Coin Manipulation

Notes, designs, and pictures on the Coin collector.

Design Ideas

 * Funnel: collect coins in a large funnel bucket, attached to the end of a robotic arm that can swing around in a circle.
 * Magnet: hold coins with an electromagnet at the end of a robotic arm, which can spin around to the back to deposit them.
 * Octopus: like a Transformer, the robot would unfold 3 retractable arms that span the distance from the server to the three exchanges. Coins would slide along the arms into each of the servers.
 * Conveyor belt: drop coins onto a conveyor belt to transport them to the back of the robot.
 * This was our initial favorite, but we decided against it because it requires too many moving parts. Adjusting the tension of the belt also seemed like it would be particularly challenging.
 * Turntable: drop coins onto the front of the robot, and use a rotating pinwheel to slide them to the back.
 * This is the simplest approach because it only has one moving part and one motor spinning in one direction.
 * Additional ideas:
 * Sensor to tell when a coin has been collected
 * Sensor to tell when pinwheel has completed a quarter turn
 * Funnel in the front to catch falling coins

Turntable Design Sketches
One challenge the turntable idea poses is how to get the coins to fall out the back. We have three ideas:

1. Ramp: cut a slice out of the bottom plate in the back, and put a ramp underneath so the coins slide away. Unfortunately, there might not be enough of a slope if the entire turntable is tilted upwards in the back because there is only a 2" height drop from coin dispensation to coin delivery.

2. Slider: Attach pegs arranged along a radius of the plate near the hole in the back. As the pinwheel pushes coins against the pegs, the coins will be pushed out the back. This approach may not be easy to implement because the coin may get stuck when being pushed against the pegs.

3.  Cone: Instead of a flat bottom plate on which the coins slide, there will be a cone sloping downwards. This forces coins to slide along the outer ring of the turntable, which allows them to fall out a hole in the back. One challenge will be creating a smooth, conical surface.

Choosing a Motor
See "Choosing a Motor" in the "Drivetrain" section for calculations. Since the turntable needs high torque and low angular velocity, we chose the Jameca 153438. Since it operates at 30 rpm, each quarter turn would take roughly 0.5 seconds (a reasonable time to dispense coinse).



Circuit using LM293 driver (H-bridge for bi-directional rotation)