Trekker Functions

The trekker is a robot that can drive around your house, apartment, office, garage...� It even works outdoors on short grass!

The Trekker is designed around the OOPic. OOPic is an acronym for Object-Oriented Programmable Integrated Circuit. It is the first programmable microcontroller that uses an object-oriented language. For more on programmable microcontrollers see our PIC page.

The Trekker becomes more and more autonomous as you add on the peripherals. The SuperDroid Trekker will operate with just the OOPic driving the chassis wheels, but as sensors are added, the Trekker becomes more aware of its environment and is able to respond to obstacles.The following sections explain the features and functions of the SuperDroid Trekker.

• How the SuperDroid Trekker Sees
• SuperDroid Trekker Scanner Options
• Trekker Outputs (LCD)
• Programming the SuperDroid Trekker
• What the Trekker Does

How the SuperDroid Trekker "Sees"

The Trekker is currently sold with three ways of seeing. They are:

• Infrared: This method sends an infrared signal out (invisible to the human eye) and times how long it takes for the signal to reflect off an object and return to the infrared receiver. The time it takes to reflect is then converted into a voltage. Using the OOPic code, an oIRRange Object converts the voltage to a distance. An IR signal is good at reflecting off most surfaces that have some reflective properties. The Trekker IR detectors are Sharp GP2D12 IR detectors that mount to the rear or front of the Trekker chassis, front scanner brackets, bumper switches, or as part of a sweeping detector. The IR detector will detect obstacles and cause the robot to stop.� The IR detector can detect from a range of 4 inches to 30 inches. The tabs on the chassis and limit switches can also be bent back to aim the detector at the floor so that a loss of the floor can be detected. Doing this will prevent the Trekker from driving off a cliff (or more likely down the stairs).
• Ultrasonic: This method is similar to the IR except it uses sound to reflect off objects. The time it takes to return the sound is converted to a distance using the oSonar OOPic Object. The ultrasonic sound is considered the "ping" and the returned sound is called the "echo". The ultrasonic signal is good at reflecting off most hard surfaces.� Surfaces that absorb sound do not work as reliably. The Trekker ultrasonic sensors are Devantech SRF04 Ultrasonic rangers that mount anywhere an IR detector can mount.� The Ultrasonics can be mounted in the same locations as the IR detectors or with the IR detector on the dual sweeping arms. The Devantech SRF04 Ultrasonic detector can detect from a range of ~4 inches to ~10 feet.
• Bumper Switch: This acts as the name implies - if it bumps into something the switch contacts are closed and the OOPic gets the signal. The Trekker will then stop once the bumper switch is activated.� The Trekker can be equipped with bumper switches on the front and back.

The combination of the IR and Ultrasonic are good at detecting 95%+ of obstacles in the line of sight of the sensors. The Trekker offers these sensors on sweeping arms to increase the range of view. The other important item to consider is the reflection angle. If the IR or Ultrasonic Ping hits an angular surface, it may not reflect back to the detector, hence the instrument will not detect the obstacle. Again the sweeping arms help reduce this by varying the sweeping angle of the detector. See figure below:



Virtually every obstacle can be detected with these detections systems.� An example of an object that may avoid detection would be a thin wire at a level above the limit switch, but at a height that the wire will hit the boards or scanners.� Nothing is perfect - even humans bump into things.� With the scanners attached, the SuperDroid Trekker has new perfect vision.

SuperDroid Trekker Scanner Options

The least expensive option is to start with just the Trekker Chassis and OOPic II. The drive motors have to be run with a different power source than the OOPic, so the Trekker OOPic Expansion Card is recommended If the Trekker is not equipped with any sensors, the OOPic can be programmed to drive for timed intervals and navigate blindly. Starting out with this is an excellent idea if you're new to programmable autonomous robotics because it will allow you to program and experiment with the OOPic. With the Trekker OOPic Expansion Card, you can experiment with operating servos, LEDs, potentiometers, beepers, and switches without having to worry about power supplies, electronic noise, and wiring issues because the Trekker OOPic Expansion Card has all that covered. (Electronic noise can be a very frustrating and painful learning experience, avoid this with the Trekker OOPic Expansion Card). Follow this link for details on the Trekker starter package.

