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Posted by on Jun 4, 2013 in Blog, Ramblings

AC1 V5 Build Log – Testing DJI Naza-M V2

AC1 V5 Build Log – Testing DJI Naza-M V2

Rising from the Ashes…

…but at the sort of speed dictated by postmen who can’t quite manage to find my house.

Yes, it has been too long, but today I finally had everything I needed to get airborne, and set aside a whole day to rebuild my hex from scratch – I started early, picking up the parts at 6.20 am, and 13 hours later I was in the air doing the first of my drive tests.

Cautiously does it…

I haven’t forgotten the recent sight of my beloved flying machine tumbling from the skies, so this build is going to get tested to high hell while things are nice and low on the ground. So, first we had a bench test before everything was bolted down, to make sure all the connections looked good. At this stage I had the Naza flashing yellow failsafe at me, and my receiver was indicating it suddenly didn’t know anything about my transmitter ! I suspect this had something to do with me trying to bind my Devo 10 to my Ladybird 2 the other day, and I fixed it by clearing the SSID from the RX with the bind plug, and then turning off Fixed ID on the TX. Then it was TX off, RX on, TX on, binding, and then re-enable Fixed ID, and boom, we have our TX lock back… cue some relief as it looks like the Naza-M isn’t damaged by the crash and repeatedly boots normally.

Bench Test Part 2 – config / machine test

We failed this one too. Having set up the DJI V2 assistant software, and re-flashed my Naza with the 3.12 (V2) firmware, I proceeded to check motors / spin directions – something I hadn’t done since the crash that caused this rebuild – how many would survive ? My hopes were high for all of them. But no. All span up fine except one, which just juddered ominously. My spare motor connected in did the same, so next in the blame queue was the ESC, and indeed that was the problem. So now all my motors were working, and going the right way. Worth noting at this point that I hadn’t thought of the Naza firmware upgrade as being much a of a big deal. More about that later.

Final Checks / Maiden Flight Test

Well, all problems seemingly solved, I went to fit my trusty Carbon Fiber 11 x 5 props only to find the crash has taken too many and I am one short, and nobody’s got them in stock ! Dammit. Right – I’ll try these carbon Fiber 11 x 4.7 slow-fly jobbies I was going to put on my Tri-copter. I don’t like slow fly props on a heavy hex – all my experience of them is that they give treacle-slow, unresponsive flights, even on 4S. Strictly speaking, these props are more suited to 3S power, which might go some way to explaining the way the craft behaves.This is especially true of the cheapy plastic ones, so I have a dim and distant hope that these particular slow-flyers may be slightly better because they are pure CF, and therefore stiffer, and better at cutting the air.

My theory is that if I swap these 11 x 4.7′s for Graupner 10 x 5′s then I’ll have a lot more control and wind resistance (sharper, narrower blades, less blade area) at the expense of lift. how much lift I lose may or may not be a problem. It needs to lift 3.4 KG which is a big ask for the Graupners – they certainly couldn’t do it if they were on 3S DJI stock motors. In theory my 4S Tigers should make it happen.

Off up to my ground zero test field then, with aerocat, to see if what we have built (she ‘helped’ all day) will take to the skies. The gain settings are the same as form my last Naza-M V1 setup. as I said before, I’m not trusting anything yet, so no landing gear or camera or gimbal – I just want to see if she’ll reliably fly, go where I tell her to, and respond in a way that I might be expecting…

What the F*%&* is it doing ????

So, I started up (Atti Mode), checked prop and motor direction, which was fine, and started the machine. She started, and idled gently, as I raised throttle to 15%. ¬†At 25% I was wondering why the motors weren’t turning any faster, and at 45%, when they still didn’t, I began to think I had a serious problem I didn’t have the first hope of trying to diagnose. A couple of power cycles, and it does the same every time. On the second time, however, i go above 60%, and suddenly, the hex takes off on its own, and jumps 20 ft into the air. Not expecting this, I drop throttle, which then resulted in the craft coming down for a rather hard landing onto the soft recently mown grass of the test field (no damage).

What I didn’t know until I subsequently read the manual for the Naza V2 upgrade, DJI have made 50% more important than it used to be, and now we take off by raising throttle slowly to 60%, and then dropping to 50% when we get to the hover level we want. It’s almost an auto-take off, and is a feature of the new firmware. Ok – I’ll be ready for that next time. I sort of wish I could turn it off without resorting to manual mode.

