Because there was a hardware problem with the Exceed X8 PRO helicopter of a friend, we decided to remove all the hardware and replace it with custom build hardware. The first thing I did was replace the hardware in the remote controller, here is the blog about that part. In that blog there is also a part about the receiving end, but the hardware used there has been taken out of commission for my newly designed hardware.
Hardware – circuit boards
On the MOSFET board there are two identical MOSFET circuits. Each circuit controls one output which is an amplified version of the input for that circuit. By putting the two circuits on one board space could be saved and the heat dissipation capabilities are enlarged. It also means less wire clutter in the helicopter. The board is designed to be used with IPU06N03LA MOSFETS, but any TO251 package N-channel MOSFET can be used as long as it meets the requirements needed for your motor and controller. Because I’m using brushed DC motors a flyback diode is incorporated in the design. Each MOSFET has its own pull-down resistor to make sure the MOSFET is in the off position when it’s supposed to and to protect the Arduino there is a current limiting resistor placed between itself and the MOSFET. I use 47 Ohm 0805 resistors for R1 and R2 and 10kOhm 0805 resistors for R3 and R4.
Arduino control board
The control board was designed for this project but is released as “wireless board V2.0” on OSH Park shared projects. Because it was difficult to get 3.3v Arduinos with the right pin-out the board is now designed to accept 2 different Arduino pin-outs. Namely the “deek-robot” pin-out found in figure 6 and the cheap “ebay” pin-out found in picture 7. Accept being able to handle two different pin-outs the board is upgraded to accept 3.3v Arduinos and 5v Arduinos. That’s also why there is a 5v regulator and a 3.3v regulator onboard so that the Arduino can be controlled by a unregulated or higher voltage power supply. The nRF24L01+ module is powered by the separate 3.3v regulator so long range nRF24L01+ modules can be used, without asking too much power from the Arduino and so that a 5v Arduino can be used. After having having not enough PWM outputs on my previous wireless boards I’ve decided to change the routing, the new pins are the one used in the Mirf library and can be found in table 1. On the bottom side you can see that there are 3 resistors so the voltage applied to the BATT header can measured thru a simple voltage divider network. Having to voltage regulators makes it also easy to have a 5v and a 3.3v line broken out.
Table 1: nRf24L01+ routing.
|Signal:||RF module pin:||Arduino pin:|
The H-bridge is the only circuit board that was not custom built but bought. The board is called “Mini VNH2SP30 Monster Moto Shield Stepper Motor Driver ” and uses the VNH2SP30 H-bridge motor driver chip. This board is a bit overkill, but was chosen because of it’s light weight, it needs just one PWM input and it has advanced protection features.
Hardware – helicopter
As mentioned above the helicopter used for this product is an Exceed X8 PRO. This is a coaxial helicopter, which means that going forward and backwards is controlled by the tail rotor and rotation is controlled by the ratio of the rotor speed.
As of now the helicopter is still being calibrated for stable flight. Because the main rotors are not identical the amount of throttle for each rotor still needs to be adjusted. The other thing that needs to be adjusted is the center of gravity that needs to be beneath the main rotors.