The Trekker has two basic types of obstacle scanners/detectors. They are:

• Fixed scanners: These are hard mounted to the chassis or bumper switch and can not have their field of view adjusted relative to the Trekker itself (i.e., to look to the right, the robot has to turn to the right)
• Sweeping scanners: These are scanners that are attached to a servo via a bracket and allow the scanner/detector to look with a field of view slightly greater than 180 degrees. They can look without the robot having to rotate/drive.

Setting up the Trekker with scanning capability starts with the Trekker Starter Package combined with one simple inexpensive upgrade to an IR sensor kit or Ultrasonic sensor kit, which can be added to the Trekker chassis to give the Trekker a set of eyes that look straight ahead.� The OOPic can be programmed to drive and turn when it sees something in its way. You now have the start of a truly programmable autonomous robot!� Follow this link for details on the Trekker Basic package.

The next evolutionary step with the Trekker is adding a sweeping scanner.� There are currently 4 different scanner brackets for the Trekker. Attach IR, Ultrasonic, or IR and Ultrasonic sweeping scanners to the brackets and the scanners can be programmed to oscillate/sweep as the Trekker scans the area for obstacles.� Once an obstacle is detected, the scanner can look for a clear path. The scanner brackets include:

• Front Scanner brackets: The front single scanner bracket and the front dual scanner bracket will allow scans from left to right. These give the Trekker scanning capabilities while maintaining a low profile.
• Top Scanner brackets: The top single scanner bracket will yield 180 degrees of viewing. The direction is up to you. It can scan from front to back, or side to side. When using the Top dual scanner you can achieve a full 360 degree of viewing. The top scanners sit about 8" off the floor so very low profile obstacle will not likely be detected with these detectors.
• To scan high and low, one can combine the front and top scanner brackets.

The scanner brackets can then be equipped with either an IR sweeping detector, ultrasonic sweeping detector, or a dual sweeping detector (both IR and ultrasonic).

The SuperDroid Trekker can also be equipped with a front and/or back bumper switch. The limit switch is a scanner in the sense that it will detect obstacles. It does this by making contact, whereas the IR detectors and the Ultrasonic sensors are non-contact sensors.

To help the Trekker know where it is going, it can be equipped with an electronic compass. The compass will interface with the OOPic and tell the Trekker which way it’s heading. This feature is very useful in robotic navigation. The user can program in desired headings so the Trekker can navigate in the same direction and go towards a goal.

Another aid to robot navigation is line following. The Trekker can be equipped with a line following system. Line following is a very popular competition amongst robot enthusiasts. The Line following feature requires 2 to 4 sensors that work just like the IR sensors discussed above. An IR light is emitted out of the sensor and reflects back to the IR sensor. A black line does not reflect as well as a white surface, so the sensor can determine if it sees a line or not. Programming and positioning the sensors can be optimized to achieve very good line following. In competition the object of line following is to follow more and more difficult courses the fastest.

Fire Detection is also a very competitive event. The object of the fire detection is to navigate the robots through a maze of walls and look into the rooms and see if there is a fire.� Using a UV sensor, a flame the size of a single candle can be seen 5 meters away. The Trekker utilizes a Hamamatsu UV sensor that can be mounted onto one of the Trekker sweeping sensor brackets. The Trekker can then scan a room with its sweeping servo and report if a fire is detected. Added variations on this contest will include putting the flame out and returning to the starting point. The Robot that finds the flame the fastest is awarded the most points.

Soccer robots are also gaining popularity. The object of the soccer robots is to work as a team and push a soccer ball towards a goal. This is a very complex and competitive sport. The Trekker can be equipped with brackets that attach to the front bumper switch. The brackets will detect if it has caught a ball using a IR sensor that shoots across the front of the bumper switch. The soccer robot works best with a Trekker that has a front scanner attached to the bumper switch and at least one sweeping scanner attached to the top of the Trekker on a scanner bracket. The basic principle of finding the ball is to use the top scanner and scanner attached to the bumper switch. If the lower sensor sees something the top scanner does not see, then it’s likely a ball. The top scanner will not see the ball since it is below its field of view. The Robot can then drive towards the ball, fetch it, and drive it to its goal.

