====== How To Modify Dynamixel SDK code ======

**Author:** Yunki hong(05/2019), Myong Geon Kim(07/2019), Brandon Seo(Current) Email: hyunduck1024@gmail.com 
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**Date:** Last modified on <06/20/19>
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**Keywords:** Tutorial, how to, step-by-step, dynamixel-sdk
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This tutorial is an exercise session which means not only reading this session, please trying to write your own code.
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===== Motivation and Audience =====
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Readers of this tutorial assumes the reader has the following background and interests: 
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<fc blue>  
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  * Basic background of CPP 
  * Full understanding of dynamixel set up : [[dynamixel_set_up|Dynamixel Set Up]] 
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The rest of this tutorial is presented as follows:
  * [[dynamixel_modification#wheel_mode|Wheel mode]]
  * [[dynamixel_modification#actuationg_time|Control actuating time]]
  * [[dynamixel_modification#direction_change|Direction Change]]
  * Final Words
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==== Wheel mode ====
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Default setting of dynamixel has CCW angle limitation.
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If we want to actuate dynamixel both CW and CCW, we need to unlock that limitation.
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We call it "Wheel mode".
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For unlock CCW limitation, We will use 
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dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL1_ID, ADDR_CCW_LIMIT_ANGLE, 0, &dxl_error);
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function.
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Here we can find an address for CCW Limit angle.
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=======================================================================================================
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 Exercise. Make the code for two Dynamixels to actuate in wheel mode on the same speed via Input speed. 
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Here is an {{https://drive.google.com/file/d/1Lh8SF3xtb9EvSjx5d_uSam0nXvXJ-Hkg/view?usp=sharing|answer}}
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==== Control actuating time ====
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For controlling actuating time, we will use "sleep" function in "window.h" header file.
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Search on Google if you have no idea about sleep function.
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function is
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Sleep(time)
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In this function, Time is millisecond(1/1000 second).
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<fc blue>
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Exercise. Modify previous code for Dynamixels to actuate during input time
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Here is {{https://drive.google.com/file/d/1_BO2PKD7thJg1jXfoisZ7NxwpFquCt0c/view?usp=sharing|answer}}
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==== Direction Change ====
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Know how to change the direction of rotation is important for controlling Dynamixel.
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Dynamixel speed has its own speed scale.
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Read e-manual http://emanual.robotis.com/docs/en/dxl/mx/mx-28/#control-table-data-address
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As you can see, 
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CW speed + 1024 = CCW speed
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Now you know how to change direction.
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=======================================================================================================
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Exercise. Modify previous code for two Dynamixels to rotate on different direction. 
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Answer :
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dxl_comm_result = packetHandler->write2ByteTxRx(portHandler, DXL1_ID, ADDR_MOVING_SPEED, spd, &dxl_error);
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dxl_comm_result = packetHandler->write2ByteTxRx(portHandler, DXL2_ID, ADDR_MOVING_SPEED, spd + 1024, &dxl_error);
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=====  Multiple Dynamixel Control =====
when you understand all above of the code, you can finally control each dynamixel.
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Here is the{{https://drive.google.com/file/d/13vAPs-_guWaK6iAprfK9gJNgOi7UekHC/view?usp=sharing=sharing|answer}}

Now you know how to move gantry.
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==== Final Words ====


For questions, clarifications, etc, Email: m.geon.kim@gmail.com