The Brushless Controller
In total there are four Brushless Controllers (BL-Ctrl) needed for the quadcopter. Each controller controls a brushless motor. Brushless motors don't use brushes for energy-distribution to the rotor. In contrary to the motors with brushes, the magnets are rotating while the coils are steady. That's why we can't use a DC current, an AC current with precise pulses is needed to drive the motors. This AC current is provided by the BL-Ctrl. The BL-Controllers are connected to the main board with a bus system (I2C). Each controller has an address, which are used by the main processor to communicate with the BL-controller. It is possible to control the BL-controller with a standard RC-receiver. An input for PPM signals is present .
- Controller: AVR ATMEGA8 of Atmel
- Placed with six 60 Amps MosFets
- integrated current measurement
- Current limitation at the DC current-side
- Designed for approx.110W at 11.1V or 150W at 14,8V (10A continuous)
- Peak current approx.220W at 11.1V or 300W at 14,8V (20A peak)
- two LEDs (Okay and Error)
- Battery voltage sensing with low-voltage detection
- Software is totally in C
- As setting point either the rpm can be controlled or set (per PWM)
- several inputs for setting point
In general, for a Quadcopter four brushless motors are needed. The brushless motors are different from simple d.c. motors because of:
1. High rpm
2. Low noise
3. Better thrust producing capacity
4. Easily controlled.
5. Lesser weight.
Two Clockwise (CW) propellers and two Counter Clock Wise (CCW) propellers are needed.
- Front = Motor #1 and Back = Motor #2 clockwise
- Right = Motor #3 and Left = Motor #4 counter clockwise
- EPP 1045
- X-Ufo Props
The receiver receives the orders given by the pilot and converts them to electrical signals. These are read by the Flight-Control. A receiver with a summing signal is needed for a quadcopter. This signal contains information of all the channels sent by the transmitter, and has to be available as an output on the receiver to feed the FlightControl mainprint. This summed signal will be processed by the Flight-Control software into separate channels and will be used to drive the Quadcopter.
To control a Quadcopter a transmitter is needed. Any commercial RC-transmitter with at least four channels is usable. A movable axis of a joystick is seen as one channel (f.e. up-down). So two joysticks with two movable axis each are sufficient.
More channels can be controlled with turning or moving potentiometers, or with switches. These can be used to control height, switch lights or control camera-movement.
A frame is the 'skeleton' of the Quadcopter. The motor-motor distance can vary between 35 cm and 60 cm, depending on motor and propellor size. Frames could be of the following material:
1. Carbon fibre: one of the most costlier material for frame because of its high strength and lower weight.
2. Aluminium: Right now we are using aluminium frame for our helicopter
3. Thermocol: Could also be used to make frame
For power-providing usually Lithium-Polymer batteries or LiPos are used. These types of batteries differ from other types by a light weight combined with high capacity. Handling these batteries is not without any danger, so some rules have to be kept in mind. These types need a special kind of charger, because the charging procedure differs a lot from other types (like NiCad and NiMh). The cells should not be overcharged, neither should they be unloaded to deeply.
To keep the charge difference between cells to a minimum, a balancer must be used. This balancer might be integrated in the charger, or a separate balancer should be attached to the charger. All LiPo-packs have a connector for a balancer.
For a Quadcopter LiPo-packs with three or four cells are used. They have a voltage of 11.1 V or 14.4 V. [[BRR]] Commonly advised:
.Advisable: LiPo 3s 11,1V ca2100mAh, 20C