Robot | robot

CONVEYONNAISE

DESIGN OVERVIEW

Our robot, Conveyonnaise, was designed to both meet the criteria of the competition, and to be as robust for the task as possible. As such, the robot utilizes a conveyor belt storage and drop-off system to store multiple passengers to increase travel efficiency. The robot also does not rely on a map of the course, using an array of infrared sensors to detect the roads and passengers, and therefore could run on any course that meets the competition regulations. The robot is able to use these sensors to turn toward any passengers in front of it, and uses a stable arm configuration to consistently pick them up. Once the robot has acquired the maximum number of passengers, it can use the conveyor belt to drop them all off at the same time.

For a more information about the competition visit “http://projectlab.engphys.ubc.ca/enph-253-2016/competition-2016/”.

Click to view design proposal:

DRIVE TRAIN

The robot is driven by two wheels at the back of the chassis, while the front was supported by a third wheel.

To allow sufficient speed with precise handling within the city, we designed the drive train with a gear ratio of 3:1. The 10-teeth gear was laser-cut from delrin so that the teeth did not snap, as it is a small gear. The 30-teeth gear was laser-cut from acrylic and was directly screwed onto the wheel. The wheel was water-jet printed cut using 0.5” polycarbonate with a diameter of 3”. A rubber tire was glued onto the wheels to increase traction so that wheels did not slip. Geared Barber-Coleman motors were used to run the wheels and steel brackets were made using the waterjet to hold the axle and the motors in place.

The front wheel is a 1 ½” swivel wheel. The height was chosen so that the chassis can be level with the playing surface.

PICK-UP MECHANISM

The pick-up mechanism consisted of an arm and a claw. The design of the arm allowed for the claw to remain at a constant angle with the ground, at 0 degrees. This allowed for easier pick-up and drop-off of dolls because we did not need to worry about the dolls orientation. The design consisted of three servo motors, one for the rotation of the arm and two for the vertical and horizontal movement of the arm. Because the motors produced a limited amount of torque we used a gear ratio of 2:1 for the two servo motors responsible for vertical and horizontal movement. Note that a 1:1 gear ratio was enough for the servo responsible for rotation. The claw consisted of one moving arm powered by a motor. This design is simpler than the traditional two arm powered claw and also contributed less weight on the end of the arm. The arm and claw were both mainly fabricated out of acrylic with spacers made out of hardboard. The geared parts were made out of polycarbonate/delrin which is a stronger material to allow for the forces that are present when the arm is moving.

CONVEYOR BELT

The conveyor belt was an idea that spawned because we wanted to hold more than one passenger. Only 2 other groups accommodated for more than one passenger. We decided that the easiest and most simplest way of holding multiple passengers was a conveyor belt because it allowed for easy pick-up (the arm would only have to load the passengers in one position) and easy drop-off (the passengers could be spun off). The design of the conveyor belt was based off o-rings as it was more reliable than the conventional belt-design. The o-rings were held in place by bearings with 3D printed guides on a metal rod. The bearings were spaced apart with heat-shrink. Only one side required bearings to allow the o-rings to move freely while the other side consisted of a metal rod with heat shrink to allow for friction. The friction was required because the rod was being rotated by a Gear Barber-Colman motor with a gear ratio of 5:4 which in turn spun the o-rings on the conveyor belt. Note that the conveyor belt was also elevated to allow for storage space for wires and circuitry underneath.

SENSORS

The robot used an array of infrared (IR) sensors to be able to detect passengers, the drop-off zone, and the roads. An array of 3 IR detectors were attached to the front of the chassis, facing left, right and forward, so that the robot could detect passengers on the roads ahead of it. Likewise, another 3 sensor array was mounted on the top of the robot to detect the IR emitting drop-off zone. Two more IR sensors were mounted on the side of the robot, so that it could align itself with passengers for acquisition. Additionally, an array of 4 IR reflectivity sensors were mounted, downwards facing, to the front of the robot, in order to detect the roads and intersections. All IR sensor signals were run through a filter circuit, consisting of TL082 operational amplifiers and a collection of resistors and capacitors, in order to filter out noise and all unwanted frequencies.

SOFTWARE/DECISION MAKING

The software framework for the robot consisted of constant tape-following loops, with interrupt handling for any additional actions required (intersections, passenger acquisition/drop-off, etc.). The code was written to be able to handle the robot’s actions on a per intersection basis, meaning that it could run any course given to it.

In order to have the robot follow the roads, a simple PID control loop was used to adjust the wheel speeds. While this loop was running, the robot would constantly query its IR sensors to detect intersections and passengers and act accordingly. Using the forward facing IR sensors, the robot was able to find the direction of an upcoming passenger or drop-off zone, and make the correct turn at any intersections accordingly.