controlling a servo with an accelerometer

Projects General Guidance
1

Ive had an idea for a while for getting a servo to move to a certain location when the accelerometer is in a certain position.

I want to use this in my model rockets I launch. As a way to provide an active flight stabilisation.

basically the fins move using a separete servo to keep the rocket flying on a straighter flight.

ive seen this project someone has done http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235613861

maybe it is possible to modify it so that instead of LED's, they are servos instead.

at the moment im looking at sorting out the pitch and yaw of the rocket. if the spin can also be elimitated that would be a bonus

Looking forward to the experts on here to help me out, on where to begin XD

Thank you

Adam Webb

p.s. If you need more info fell free to post a reply or send me a PM

2

That project is using the acceleration due to gravity to provide a local "upwards" vector.

This isn't going to work in a rocket as the dominant acceleration will be due to the rocket's propulsion system. In fact most accelerometers go to +/-8g and most model rockets will exceed that substantially at times I reckon!

So all you will be doing is measuring the angle between the rocket's thrust axis and the accelerometer's axis.

To do the kind of stabilization you are wanting you need rate gyros - these shouldn't be (much) affected by linear acceleration but will detect rotation rates. There are lots of resources out there about flight stabilization using 3, 6 and 9 DoF inertial sensing. Look for these.

Silicon MEMS rate gyros have significant drift, but on a timescale of 10's of seconds, probably not a worry for a rocket!!

3

i know a nooby question as well,

but which Arduino board will be best suited to this project

Thanks as always

Adam Webb

4

I have a feeling adding any kind of active guidance to a rocket is going to be illegal in many jurisdictions - be careful

5

I never though of that. guessing you are thinking that it could be seen like guided missile. done a little bit of googling and its safe as long as the rocket weights less than 20KG and doesn't fly higher than 1.5k feet.

im just interested in stopping my rockets having an erratic path going up. also a great project to show off for uni next year. going to be doing electronics systems engineering, so refining my skills while i'm on my gap year is always a good thing :slight_smile:

if I can get a bit of help with the basics to get me going then I can finished off the rest XD

Thank

Adam Webb