Solar Powered Outdoor Trike

• Locomotion powered solely by Solar
• Steering is controled R/C (operator controlled)
  • A small Li-Po battery powers the R/C reciever and steering servo

Project goal: Replace R/C steering control with pre-programmed (waypoint to waypoint) navigation using an onboard PICO microcontroller

• Pose data comes from GPS & IMU
• Pico coordinates everything:
  • Power comes from an onboard 3S (11.1v) or 2S (7.4V) LiPo battery
  • Buck converter to (5V)
  • gps (X-Y location)
  • Bosch BNO08x IMU ($\theta$-Z orientation)
  • Calculates steering to next waypoint
  • Controls steering servo to follow path to next waypoint.
    • can loop or drive to a destination
    • Upon arrival at final waypoint in list, a relay cuts the solar power

Collecting GPS data

Converting GPS coordinates to a local X, Y Coordinate Frame

• It's typical practice for a robot in its Home position to be located at the Origin (0, 0) of its World coordinate frame, with its own Local coordinate frame initially superimposed thereon.
  • This is ideally suited to robots that use wheel odometry to reckon their location. (Our robot doesn't need to do that. It uses GPS for its location.)
• Until the robot leaves its Home, it is poised to go forward in the X direction with a theta-Z value = 0.
  • The robot's initial Pose is (X, Y, theta-Z) = (0, 0, 0).
• However, in the case of this robot it isn't neccesary that the robot's Home position must be located in any particular place, but it is important that the IMU yaw = ZERO when the robot is facing in the X-direction.
  • It is important for the robot to have an IMU that gives reliable values for its Theta-Z orientation without drift

Transforming from Lat/Lon --> Easting/Northing --> X/Y Reference Frame

• GPS technology is wonderful for allowing our robot to figure out where it is, but we have to do a couple of transformations to get our desired X, Y coordinates in meters.
  1. First we declare the Latitude / Longitude of our chosen Home postion to be our reference coordinates. All other Lat/Lon coordinates are considered to be relative to the coordinates of our Home positon.
  2. With the Home position as the origin, we can come up with a 2D frame which looks like a normal map, with East-West direction along the horizontal axis and North-South direction along the vertical direction.
     • A Northing value (meters) is calculated from the latitude of any other location.
       • Measuring the Earth's circumference C in a longitudinal direction allows us to come up with a pretty simple relationship between latitude and Northing distance that holds true everywhere.
     • An Easting value (meters) is calculated from the longitude of any other location.
       • This isn't as simple. It also depends on your latitude. At the equator, you would have to travel a great distance East or West to go 360 degrees and get back to where you started, but if you are near one of the poles, you only have to travel a much shorter distance to get back to your starting point. So you have to know your latitude in order to know the distance around the world in the E/W direction.
  3. Finally, set the X/Y coordinate frame at the desired rotation. Zero rotation would align the X-axis to the East (Y-axis to the North). If it is desired to have the X-axis square to the face of the garage as shown above, the Easting/Northing map would need to rotate 148 degrees CCW about the origin.

Test drive CCW around circle

• The picture below shows the locations of waypoints numbered 1 through 9.

• At power-up, robot orientation must be aligned along the desired X-axis (square to the face of the garage)
• After power-up, the onboard led flash's quickly, until the start button is pressed.
• Once the start button is pressed, the robot then waits until the GPS module is providing good 3D fixes
• Once valid GPS values are produced:
  • a relay closes, allowing solar power to the motor
  • robot steers toward the first waypoint
  • upon arrival at the waypoint, the current waypoint is set to next in list.
  • upon arrival at the final waypoint, relay cuts power to the motor and program exits.

This is how I did the steering