A Versatile PIC16F876A Based Robot




Design   Summary:

Our group designed  and  manufactured a  miniature  robotic  vehicle  that  conquers  various terrains.    The  vehicle  was designed  with  a  track system  which is  powered  by  two  DC motors. The  motors   use a  Quadruple half  H ‐Driver in  order to  drive the  motors  in  both  directions.   The track system  incorporates a  four  bar linkage  for each  tread.    These two  linkages  allow each  side to  be independently  raised  which gives the  robot multiple configurations.   These configurations
allow the  vehicle  to  drive on various  terrains.

PIC16F876A Based Robot

The  robot is   initially  turned  on with  a  simple  switch.    The  LCD  displays multiple mode options and  gives directions for selecting  a  mode.   Once the  user  selects  the  mode via the  keypad  they are then  asked whether they  want full speed,  half  speed,  or  stationary.   Once selected  the robot carries  out the  chosen  mode and  speed.    While running,  the  LCD  displays what current action  the  robot is  carrying out.

During  mode 1 the  vehicle  tracks  remain  flat  and  the  proximity  sensor  becomes  the  main input. Once the  sensor  passes   a  certain  threshold  the  robot reverses,  turns,  resumes  forward motion at  half  speed  via PWM for one  second, and  then  continues  on at  full speed.    Mode 2 will be the same as  mode 1,  but the  tracks  remain  in  the  raised  position.  For mode  3 the  tracks  default position is  raised  but the  accelerometer  becomes  another source  of  input.    The  accelerometer
data  is  used  to  tell the  robot’s  position relative to  gravity.   If  the  robot is  climbing  steep terrain the  y  output  from  the  accelerometer  will pass  a  determined  threshold.   Once this  occurs  the robot will reconfigure  to  flat  configuration  for lower  center  of  gravity  and  maximum traction.    If
the  robot is   traversing along a  slanted  incline  or  object  the  x  output  from  the  accelerometer  will pass  a  set threshold.   Once this  occurs  one  side  will reconfigure  to  flat  dependent on which side
is  tilted.

Design Evaluation:

The robot and all of its elements worked very well. Our output displays worked the way we needed them to. We have a simple LED that  lights up when the robot power is on and the LCD displays our mode and speed menus exactly how we  wanted it to. For our  audio output device we used a buzzer. There is a very short buzz about once a second while the ro bot backs up. This is
one element that we could have chosen to use  something more difficult, but there were other elements that were far more crucial to the functio nality of the robot that we chose to spend the extra time on.

PIC16F876A Based Robot schematic
Our three manual data inputs are a potentiometer, switch, and keypad, all of which work well. The switch turns the robot on and off, the potentiometer is used to control the contrast of the LCD, and the keypad is used to select the  track configuration mode and motor speed. We also used two automatic sensor inputs which were an accelerometer and an IR sensor. The accelerometer works great. When the robot is tilted  past a certain point the servos will change the track configuration depending on wh ich way the robot is tilted and then set them back to normal position once level again. The IR sensor works great, too. We used it to tell the robot when it is about one foot away from a wall or tall obstacle,  at which time it stops, backs up for about a foot, turns right for 1.5 seconds or about 60-70 degree s, then proceeds to drive forward again.
The actuators we used were two servo motors and two PWM speed controlled and reversible DC motors. The servos control the linkage for the tracks and puts them at either 45 degrees or flat which is exactly what we wanted them to do. The two motors are for the robots drive train. We were able to get them to reverse and change speed just as we wanted. They also turn separate
directions simultaneously, which we  used to turn the robot.

For more detail: A Versatile PIC16F876A Based Robot




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