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 It's a bit outdated now.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.

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