If it needs to be calibrated with a torque wrench why not incorperate the strain guage to the motor mount or make the guage part of the mount. Even though the mounts are ridgid they still see the load. If it is buffered you should be able to correct for it. Tell me if Im wrong.

Mine will be calibrated on the bench with a 3' lever arm and a known amount of hydraulic force applied to it.

tomcat,
i always enjoy reading your posts. you always have some creative ideas.
just my opinion here, but i think it would be a very tough challenge to measure propshaft torque accurately. i agree with insptech about reading the coupling or somewhere on the driveline before the verticle shaft in the drive. in my opinion the propshaft has too many variables that would make accurate calibration very tough. critical speed harmonics, propshaft bearing wear, gear wear, oil viscosity, prop cavitation, different gear cuts, 90* gear loading and trim angles just to name a few things. sorry for the negative input on a good idea i don't know if you were going to read millivolts but that is another can of worms underwater.

So if we can't measure propshaft TQ and HP then how about the next best thing and engine or drive input shaft TQ and HP. Loss thru the drive is a constant not changeable.

marty,
i agree with you about parasitic horsepower losses being constant. my thinking was just that calibration that far removed from the power source would make the calibration under those conditions extremely difficult. if the input shaft was read, the horsepower loss could be calculated into the formula and still get accurate propshaft horsepower data since the loss remains constant.

Have been looking at your post and Know that I am not in your league as Knowing about building a onboard Dyno,However you might care to check with Boostpower In Newbury park Ca, He has a dyno that hooks up to the prop-shaft and he uses it for fine tuning in his shop, plus for R&D on their race boats. Like I said I know very Little about this subject, but If this little word will help, Great!!Otherwise, Please forget that I even Mention it!!

eliminator219

Why would the L&S concept work on a Stellings box, but not on an IMCO box? Both boxes use a driveshaft. Why can the magnetic strain be mounted to the driveshaft on the Stellings and not on the driveshaft on the IMCO?

I haven't priced the L&S, but if the unit requires having the transducers plugged into a computer, then has anybody checked to see if the unit could be run into a PALM device or a WindowsCE handheld unit?

This thread is very interesting to me.
(I do, however, see obstacles that may be difficult to overcome in measuring torque on any shaft inside the drive case - iron particles in the lube would have a definite impact on any noncontact magnetic sensing device).

M

It is not a magnetic strain guage. The strain guage needs to be bonded to the shaft.
The IMCO shaft is a long input shaft for the drive and it must slide thru the gimble to the coupler and if anything is mounted to the shaft then it won't be able to slide thru the gimble.
The Stellings box has a coupling flange inside the box where the standard length drive input shaft goes into and then a mini drive shaft connects to the engine crank. It is on this coupler that a strain guage can be permanantly mounted.
The signal from the strain guage then goes to a contral box and is processed and it's output is a 0 to 5 volt signal porportional to the TQ and HP and can be displayed on a digital readout, sweep guage or to a data logger. My device can meassure the TQ of any shaft provided that the shaft is accessable and at least 1" length of shaft to allow "organization of the TQ" thru the metal.
The L+S prop shaft dyno requires the boat to be out of the water and connected to water supply. It can't give real time numbers on the fly. Boats and propellers and really just a water brake- think about it.

Marty


The strain guage I saw was on a superflow dyno a few years back. It looked like an exaggerated "S" made out of aluminum and mounted between the frame and the pump. I suppose the best way to mount it would be to float one side of the motor and mount the strain guage on the opposite side. My question to all is if the engine is mounted in the conventional fashion can this guage be used as a motor mount/load cell even though the motor is mounted ridgid? My thought is the strain guage should be able to be calibrated for this

? So it measures the pressure on the motor mounts and by some corralation comes up with TQ of the motor?