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--- lego_dynamixel_2d_plotter [2019/04/25 22:05] – [Running, Testing and Analysis] ntorresreyes
+++ lego_dynamixel_2d_plotter [2019/04/26 20:11] (current) – removed ntorresreyes
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-====== LEGO 2D Plotter with Dynamixels (IN PROGRESS) ======
-**Author:** Norberto Torres-Reyes Email: torresre@unlv.nevada.edu
-\\
-**Date:** Last modified on 04/23/19
-\\
-**Keywords:** kinematics, planar, robotic arm, 2 link, lego, NXC, NXT, mindstorm, dynamixel, plotting
-\\
-=====Motivation and Audience=====
-This tutorial is for anyone who wishes to create a 2-link plotting robotic arm using LEGO Mindstorm, NXC software, and Dynamixel RX-28 servos. This tutorial will also reinforce theoretical knowledge about 2-link planar mechanisms, serial communication, and servo control. Readers of this tutorial are recommended to have the following background and interests:
-<fc blue>
-  *Previous experience with LEGO Mindstorm
-\\
-  *Matlab and/or C-based programming experience
-\\
-  *Knowledge of linear algebra
-\\
-  *Some knowledge in serial communcation
-\\
-  *Experience with using servos
-</fc>
-\\
-\\
-The rest of the tutorial is presented as follows:
-  *[[lego_dynamixel_2d_plotter#parts list|Parts List]]
-  *[[lego_dynamixel_2d_plotter#theoretical background|Theoretical Background]]
-  *[[lego_dynamixel_2d_plotter#build plans|Build Plans]]
-  *[[lego_dynamixel_2d_plotter#nxt brick code|NXC Code]]
-  *[[lego_dynamixel_2d_plotter#running, testing and analysis|Running, Testing and Analysis]]
-  *[[lego_dynamixel_2d_plotter#conclusions|Conclusions]]
-====Parts List====
-A few parts for controlling the Dynamixels will be needed along with some parts used to communicate between the NXT Brick and the Dynamixel. The LEGO parts list is shown in the [[lego_dynamixel_2d_plotter#build plans|Build Plans]] section.
-\\
-\\
-**Dynamixel RX28**
-\\
-https://www.trossenrobotics.com/dynamixel-rx-28-robot-actuator.aspx
-\\
-{{:torres:tutorials:nxt_dynamixel:capture4.jpg?nolink&300|PHOTO}}
-\\
-**Lego BreadBoard Adapter**
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-http://www.mindsensors.com/ev3-and-nxt/58-breadboard-connector-kit-for-nxt-or-ev3
-\\
-{{:torres:tutorials:nxt_dynamixel:capture5.png?nolink&300|}}
-\\
-**SMPS2Dynamixel**
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-http://www.robotis.us/smps2dynamixel/
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-{{:torres:tutorials:nxt_dynamixel:capture6.jpg?nolink&300|PHOTO}}
-\\
-**(Optional) HiLetgo USB Logic Analyzer**
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-https://www.amazon.com/gp/product/B077LSG5P2/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
-\\
-{{:torres:tutorials:nxt_dynamixel:capture7.jpg?nolink&300|PHOTO}}
-\\
-\\
-Other Parts Needed:
-   *NXT Cable
-\\
-{{:torres:tutorials:nxt_dynamixel:capture8.jpg?nolink&300|}}
-\\
-   *Dynamixel Connector Cables
-\\
-{{:torres:tutorials:nxt_dynamixel:capture9.jpg?nolink&300|}}
-\\
-   *USB A-to-C cable
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-{{:torres:tutorials:nxt_dynamixel:capture10.png?nolink&300|}}
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-   *12V 2-Amp Power Supply
-\\
-{{:torres:tutorials:nxt_dynamixel:capture11.jpg?nolink&300|}}
-\\
-====Theoretical Background====
-The theoretical background pertaining to this tutorial includes [[lego_dynamixel_control|NXT/Dynamixel]] communication and [[2_link_kinematics|2-Link 2D kinematics]]. A review of these two tutorials will provide theoretical and practical knowledge for the reader in topics such as RS485 serial communication, NXT control of Dynamixels, 2-link planar kinematics, and geometric/algebraic solutions to inverse kinematics.
