The Seeker

By:Greg Courville
My application is in the category of robotics. This robot was created for a creativity competition (www.destinationimagination.org) in which the following obstacles had to be overcome: (1) knock down an object, (2) elevate an object and place it on a platform, and (3) ascend a ramp. While others pondered solutions with toy cars and strings and sticks, I thought, "BASIC Stamp® !!". The product is literally of hundreds of hours of work, the SEEKER won our team the " Destination ImagiNation Renaissance Award for Outstanding Skill in the Area of Engineering. "

The system drives two motors at joystick-controlled speed, raises a platform on a tower, and drops the platform using a servo... all controlled over a 2400bps 433mhz RS232 serial link . The SEEKER consists of a drive base, a motherboard, a BS2 daughterboard, a radio reciever board, a tower, and a 6-cell, 7.2V, 2100mAh battery pack.

The base is a modified radio-controlled toy vehicle. It has two independent drive trains, (each with a motor, gearbox and two wheels) one driving the left side and the other driving the right. The motors provide enough torque to do what they are needed to do, and the large, air-filled monster-truck wheels provide excellent traction and minimum travel resistance, for optimal performance on both carpet and tile. The internal electronics are removed and the motors are connected, via a medium-duty ribbon cable, to the main board.

The main board is built upon a self-fabricated, printed circuit board and holds all of the electronic components including the home-built BASIC Stamp 2 module, the motor drivers, and various power and support components. The drive-train motors are driven by a pair of National Semiconductor LMD18245 full-bridge DMOS motor drivers with built-in PWM, controlled by a 4-bit data bus for speed control, as well as BRAKE and DIRECTION lines. Input current to each driver is regulated by an LM317 adjustable regulator (in current-limiter configuration) and a 1-ohm resistor. The tower motor is driven by a pair of L293D full-bridges stacked together. The home-built BASIC Stamp daughterboard ( PBASIC Interpreter Chip , EEPROM, high-power regulator, power filter capacitor, and RS232 interface including programming connector) mounts via a special 24-pin DIP socket. Headers on the top of the board connect the receiver board, the motors, the tower winch motor, the platform servo, the limit switches, the drive motors, and the battery pack. Three LED's indicate power, recieved data and current status.

The tower mechanism consists of a servo-supported platform mounted on a sliding tower made from a ball-bearing drawer slide, and a home-made winch. The winch winds up a string, which passes through a pulley at the top of the tower support, is attached to the bottom of the sliding tower. When the string is pulled by the motor, it raises the tower until a catch engages a limit switch, at which point the Stamp cuts power to the motor. The servo can lift and drop the hinged platform to drop the object on it.

The radio receiver consists of a TWS-433 receiver board ($5.80 from www.qkits.com), a resistor, and an antenna. The receiver connects to the main board via a 3-line ribbon cable. Data is transmitted from the computer by a hand-made transmitter module that consists of a board mounted directly on a DB9 connector holding an optocoupler, resistor, and diode for RS232 level conversion, as well as an RWS-433 miniature 433mhz 2400bps transmitter , an LED, and a wire antenna. The board mounts directly to the serial port connector on the laptop PC, and power is provided via a USB connector .

The SEEKER is controlled by software written for robot remote control, called GeeDrive. It reads a joystick via Microsoft DirectX, then calculates motor speeds and direction, and creates a 4-byte data packet made up of a synchronization byte, 2 data bytes, and a confirmation byte. The data bytes contain the motor speeds and directions, as well as data for other application-specific functions. There are 3 available function controls, each activated by a key on the PC's keyboard. The SEEKER uses two of them, for the tower elevator control and the platform servo control. The program is written in C++, and runs in console mode under Win98 (other OS's untested).It is highly flexible, can use COM1-COM4, and has a selectable transmission baud-rate. During operation, the transmitter can be brought enabled and disabled by pressing the "T" key, so you can leave the program running and the bot won't run away. This program may eventually be released upon request.