameter for controlled flight.  ~mww

batteries and charging

Batteries on the x9503 are charged to 11.7v and the unit is unplugged.  mQX battery started at 10:15.