SKILLS Robotics 2006

Introduction
The 2006 SKILLS robotics challenge was centered on being able to play a modified version of basketball. Specifically, the game was to be played by a maximum of four robots at a time, with a center net approximately five feet above the ground, as seen in Figure 1. The objective of the game was to score as many junior sized footballs into the single net as possible within the allotted time. Increasing the challenge of reaching the five foot high net was a constraint requiring a robot volume of eight cubic feet. Eden High School sponsored two robotics teams with a budget of one-thousand five hundred dollars. Many of the used components were recycled from previous robotics teams to save costs.

Figure 1- A view of the center net into which the junior size footballs must be scored. The net stands at a height of 5 feet.

Each robot's starting position was within one of the four field corners. The playing field consisted of a 24 foot square area with a four foot square area in the center which contained the scoring net. Outside of the playing field were designated driver and spotter's areas as seen in Figure 2.

Figure 2- Above is a plan view of the playing field with given dimensions[1].

Design Solution
The solution was concieved from a loophole in the rules. The requirements stated that only six PWM channels were to be used to communicate with the robot. By using two receiver units, two robots could be used with one controller. The initial idea was to enable one of the two sections of the robot to be fully autonomous. The purpose of the first section of the robot was to gather footballs and queue them onto the second, such that one would be a stationary conveyor belt, and the other would be the fetching slave. Figure 3 shows the initial wire frame AutoCAD sketch. The blue and white lines indicate the base T unit, which carries the conveyor system. Whereas the C unit is indicated by the red lines, and was the “fetcher”.

preliminary AutoCAD wireframe
Figure 3- From hand sketches, a 3D AutoCAD wire frame was made to couple the two robots together, and allow for quick modifications and general build guidelines.
-The Red lines indicate the fetching robot (C unit)
-The Blue lines indicate the conveyor linear bearing assembly that could be extended.
-The white lines outline the base T unit, namely the section that remains stationary during the competition and “dunks” the footballs into the net via a conveyor belt.

Since the most complicated piece of the design was the conveyor system AutoDesk Inventor modelling was performed in order to ensure that the system would be functional. The simplistic solid model could be used to extend the collapsing conveyor and ensure that lengths and angles were correct. The sliders were modeled from a factory 2D AutoCAD drawing including bearings and plastic friction joints, seen in Figure 4.

A detailed assembly of the left slider configuration was constructed. Pulleys were placed in key areas. Figure 5 shows this configuration in detail. Figure 6 shows an aerial view of the base T unit fully extended.

Figure 4- Above is the front view of the desk drawer linear bearings used in the conveyor assembly. The AutoDesk Inventor model includes all bearings, and friction couplings.

top view of left lift assembly
Figure 5- Above is the left slider stack, including pulleys that maintained tension on the aircraft cable which held the conveyor up.

top view of the base T unit
Figure 6- Here is an aerial view of the complete base T unit, with focus on the basic extended conveyor assembly.

The Build
Since there were two robots to build, time and commitment was of the essence. The team of four was split into three. Liz was in charge of the assembly of the C unit, David was in charge of the base T unit, with Chris and Shane who built the conveyor assembly. Along each critical point of construction decisions were made as a team. Because of the sketching and modelling done prior to construction, the frames of each part of the robot were completed quickly. It was the finalization of the machines that was time consuming. Electrically deprived frames of the robot are shown in Figure 7. At this point of construction only accessories such as the ball retrieval mechanism on the C unit, and the conveyor on the base T unit were in need of completion before electrical systems could be mounted.

completed frames
Figure 7- This figure shows the preliminary structures of both the base T unit (top) and the C unit (bottom). In this image, the base T unit does not have the conveyor mounted, and the C unit does not yet have the retrieval claw attached. At this stage all of the mechanical components were assembled, excluding the electrical system body mouldings and accessories.

Software code
Programming was done in the ANSI C language on a Microchip 18F8520 PICmicro microcontroller and was planned to govern the base T unit completely. Although all planned features were not implemented, the controller still controlled aspects such as sequentially raising and lowering the conveyor, anchoring the base to the ground so that it could not be moved, as well as the electromagnetic attachment between the base T unit and the C unit. Features that were not implemented included automatic control of the conveyor.

A view of the InnovationFirst MicroChip PIC
Figure 8- The controller is shown on the left side of the image. The microcontroller was intended to govern the whole base T unit. Due to time restrictions, it only controlled basic movements such as interactions between the C unit and the raising of the conveyor.

The Competition

The competition results left this team in third place out of four. During the competition (Figure 9), several performance issues were encountered. The main problem was that the design of the retrieval claw on the C unit was inefficient and unreliable. The design made it too difficult to orient the robot into the correct position and pick up the football. Another problem was that there was not enough time to make the base T unit fully autonomous, placing more strain on the operator of the robot. Needing to control two robots at the same time slowed down the retrieval and ascending process that was needed to score a point. Although there were problems with the design, there were also positive features. The two tiered concept of using more than one robot would have been very efficient because while one was raising the ball to the net, the other would already be fetching another. The small C unit contained a very solid drive system that enabled it to run circles around other machines, meaning that it could locate a ball faster. Yet, because the claw was so inefficient it was not able to secure the ball. The complexity of the machine allowed the team to learn more, such as programming, CNC manufacturing, and electrical design.

A Picture from the competition
Figure 9- As can be seen above in the round between only two teams, the two blue robots belong to the Eden #1 team. Here the base T unit is fully extended and is waiting for a football to be placed in its queue. Meanwhile, the C unit is in the process of picking up a football. Once picked up, it will drive to, and straddle, the blue area on the base T unit, and place the ball in the queue. Near the top of the image, the scoreboard can be seen, amplifying overall results. As can be seen, Grimsby (the Canadian Champions) took a far lead to other teams such as West Park. The average number of balls we would enter in one round was maybe one or two, since the majority of the game time was spent fumbling with the ball in an attempt to pick it up.

The Team

Chris Wiebe
-Conveyor construction & design
-AutoCAD
David Mikolajewski
-Team leader
-AutoCAD
-AutoDesk Inventor
-Electrical system
-Programming
Liz vanOverbeeke
-C unit frame construction
-C unit claw construction
-AutoCAD
Shane Dirksen
-Conveyor construction & design
-AutoCAD

Refferances
[1] 17TH ONTARIO TECHNOLOGICAL SKILLS COMPETITION, October 21, 2007, http://www.skillsontario.com/competitions/pdf/2006/Robotics%20Scope.pdf [view mirrored pdf document]

Fast Fact

SKILLS Robotics 2006