AL5A I2C Servo Based Robotic ARM Control Blue Print

Videos

Item	Description	Video
1	I2C Control AL5A ARM with Java/Pyroraptor
2	I2C AL5A Java Serial Control Sequence File Playout
3	New Base for the ARM
4	Self Test and Default ARM Position
5	I2C Servo Control with Current Measurement Java Graphical Interface
6	Changing the I2C Address of the I2C PWM Slave stored in PIC EEPROM.

Introduction

We describe the design and the control of a 6 degree of freedom AL5A Robotic ARM using an I2C Master. Each servo is controlled by an IONOTRONICS MK-44149 I2C Slave PWM Servo Controller (based on the PIC16F1825).

The I2C AL5A can be controlled using the Pyroraptor Java Graphical Interface using the Pyroraptor USB/I2C Bridge. In addition, using the PIC32 and Eoraptor Robotics Plateform, a Java Application can control the AL5A Arm using a serial port. Finaly, the AL5A or any other Robotic ARM can be controlled through a Wireless TCP/IP connection using the JavaRoboticsApp. In this way, any Robotic ARM can be added to an I2C Rover and controlled remotely through Wirless TCP/IP.

Design

Each joint of the AL5A ARM is controlled by an MK-44149 which converts a PWM Servo into an I2C Slave. In addition, the MK-44149 can measure the servo current. See the video. Six joints are controlled. A scan of the I2C bus with the Pyroraptor is shown below with the I2C Address for each joint.

See the video on changing the I2C address for each MK-44149 PIC16F1825 I2C PWM Slave.

The photos below show the Servos and their associated I2C address in Hexadecimal.

Base, Shoulder and Elbow with I2C Addresses

Wrist Rotate, Wrist and Gripper with I2C Addresses

New Base for the ARM

IONOTRONICS¬ has developed a new base for the ARM to replace the base from Lynxmotion. The IONOTRONICS base provides smooth movement and handles very heavy loads. See the vidoe here. Contact IONOTRONICS for availability and design.

I2C PWM Control

Each joint Servo is controlled through PWM (1500us at 50 Hz). The PWM signal is generated by the MK-44149 I2C Slave PWM Servo Controller (based on the PIC16F1825). In this fashion, the Servo is effectively an I2C Slave device. The Photo below shows six MK-44149 parts mounted on a platform and bused together. Each Servo is connected to each MK-44149 . The MK-44149 provides the 6V supply for the Servo as well as the PWM signal and Ground. Each MK-44149 monitors the current per servo. The current is available through I2C. The PIC16F1825 performs the averaging necessary to get the current. It must be noted that we need the average current when reading the Servo current.

Important Note: When connecting the Pyroraptor USB/I2C Bridge to the I2C Bus, make sure to connect to the 4 pin Molex connector on the MK-66501 6x I2C Bus. The Vdd (5V or 3.3V) on this I2C connector is isolated from 6V.

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Six MK-44149 I2C to PWM Devices Mounted on Platform and Bused to 6x I2C Bus. Each MK-44149 Controls a Servo.

Six MK-44149 I2C to PWM Devices Mounted on Platform and Bused to 6x I2C Bus. Side View

6x I2C Bus by IONOTRONICS ( MK-66501) used to bus six MK-44149 I2C to PWM Devices Mounted on Platform.

AL5A ARM Control with Pyroraptor USB/I2C Bridge

The I2C based AL5A Robotic ARM can be controlled with the Pyroraptor USB/I2C bridge. To facilitate testing of the AL5A ARM, we have developed a TAB in the Pyroraptor Java Graphical Interface. Using this TAB each joint can be controlled (position and time duration to move to the position). A TAB is also provided to control indvidual servos.

Pyroraptor Java Application TAB for Control of the I2C Based AL5A

Pyroraptor Java Application TAB for Individual I2C Servo Control

Important: When connecting to the Pyroraptor DO NOT connect the I2C power. Only the Clock, Data and Ground. Use the special 4 pin Molex connector or 4 pin DF-11 connector on the MK-66501 which is conveniently provided.

AL5A ARM Control with Serial Port Using Eoraptor Robot Platform and SoC Adaptor

In many applications local control of Robotic Arms through a serial port is desired. In this case, we use a 32 bit PIC or an 8 bit PIC as the I2C Master controlling the I2C based AL5A arm. The PICs also support a dedicated serial port through an on-chip UART core. In both cases the PIC System on a Chips (SoC) have a dedicated I2C core on-chip. In the case of the 32 bit PIC two I2C cores are supported. The 8 bit PIC is based on the PIC16F1947. The PICs can be programmed with the Remote Robot Control Program (RRCP). With RRCP, a command is provided to control multiple I2C based PWM servos. Through the serial port, this ASCII command can be sent and it can cause multiple or a single servo to update its postion over a defined time duration. By sending multiple sequences, complex ARM movements can be played out. For example, a repetitive pick and place movement. Or sequences for following a certain path. See video .

Note the 32 bit PIC and 8 bit PIC RISC System on a Chips are preprogrammed by IONOTRONICS with the RRCP firmware. So no programming is required.

Important: When connecting to the Eoraptor I2C connector, DO NOT connect the I2C power. Only the Clock, Data and Ground. Use the 4 pin Molex or DF-11 connector provided on the MK-66501 6x I2C Bus.

IONOTRONICS has developed a Java Program that incorporates an open source Java serial port library so that an ASCII sequence file can be played out for the Robotic ARM with I2C PWM Servos. The program runs on Linux, MAC OS SX and Windows. The Java program can form the basis for a complete Robot control progarm using the serial port in combination with the PIC SoC and Eoraptor Robot Control Platform. Below is a sequence of movements that are played out by the I2C based AL5A robotic ARM in this video .

@ p58 2000 p59 1500 p5a 900 p5b 1500 p5c 900 T5000
@ p59 1300 T2000
@ p59 1000 T2000
@ p58 1500 p59 1100 p5a 1200 p5b 1500 p5c 900 T5000
@ p5b 900 p5c 900 T1000
@ p5b 1100 p5c 900 T2000
@ p5d 800 T2000
@ p5d 2000 T1000
@ p5d 800 T2000
@ p5d 1500 T1000
@ p5c 900 T2000
@ p5c 1800 T5000
@ p5c 900 T1000
@ p58 2000 p59 1500 p5a 900 p5b 1500 p5c 900 T5000

See the RRCP for description of the syntax.

The Pyroraptor USB/I2C Bridge Java Graphical Interface provides the capability to read the sequence file and and send the sequences to the I2C ARM.

Here is what you need to make this happen (in addition to the I2C AL5A Build ).

AL5A ARM Control with Wireless TCP/IP Using Eoraptor Robot Platform and SoC and WiFi Adaptors with JavaRoboticsApp

You can build an ARM or multiple ARMs on a Robotic platform and control the arm through wireless. For example, you can attach the ARM or two ARMs to a Rover and control the ARMs as well as the Rover. The Rover Blue Print implements all you need. Just attach the I2C based Robot ARM to the Rover and plug it into the I2C bus. The Euroraptor Platform and the WiFI Adaptor provide Wireless TCP/IP. You can test through telnet or using a Java or Python Application for example.

Building the AL5A I2C Based Robotic ARM

The I2C AL5A can be built using the parts and suggestions in the Table below.

To build the I2C Rover you will need:

We recommend that you use a thick Plexiglas platform to mount the six MK-44149. Use 2-56 spacers.

In addition to the above you will need: