Design Of A Controlled Platform Using Open Source Hardware

Manuel Zeno10/26/2011

Platform Designs• There are many types of controlled platforms

– Some are autonomous, i.e. self-leveling to the horizon– Others can be controlled remotely

• The proposed platform is designed to be autonomous while providing the user with angular control while costing less than $100

• Applications include nautical satellite tracking, camera stabilization, etc.

Proposed Design

• The concept design uses inexpensive parts to prove the open source hardware control works

• The platform will autonomously control two axis of rotation, pitch and roll using an Arduino Board

The Control System

• The platform is controlled via an open source Arduino microcontroller board

• The Arduino platform uses a variation of the C programming language as input and a ATMega microcontroller chip.

Tilt Sensing Using an Accelerometer

• The Arduino board reads data from an accelerometer to measure tilt angle– The measurement is indirect – In reality the accelerometer is measuring the acceleration

due to gravity in a given sensing axis

• The sensed acceleration allows the board to infer the angle the accelerometer is at any given time

Going from Gs to Degrees• The accelerometer measures

acceleration due to gravity in this case• As the sense axis is tilted, the

acceleration due to gravity sensed changes by the cosine of the angle of tilt

• Nothing in real life is ever linear…– Sensing sensitivity drops off as the sense

angle increases

• The sensitivity drop-off can be approximated using the inverse sine (arcsine) function

• Some error remains, but its smaller than the mechanical slop exhibited by the servos and hardware

Control System 2• Arduino programs are called

“sketches”• The Arduino program includes all

the aforementioned control schemes and also an “averaging” function

• Raw data from the accelerometer is “twitchy” and prone to outliers

• The code includes an “outlier eliminator” function which removes readings higher than limits from being averaged

• Averaging function allows for bulk measurements to be read

Control System Concluded• What distinguishes this design from others is the ability to control the

angle at which the platform attempts to remain at autonomously• This is done by having the user control the angle using potentiometers

– Twisting the potentiometers in one direction or another will change the resistance of the pot

– The resistance change read by the Arduino board will change the default angle value sent to the servos

Platform Demonstration

• Goto webpage