I am also thinking of mounting
 one of the cheap $80 12 bit AD to D data acq system back there
 with the USB interface to monitor the 555 EFI system and its
 sensors on a notebook computer. Add a few ten dollar pressure
 sensors and lots of things are possible. The A to D can also handle
 the fuel flow read out and fuel totalizer in software.

 http://www.hytekautomation.com/

 I just came up with another idea using a tiny electronic load cell
 out of a cheap bathroom scale incorporated into the motor mount to
 measure prop torque. Knowing prop torque and prop RPM you know HP
 out of the gear box. The A to D system can measure that as well.
 I got the idea by watching the TV program Deconstructed on the Science
 Channel. I'll appropriate  Robin's  bathroomscale :)

 -----------------------------------------------


 Here are some pictures of the load cell in Robin's bathroom scale :)
 I'll have to buy her a new one at $34.

 It is battery powered for the life of the scale in that black container
 behind the LCD read out.

 I'll work on a 3D dwg for the mechanism for the end of the S-beam
 motor mount. One side has all the load due to engine torque.
 The 12 bit A to D has such  a high res and a wide dynamic range
 it does not matter if it is measuring the weight of the engine only
 when the engine is not running. The trick is have it bottom out
mechanically
 so it does not damage the load cell during hard landings and high G pull
up loads.
 That would be like having an over 300 pound person standing on the scale.

 Paul Lamar

Hi Paul,

Those things like to turn themselves off after a few seconds.  The ones
I have make you tap the scale, then it goes through several seconds of
a power up sequence.  You may have to figure out some way to bypass the
automatic power feature and supply a larger battery.

Bob W.
--
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
3.8 Hours Total Time and holding
Cables for your rotary installation - http://roblinstores.com/

I figure I could use just the load cell part.
It is probably The crystal type.
The force is applied to a piezoelectric crystal
and you measures the voltage across the crystal.

---------------------------------------------------
Preliminary design.

Here is what it would look like on the end of the S beam.
It is possible to retrofit an existing motor mount by
cutting off one cup and welding this on.

The lever reduces the load on the cell.

Does anybody see any problems with this

Paul Lamar


Paul,
instead of adding an additional moving elements,
use the beam or the mount as a flexture and mount a strain guage on it.
price on strain guages have come down to $88 at omega.
http://www.omega.com/ppt/pptsc.asp?ref=Prewired_GP_Strain_KFG&Nav=pree02
just put the strain guage amp on the 555 board with trim pot to calibrate
the gain.
Larry


Kind of complicated Larry. One would need a computer.

Here is the rational for that statement.
The p-port engine torque could be as high as 200 foot pounds depending on
the tuning. The beam is seeing the prop torque due to the GB which could be as high as
570 foot pounds. (2.85 X engine torque) That is an up load on one end of the 36
inch beam of 190 pounds and a down load on the other side of 190 pounds.
Each side of the beam also carries a down load of about 150 pounds due
to the 300 pound weight of the engine/gear-box/prop/starter at one G.
So one rubber bushing sees 340 pounds down and the other sees only
40 pounds down under full chat. A lot less at cruise on the heavy end
and a lot more one the light end.

Looking at it from the pilots point of view the prop rotates the same as
the engine with the 2.85:1 GB or clockwise. There fore the left side sees a
down load of 340 and the right side sees a down load of only 40 pounds.

Unless of course you have a 2.17:1 GB and then the prop rotates the other way
things are reversed and the torque readings on the bushings are lower.

Now the question is where do we mount the strain gage?

The hydraulic cylinder sensor is beginning to look easy to me. It's like
the carb verses the fuel injection. Something even I can understand.

Don't let me discourage anybody if they want to take the all electronic
approach.

BTW There are some radio transmitting strain gages on the market that
can be mounted on a rotating shaft but they are rather expensive.
http://machinedesign.com/article/torque-telemetry-goes-digital-0724

Another way of doing it is measure the twist of the e-shaft directly
by using two ABS sensors, one on the front of the engine and one on the
rear. a high speed single chip computer can then measure the time
difference between the two sensor signals. Lets say it takes 6 ms to rotate.
That is 6000 micro seconds ( I think :)) One degree of twist
would be 16.66 micro seconds. You might get a single chipper
to measure that. GPS receivers do it all the time.

Another way is to convert the ABS sensor signals to
square waves and subtract one from the other using an op-amp.
If the diff. is zero there is no twist. The more the twist the
higher the voltage difference.  I don't know how much an E-shaft
twist under power but I'll bet it is a lot less than a V8 :)


Paul Lamar