The Dead Cat Quad

Yesterday was a good multi-rotor day.  I spent the day with my buddy building quads and putting together my ”Dead Cat” or Alien Quad, while he assembled his High Dollar Team BlackSheep Quad.

Basically the same basic layout, a Quadcopter, where the front arms are spread more than the rear, to allow for better camera clearance from the props (as in getting them out of the picture).

The ultimate goal will be to make these FPV or First Person View fliers.

Two completely different approaches.  He, plopping down major cash for a TBS kit, with TBS motors and ESC’s.  The TBS board, with integrated gimbal is amazingly well done.   The onboard core will be outstanding when finished.  He set it up yesterday migrating a Naza flight controller he already had.

I on the other hand was going the cheaper route.  A simple frame.   I was still waiting for some parts, so I robbed/borrowed ESC’s and motors from a failed DJI F550 hex build that he had on hand.   I did however use my shiny new PixHawk flight controller, 3DR Ublox GPS and 3DR telemetry radios.   Basically the same gear I have on my Hex, with the exception of the newer PixHawk over APM 2.6 I’ll have some pretty significant comments about the PixHawk towards the end.

This is a super cheap frame ($25.00 on amazon, complete with knock off arms), I’ll replace those with legit arms after the first crash, and when I really go FPV, I’ll probably upgrade to the TBS plates minus the gimbal.

It turned out pretty nice and flies pretty well, still needs to be tuned but it’s too windy today.

DeadCatFrame001

DeadCatFrame002DeadCatFrame003

I tossed some DJI Landing gear on it so that I could mount the battery underneath.  Without the camera gear up front, putting the batter in the back where it’s supposed to go simply wrecked the center of gravity.   In FPV mode that won’t be the case.

PixHawk Critiques and Observations

I so want to like APM, and I so want to support 3DR but they are making it harder every day.

APM, on my APM 2.6 Flight controller works pretty well.  I know it’s basically out of resources so they are moving to PixHawk.   I know BeagleBone will be 100x better and that’s coming.   I know they are trying to make this ‘consumer friendly’. 

It’s not plug and play, at least with 3.1.2 copter code, there are too many hoops to jump through, to many places you have to rub your head and your belly in opposite directions at the same time.   Maybe these are mission planner issues, but they don’t exist with my APM and they do with PixHawk.   Connecting, downloading, fetching parameters and logs.  It works, oh about half the time.   Try to do something more than once and you’ll probably have to reboot the PixHawk.   I know it’s “Open Source”, but some of this is pretty stinking buggy.   No other way to say it.

The PixHawk is noisy, too noisy and by that I mean too many sounds, and beeps.   My ESC’s hate life until you push and hold the button.   Maybe this is their way to make ‘drones’ more conspicuous.   It’s just an annoyance.  We should be able to turn the sounds down or off.   We should also be able to make my ESC’s happy, pre button push.

Speaking of the button.  The button is dumb.  I have to pre-arm the PixHawk with a button push and hold before I can arm it?  What the hell?   A lawyer probably made them add this.

Ok fine, put the button in/on the PixHawk, allow the remote button if and only if you need a remote button.  I don’t, so it’s one more thing to mount, one more set of wires to route and tend too.   But let me, as a non-novice, disable this silly preflight, preflight check.

I don’t hate the case, others do, in fact someone’s already making square non-sexy case for it.   I actually like it.
side_back

I do like the LED’s, tons of them.  The status LED is really nice.   But if I can see that, I can push it, that remote button should have a multi-color LED like the top.   So when you remote mount it you get the light where you can see it.

OK, I think my batteries should be charged…

Update: 03/11/2014

OK, so on assembly day, it got dark, all we could do was hover it, and it was clear there that the battery w/o camera in the battery slot was bad.  It was woefully out of balance.

So I put landing gear on it to put the battery underneath.  It flew, in fact in Stability mode it flew just fine.  It loitered OK too, and looking the logs, vibrations on the PixHawk were all OK too (under +/- 3).  The darn thing would NOT auto-tune.   I  chalked it up to being windy Sunday, too windy.

Today was a different story.   Nice and calm.   It still would NOT complete an Auto-tune.  It would ‘finish’ but if I tried to switch back and forth between the pre and auto-tuned values, it would drop like a rock, get hung up in it’s own prop wash and crash.   Luckily after 3 attempts the only thing I broke was a single landing leg.   After looking at logs, I just couldn’t decide if this frame sucked that bad, or if PixHawk was just crap.   It’s less than ideal for a product that was supposed to ship in Sept/Oct of 2013.  It’s now March and it’s still less than polished.  So on a whim, I decided I had spare arms, let’s replace this HJ DJI knock off arms with legit DJI arms.   So that’s what I did.

WOW, that’s all I can say is WOW, with stock pids, it’s amazing.   Now I’ll try an auto-tune.

So yeah, when you read in the internets that the HK knock off arms are bad.  Believe that player.  While they don’t look or feel horrible, they just are.

Leave a Reply