Sorry this has taken a while to update, had some issues and have been awaiting feedback so I know which direction to head in next.
After choosing the parts (part 1) and completing the build (part 2) I've added some extra parts to make this more suitable for racing. Namely a ufl/ipex to right angle sma female connector and a RHCP pagoda antenna. A circular polarised antenna is compulsary for my local multiGP chapter running on 25mW transmit power. This has bought the dry weight up to 250g with the Dalprop t5045c cyclone propellers.
Initial flights: So responsive
I was hoping to report on my first race but unfortunately bad weather had meant it was cancelled. The weather did clear though and so I got the chance to discharge my batteries the RIGHT way.
Quad: 245g dry weigh as per part 2 build plus pagoda antenna, Dal 5040V2 instead of t5045c cyclone
Battery: 4s 1000mah Turnigy Graphene 65c 145g
Pids were fine stock and no excessive motor heat from the dynamic filtering with all notch filters off. Went for some slower light props because I was flying in a smaller space. Combined with a 2450kV motor this meant I didn't have a massive amount of top end speed but wow the pick up was obscene. Between the light dry weight, lower capacitor batteries (light) and the light props that are very easy to spin I found it super responsive and so very easy to change direction at pace. My goal is agility and manauverability while I become more familiar with racing and I wasn't let down at all.
I'm really enjoying the lightweight for another reason too. I am using a micro FS82 flysky receiver with no diversity as a placeholder until my new frsky setup arrives. This reciever is fine for a close-range micro quad like the leader 120 but I got carried away with the floss 2 and failsafed about 20m above tarseal. The quad went down and I lost video signal. After trying my hardest not to run over I was surprised to see everything intact. I only lost video because the ufl connector popped off (which I then popped straight back on. There was also a small scratch on the prop nut and a kink in the pagoda antenna - it seems the antenna had taken most of the hit. I was obviously lucky on the angle it landed but think the lack of inertia through lower mass had helped too. Not even a bent prop!
I put 7 packs through that day and on the second to last I re-armed after a nothing crash and found motor 1 not idling. I unplugged and re-plugged the battery and got that horrid smell of burnt electrical circuit. I powered down once more, waited 5 minutes and re-powered with a new battery. Got idle this time but when I went to throttle up, it dipped on motor 1 before the flight controller took over and limited power to the other 3 motors in order to maintain attitude. Either the motor or more likely the ESC was sick.
Usually when an ESC goes it is catastrophic and it passes no current whatsoever or if it does, has major desyncs and brownouts. Mine behaved differently. To see that the issue was still present I strapped the quad to the bench with all props free to rotate. I then connected a full battery and betaflight configurator so I could power up 1 motor in isolation at a time. Motors 2, 3, 4 were all able to generate maximum thrust but motor 1 was limited to about 30 or 40%. I then swapped the motors attached to ESC 1 and 3. After repeating the test the issue was ties to ESC1 meaning the fault was with the ESC. Not a great outcome since this is a 4 in 1 esc.
Dealing with HGLTech and looking at other options
My first though was that the ESC is just not capable of managing the power for a 5" build. The 20mm x 20mm stacks were originally for micros and although this one is supposedly capable of 28a per esc, the rating may have been overly generous. This got me thinking of expensive replacements like the Asgard V2 and other ESC/FC combos since this FC cannot easily be reused with different ESCs.
For the sake of research and seeing it though I got in touch with HGLTech, makers of this unit. They responded the following day recommended that added capacitance should help manage dangerous voltage spikes and reiterated that the ESC should be capable of 28a continuous and 35a burst. After sending pictures of the build (including the capacitor) I came straight out and asked if it was a manufacturing fault and if so, could they send a replacement. To my pleasant surprise, they said yes. Really I should have gone through the retailer (Gearbest) here but really wanted to get the technical explanation more than just the free replacement ESC. Credit to HGLTech, they got me both!
Simple really, I'll wait for the replacement ESC to show up, wire in 2 capacitors this time (with 1000 microfarad total capacitance) and try again. If it fails it is more than coincidence and the technology is not quite there yet. If it succeeds then it supports the seachange of miniaturisation in racing quad electronics. I'll make another part to this blog series once I've had a few packs through the replacement escs and hopefully make it racing.
Update Jan 2018
A quick update, since installing the backup 428 esc and external capacitors I have not had another issue. From photos of the damaged ESC it was a FET that had burned out. What I failed to mention here is that the ESC burnt out shortly after I had realised the original capacitor I installed was knocked off in the crash I mentioned. My hypothesis is that due to the small size of this board, there is not a lot of capacitance so voltage spikes likely as a result of regenerative motor breaking are causing the damage - hence why the capacitors help.
I still think the this quad is pushing this small stack to it's limit but there are a lot of success stories here: https://www.rcgroups.com/forums/showthread.php?2971570-20mm-x-20mm-FC-ESC-VTX-stack-in-a-5-inch-racing-quad
In the meantime HGLRC has since releasted the XJB F440 tower based around a 40a BLHeli32 esc. I've not tried one myself but this would looks like it may be a better candidate for 5". Link to the F440 direct from HGLRC is below:
This is the build log for my floss 2 racing 5 inch quad that is based around the HGLRC F428 TX20 Elf 20mm x 20mm electronics. In part 1 I covered the reasoning behind all of the components in the build. Although this kit does include a micro CCD camera, I ended up using it on my Leader 120 since it was slightly lighter. I'll cover the steps that can be seen in each of the photos below. Click on the pictures to embiggen.
