Emax Nighthawk 280 Pro circuit board replacement…

Emax Nighthawk 280 Pro circuit board replacement… using Naze32 rev6 full, emax ESC 20A, CC3D PDB – by David HK, 2016 July

[video link: https://www.youtube.com/edit?video_id=v-pXoXqoXuk&video_referrer=watch]

Why need to replace the CB?....

The NH is my 1^st FPV quad, last month the Vbat socket came off, so I tried to solder the Vbat wire directly without the socket.  However, the +- wires for the Vbat socket I got was swapped when I first installed it 6 months ago, which has been all forgotten, and become a time bomb! L [lesson learned #1: never, never, swap the wire colouring rule]

It was in the middle of night, without any thinking, I soldered red wire (which was in fact ground) to +, black wire (which was in fact live) to -, connected the battery… Bomb! Smoke+Sparks!  So the NH circuit board is fried! Woo woo woo….

I was also worry whether I fried any motors as well, as 2 of the motors where very hot when touching.  So I searched how to test DC brushless motors, not easy, multimeter would work, need LC meter, etc.  however, found one simple test that can be done by hand, that’s to connect any 2 wires from the motor, then spin the motor bell by hand, there should be more resistance and stop more quickly vs all 3 wires not touching each other.  Tried all combination of 2 wires (ie A+B, A+C, B+C), all motors shown the same consistent extra resistance when 2 wires are connected while spinning by hand.  So this gave me more comfort that the motors should be still okay, which turned out correct.

Decision making: what should I buy?…

• The NH circuit board replacement?

Pros: easy to replace as it is a direct replacement, plug&play, no need for soldering

Cons: slightly more expensive, but then all eggs in one basket again (you fried 1 component, then the FC+4x ESC be gone), the NH version of the naze32 is slightly old, also the ESC is only 12A

• Separate naze32 + 4x esc

Pros: slightly less expensive, can get the latest naze32 rev6 full version, with baro meter / black box etc to play with, and also can buy 20A ESC instead of the NH’s 12A, spread the risk of frying with separate components. Lastly (and a big bonus) is an educational experience for myself to build future quads.

Cons: could be difficult, need soldering, could short circuit easily if incorrect wiring J

Decision made: buy separate components, here is what I got:

·        

   

      Cheap naze32 rev 6 full from China – risk taking, it turned out it is an earlier version without the diode, which will power back the motors from PC USB power if ESC BEC is connected, more on this later. Around HK$170 US$22.

·         

      Emax 20A ESC x 4: I regretted this purchase as soon as I open the box; it is so BIG and Heavy!!! @28g each, total 112g! I thought all ESCs are similar in size and weight, but they are not.  [lesson learned #2: pay attention to physical size and weight of your quad components before buying] Other brands’ 20A only weight 7g-10g, anyone know why such a big difference? Is it due to different technology?  Also, because the size is so big, fitting them on the arms is a big straggle, so in the end I stacked them 2x2 in front and behind the Naze32 on the frame body, it turns out quite neat and better centre of gravity. J Around US$6 each.

·         PDB – a clone CC3D PDB with 5/12v BEC & LED Switch, US$8

Upon received the naze32, I immediately connected it to my PC, and successfully flashed it to the latest CF 1.13, which was a relieve! J 

Here is the NH without the circuit board and the motor wires re-tracked onto the top of the arms, I also marked the motor wires connection order, hoping when I solder them I will get the correct spinning direction (but it turned out only 2 motors were soldered in the correct order, 2 didn’t, which I need to swap any 2 wires and re-soldered L)

As I am new to soldering, been watching lots of videos on quad building, in the end, I told myself, not bad, but next time will be much better and smoother. J

Having decided to stack the ESC in 2x2 layout, the difficult decision is what to do with the 3 black wires from the ESC and the motors.  I read somewhere that the emax motor wires have some kind of insulation coating, couldn’t be soldered directly, thus I don’t want to cut the motor wires, but to cut the ESC wires instead so that it is just long enough to join the motor wires.  But this way, the ESC wires is quite short, difficult to solder + heat shrink, after joining 2 motors in this way, I simply stop cutting the ESC wires and just join them to the motor wires, although a bit too long, but I will have more room to do soldering and future repair.

For the PDB layout, I decided to position it such that the +/- soldering pads are in the front/back direction instead of the normal sideway, as I want to hide most ESC wires ‘inside’ instead of expose them outside, to minimize the chance of damaging the wires during crash.  When halfway through the soldering of the ESC wires, I realize some of the solder are too close to the PDB components nearby, I worry I may have created short circuit already.  So I used a magnifying glass to inspect the soldering done, and apply some insulation glue to cover the nearby components join, then complete the rest of the PDB soldering.  [lesson learned #3: before soldering the PDB, paint some insulation glue to cover the nearby components first]

When the core electrical wires are done (other wires require a servo crimping tool, which I have ordered and waiting for delivery), I temporary connected 1 ESC BEC power wire (red) to the Naze32 (my permanent solution is to use the PDB 5v BEC, which is more stable and less heat for the ESC) so that I can start testing for motor spin and calibrate the ESCs. 

