6. Testing and Refinement Phase

6.1 Testing and Problems Encountered

Failure Analysis Report of Chalk Dispenser - 12-04-09






Problem Reported through Testing

Following the first trial run with the final working prototype, the Smart Car group encountered major setbacks with the Chalk Dispenser system. The code was written and uploaded to the Arduino - however, the RC car failed to accelerate due to the weight of the chalk dispenser. Although the servo arms were functioning properly, when the RC Car turned on, a servo arm broke off.

Results of Inspection and Testing

After further inspection of the RC Car, the group was able to pinpoint exactly what caused the failure to accelerate:
  • Heaviness of the Chalk Dispenser caused the back of the RC Car to be weighed down - to the point where it dragged on the concrete floor.

  • Poor assembly of the servo arms caused them to be flimsy and fragile. Apoxy glue, instead of Acrylic glue, was used in the process of assembling the vehicle.
Analysis and Conclusion

Throughout the design process the excessive weight of the overly built chalk dispenser was never taken into account. When initial testing for the car began it was elevated on a wooden block, and once it the car was ready to move onto road testing it became apparent that it was far too heavy. Unnecessary thickness of the materials used contributed to the weight. The support bar, for example, was 1'' thick when it is perfectly capable of being .5''. Also, the Chalk Dispenser was too far out, causing an unbalance of distributed weight.

The servo arms came off due to the shakiness of the car when turned on. Poor build quality and assembly (largely in part to what glue substance was used) made the final prototype incredibly unreliable.



Recommendations
  • Complete overhaul of the Chalk Dispenser is required. A new design that will meet the weight restrictions.

  • If possible, with the new design, it will be more reliable if screws were used in place of gluing. The servo system is an excellent location to implement this procedure.

  • The new model will have to not be so far out the back so that weight is distributed evenly.

  • If possible, increasing the suspension will help elevate the car to make up for any heaviness that the new dispenser may have.


Pull Start Problem Encountered 12-14-09

Problem Encountered

During the testing of our code, we encountered a major setback: the pullstart mechanism on our vehicle broke. While working after-school hours, one of the team members accidentally pulled too hard and disrupted the spring mechanism found inside. The screw also became loose. The following images show exactly where this problem occurred:





After thorough refinement, the pulling system still failed to work. The spring was put back in place and everything seemed fine until we tested it and it still failed to start the car. When pulled, the mechanism failed to retract the rope. This made start-up nearly impossible and prompted the group to buy a new pulling system.


6.2 Refinements

Chalk Dispenser and Servo System

After addressing the weight and arm issues, a new Chalk Dispenser was designed to meet the required performance criteria for this component. With this new design, the chalk dispenser no longer weighed down the RC Car and had working servo arms. Along with this new chalk dispenser came a redefined servo system. Our old system had one inconsistent servo. After each run-through, the placement of the arm would be different than where it had originally had been set. Resetting the arm proved to be inconvenient. This issue was resolved through simply getting rid of the inconsistent servo and using only one. The following image displays these new systems:



Pull Start Problem

With Exhibition Night only three nights away, finding a replacement pull start was first priority. After scouring the internet, it was nearly impossible to order one without having it arrive with only one work day left for the group. Karl Wendt, the course teacher began calling local hobby shops till he was able to contact a shop that not only had the pull start but a more reliable one at that. In the end a day of tinkering and brainstorming proved informative but inevitably wasteful as we found a new pull start in time.



Vehicle Tolerance Issues (Continuous)

One of the biggest issues we encountered through the coding process was making up for the front right wheel's alignment. When driving, the RC Car would slightly move to the right although it is commanded to drive straight. This threw off the path written in the code and made the shapes that were being traced out unrecognizable. This had been a previous issue throughout the entire project process. While there have been efforts made to fix the wheel system, it had proved impossible to fix without professional help. To make up for this issue, the group had simply adjusted the code to make each turn made by the RC Car in compliance with the wheel system.


Coding Issues Manipulations

Our initial goal was to spell out HTHMA-E. Through the entire coding process, limited space as well as vehicle tolerance issues have proved this goal difficult to meet. Because of time constraints, the RC Car is now tasked to write out MAE (Media Arts Engineering). Although the code remains the same, constant refinement and tweaking of turn angles have been made to meet this performance criteria. This makes the demonstration of the RC Car on Exhibition Night possible.

Re-wiring of Arduino and Breadboard

To make sure nothing in regards to the wiring system goes wrong on Exhibition Night, the wiring was changed from 20 Gauge to 18 Gauge. This allowed for less probability of the wires falling out when the RC Car is running. The following image exemplifies this re-defined system:



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