I don't think the accelerometer is a bad idea, its a senior project
afterall, here are some suggestions
1) You could limit the r/c car to travel on a smooth flat surface
This might work. You will still need to deal with bias (offset).
2) Use a big heavy slow r/c car and soft mount your electronics on the
car with foam
I don't see what good the foam does. I would rather have the thing rigidly
mounted to a rigid frame rolling on very hard wheels. Any freedom of
motion between the accelerometer and the vehicle will just lead to errors.
3) If you want to get carried away add a analog devices gyro to your
dual axis ADXL202 accelerometer and you have a complete 2 dimensional
inertial navigation system which is a very good learning experience.
Basic idea is the gyro tells you what direction your pointing in the
then you determine your acceleration in that direction with the dual
axis accelerometer you are using. Integrate that to get your velocity
and position.
Touching a hot soldering iron is a great learning experience, too.
4) Take 64 or so readings of the gyro and accelerometers and average
them before using them, this will lower the noise level. Since your
integrating the accelerometer outputs, any noise left will tend to
averaged out (its the constant offsets that kill you)
The drift of analog devices gyros are good to about 70deg/hour (after
some simple calibration), so you should have plenty of accuracy for a
few minute demo before the car gets lost and doesn't know where it is.
The car should be able to drive itself around a simple maze in this
time too.
The gyros might be OK for providing yaw information over the short term,
but I still don't think the accelerometers will work very well.
Everybody comes into a project with a different set of skills and
experiences. It is my opinion that unless the OP has a lot of talent or
some really good people on his team, he needs to keep it simple or he will
not submit a working project at the end of the allowed period.
If the floor is even half a degree out of level, the error will be totally
intolerable after 60 seconds. If my calculation is correct, the velocity
error will be something like 5 meters per second,(using v = at, with a
being 9.8m/s * sin(0.5 deg)) and the distance error, using d=0.5at^2 is
over 100 feet.
If he really wants to do telemetry, maybe he could just put a microphone
on an RC car, digitize the audio, and send it over the wireless link. It
would sort of be a spy-mobile. A camera might be even better.
Or why not just take speed off of the axle or motor?
I'm just trying to save Ben's butt.
If an accelerometer MUST be used, some ground truth needs to be applied to
rein in the drift. Maybe the car could be stopped periodically (every
couple of seconds) at which point a message would be sent to the
u-controller, somehow, telling it that the current bias readings
on the accelerometer should be zeroed out.
--Mac
