 RepRepBot Mrk I. | 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. |
 RepRapBot Mrk I. Renders in CAD | 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. |
 Front view |  Side view |
| |
Printing process
 Complete build of Motor Bracket |  Motor Bracket during extrusion |
 Complete build of Front Chassis with denser build raft |  Using the updated software, it was possible to build small and tall build using the cool function in skeinforge. This image show the fork for the small front wheel. |
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.
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.
 The biggest problem was warping of the largest piece (back chassis), but with fine tuned build raft the warping did not occur in this build. |  Complete extrusion of part above. No warping what so ever. |
 It was quite difficult to remove the plastic part from the build base. |  The setting for the percentage coverage is called Base Infill Density (Ratio). The second layer is called Interference Infill Density (Ratio) |