It was only a matter of time before I got hooked by the idea of a 250 size quadcopter. I love the look of the “long frame” style quads made popular by designers like Blackout and Lumenier, so when HobbyKing released the FPV250 quadcopter long frame version I couldn’t resist…
FPV250 Quadcopter from HobbyKing
HobbyKing is making a habit of bringing out affordable versions of some of the world’s most popular multirotor frames. I personally already own the SK450 Deadcat quad (TBS Discovery layout – although the Reptile is closer) and Q450 quad (DJI Flamewheel F450 clone). Both of these are fantastic frames that cost only a fraction of their “brand name” counterparts.
The FPV250 racing frame continues this trend by being a pretty close match for the popular QAV250 by Lumenier. It isn’t identical though. In order to keep their development cost down HobbyKing have taken the already successful FPV250 quad and added a long frame conversion. This is made up of two short plates that extend the base of the frame and a long top plate (full length unlike the 2/3 length plate on the QAV frame). These are joined by 8 threaded tubes that are anodized a tasty red colour.
Planning for some fun…
For my FPV250 quadcopter build I wanted to go the whole hog. It was going to be FPV ready obviously with a board cam for vision married to the awesome ImmersionRC 600mw VTx. Recording my feats of daring-do would be handled by the new Mobius B Lens camera.
I had a few KK2.1 boards on the shelf so the flight controller was sorted. I wanted to use the recommended HobbyKing setup for power so I also ordered in the Multistar 1900kV micro motors, GemFan 5×3 3 blade props, Afro 12A ESCs and 1000mah 3-cell LiPos.
Putting it all together…
The main frame is a solid one piece affair so it was only really a case of adding the top and bottom plates. Some nicely thought out metal bushes ensure the bottom plates lock perfectly into place.
TIP: Don’t attach the top plate until you have mounted your flight controller, ESCs and motors, and sorted out all the wiring.
I decided I was going to get fancy with the wiring to try and save some weight. To that end I created a custom wiring harness that connected all four ESC’s to the power input without the need for a breakout cable.
Attaching the motors was where I hit my first snag… The mounting holes and screws are so small on the tiny Multistar motors that there is no way to mount them to the thick arms of the FPV250 quadcopter frame. In the end I decided my only solution was to attach the mounting plates to the motors and use cable-ties to fix them to the arms. In hindsight this is a good idea as this frame will no doubt suffer some abuse and the ties make for easy maintenance.
TIP: Use ties in all four holes as the mounting plates are thin and bend easily if only fixed at two points.
Big problems with small ESCs…
Skip forward then three hours to the point where I discovered that these ESCs put out 6 volts at the BEC instead of a more normal 5 volts. Yes, you may well shrug your shoulders. “So what?” you are thinking. Well, try applying 6 volts to a KK2.1 board and then try setting up your receiver… not so funny now eh? For some reason the KK2.1 does not like 6 volts. It looks okay until you try to use it and discover that extra volt has somehow scrambled the incoming receiver signals and nothing works. Trust me, I tried it on 5 KK2.1 boards including two in flying airframes – nothing.
In disgust I snipped the wires, tore out the ESCs and threw them in the cupboard – ordering some Multistar 10A replacements. I didn’t want to use an external BEC as they were all too big and I didn’t want to wait (even now though I would have to). After I had calmed down though I had an idea…
In my box of bits I was sure I had an old 5A (ish) ESC from my Shockflyer days. I dug it out and tested it – 5 volts steady at the BEC. So I stripped off the coating and removed the motor wires and signal wire leaving only power in and power out. When I was finished it was not only smaller and lighter than the smallest BEC (I could find quickly on HK), but it was here already and FREE!
Fitting it to the frame was just a case of removing the red and black wires from the M1 ESC and replacing them with the BEC output. Power up and job done!
Kitting out the FPV250 Quadcopter…
I sat the ImmersionRC 600mw VTx at the back. The flight cam is one of the new Turnigy 700TVL units. These are truly tiny which is awesome, but also makes for some mounting conundrums. In the end I used the supplied mounting bracket and yet more cable-ties to fix it into place. The FrSky FASST Rx sits neatly on top with the Mobius held in place with a simple velcro strip above the flight cam.
The gap in the rear of the frame is perfect for a small 3-cell LiPo and I used a little mouse-mat gel to ensure a snug, slip-free fit.
Finally the GemFan props are perfect for the little Multistar motors. I think this is the first time I haven’t had to adjust a prop-center to get it to fit on a motor! I had intended to try some 6 inch props on this quad but the long frame prevents anything larger than 5 inch props swinging.
Ready to go this FPV250 quadcopter weighs in at 540g with the Mobius attached (499g without).
Let’s go flying then!
I was so excited to get this quad flying that it was really annoying when the first flights were a total disappointment!
On the plus side, the KK2.1, flashed with the latest Steveis Pro firmware flew perfectly out of the box without me touching any settings.
On the downside, the power was marginal. Hover was achieved at around 60-70% throttle and the low voltage alarm (set to a dangerous 3.3v per cell) was kicking in within seconds of leaving the ground! Something wasn’t right. The batteries were toasty when I landed so I could only surmise that the little 1000mah 3 cells, despite being a 25-35C rating just weren’t giving enough juice. Whilst I was at it, HK had just released the “Baby Beast” 2150kV motors so they might help too! So I jumped online and soon had some new motors and 1300mah 30-40C cells on the way.
Into the air… again…
The 1300 cells were the first to arrive so I decided to give them a go with the current motor setup. The difference was stunning! Hover still required a little more throttle than I would like but there was definitely more power on tap and the low-voltage alarms were silent. I bumped up the stick scaling on all axis as well to make the frame more responsive and turned on the Mobius for the first time…
Bear in mind that this is raw, unstabilised footage. It’s an essentially untuned airframe and it was the first proper flight so no FPV, self-levelling was on, and all I did was beat up and down the reserve behind the house.
People are going to ask me for some settings so here they are:
Controller: HobbyKing KK2.1 | Firmware: Steveis V1.17S2Pro
PID Values – Pitch/Roll: (P) 65, (I) 30 | Yaw: (P) 65, (I) 50
Self-levelling: (P) 45
Stick Scaling – Roll: 45 | Pitch: 45 | Yaw: 60 | Throttle: 105
All other settings remain unchanged from the default firmware settings.
The FPV250 Quadcopter with the long-frame conversion is another winner from HobbyKing. I’ve only given it 4 stars because of the problems I had with the motor mounts and the BEC voltage. The frame itself however can’t be faulted and the flight performance even before the coming upgrades is good enough to make me forget any small problem I had getting there.
There will always be those who will say “Yeah, but carbon fiber is stronger and the Blackout/Lumenier micro quads are better frames.” To be honest I totally agree! But they also cost 8-10 times the price of the HK frame. If I am going to have some fun and push the limits with a micro racing quad, I’m going to feel a lot braver if I know the whole frame can be replaced for less than I paid for the breakfast I just ate while writing this…
Watch this space for more videos and details on the upgraded motors, props and power distribution board that HK released yesterday!
See more of my projects and articles at www.red20rc.org
UPDATE! My FPV250L has now had a complete rebuild. Catch the FPV250L Rebooted article at red20rc.org.
Was it worth all the effort?