At 21.45 2012.06.19, you wrote:
>Em 19/6/2012 15:06, Robert Rolf escreveu:
>> ML is correct.
>> If your mems sensors are hitting a physical limit, they will no longer
>> produce a correct average
>> due to clipping.
>>
>> The typical solution to your problem is having an accelerometer with
>> sufficient dynamic range that it
>> does not clip, and low pass filter the heck out of it. Then use a rate g=
yro
>> to get your dynamic tilt.
>> Combine the two signals to get a noise free tilt signal. LPF accel+ HPF
>> gyro at same break point.
>> Given your extreme vibration, you will want to find a gryo with the lowe=
st
>> acceleration induced errors.
>>
>> See the 'composite filter' techniques used in the DIY Segway software.
>>
>> Robert
>
>
>I am sure the OP said he can't mechanically filter the signal. Why?
>I think it is easy to stick the entire board to a heavy metal plate and
>below them put a soft sponge pad. Is the application that space constraine=
d?

It has to be swapped with the original ECU, which is already (like mine) on
silent blocks (not so effective it seems), space is so tight I cannot use
neither 1mm (no joke, really) more than I already do, and to find the right
box already took me many weeks. :( Also, there's no way I can make it thinn=
er,
to reach this "thinniness" (spelling? :D you see English is not my native
language ;) ) I had to work truly a lot, and my ECU is packed with a lot
of features and components, while the original was truly basic, so it was
already a huge effort (even using small LGA, Micro8 and 0403 components)
to pack all into the original space.

In answer to other messages, the accelerometer I'm using is +/- 6g on all
3 axis, I don't think it's clipping anymore (it was when it was +/- 2g ),
this board is potted on epoxy now, but next week I'll make another one
without the huge LP RC filter I made, and I will try to sample it very fast
and do a FIR filter or try again my favourite solution, i.e. one sample
per engine revolution, but (as Trevor suggested) synchronized to a certain
degree relative to the top dead centre, where maybe vibrations will cancel
out enough (hopefully). I know it's not only the piston or the crankshaft
which cause vibrations, there's the gearbox, the clutch, etc.. but it's
worth a try anyway, maybe the thing become usable.

Cheers,
Mario

>
>
>Isaac
>
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