Autonomous Sumo Wrestling is another sport the Trekker can perform. It uses many of the sensors listed above. The line following sensors can be used to warn the Trekker that it is about to go or be pushed out of the circle. The Trekker uses its sensors to seek the other robots and simply tries to push it out of the circle.

SuperDroid Trekker Outputs (LCD)

It is always a good idea to get a Liquid Crystal Display (LCD) to help troubleshoot your programs or to display data. The LCDs plug straight into the Trekker OOPic Expansion Card. They mount mechanically to the back of the Trekker with the supplied bracket. Again, the back of the robot is considered where the caster wheels are, but if desired, the OOPic can easily be programmed and operated as the front.

Programming the SuperDroid Trekker

Don't be afraid of the programming! The Trekker OOPic Expansion Card comes with sample programs for all stages of the Trekker and the OOPic website has great programming help and examples. If that is not enough, there are several chat boards, the most popular of which is Yahoo, where help can be obtained at all levels. All the programs can be written in basic, C or Java. The Trekker example programs and the majority of the examples on the OOPic website are in Basic. The assembled Trekker packages will come wired, tested and programmed.

Here's how the programming works: The OOPic software must be loaded onto your PC. The software is supplied on the CD that comes with the Trekker OOPic Expansion Card or can be downloaded from the OOPic website.� Once the program is on your PC, you write or load a file, then download the file to the OOPic using a program cable.� The parallel port programming cable plugs directly into the back of your PC and the other end plugs into the OOPic board. When your program is ready to be run, you turn on the OOPic and click RUN on your OOPic PC program. The OOPic software compiles the program and sends it to the OOPic chip.� The OOPic will then immediately start to run the program.� The program is not lost when the OOPic is turned off (well, at least not for about ~90 years!). Unplug the cable and the SuperDroid Trekker is on its own running the program.

Finally... What the Trekker Does

So with all this said, what does the Trekker do? That's primarily up to the user on what scanners and accessories are added.

With just one fixed scanner mounted to the front of the Trekker (see Basic Trekker Package), the supplied program will allow the Trekker to drive forward until it encounters an obstacle. Once it sees the obstacle, the OOPic gets the signal from the detector and directs the motors to stop. The Trekker will then turn and look for a clearing. If the Trekker detects no clear path it will continue to turn until it sees an opening. Once it detects a clear it will continue to drive forward until it detects another obstacle. With just a front bumper switch installed, it will act much the same, except it will look for intimate contact before stopping.

With just one more simple addition of a single sweeping scanner, the Trekker becomes a lot more autonomous and flexible. The sweeping scanner allows the Trekker to have a larger field of view by oscillating back and forth as the Trekker is driving (see scanner section above). The other big advantage is that the Trekker can look for an alternate route when an object is encountered by moving the scanner versus moving the entire robot. Since a single scanner can only look a little more than 180 degrees, it is best to set the scanner to look forward and be capable of looking left or right. This leaves the back as a blind spot, but since the Trekker was driving forward when it encountered the obstacle, there aren't likely any to be new obstacles in the rear. However, a rear detector can be added to the back of the robot chassis to make sure all is clear before backing up. The other way of looking to the rear is to set the single sweeping scanner to look forward, right and reverse or forward, left, and reverse. The best technique is to get the top dual scanner and have one scanner look forward, left, reverse and the other detector look forward, right, reverse. The dual scanners give the Trekker double the eyes and also make looking for a clear path quicker because it can look right and left at the same time. So with sweeping scanner(s), the Trekker can be operated with a single fixed scanner, except when an obstacle is detected. The Trekker can look for an alternate route without moving the wheels. Once a clear path is detected, it can change its course and go on its way.

As discussed in the sensors section above the robot can be used to drive towards a common goal with a compass. It can be used to find a fire. It can follow lines. It can be used for sumo wrestling. A lot more can be added to the program including wall hugging, motion detection, etc. as you learn more and more using the Trekker with the OOPic Microprocessor.

A lot more can be added to the program including wall hugging, maze navigation, etc. as you learn more and more using the Trekker with the OOPic Microprocessor.