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Design of an electronic circuit to control 8 servo motors and DC motors

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Example of design of an electronic circuit to control 8 servo motors and 2 engines continues (through external power amplifier) to control a mobile Manipulator.

The robotic arm designed by Antonio Castro and published here, has been modified and adapted to include a mobile wheeled base, as described here.

arm

This mobile manipulator, used two wheels 100mm diameter and 12mm internal diameter, wheels material is rubber, but can be any other type of wheel. The wheels can locate here (code RS 337-9797).

Two 24V DC motors has been chosen to attach to the wheels, 1. 62W that rotates at 6300 rpm motor shaft and 67 rpm to 4 mm, complete specifications wheel hub you will find them here.

For simplicity, motors were bolted directly to the base, on the back of this. To join shaft engines with wheels, you choose to manufacture a small shaft enabling the union, that matches the diameter of the bore of the wheel and the shaft diameter of the motor (to wheel hub).

To connect the shaft designed with the motor shaft has been made a plunge with a router that allows the functions of screw prisoner of adjustment between the two parts.

The next step is to provide a third point of support to the base so that allow the robot to stand. The used solution is the use of a wheel caster, through a marble, which will be screwed into the base of the robot.

Finally after mounting, we get the following:

Base-modified - 300 x 225

P1070110

So the final Assembly of the arm and the base is:

Brazomod

A file with .rar files from solidworks employees in the core design is then attached.

Plate design

We will then describe the Assembly of a PCB (Printed Circuit Board) that allows us to using an arduino mini for control of motors and servos of the arm.

Driver for engines.

Controlling the two engines simultaneously through a single arduino is used for a stage of power control, in this case the MD22 plate has been used.

MD22

The plate supply is 5V and 50 mA, and this is capable of powering the 5V and the 24V motors. The plate has two inputs (SCL and SDA) to control the motors. Different control modes available to plate, will use the I2C mode.

Microcontroller.

The used microcontroller for controlling the motors is the Arduino mini 5. In the following diagram we can the different pins available to the controller.

schema-arduino5-pin - 300 x 289

To connect the microcontroller to the computer, use the following USB adapter (programming only):

USB

TX and RX of the arduino entries are used for transfer of data between the PC and the arduino. The connection is simple, we must connect pins TX and RX of the arduino with the RX and TX adapter pins, respectively, since the lines of communication must be crossed.

 PCB diagram.

Below is the scheme of the design of the plate:

schema-electricopcb-extension-pin

Both previous wiring diagram and the subsequent scheme of distribution of electronic components on the plate and the design of its lines of connected, has used the free version of the EAGLE program.

In the diagram you can see that each output is pulled out a set of 3-pin, with separation of 2.4 mm, which are compatible with the servos using the robotic arm.

Electronic design has been designed so that the battery could feed both engines and the power plate and the arduino. In this sense, as the power plate needs to be fed to 5V for the part of the logic circuit and voltage operating 24V motor, strips that allow supply tensions have been included.

Also using the 7805 voltage regulator, we will reduce the voltage of 24V applied on the Terminal 5V that allows you to supply the voltage to the pins of the servos, and another Strip where you can get a cable to feed the control board for power and the arduino.

Say, that both reduce stress causes an excess of heating in the controller, because it’s a linear regulator, so the use of switching power supplies is recommended to avoid this problem.

Another element to be highlighted in the wiring diagram is the use of resistors 10KΩ between A4 and A5 of the arduino and the plug. These outputs are the outputs I2C that has the arduino. 10kΩ resistors are recommended.

The design to create the PCB is as follows:

PCB.extensionpines

A small CNC machine, the iModela, which allows machining with instructions gcode, portraying the machine was used to manufacture plate PCB.

P1070090

In our case, the maximum plate size is determined by the machine, being able to use a larger copper plate using a different machine, or is manufactured using a home insulation and attacked acid process.

Below is the result after soldering all the elements and place the arduino.

plate-extension-completed

Then include the zip file with the eagle files containing the electrical design of the plate and the pcb, along with a pdf of the list of materials used in the Assembly and the pcb.

 

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