hardware

An easiest way to build a robot is to use an already built RC car. It is sturdy and reasonably accurate in motion. However with budget of $75, we could not purchase a RC car. Instead, we decide to build a robot from the scratch to meet our requirements.


Requirements

•Accuracy

•Must be able to turn in place (or at least 90° turn)

•Hold pen and must be able to lift it up fast

•$75 budget


We have used Rapid-Proto-Typing to make bodies and basic structures easily. After simply designing parts with Solidworks, we can use laser cutting on acrylics to produce reasonably accurate parts. Also the Rapid-Proto-Typing was very favorable since we do not have any machining experience and mechanical professor had let us use the machine without any cost.


Our largest concern was the motor implementation. DC motors are very easy to use but it is very inadequate for system that requires accuracy. In terms of accuracy, the servomotors are very favorable, however, the cheapest servomotor cost about $15 and it takes significant part of the budget. Instead of servomotors, we had chosen a stepper motor, which is accurate enough for our use and it was very cheap (we had scavenged it from previous project).


How can we rotate a body by 90° with minimum number of motors (since number of motor is limited by budget)? This is a question that we had struggled to find an answer. The rotation motion is crucial since any error can lead to a larger error after long run of drawing. Robot can be indifferent of its sensitivity to error if there is a feedback system. Originally we had decided to use optical mouse sensor as a feedback system but we had failed to decode PS/2 communication initialization of the optical mouse sensor. The most sensible answer to the question is using two stepper motors to rotate in different directions.


While scavenging previous projects, we had found very interesting part, a solenoid (191172-001). Current induced through the solenoid pushes the pin of the solenoid while pin becomes loose without any current. Using these characteristics, we built a simple lever system that goes up when pin is pushing.