Mini Tankbot

Homing Vehicle with Obstacle Avoidance

By Jamie Mitch

The Idea

Build a small mobile robot on treads (a tank) Add some sensorsGet it to find a beacon within a roomKeep it from running into things

Basic Logic

Look for Beacon If not found, wander

Head towards Beacon If obstacles detected, avoid Periodically check location of beacon

and adjust direction

Find Beacon

The Parts

The robot kit Tankbot from BudgetRobotics.com

High-power Tamiya Twin Motor gearbox kit Tamiya rubber tank tread kit (treads, sprockets,

axles) Precision pre-drilled and pre-cut plastic base --

includes second deck for micro controller or other electronics (hah.)

Assembled Mini Tankbot

The Parts (2)

Motorola HCS12 micro processor 76 configurable I/O lines 8 channel, 16-bit enhanced capture timer 256K Flash 12K RAM 4K EEPROM

The Parts (3)

Sensors SHARP GP2D15 Detector Package

Infrared ranger which will detect an obstacle within approx. 24 cm

Returns a logic 1 if detected, 0 if not detected

Optek OPB745 Reflective Object Sensor Detects a reflective object within its field of

view Range is approximately 3.8 mm

The Parts (4)

A quadruple half H driver chip Allowed logic output from the

processor to drive the two DC motors

The Parts (5)

PNA4612M IR Detectors Can have a range of 11m or more Carrier frequency is 38kHz Will be mounted on the Tankbot

LN64PA IR Emitters Angle range of approximately 45° Will be mounted on the Beacon

Obstacle Avoidance

There will be 5 IR rangers on the tankbot 3 in the front to detect obstacles 2 in the rear to aid in determining if

the obstacle has been successfully avoided

The sensors will stop the tankbot approx. 9” from an obstacle, leaving plenty of room for maneuvering

Obstacle Avoidance (2)

Ideally obstacles will be box shapedThe logic If the model finds an obstacle, it will run a

recipe to avoid it The processor will keep track of how far off

course the avoidance recipe puts the tank, and will compensate after the obstacle is no longer a danger

Problems with Logic What about walls?

The Tankbot

The Beacon

The beacon will be a freestanding tube Will house the IR emitters Will contain the circuitry required to run the

emitters, including one or more 555 timer chips

Will be surrounded by reflective tape, to allow the model’s optoisolator to determine if the beacon has been found

Will *not* be connected to a microprocessor

The Beacon (2)

User InterfaceOperations & sub-modes Controller Indicator Description

ON/OFF Switch (on/off)

Red LED is on when Power is

received

Simply turns the power to the vehicle and controller board on and

off

- Switch (on/off)

Green LED is lit The vehicle will find its beacon, and move toward it

Reset Button - Acts like a Panic Button: resets the system to Standby

Seeking - Blue LED is flashing

The vehicle is currently seeking the signal from its beacon

Found - Blue LED is lit The vehicle has found its signal, and is following it to the source

Collision Detected - Orange LED is lit The vehicle has detected a collision, and is avoiding it. The LED will go off after the collision is no longer a

problem

User Interface (2)

The interface display and described is a simplified version that can be expanded if time allows

Cost Estimates

Component Quantity Cost per

Each Total Cost

Tankbot 1 $ 45.00 $ 45.00 Sharp GP2D15

Detector Package 5 $ 12.18 $ 60.90 Optek OPB745 1 $ 3.60 $ 3.60 PNA4612M IR

detector 8 $ 1.43 $ 11.44 LN64PA Infrared

Emitter 8 $ 1.43 $ 11.44 HCS12

microprocessor 1 Free $ - LED's & other misc

components 1 $ 25.00 $ 25.00 Grand Total: $ 157.38

The Problems/Obstacles

Accurately designing the IR emitter circuit to create as close to 38kHz as possibleRunning into obstacles at an angleSolderingWorking aloneBatteries, Batteries, Batteries