Motors and frame.
So yeah, skipped a few steps to get to this point but I was a bit excited getting it together:
-Raceday quads Returner R2 2450kV motors were attached to arms using screws with loctite. Heat shrink placed over the arms with wires inside for a clean look and to keep wires away from possible prop strike or tangling.
-Hyperlite Floss 2 5" frame assembled
Strengthening the ESC battery pads
This part is important. I've seen people mention that earlier reports of other HGLRC ESC have had VBAT pads wripped off when batteries have ejected on crashes. In addition these pads are small and I'd struggle to get a connection even with 16 gauge wire - the minimum I'd want to use on this build. The solution I used was to take some copper strand from the core of home wiring and thread as many as possible through the VBAT holes. Then twist tight and trim to about 4mm long. It's not shown in this image but then tin the pads and wire with a good hot soldering iron - I used 380°C on my TS100 soldering iron.
ESC and receiver mounting
Here the ESC has been mounted on the supplied m2 nylon standoff which have been attched to the frame with m2 x 6.5 screws. A FS82 flysky receiver that I previously bound was heatshrinked with power and signal wires passing underneast the ESC. I'll replace this later when I upgrade to the FRSKY Taranis Q X7S. Note the orientation of the ESC. Motor pads need to go to front and back as the FC must rotate with ESC due to pin connection. If the pads go side to side then the USB port on the FC becomes inaccessable at the front or back.
Rx antenna strengthening
Shoved the end of a cable tie between reciever and heat shrink here. Added heatshrink on top of this and the monopole antenna to keep it stiff andaway from props.
Motor wire connection
Motor wires solder up to ESCs. Order is not important as this can all be changed via software in BL Heli and Betaflight.
VTX wiring and capacitor
5 things in this image:
-Flight controller added to stack
-XT60 added with cable tie to right rear standoff for strain relief. Wires had extra heat shrink so rubbing doesn't wear the insulation off.
-Capacitor added - 25VDC 470 micro farad to supress potential electrical noise
-Receiver soldered to the flight controller
-VTX wired and added to stack
FPV camera mounting
Runcam micro swift 2 added to the TPU mounts to check for size. Heaps of room!
FPV camera wiring to FC
Camera has been wired up here with the F428 flight controller having unique pads at the front of the board specific for the camera - 5v/ground/Vin - very clean and easy to wire.
Finishing up and software updates
Here is the money shot with all the software updates and changes done:
-BL Heli updated to 16.3 with motors running reverse
-Betaflight updated to 3.2.1 with Omnibusf4 target
-Top plate and props added
-OSD turned off in swift micro due to betaflight OSD
In summary this was head and shoulders the easiest build I have done thanks largely to the HGLRC XJB F428 TX-20 Elf electronics. Why? No wires between ESC and FC, all pads for the vtx at the back, all pads for the camera at the front and ESC, FC and VTX fit in a nice small, light stack. The only down size was the small VBat pads which I think I have a good solution for however only time will tell. The build is light and well enclosed so should be strong. Everything fired up perfectly first time with no smoke which is always a bonus. So far as the build is concerned I am very pleased with all the components I've chosen here but I really need to put them to the test in flight to be sure.
This year I have decided to try racing with Multi GP in my local NZ chapter and rather than using my trusty but heavy Martian II, I will be building a new 5" lightweight racer. I've decided to break this into 3 parts to cover in detail what is going on:
1. Parts choice and reasoning
2. The build
3. First flight and performance
I find with a new build that sticking with a clear primary objective will help you better choose your compoents. My objective for this build was lightweight and durable, built specifically for multi GP racing rather than a jack of all trades. Durability includes reliability since gear failure is probably the most disappointing way to DNF based on my days racing RC cars.
Parts choice and justification
GLRC XJB F428 - TX20 - ELF F4 Flight Control System - As soon as it was announced I new this would be perfect for the floss 2 frame I'd already pre-ordered.
Why did I choose this:
My only concerns are: will the VTX signal be clean enough for group racing? Are the ESC VBAT pads too small for a suitable wire size (16AWG)? Can this actually push 2205 or will it go up in flames or less spectacular blue smoke?
Hyperlite Floss 2 5" frame - The only issue I had in choosing this one was to decide between this and RCAddicts newly designed Mode 2 Ghost frame. Very much neck and neck but the floss 2 was available locally with immediate delivery.
Why I chose:
More of an observation than a requirement but the frame is also simple, easy to build and service.
RACEDAYQUADS BADASS 2205 2450KV NAKED BOTTOM RACING MOTORS - I always knew I wanted a mid kV 2205 motor for this build to stay light. I looked at the various returner r2 variants and decided the raceday quads were perfect due to the 7075 aluminium. Notable mention to CATALYST MACHINEWORKS FREEDOM 2205 MOTOR and Returner R2 Ghost Edition 2205 2555kv.
Why I chose:
DALPROP T5045C Cyclone 5 Inch 3 Blade Propeller Props are of course a personal choice but I'll be starting with my favourite brand Dal prop. I chose not to start with the Cyclone 2 5046 to try keep the current draw down a little.
Why I chose: