The Rover was created to show how a robotic base can be made utilizing the Finger Board as the embedded controller. One of the design goals was to keep it simple and inexpensive but with enough flexibility to add additional sensors.
Standard radio control model servos were chosen as the drive units. They can be purchased for around $10-$15 from the local hobby shop. Ours were purchased from Tower Hobbies when they had a sale. Using servos instead of regular gear motors kept the drive circuitry simple. There was no need for a H-Switch motor control chip, instead the servos are controlled by sending a Pulse Width Modulation (PWM) signal directly from a processor I/O pin. The two drive servos were modified to move the full 360 degree rotation. Please see our Servo modification for 360 degree rotation page for info on how this is done.
Two separate battery packs were used, a 7.2Volt nicad pack (yellow) to power the Finger Board and a 4.8Volt pack (white) to drive the two servos. At first we tried a single 7.2Volt nicad battery but we were experiencing low voltage CPU reset errors when both servos were driven simultaneously. Switching to separate battery packs solved this problem. An added advantage to this configuration is a much longer run time. The battery packs are surplus cordless phone nicads purchased from mail order electronic catalogs.
The software program for the Rover is written in Interactive C. The Handy Board dual servo routine written by Fred Martin was used to control the servos. We will be posting a copy of the Rover program as soon as it is cleaned up a bit.
|As a base to mount the processor board and servos, we used a standard prototyping board that was cut to 4"x3.5" size. Any size board will do but we wanted the rover to be small and compact. The first step is to layout an area on the protoboard to mount the processor board and servos. Make sure all the pins of the processor board are accessible from the bottom of the protoboard and are not covered by the servo case. Use female headers to mount the processor board so it can be removed from the robotic base. Please see our Finger Board prototype board page for more info. The servos are secured to the board using double stick foam tape. The type that 3M sells works really well.|
|The two forward bump switches are held on with screws.
Small diameter piano wire was bent to form the "whiskers" and
then soldered to the leaf switches. The two light sensors are mounted
using double stick foam tape to the underside of the protoboard. Kynar
wire (wirewrap) was used to connect the sensors to the processor board
using point to point soldering techniques.
Rover sensor interface schematic.
|The wheels used on Rover were purchased from the local
hobby shop. These are 2 1/2" diameter Balloon Tire Scale Wheels
made by Williams Bros. Inc. They have a nice rubber compound for good
traction and a inner rim made of plastic. A servo control horn was used
to connect the wheel to the servo. I used some hot glue to center and
hold the control horn on the wheel and then drilled small pilot holes in
the plastic for screws to fully secure it. The small screws that came
with the servo worked well for this.
The "third wheel" is just a 3/4" wooden dowel that has the bottom rounded off and then screwed onto the protoboard. A furniture caster wheel may work better but I haven't found one that is small enough.