Hey James,
  I set up an ADXL accel. in analog mode for static tilt measurement
(following the datasheet) about a year ago and it worked fine with only a
little averaging. Differentiate that signal to find the rate of change of
angle. The only thing I could see holding you up is that to calculate tilt
you have to take a sin or cos.. that could limit your sampling rate.
 I have built a balancing robot before (from the same inspirational source.=
.
nbot) so I'll be happy to offer any experience I have from that. I used a
pot to measure tilt for simplicity.
 James

 On 11/16/05, James James <james_ibox@yahoo.com> wrote:
>
> Hi Robert,
> Thank you for your reply. Are you suggesting to only use the gyro and
> forget about the accelerator? how about the Freescale accelerator? Is it
> noisy too? Thanks!
>
> Robert Rolf <Robert.Rolf@ualberta.ca> wrote:
> 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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