October 12, 2016

QX90; beyond expectations

So I finally got the QX90 I ordered maybe a month ago. I wasn't sure what to expect from the odd mix of a F3 flight controller and a brushed motor setup. I had read and seen much online and people seemed to like them and similar models and 50 $ isn't that much to argue about. And I wanted a replacement for the crappy flying WLToys Q282G I have been trying to fly FPV with at work.

When it arrives it comes in a small box with "everything assembled". In fact, there isn't much to assemble at all. The simple design consists of a flight controller board with brushed ESCs and two-wire brushed motors simply pressed through a rubber bushing sitting in a hole in the carbon plate which alone serves as the entire frame. On top of that a small camera with video transmitter and antenna all soldered together. Fills its purpose perfectly. But no telemetry, and no OSD.

I ordered mine together with a FM800 FASST receiver, since I fly Futaba. I knew the only assembly step I would have to take was to solder the receiver to the board. So I did.

SP Racing F3 on the QX90

But wait someone had already been dripping their solder on the solder pads I needed to use for the SBUS connection. This gives me an indication that this model, or my specimen, was produced as an BNF (with FrSky receiver) but was downgraded to PNF as I didn't want a FrSky receiver. And this is not a very nice thing to do.

I spent some time carefully trying to heat and remove the solder from those pads. The pads are smaller than usual and I know from experience that heating those pads too much will make them come off.

FM800 on the QX90

Other than that all was setup and ready. But not really. I configured the board in cleanflight. In fact everything was already done (since it was configured for SBUS already). I only had to trim in the transmitter to cleanflight. Done?

No. The board refused to arm. I spent hours trying to figure this out. There are millions of threads on how to setup the transmitter to properly arm a naze board. But this was not my issue. The would only arm while connected with the USB cable. I could arm it with the USB and then unplug it. And fly. But once disarmed without USB it refused to arm once again. And on this unusual occasion the internet was no help to me. I finally started thinking in terms of what the USB connector provided that could make it work: Solid 5V. I figured there was either a problem with the onboard voltage regulators. Or there could be an issue with the board mounter with only two miniscule patches of foam tape to the carbon fiber plate.

I was lucky. The board wasn't faulty. I applied a patch of electrical tape to the plate before mounting the board. And it worked. And it works still.

So now for a short flight review. It's great! Very slippery in rate mode, since it's very light, but it's very responsive and precise with the pre-configured PID settings it came with. And when you need attitude/angle mode, it's there for you and it is good. The quad straightens up i a split second to get your orientation right. The angle mode doesn't even makes you feel hindered while flying like I've experienced before. But that might be because I'm indoors in the office and I don't dare pick up too much speed anyway.