-====Build Plans====
-The build plans as well as the parts list are included below.
-====NXC Code====
-The code required for this project is shown below. The code is also attached in a .zip file along with the required header file to interface with the Dynamixel servos.
-<code>
-//2-Link Inverse Kinematic Control
-//Norberto Torres-Reyes
-//Date: 04/25/19
-//Calculates the angles needed to reach desired end-point using two dynamixel
-//servos for a 2-link planar mechanism.
-#include "Dynamixel2.h"
-#define ID1 91
-#define ID2 90
-float TwoLinkIK(float linkLength1, float linkLength2, float pX, float pY);
-//Global Variables
-float theta1 = 0;
-float theta2 = 0;
-//Program variables
-int servoOffset1 = 200;  //Zero offset value for servo 1
-int servoOffset2 = 468;  //Zero offset value for servo 2
-float posX = 16.9706;       //X and Y coordinates of desired position
-float posY = 0.0;
-float linkLength1 = 12.0;   //Lengths for both links
-float linkLength2 = 12.0;
-task main()
-{
- int servoPos1 = 0 + servoOffset1;  //Initial zero-angle position
- int servoPos2 = 0 + servoOffset2;
- UseRS485();                            //Initialize RS485 communication
- RS485Enable();
- RS485Uart(HS_BAUD_57600, HS_MODE_8N1); //57600 baud and 8bit, no parity communication
- Wait(100);
- setMode(ID1,SERVO,0,1023); //Initialize Dynamixel mode and range
- setMode(ID2,SERVO,0,1023);
- Wait(5);                   //Give time for dynamixel communication
- servo(ID1,servoPos1,50);   //Home both servos to zero-angle position
- Wait(5);
- servo(ID2,servoPos2,50);
- Wait(100);
- while(!ButtonPressed(BTNCENTER, FALSE)) //Program runs when orange button is pressed
- {
-  TextOut(0,LCD_LINE1,"Press Orange" );
-  TextOut(0,LCD_LINE2,"Button" );
-  TextOut(0,LCD_LINE3,"To Begin" );
-  Wait(10);
- }
- while(true)  //Loops following code until program is terminated
- {
-  ClearScreen();
-  TwoLinkIK(linkLength1,linkLength2,posX,posY); //Runs the 2 link inverse kinematic function
-  servoPos1 = theta1*(180/PI)*3.41 + servoOffset1; //Assign corresponding angles to each joints
-  servoPos2 = theta2*(180/PI)*3.41 + servoOffset2;
-  TextOut(0,LCD_LINE1,NumToStr(theta1*(180/PI)));  //output current link1 angle
-  TextOut(0,LCD_LINE2,NumToStr(theta2*(180/PI)));  //output current link2 angle
-  servo(ID1,servoPos1,100);  //move servo to new position
-  Wait(5);                   //allow time for dynamixel communication
-  servo(ID2,servoPos2,100);
-  Wait(5);
-  posX = posX + 0.0;     //increases desired position if desired-
-  posY = posY + 0.0;     //by a constant value or by some arbitrary function
- }
-}
-//calculates inverse kinematics for given parameters,
-//elbow up/down position can be changed by changing signs
-float TwoLinkIK(float linkLength1, float linkLength2, float pX, float pY)
-{
- theta2 = -acos((pow(pX,2) + pow(pY,2) - pow(linkLength1,2) - pow(linkLength2,2))/(2*linkLength1*linkLength2));
- theta1 = atan2(pY,pX) - atan2((linkLength2*sin(theta2)),(linkLength1 + linkLength2*cos(theta2)));
-}
-</code>
-====Running, Testing and Analysis====
-To run the code, open it using "Bricx Command Center" and set the zero offset values to 512. Compile the code and upload it to the NXT. Run the program before you install the servos to the 2-link arm. The servos will go to their zero offset position, which has not yet been dialed in. Install the servos on the arm (make sure each servo goes to the correct joint) and try to align as close to the zero-angle position as possible. Once installed, adjust the zero offset values until the zero-angle position is achieved.
-====Conclusions====