Sunday, January 31, 2016

Building a 280mm Quadcopter out of spare parts (Motors and ESCs)

While waiting for more spare parts to arrive (batteries, some adhesives, a PPM/PWM converter and some connector cables), it was the perfect time to install the motors and ESCs to the frame. If you have not read the first part of the build log, I used the EMAX Nighthawk 2204/2300kV motors and EMAX BLHeli 12A ESCs.

Before you start installing the motors and the ESCs, it is advised to have some threadlock liquid available. Use the threadlock on screws that mount to metal only and not the ones that mount to plastic. Use medium strength threadlock – the blue one - and not some other type like the red one which is permanent. I cannot stress enough how important is to use threadlock on frames. Apply minimal quantity – in most cases one drop is more than enough – to each screw before fixing it on the frame.
Using the supplied torx key that each motor had in the box, installing the motors was a breeze. The motors with the silver cap are marked as counter-clockwise (CCW) and the motors with the black cap as clockwise (CW). Of course the motor rotation can be changed by switching two wires from the motor to the ESC but it is best to follow the manufacturer’s advice in order to safely install the blades and bolt them with each cap.
The Tarot 280H “RoboCat” frame is unique in design and functionality as it is focused on pure FPV racing. The specifications on the box provide a list of specific parts that can fit on it and critical parts like the flight controller are not the ones I had available. The frame can accomodate 12A ESCs but not every ESC available. The ones I had needed some trimming in order to fit. The picture below shows the unmodified ESC on top and the trimmed one at the bottom. You have to remove about 0.3-0.5mm insulation from one side.
I had to remove a small piece from the trimmed underside of the ESC in order for the cables to fit through the arm holes without twisting them.
Fitting the ESC inside the ESC-cage each arm has needs caution in order for the cables to be as tidy as possible without twisting them. You have to be careful not to bend or brake the capacitor the ESC has and it is advised to losen up each cage screws in order to install them. After installation apply threadlock to each cage screw to secure them in place.
At this phase, the motors and ESCs are installed but not connected or programmed. This comes next and it is advised to do this now as you have to remove most of the servo cable of the two rear ESCs in order to connect them to the frame power distribution board.
Each motor has three wires that connect with the three wires coming out of the ESC (on the other side of the ESC we find the two power cables and a 3-wire servo cable; we will deal with them in a moment). Motor rotation is determined by the way the 3 wires are connected to the ESC. In reality, a brushless motor is not clockwise or counter-clockwise as the direction is determined by the ESC; however, this does not apply to the blade nut of each motor. The nut should secure the blade by turning at the opposite rotation of the motor, so a counter-clockwise motor should have a clockwise screw (they usually have different nut colours). The following picture acts as a guide to set the rotation of each motor.
ESC motor
The rotation of the quadcopter motors are as follows
After connecting a motor to the ESC, we have to program its parameters. You have to consult the documentation of your ESC, regarding the software it uses (BLHeli, SimonK or something custom). The ESCs I bought run BLHeli and to program them - without performing soldering and removing a resistor and capacitor – you connect their servo cable to the RX (using Channel 3/Throttle stick to program). The problem with the FY-Q7 TX/RX combo is that it uses PPM encoding instead of the PWM encoding BLHeli requires. So, to decode the PPM signal properly and overcome this obstacle, I used a PPM/PWM signal converter module; this is used only while programming the ESCs and is not required for the normal operation of the aircraft. After connecting the RX to the ESC servo via the converter, I was able to program the ESCs using the following parameters (these are for EMAX BLHeli 12A ESCs):
Parameter Value
Brake Type Low
Timing Mode High (30)
Start Force 0.19
Control Frequency 22kHz
Low-voltage protection 3.0V/cell
Cutoff Mode Soft-cut
The Flying3D FY-Q7 (a 9-channel rebranded FlySky TX/RX system with proprietary 2-way protocol supporting telemetry) needs Channel 3 to be in reversed state (press OK > Function Setup > Reverse). The following pictures show the correct settings for programming ESCs and for normal (flying) operation respectively.
A good video tutorial on how to program the ESC using the TX, is the following. Do not worry regarding the SimonK firmware, the same procedure (moving the throttle while guided by sounds) applies to BLHeli aswell.
Programming ESCs with a TX
Repeat this procedure for all ESCs, setting the correct rotation for each motor.
After all motors and ESCs are correctly set-up, you have to cut the servo cables in order to solder them to the Tarot TL280H power board. The two rear ESC connections are outlined inside the Tarot TL280H manual, on page 3:
As shown in the picture, the positive “+” solder points are used to connect the positive cable (the RED one) of the ESC and “-“ is for the ground (the BLACK one). The positive and negative (GND) are opposite each other, so care must be taken for the rear ESCs regarding the length of their power cables and servo. The two rear ESCs have two solder points for the servos, the image which coresponds to the WHITE cable and is the actual ESC signal line and the “-“ (negative) point which coresponds to the BLACK cable and is the ESC servo ground line. Be careful when soldering because the points are close to each other and you do not want them to short-circuit. The final result should look like this (a bit messy but soldered securely and it works Smile ). On the completed quadcopter, this area is covered with a soft adhesive material that protects the cables and connections from damage.
On the front side, things are a lot easier (but still a tight fit); you do not have to cut any servo lines and ESC power cables are easy to solder, as seen from the picture above.
At this point you should check all your connections with a voltometer, so that nothing is causing a short-circuit.
This concludes the motors and ESCs installation and now we can proceed to the quadcopter control elements (the flight controller and receiver), which will be addressed in a future blog post.
Parts used in this session (affiliate links at absolutely no cost to you):
Thanks for reading, please state tuned (and subscribe) for the next part Smile

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