EEZYbotArm MK3
Programmable robotic arm
DESCRIPTION
OPEN-SOURCE
PROJECT
Problems addressed
After printing the 3D files downloaded from thingiverse I noticed two design flaws:
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GRIPPER, among the stl files there isn't any connection gear between the servo and the "fingers" of the clamp. Without them it is not possible to obtain the movement of the gripper and therefore the arm could not grasp any object. So I adapted the components of the MK2 model to be able to mount them on the MK3.
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ENGINES, the 28BYJ-48 stepper motors were too weak, so much so that it was hard to lift the weight of the arm components alone. In the description of the project in thingiverse it is suggested to make modifications to the motors taking them from polar with 5 wires to bipolar with 4 wires to increase the torque. Doing so would no longer be possible to use the ULN2300 card. I preferred then to design supports that would allow the use of two MG90S micro servos in place of the two stepper motors that should move the arm. In addition to the supports I also had to design new types of gears, with appropriate spacers, to adapt the "pinion" of the servos with the movement mechanism of the arms. In this way I was able to perfectly control the movements of my MK3.
The use of the servos has also proved to be very useful in the programming phase because, with the encoder iside the servo, arduino is able to receive feedback on the position reached. Regarding the motor that allows the vertical rotation of the arm I have maintained a stepper motor 28BYJ-48.
Improvements
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PHOTOCELLS, once the arm is finished and assembled I realized, during programming, to need feedback on the vertical rotation to be able to identify the angle of rotation to which the arm should be stopped and then execute other commands. So I design a KY-008 laser module support to be connected to the base of the arm (file stl: EBA3: 004.STL) that allowed me, through the photoresistors fixed on the work surface, to make photocells. In this way I was able to send feedback on the angle of rotation of the arm to the Arduino.
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CONTROL THROUGH SMARTPHONE, for the initial phases of the project I used for the movement of the arm a control panel specially created on breadboard. Once the setting is finished, I have implemented an android app with which you can control all movements via a bluetooth connection with arduino using the HC-06 module.
YOU CAN FIND ALL THE STL FILES OF THE COMPONENTS DESIGNED IN THE FOLLOWING LINK:
PRINTING
For the components printing we used our Flashforge Creator Pro with two different colors of PLA: white and blue. The filling varies according to each component, for example the gears have been printed with 100% infill while the base and the arms with infill 30%.
Furthermore, thanks to careful design of the components, it was not necessary to add print media.
ASSEMBLY
For the assembly of the components were used M3 and M4 screws and nuts of different lengths, washers, self-tapping screws to fix the base cover and the support for the laser module and a 4mm diameter plug to connect the arm to the base.
I have also used 2 bearings 606 (6x17x6) fixed in the base that allow the vertical rotation of the arm through an M6 bolt that acts as a pivot.
Here is a very detailed list of the thingless MK3 page.
PROGRAMMING
For the programming of my MK3 I used arduino mega connected to different devices:
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1 MG90S micro servo to control the clamp
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2 MG90S micro servo to move the arm
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1 28BYJ-48 stepper motor for vertical rotation connected via ULN2300 board
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1 KY-008 laser module and three photoresistances for feedback on the angle of rotation
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1 HC-06 module for bluetooth connection with smartphone
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8 buttons to manually control arm movements
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1 power supply for breadboard MB102 as the only power supply of arduino is not enough to run all the motors / servo
Initially I compiled a program for the manual control, by means of a push-button panel, of the arm with a serial computer / arduino communication that allowed to receive the position reached, for each movement, of each servo. This step is essential if you want to write a program for an automatic cycle as it is necessary to know the coordinates in the space to be reached in order to perform, afterwards, operations such as grasping an object.
Once the manual setting was completed I proceeded to compile an automatic cycle whose objective is to move a packet of cigarettes and a 3D cube in three positions in space at different distances from the base of the MK3.
It is at this stage where I realized the need for the photocells described above.
After verifying the correctness of each program I have developed an android application through which it is possible to manually control the arm and start the execution of the automatic cycle.
At the end of the page there is a video of the complete project.
YOU CAN DOWNLOAD THE ARDUINO CODES AND THE APPLICATION BELOW:
I have developed two applications one without automatic cycle option (MK3) and one
complete with cycle start button (MK3 +)
