The idea behind the JARA project was to introduce my students to a basic application of robotics by developing a 6DOF (Six Degrees Of Freedom) robotic arm from scratch.
For this project, considering the input/output requirements, the adopted control board was the Arduino MEGA (2560 REV3), which offers 54 digital input/output pins, 15 of which can be used as Pulse-Width Modulation (PWM) outputs, 16 analog inputs, and 4 Universal Asynchronous Receiver-Transmitter (UART) ports.
In addition, connected to this board, we have a MicroSD memory card reader to store information when the device is powered off, a pressure sensor RP-C10-ST (with a range from 20g to 2Kg) positioned on the jaw to calibrate gripping force, a DC-DC converter Arceli-AA0003 that allows us to use a single power source for the 6 motors (that approximately required 7 volts), and the board (that required 5 volts).
The choice of servo motors was oriented towards the Longruner LDX 218 model, which uses metal gears that offer good torque (max torque 17kg x cm) and are controlled through PWM signals.
After the prototyping phase, where the connections were made using jumper wires with Dupont connectors, the final connections to the board were made using an Arduino shield that allows the use of screw terminals for each board pin.
An I2C LCD1602 display (2 lines of 16 characters) was used to show relevant information during device operation.
The main unit that contains the board was placed inside an aluminum box for electronic assemblies, on the front panel of which necessary holes and labels were created (the labels were made using LibreCAD, an open source CAD software, printing them on a self-adhesive transparent sheet).
A second plastic box was used to assemble the control unit, which provides 2 dual-axis joysticks (QM070905), 2 micro-buttons (normal open) , and a micro-switch (deviator) that allow us to perform all possible motor movements, as well as record them and regulate the servomotor movement speed.
The two units and the arm were interconnected using 8-pin metal plug connectors (AC 200V 5A 16mm 8 pins female and male aviation connector plug), and power is supplied through a 12-volt, 5-ampere power supply.
A relevant part of the project was the assembly of mechanical parts, where, in addition to ensuring the stability and range of motion of each motor, the balancing of the arm's joints had to be considered.
Counterweights and springs were used to counteract unwanted movements when the motors were not powered.