The Mechanics

For it to work, we had to:

- build a sturdy frame that would hold the chute at an angle so gravity would do the work

- test ways to distinguish between glass, metal, and plastic

- control the gate's opening and closing

- figure out a way to have the robot move intelligently

We built terraced walls to prop the chute at a good angle. They were reinforced with vertical beams pegged in to their sides.

To distinguish materials, we considered using a combination of reflectance and resistance sensors. The reflectance sensor could not tell a Coke can from a plastic bottle, so we dumped that. The resistance sensor failed to register the can, presumably because the coating stops current flow.

Robbie mentioned a project that used an LED and photo sensor as a break-beam object sensor. With his help, we built an LED for the Handyboard and mounted it opposite the photo sensor. Our theory was that each material would let a different amount of light through so the robot could tell what it was carrying. Our first test took us to the bathroom on the first floor of the Science Center, a single room without windows. We turned off the lights and tested the bottles. Our theory was right!

For the gate, we topped a long Lego brick with flat gear teeth and ran it through two holes on either side of the chute A 24-tooth gear attached to a Lego motor moved the gate back and forth. We added stops at both ends of the gate to keep it from flying out. The outside stop is a Lego peg; the inside stop is a piece of plastic Linda cut out of a lid.

RecycleBot has to move across the edge of a table in a side-to-side manner so the chute can face you. We attached medium-sized wheels, four per axle, to the geartrain running up the back of the 'Bot.

The geartrain is a 16-tooth gear attached to the motor connecting to a 40-tooth, which is on the same axel as another 16-tooth, which goes to another 40-tooth, which moves two 24-tooth gears that connect to another set of 24-toothers which are on the main axels. The gear ratio is about 1:9.5. This system gives the 'Bot enough torque to move itself, the HandyBoard, and heavy items like glass bottles.

An infrared reflectance sensor in the middle of the front directs it. The sensor shoots out an IR beam and measures how much of it is reflected back. It can distinguish between the table's surface, the table's edge (by 'seeing' the floor), and the strips of black tape we used to mark the bin locations.

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Created by: Linda Fung and Catherine Lee
January 2007
Background image from: www.lancashire.gov.uk/
Background music from: Captain Planet