[Diy_efi] Strain gauge on engine mounts

[hugh at sol.co.uk]

Milosz,

I have accelerometers on the vehicle as well, but the two axis
accelerometers will not resolve for bumps in the road / hills etc. A three
axis accelerometer set-up might be better as it would resolve out the
unknowns.

I beleive airbag accelerometers are very cheap to buy and might provide a
reasonable and complete solution.

I also have a digital speed measurement which is easier to use, but also
does not allow for bumps in the road / hills etc.

Thanks

Hugh


Original Message:
-----------------
From: Milosz Kardasinski miloszk at gmail.com
Date: Tue, 19 Apr 2005 05:23:14 -0400
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] Strain gauge on engine mounts


>Using one on each mounting point will, I hope, allow you to delete the
>effects of bumps in the road.

It's a bit more complicated than that because the loading on your engine
mounts
is combined loading...axial, lateral, bending and torsion. Don't forget that
strain
gauges have a temperature drift that you need to account for and lastly,
they are
fragile devices, when I played with them 10yrs ago you could break them
pretty
easily not to mention that it was a pain in the but to get them to bond
well.

>Going over a bump, each strain gauge will be compressed by the weight of
>the engine, but the difference should I think still equal the engine
torque.

Probably not, the reason is that I have seen very few engines that have
their
CG colinear with centerline, but you might be lucky something you have to
check. You'll have to figure what the weigh distribution is side to side and
front to back if the mounts are not on the same plane.

>There will obviously be calibration issues, but I am looking for a tuning
>aid rather than a definitive torque number.

Complicated way of going about it...but that shouldn't stop you. How about
using an accelerometer instead? You could zero all the extra variables
introduced
by using systematic and methodical approach to your testing. A one axis
accelerometer
will give you acceleration, braking....with a 2-axis you could measure your
lateral
accel (cornering) as well.

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