February 29, 2016

Pieces of cable from Hobbyking

Really Hobbyking!? If I order 2 meters of cable, don't you think I want a 2 meter cable and not two pieces of 1 meter cable?


I recall having ordered longer lengths of wire before without this surprise. It's probably to cut some logistics and packaging costs. I can accept it this time and I rarely need lengths longer than 1 meter. But even if I wanted 3 pieces slightly longer than 0,5 meters I would have a problem and a considerable amount of waste.

February 14, 2016

Turnigy Mobius gimbal and the ZYX BMGC controller

I've got a Turnigy mobius gimbal from HobbyKing for the XJ470 build. I got this at a bargain price during the black friday sale for only $25. It includes the gimbal, motors and the controller.

The controller is a Tarot BMGC (T-2D) which is originally designed for the Tarot GoPro gimbal. Chris at HobbyKing obviously figured out how to reconfigure it to work with a gimbal designed for the mobius instead and they didn't need to design their own for the mobius gimbal.

I probably hit all obstacles while setting up the gimbal. Make no mistake, it has to be assembled and fully configured before it works with a mobius and the motors that are bundled, otherwise it will just go crazy.

I use a virtualbox installation of windows in a Ubuntu machine, which adds some additional issues. Windows users won't see those of course.

Linux configuration

First off, you need to get the right permission for the included dongle device. Almost all RC-equipment that connects to you computer uses a dongle which is a USB-UART serial adapter. But instead of using a generic device all vendors sells or bundles their own device, like the DYS ESC programmer, the Futaba CIU-2, the BeastX dongle. The list can be made long. In this case it is a "Prolific" device and this particular device has no preconfigured udev rules in Ubuntu. As always. To fix this and make it usable add this line to a new or existing file under /etc/udev/rules.d/.

SUBSYSTEM=="usb", ATTRS{idVendor}=="067b", ATTRS{idProduct}=="2303", GROUP="users", MODE="0666"

Please note that those permissions may not adhere to your personal security preference.

Virtualbox configuration

Running the Tarot configuration programme in a virtual windows machine might not work. For me it just immediately exits with the message "Program has exised!". If found this page about the issue and in the comments you can find the solution. It's a bit outdated now. In fact, while installing the addons you should check the "3D Support (experimental)" and you will then get a dialogue asking something like "Would you like WDDM or just basic 3D". Click "Yes" and everything will be fine.

Flashing and configuring

I had some problems with vibrations in the gimbal and I decided to flash a new firmware. Although this was completely unnecessary since my controller already had version 1.5 I went ahead with it. I didn't succeed at first but with the help of this page I managed to get it done.

How to configure the gimbal with the hobbyking provided setup files is explained in the hobbyking product profile video: https://www.youtube.com/watch?v=zL6OqQ20Fg0

Do load the hobbyking settings to the gimbal, but controller and motor configuration. Do this first before starting to play around or you'll just be waisting time. Chris got it figured out already so work with that as a baseline.

Mobius mounting

I intended to have the mobius mounted with velcro. Why? Well to be able to remove it and use it for other purposes of course. But you can't do that. The gimbal will go crazy, mine was trying to spin around until it was stopped by the sensor cabling. You must mount the mobius with the double sided tape that comes with it. Or something similar, which is not unlikely to be found in the drawer of a hobbyist. The small tape pieces that comes with the gimbal is a bit too small and a bigger piece comes will into place.

Power supply

The power supply is specified to "DC 7.4V ~ 14.8V (Recommended 12V, three lithium battery)". Which is nice. If you are running 3S at least. But I'm not. If correctly specified it will draw a max of 500mA which isn't much. I'm using my favorite mini buck voltage converter set to 12V in the frame. It will supply 12V to the gimbal, video transmitter and potentially a camera as well depending on which I choose.

S-BUS channels

The gimbal controller supports S.BUS! I didn't know this when I bought it, just lucky I guess. The gimbal has three input signals, the two axes and a mode switch. And if it hadn't had S.BUS input I would have been forced to use a S.BUS to PWM decoder to get the three signal wires to the gimbal. Now I don't have to and it will save a lot of space, wiring and complexity in the frame.

The channel mapping for S.BUS cannot be configured but are fixed. I haven't tried this out myself yet but a quick search reveals that channels 1 and 2 are used for tilt and roll and channel 5 for mode (rate or stick position). This is good to know when you start selecting channels to use in the flight controller setup. In a way it also sucks, since I will be using the R7003SB receiver and it has PWM output for channels 2 and 3. So channel 2 is wasted. In probably won't even use roll on the gimbal which makes it even more annoying.

