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