The Edited Highlights…

Mainly for my own benefit. Unless you are a) very new to multirotors or b) unnecessarily excitable, you should skip this – it’s 8 mins of boring test manoeuvres and me doing a lot of wondering what the hell is going on. Here it is.

In-flight

I flew very cautiously for the 3 batteries-worth of testing I did with the bare frame (battery top mounted on CoG). Here’s the things I noticed in that time.

Good things
  • Craft did not exhibit any symptoms of dodgy connections, and did not fall out of the sky during the test flights
  • Control was very smooth, and movement very sailplane-like – would be good for filming
  • I think I trust it enough to put the landing gear and brushless camera gimbal on for the next round of tests…
  • DJI’s new course correction – I think I saw that working…
  • New LED sequences are clearer than Naza V1.
Bad things
  • GPS took about 10 minutes to locate all satellites, and then kept dropping in and out of GPS mode during flight
  • Directional control was not very precision – greater stick movements than normal required sometimes.
  • The Auto-take-off thing, if you’re not expecting it.
  • Slow-fly props are truly horrible on a hex – pretty much at the mercy of the wind, and seem to delay my input instructions by 3 seconds !
  • Not sure if it’s the new Naza firmware, but hex deals quite badly with ground effect. BUT – no landing gear, so closer to ground than ever before – perhaps it’s that, and the massive prop-wash you’re bound to get off those horrible 4.7″ pitch props…
What have I learned ?
  • Expect DJI to implement new stuff ! Specifically my machine to jump into the air on its own at 55% throttle
  • I still don’t like 11 x 4.7′s, though they are very smooth in certain circumstances. They require surprisingly different gain settings to 11 x 5′s.
  • Naza V2′s gain structurwe might be different the V1 I’m used to – tweaking required.
  • Have go with the brushless gimbal – even though there is minimal ‘craft trust’ and currently no way of controlling its tilt angle until a cable arrives – just keep the flights very low.
  • Try some Graupner 10 x 5′s for the test after the next one.
  • If the 10 x 5′s can lift the gimbal and GoPro3, and FPV gear (yet to be fitted), then consider losing the arm extensions to regain perfect plane symmetry. How important are 11″s ? Do we need all that thrust ?

¬†Tomorrow, we ride…

Ok, fly, in round 2 of the tests – same as yesterday, except this time with a camera and possibly ultra-slinky gimbal on-board.

For now, here’s various snapshots form the build, mainly so I can remember what went where, and why.

 

My new lower frame. Very rare you break these in a crash. I broke the top one too !

My new lower frame. Very rare you break these in a crash. I broke the top one too ! The new landing gear should reinforce the lower frame.

New isolation mount from Aeroxcraft - the end of the jello war ?

New isolation mount from Aeroxcraft – the end of the jello war ? Rubber first, silicone next if that doesn’t do it.

3 Extension plates re-squashed (sort of) flat, 6 new props, 3 new arms, and 1 ESC gives us a working set, at last !

3 Extension plates re-squashed (sort of) flat, 6 new props (invisible), 3 new arms, and 1 ESC gives us a working set of apendages, at last !

Trimmed down wiring... Just DJI VU, battery connection and 14.8v line to DC  regulator. ESC connections on Power distribution loom.

Trimmed down wiring… Just DJI VU, battery connection and 14.8v line to DC regulator. ESC connections on Power distribution loom.

Coming together - the arms join the lower frame. This is the last time it'll look neat.

Coming together – the arms join the lower frame. This is the last time it’ll look neat.

Add the power harness, and glue down your FC . DC reg board and it's getting hard to keep tidy...

Add the power harness, and glue down your FC . DC reg board and it’s getting hard to keep tidy…

I've got very high hopes for this Aeroxcraft brushless gimbal. Probably unrealistically, but it's nice to dream.

I’ve got very high hopes for this Aeroxcraft brushless gimbal. Probably unrealistically, but it’s nice to dream.

Look at that. It's SO smooth and instantly reactive.

Look at that. It’s SO smooth and instantly reactive. that’s because th Naza has nothing to do with its movement. This gimbal controls itself…

My latest Naza settings in the new DJI software...

My latest Naza settings in the new DJI software…

Got the lights working now. That even more wires.

Got the lights working now. That even more wires.

Ok, that's landing gear and cam stuff fitted. roll on tomorrow's tests !

Ok, that’s landing gear and cam stuff fitted. roll on tomorrow’s tests !