Initial and Final Design

Initial Design

Mechanical Subsystem

RC Car base
Launching Mechanism
- Carriage on linear rails connected to metal springs
- Motor will pull carriage back, carriage will automatically release at a set point
- Justification: most promising method from prototyping phase
Reloading Mechanism
- Rotating carousel, single hole in baseboard
- Bean bag will drop into launch carriage when over the hole
Range Adjustment Mechanism
- Lead screw will change the distance at which the launch carriage releases

Reloading Mechanism

Launch Mechanism

Initial Concept

Section View

Electrical Subsystem

Battery: 12V NiMH
Arduino Uno Board
- Wireless Arduino dongle to connect the computer to the onboard Arduino Uno
- Justification: Previous Arduino experience
Motor controllers for the winch and lead screw
System will be teleoperated using a Xbox controller
- Justification: familiarity with controller
Sensors:
- Smartphone camera to act as wireless camera
- Limit switch to signal system when bean bag is in place
- Laser range finder to provide distance feedback to the driver
- Encoder on launchers angle adjustment lead screw motor

Software Subsystem

Based in C
- Justification: Arduino
Five main functions:
- Reset and Retract Cart
  - Send control signal to launcher motor
- Measure Distance
  - Read output from laser rangefinder, calculate distance, and report via bluetooth
- Load Bean Bag
  - Command loader to move next bean bag into position
- Adjust Launch Distance
  - Send control signal to lead screw motor
- Control Input Interpreter
  - Map control input from Bluetooth signal to assorted functions
Justification for teleoperation-based programming: designing around teleoperation will allow us to focus our development on a robust, repeatable launching mechanism

Final Design & Comparison

Mechanical Subsystem: Chassis

Final design was a custom wheeled base
- Initial RC car base idea wasn't feasible - cars were too small with not enough power and too expensive
- Two wheels were used so that the robot could easily turn for aiming the launcher
- Caster wheel used for third wheel for simplicity

Mechanical Subsystem: Launcher

Final design was a spring loaded launch system on a linear shaft
- Initial idea used, but with small tweaks
- Only one linear shaft was used to prevent binding
- Surgical tubing used instead of metal springs as it is easier to modify the overall spring constant
- Still used motor to pull carriage back
- Launch triggered when launch pad was released from the hook by rack
Range adjustment system
- Similar to initial idea, but a rack and pinion was used instead of a lead screw

Mechanical Subsystem: Reloader

Final design was a rotation carousel
- Very similar to initial idea, but slightly changed for ease of mounting
- Only rotates through 180 degrees as only two beanbags needed to be reloaded
- Beanbags drop through hole over launch pad, as described in the initial idea

Electrical Subsystem

Our power and control system remained the same as in the initial design.
We ended up not using the laser range finder as we found it to not have the range that we needed and in the range that it could read we found it be unreliable and inaccurate.
We did not use a limit switch to tell the driver when the bean bag was loaded into the launcher, it was unreliable and we relied on the second smart phone for this confirmation during the competition.
We also did not end up relying on the limit switch to tell the driver when the launch carriage was detached from the pull carriage as the driver was close enough that the sound of the launch carriage releasing and hitting the stop was a signal enough.
A lead screw was not used to adjust the shooting range of the launcher, thus we did not use an encoder. Even with the servo, rack and pinion we did not use a feedback system as to the racks position, the adjustment of it was all based off of the drivers experience and practice with the system.

Software Subsystem

The flow diagram shown here displays a high-level flow diagram for the software subsystem. This method was largely in-line with our initial design concept, with functions to reset and retract the launch system, reload a beanbag, adjust the launch distance, and interpret the Serial command inputs. Our launch distance adjuster was changed to a rack-and-pinion based method rather than a lead screw, so the actuation provided by this function was changed, and we did not include a laser rangefinder in the final prototype, though the software still includes functionality to support one.

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