For some time now I have been thinking about the potential to add an on-screen display (OSD) device to my ZMR250 mini quad. I happened to have a spare ImmersionRC EzOSD unit available so got the ZMR250 on the workbench to see if I could shoe-horn the unit in. As I suspected it was not particularly successful, as it didn’t fit very well, but I’ve documented how I installed the EzOSD on the quadcopter in this blog post, as it might be useful to other 250-sized quadcopter owners.
I’ve been flying this carbon fibre ZMR250 mini-quad for over a year now having bought the frame kit from China via eBay. It flies very well, but I’ve always missed not having any kind of OSD unit on the FPV system. A multirotor like this generally doesn’t fly very far away, so the GPS features are not very valuable to have - but the current monitoring and battery voltage information is really useful. In the first photo below you can see the quadcopter before I started to add the ImmersionRC EzOSD unit. The specifications of this ZMR250 are as follows:
- ZMR250 Mini Quad Carbon Fibre Frame (via eBay)
- Airbot Micro Titan 2204 2300kv Motors (via Airbot Co., Ltd.)
- Gemfan 5030 Propellers (via eBay)
- Turnigy Nano-Tech 3S 45C-90C 1300mAh Batteries (via HobbyKing)
- FunFly Flight Controller “Naze 32” Acro R5 (via HobbyKing)
- F-12A Fire Red Series SimonK RapidESC Speed Controllers (via Ready To Fly Quads)
- Mobius ActionCam (via HobbyKing)
- Fatshark DominatorV2 FPV Goggles with Fatshark ‘RaceBand’ Receiver Module (via FirstPersonView)
- Fatshark 700TVL High Resolution FPV Tuned CCD Camera (PAL) (via HobbyKing)
- ImmersionRC 5.8GHz Video Transmitter
- ImmersionRC SpiroNet V2 Antennas (via HobbyKing)
- Hitec Minima 6T Radio Control Receiver (via local dealer)
The following sequence of photos show how I installed the EzOSD unit on to the ZMR250 quadcopter.
The all up weight (AUW) of my ZMR250 before adding the EzOSD was 611 grams.
The EzOSD unit comes in two parts - the main unit houses the GPS receiver and connects to the video transmitter and camera, while a second unit sits between the battery and the power distribution to monitor the multirotor’s electrical system. The two circuit boards and required wiring harnesses weigh 63 grams, which will add just over 10% weight to the aircraft. While this doesn’t sound like a massive amount, it is significant for such a small quadcopter that is designed for speed and agility.
My plan was to fit the EzOSD power sensor board vertically adjacent to the video transmitter inside the frame. Whilst the board is short enough to fit, the XT60 power connectors are too big so will protrude out of the frame.
I connected the camera and video transmitter wiring in to the EzOSD circuit boards and packed the excess cabling inside the ZMR250 frame.
The main EzOSD board was secured to the top of the ZMR250 using both Velcro underneath and zip-ties around the board and the quadcopter frame. The way the zip-tie sat over the GPS module was not ideal as it could damage the circuit board if fastened too tightly, but it was left with some slack to act as a failsafe should the Velcro come apart. The size of the GPS board meant that using slightly larger 1500mAh batteries is no longer possible due to space constraints.
The EzOSD power sensor board was fixed to one of the frame legs using more zip-ties.
It was a very tight squeeze with the video transmitter also mounted with zip-ties vertically next to the EzOSD power sensor.
The 5.8 GHz video antenna had to be bent to one side to allow the battery cable to be connected easily.
There was quite a lot of additional wiring added to the inside of the ZMR250 frame as can be seen above. This made accessing the connectors on the Naze32 flight control board rather difficult.
Once the EzOSD unit had been wired in to the quadcopter I powered the aircraft on and was greeted with the familiar ImmersionRC EzOSD video overlay, confirming that the installation had been successful.
The EzOSD stayed on my ZMR250 for a couple of weeks but I then removed it as the additional weight made the quadcopter less stable in flight. Also, the large amount of extra wiring made working on the ZMR250 awkward. My conclusion from this little experiment is that the size and weight of the OSD system is really important for a small multirotor, and having a frame with integrated wiring to save on excess cabling is a major advantage. Next time I plan to fit an OSD to a small multirotor I will be looking at the Minim OSD which is much smaller than the EzOSD.
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