RC, photos & tech


ZMR250 v2 Build – Part 10 – MW OSD Artificial Horizon Reverse

The Problem:

The default settings in the MW OSD on my configuration resulted in the artificial horizon on the roll axis being reversed.

The Solution:

Edit two settings in the MW OSD firmware.

In config.h, uncomment "REVERSEAHI" as below;

#define REVERSEAHI                // Reverse pitch / roll direction of AHI - for DJI / Eastern bloc OSD users

In screen.ino, I used these settings;

#if defined REVERSEAHI




ZMR250 v2 Build – Part 9 – ZMR250 PDB connections

In this video I go through the ZMR250 PDB and what connects to where. Oscar's site ( is a great resource for figuring this out with some great diagrams.


ZMR250 v2 Build – Part 8 – FC Power Connection

Initially I hooked up power to the Flight Controller from the 'BEC' and 'GND' pins next to the FC but this didn't work..... the reason..... the BEC pin is designed to take 5V from the ESC BEC which of course I don't have because I'm using the LittleBee 20A ESCs which don't have a BEC.

The alternative is to use the 5V regulator built into the PDB. Oscar Liang's web page has some excellent diagrams showing the layout and connections of the ZMR250 v2 PDB.

ZMR250 V2 Build Log – Mini Quad with PDB

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ZMR250 Build – Part 7 – Buzzer Connection

The early versions of the Banggood SP Racing Flight Controller have an issue where the buzzer connections don't work. To get around it is an easy fix and just requires soldering a couple of wires from the bottom side of the FC to the buzzer connections.




ZMR250 Build – Part 6 – Little Bee ESCs

The EMAX 12A ESCs don't support damped light so I ordered four LittleBee 20A ESCs. This video shows a quick comparison between the two ESCs and the effect of active braking.


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ZMR250 Build – Part 5 – EMAX 12A ESC Update

In this video I look at updating the EMAX 12A ESCs with a direct connection to BLHeli via an Arduino Uno (as opposed to going via the flight control board). Initial reading of the supported SiLabs ESCs documents indicated it wasn't going to be straightforward. After some Googling I found the video below which shows  step by step instructions how to do this.

The alternative would be just to buy one of the EMAX $10 programming cards which I guess is simple enough but then I'll never be able to do BLHeli firmware updates plus I like being able to use the BLHeli to check and set the ESC parameters.

After going through the process of soldering on a wire to each of the four ESCs and updating to the latest BLHeli, I found these particular ESCs don't support damped (damping?) light / active braking which is a bit of a bummer so I ordered four Little Bee ESCs instead. It would be interesting to compare between the two types of ESCs when it comes to flying but I'm not sure I'm up for the hassle of swapping out the ESCs.





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ZMR250 Build – Part 2 – Power & ESC Check

In this video I hook up power to the fpvmodel PDB and to the EMAX 12A ESC. I'm trying to decide whether to solder the Sunnysky motors directly to the ESC or to the ESC leads. Removing the heatshrink from the ESC shows what looked like dodgy solder job touching the pins of the ICs. I wondered if they were going to work at all. After hooking up power and successfully testing them, I decided to use the ESC leads to connect to the motors for two reasons;

  1. Unlike other ESCs that have the three points at the end of the ESC to connect to the motor wires, these EMAX 12A ESCs have them along the middle of the board which means the wires would be staggered (different lengths).
  2. The connections are inbetween ICs and some of them make contact with the legs of the ICs. I don't want to break the connections with a messy soldering job.


ZMR250 Build – Part 4 – FC Firmware Flash

In this video I hook up the SP F3 Flight Controller to update the firmware via the Cleanflight Configurator app. Even though I've done this a heap of times I still manage to make mistakes doing the firmware flash. Some of the mistakes include;

  1. Wrong settings in the app.
  2. I'm so used to flashing my Naze32 rev5/6 boards, I uploaded the wrong Betaflight firmware (now I'm using the SP F3 FC).
  3. Leaving the "flash on connect" setting active in the configurator without realising it and interrupting a firmware update before it finished.

I remember reading somewhere that "you can't brick these boards" because the bootloader is stored in ROM. Just short the boot pins and flash again. Lucky for me the boards are resilient in this way as I've had to use the bootloader pins a number of times.

I never did get the 4way BLHeli firmware update to work via the FC board so in the end I gave up on that option and looked at updating the ESCs with a direct connection to the board. More on that in the next video.

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ZMR250 Build – Part 3 – Motor & ESC Test

In this video I let Grace take the controls of the motor and test it mounted to the 4mm arm. The first thing I noticed was the motor stuttered at low throttle. Looking closely at the bottom of the motor mount I noticed the circlip on the motor shaft was stuck against the side of the hole cut through the arm for the motor shaft. For this test I simply centred the motor so the circlip spins freely however I think the better long term solution is to enlarge the hole.

Gracie gets a chance to check out the running lights on the PDB and quite likes them.


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ZMR250 Build – Part 1 – Parts List

The purpose of this build log is to document the process of building a ZMR250 quadcopter complete with FPV and telemetry. My experience building a previous ZMR250 has been that simple problems like outdated firmware can cause major headaches and heaps of Google searching / forum reading to find the solution. The plan here is to document each step no-matter how seemingly simple it may seem


ZMR250 V2.1 Mini Quad Frame Kit w/PDB Special Edition -

Mini DC-DC 12V Voltage Step-down Regulator Module



FrSky X4RSB 3/16 Channel Telemetry Receiver

Upgrade NAZE32 SP Racing F3 Flight Control Acro 6 DOF/Deluxe 10 DOF for Multicopter

Eachine 700TVL ET25 5.8G 32CH 25mW 7-24V Super Light Transmitter

MICRO MinimOSD Minim OSD Mini OSD W/ KV Team MOD For Naze32 Flight Controller



New DALprop 2 Pairs 5045BN Bullnose Propellers for Racing

Emax BLHeli Series 12A ESC For Quadcopter RC250 Mini200 QAV250

SunnySky X2204S-16 2300kV Brushless Multirotor Motor

Foxeer XAT600M DC5V-22V 600tvl Sony Super HAD CCD FPV Camera

5.8Ghz Circular-polarized Omni Cloud Spirit Tx Antenna


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