Line Following Bot


    Intro


    The IEEE Robotic club at Rutger was inviting all student to joint the line following competition to build a robot from a kit. The
    kit descriptions can be found here. They also made four classed meeting once a week for student who have no skill in soldering or programing to assemble the kit. After the four classes student have two week to prefect their bot before the competition.
        The kit costs $65, but since I already had Atmega sitting alone in a box I decided to get the kit without the Freeduino for $45. I got to use the Atmega and learn how to program it. I could not let this opportunity just pass by.

    Line Following Bot Mrk I.


     The kit only contains the electronics, motors, and the wheels. The body of the robot must be manufactured. To build the body, I decided to design the parts in CAD software. I measured all the dimension of the boards, motors, and the front sensor to build around it the rests of the body. Since the MakerBot Cupacake has limited build space, I could not have build one solid body for the bot. Therefore several smaller pieces need to be design instead. There are thee major components: the front and back chassis, and motor brackets. The the pieces are held together by T slots and leftover fasteners from CupCake assembly. The design allows for the motors to be facing to the front or back. The motor brackets themselves are symmetric, which means that they allow for the swapping of the motors. The motors themselves are held to the bracket by fasteners and the bracket are bolted to the back chassis. Mark I motor bracket are held by T slot and rubber band. However the Mark II uses fasteners, but due to the design it can be difficult to bolt it.

    Line Following Bot Mrk II.

    The new bot has few modifications that strengthen the chassis of the bot. Two I beams and two L beams are easy to install and there is no need for more fastener. The next improvement is the connection of the side motors. As the motor brackets are connected to the bottom of the back piece chassis through T joint, extra support from above is necessary to hold the motors in place. Unfortunately the MakerBot has limitation of building such connections shapes without the support material. After discovering the flaw in the first design, which prevents to add top connection for the side brackets, I modified the design to add a extra bolt on each side connecting the brackets to the back chassis. This however makes the assembly bit more complicated. Overall, the Mark II is simply modified  Mark I design for structural strengthening. If there will be a Mark III, a new design will need incorporate the height of the Atmega with the motor shield. Alternatively, the design can incorporate simple taller collum from the back chassis.  


    Bill Of Materials

    Quantity   Non-Printed Parts
    QuantityPrinted Parts
    QuantityFasteners
    1x
    1x
    1x
    2x
    2x
    Atmega
    Motor Shield
    Sensor Board
    Motors GM9
    Wheels
    1x
    1x
    2x
    1x
    1x
    1x
    2x
    2x
    Back Chassis
    Font Chassis
    Motor Brackets
    Small Wheel
    Front Axle
    Sensor Clip
    I Beam
    L Beam
     7
    4
    6
    2
    1
    Nut*
    Bolt* 8
    Bolt* 10
    Bolt* 16
    Bolt* 30
    *Not sure what exactly are the bolt types, but they have diameter of 2.26mm (leftovers from MakerBot)
    Notes:
    - The GM9 Motors did not came with cables attached so i had solder cables to them. I used cables from old computes that are used for power and reset switch.
    - The ribbon used to connect the motor shield to the sensor board is twitted because I mess up the assembly of the ribbon. I could flip the sensor board but I would have to change the code for the bot.


    Building of the largest print without warping

    The biggest problem occurred with printing the back chassis as it has the largest dimensions (86x54mm). I had to reprint it few times before the build would not peal off the build base after 10 minutes into the build. The most important thong is the contact area between the build base and the first layer of extrusion. Larger the are the stronger the force to hold it down and prevent warping. I printed parts with 90% coverage of area but it seem too much. Lower values like 70% to 50% can give same results. To be more cost effective the bonding between ABS itself is stronger that the bonding between build base. Therefore the coverage are can be smaller. I used 40% but lower values are not recommended on large prints. In addition, I recommend cleaning the build base before printing with alcohol to clean the acrylic from finger grease.

    You can download the STL files here


    Assembly Instructions







    Bill of Materials
     Bill of Only Printed Materials
     Assembly of the Small Wheel and Sensor Clip









     Assembly of Motor Brackets to the Back Chassis
    Note: put the two bolts into the bracket first and then bolt it to the chassis
     Assembly of the GM9  motors to the Motor Brackets
     Connection of Front and Back Chassis by I Beams







     Insertion of Atmega to the Chassis
     Attachment of Wheels and the Motor Shield
      Attachment of Sensor Board




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