So on to the CF Configurator, managed to configure the flight modes, all channels and sticks were working as expected on the screen, even in the Motor tab, the 4 motors diagram can go up and down from 1000 to 2000.  However, after I armed the FC (it armed successfully as per the Naze32 LED lights), the motors were not spinning at all, and also I didn’t get the pleasant 1-2-3 sounds when connecting the battery!  It was a quite depressing moment and at the same time my wife ‘informed’ me I need to start cooking as our guests will arrive soon for a Sunday gathering dinner. J

While cooking, I was thinking ‘what went wrong’, it was not the radio, as the CF Configurator GUI showed everything working as expected, CF is getting all the PPM signals correctly, so the problem must be somewhere between the CF and the ESC, and ESC is not powering the motors.  Did I get some fake ESCs from China?

So after the dinner, while everyone were chatting and thumbing with their phones (nowadays people do this all the time J ), I googled to see if anyone have encountered similar problems. 

Well well well, found 2 similar cases, and 2 issues why my motors won’t spin. 

1. current version of CF 1.13, if enabled OneShot and the ESC BLheli firmware is not flashed with BLHeliSuite to version 14 (?) or above, the motors will not spin.  Fix: so I disable OneShot.
2. I noticed 1 motor is continuous shaking a little bit when I power the Naze32 via the USB port, before connecting the flight battery! Meaning the PC USB 5V power is being passed back to the ESC via the ESC BEC power wire! No wonder when I tried to calibrate the ESC, I didn’t hear the final 1-2-3 music.  Fix: disconnect the ESC BEC red wire from Naze32.  Use the PC USB power temporary to power the Naze32 when needed. Ie need to connect to PC before armed.

With the above 2 fixed, I was able to armed and tested the motors spin via my radio & PC USB power.

While I waited for the crimping tool to arrive, I double checked the soldering and put in more insulation glue to the PDB, also I asked my daughter to buy me a small bottle of clear nail polisher, I use it to paint the Naze32 circuit to provide a waterproof environment.  Also watched more crimping tool how-to-use videos. J

The crimping tool finally arrived, initially I found it very difficult to use, confused on which slot to use, which way round to hold and to crimp, etc,  but after testing it with 5-6 servo pins, I finally got the hung of it.  I cut the ESC signal/ground wires to just long enough to connect to the Naze32, the first 2-3 pins took quite a while to crimp, but subsequent pins are pretty straight forward.  So no regret in getting this crimping tool, which is a SN-28B model.

After all crimping done, before I connect all the power wires from the PDB; 5V to Naze32, 12V to FPV cam & vid tx, and the LED power port (which is also 12V), I used a multimeter to double check their output voltage just to make sure.

During this NH circuit replacement process, I also learned and created a smoke-stopper protection connection wire, if I had this in the first place, I may not have fried my NH circuit back then. J [lesson learned #4: the smoke-stopper is a must tool to have, and always use it after you done any circuit related modification or build]

The NH frame without the bottom circuit board feels not as sturdy as original, I worry it may break the middle frame during crash as all 4 arms are attached to it.  Reuse the fried circuit board as a frame protection is an easy option, but then will add further weight, which is now heavier than original, as the 4x ESC at 28g x4 (=112g) is much heavier than the original circuit board.  Alternative is to add another NH middle plate, making a sandwich with the arms in the middle, will provide the necessary toughness needed.  However the NH middle plate is not cheap.  So in the end, I bought a cheap cheap generic middle plate, made of fiber-glass, which has lots of holes in it.  My thought was there should be some holes that matched with the NH frame screws.  But in the end, only 2 holes fit perfectly in one end, for the other end, I used iron wires to form new ‘holes’.  I think this is strong enough structure to crash! Let’s hope so anyway. J

Time to fly…

Now as I have the latest Naze32 FC, and I flashed it with the latest CF (v1.13, was v1.11), my initial thought was to use the default PIDs, and then use the new Gtune feature to auto tune the PIDs.  On my first liftoff in sitting room (just want to make sure it can liftoff and no smokes as the motors draw the current from ESCs), I noticed it was doing small vibrations in high frequency when about 1 feet above the ground.  So I changed the PIDs to my original stable PIDs (which was copied from RC Slater that he did a great youtube flying the NH280) before I fried the circuit board.  This time I went outside to test, it was in a drive tunnel to a school next to my apartment block, testing it in LOS.  First reaction was WoW! So stable, it is even more stable than before; I think it is due to a number of factors: heavier weight, latest CF firmware (better formula calculation), new gyro sync feature, and faster Naze32 CPU chip and faster looptime (was 1500, now 1000). So now there is no need to go through the Gtune path anymore, I was a bit skeptical on Gtune anyway, as I can’t found much successful cases in the web. 

Second reaction was “so much power” than before when I punch the throttle! I think this is due to the more heavy duty and powerful ESCs!

Conclusion…

Though it took me just over a month of waiting for parts arrival and actual DIY of the replacement process, and buying extra tools like the crimper, wire stripper, hex driver, etc. I truly enjoyed the whole replacement experience and learned a lot in quad building.  I now have more confident in building a new quad from scratch.  

As for the actual result, after some initial LOS test flights, the NH280 v2.0 seems to fly better, more stable and more power.  I think this will be my ‘training’ and FPV recording quad for the next 12 months.