February 9, 2016

What was I thinking?

So I started to take care of the 550 that has been sitting on my desk taking up space since last summer.

I knew there was something that wasn't pretty about the cabling, so I flipped it over on my desk.

The not-so-tidy heap of wire on the bottom of the 550.

WHAT was I thinking? Well, I had to figure this out before I could move on and do something about it. There seems to be three reasons for all those cables. First, there is a need for a Y-harness to power the gyro through the throttle connector. I'm using a CC BEC Pro and not the ESC BEC. Secondly I wanted to be able to disconnect the ESC while testing the setup, this comes handy with a Y-harness. And lastly I have used a connector between the power lead and the BEC, probably to be able to disconnect the BEC while powering the ESC. But why, I don't know.

There's a big difference between how I used to build helicopters and how I build multi-rotors. Nowadays I'm soldering almost all the cables instead of using servo connectors. To save space and weight, to cut wires to the exact length and to make it look nice. And because there is really no need for servo connectors when using flight controller boards that are not encased anyway.

But on the helicopter every component is encased. There are little to no possibility to solder wires to the components and you are therefore left out to using things like clumsy Y-harnesses. Something I would never dream of squeezing into a 250 quad of course.

So I cleaned up the installation. I had to heat up the screws to the bottom plate to remove it and attach all the wires inside the frame instead. I added a bead of hot glue to the Y-harness connectors as they felt a bit loose and left out the possibility to disconnect the ESC. Instead I will need to disconnect the motor, which has accessible wires in the front.

At the same time I flashed the new 2.0 firmware onto the CGY750 gyro which should save me some setup time when the flying season approaches. Until then I'll let the helicopter rest.

Somewhat improved cabling on the 550.

February 8, 2016

XJ470, build queue is piling up

I had future plans to build a large multi-rotor for a slightly better aerial photography than what I can do with a 250 racer today. I intended to start planning this build during spring and probably get to work with it during the summer. Being on parental leave, the hobby budget it quite tight and I did envision letting it drop if the build calculations turned out to expensive. A friend of mine built a similar sized multi-rotor a year ago and it turned out more expensive than I expected.

But then HobbyKing had a sale. A real sale. And there was lots of stuff. And I saw the XJ470 that I had never heard of before. So I quickly (maybe too quickly) scanned the forums and made my calculations. And I ordered the major parts for the build as they where on sale. It all comes down to a lot of compromises, I hope it will work out in the end.

The frame itself was at nearly half price, which was great. I ordered the frame for $60 together with a motor/ESC combo for $80. The choice fell on a MultiStar 2216 with a 20A afro ESC. The motor is speced at 3S, but community says it takes 4S and 20A might be a bit tight, but should work fine.

I picked a APM set with everything (GPS, sensors, OSD and cables and shit) for $65. The main drawback here is the lesser GPS, I would have preferred at least a 6H GPS. And it also turns out the kit does not contain a GPS mast, which surprised me as most kits do.

I will use a Mobius 2-axis gimbal. I had this one in the drawer from a previous sale where it sold at $25 (it's at $95 now).

I will be using a Futaba telemetry setup, since I can't really live without it anymore. But only receiver and power sensor will cost at least $150 and therefore I'm planning on rebuilding the Ghost 250 and replace the telemetry system with a cheap OrangeRx receiver and an OSD. That quad is not ready for decommissioning yet.

All in all I should be able to put it together for around $400. I hope. And I hope it works.

I'm looking forward to this build as it includes a lot of new technologies I haven't worked with before;

  • A bigger folding quad, capable of carrying a camera gimbal.
  • Advanced flight controller capable of autonomous flight, I've only used simple FCs so far.
  • A gimbal. With a camera.
  • Head tracking. I have an external head tracker I haven't tried yet.
  • More advanced OSD.
  • 1.3Ghz FPV system, I have the stuff and I have a license. It's about time!

But before that. I should really finish a T-Rex 550 upgrade that has been sitting half-done on my desk since last summer. And the rebuild of the Ghost 250.

February 7, 2016

CC3D adjustments for the FPV150

I did some adjustments to the PID settings of the FPV 150 today. It's very impractical as I have to unscrew the top plate to access the USB connector of the CC3D installed in the front of the air frame.

After a few adjustments I reached a good-enough setup and it flies agile and without any oscillations now.