The accelerometer signal needs to be differentiated to get
velocity. The ADXL signals are quite noisy so you are better
off having a direct velocity signal from a gyro, particularly if
using PID control.
Robert

James James wrote:

> Hi everyone,
> 
> I am thinking to build something like the nBot from
> David:
> http://www.geology.smu.edu/~dpa-www/robo/nbot/
> 
> I think it would be very cool to put the Feedback
> Control Theory I learned to practice.  I am currently
> gathering information/parts to build the robot. 
> Anyways, I have few questions:
> 
> 1.  Isn't the accelerator alone enough?  I mean all
> you need to know are how fast the robot is tilting and
> the current tilt angle, right?  Couldn't the
> accelerator alone do all that?
> 
> 2.  What's the role of the gyroscope?  I understand
> that the output voltage change of the gyro is
> proportional to the speed or rate of the tilt angle. 
> Isn't it the same as what the accelerator does?
> 
> I am refering to the DXRS150 gyro and the
> ADXL203/MMA7260 accelerators.
> 
> Best regards,
> James
> 
> 
> 
> 
> 		
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