rotational torque

littlerich

Well my first basic stamp order is in transit down under.

My first project is messing around with wind turbines.

Is anyone aware of a way of measuring rotational torque without buying an industrial sensor for approx $1000 to $1500 ?
Of course I want reasonable accuracy - don't we always.

Second question:
I will be using a stamp pin to count rotations also.
Does anyone know whether a reed switch will switch quickly enough or a standard proximity switch?

Or will I have to bite the bullet and get a transister output prox?

Sorry first questions not so stampy but there is amazing knowledge in here.
I did however write my first we program and it appeared to compile without error - lets see whether it works.

Cheers
Richard
·

CCraig

Richard,

Depending on RPMs, a reed switch should work. Watch for bouncing.

NOTE: I know nothing about measuring torque. (except for cars)

Won't measuring torque require a 'load' to measure it? So if you use a sensor, wouldn't it always be applying a load? Could you calcuate mass and RPMs. or Use wind speed, a known resistence, RPM, etc to calculate a 'standard' and calculate the rest for various wind speeds.

Sorry, know nothing of which I speak, just trying to help.

Chris

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I'm not scared of your robot. I'm covered by Old Glory (youtube)

Mike Green

Torque is the force applied in a circular direction. If you will, it's the "twist" applied to make something turn. A reed relay or the like would measure RPMs, but that wouldn't give you the torque. If you have a constant load or a load that's somehow proportional to the RPMs, you could use that to estimate the torque. That's why the sensors cost $1K+.

RE: Reed relays ... what kind of RPMs are we talking about? If you can mount a small flag or patch on the shaft, you could use a photosensor.

FerretMK4

For rpm sensing (the abreviation for revolutions per minute is rpm not RPM'S), use an IR emitter / receiver pair and a shutter wheel. The IR pairs are available in many styles already mounted facing eachother with a small gap between where the wheel goes. If you have an old printer around you can find at least one of these inside.

If the shaft turns slowly and is long and small enough to develop substantial twist, you can use mirrors and a light to measure twist of the shaft, but it may be easier in the long run to use strain gages. Gages are about $80 and the special adhesives another $75 or so, and you'd get the best results putting an instrumentation amplifier on the shaft so you boost the signal before it gets to the sliprings.

Capt. Quirk

There are 2 ways that I know to measure your torque. (1)Is a Alternator Dyno, it figures out the torque mathmaticly based off the horsepower required to produce a Voltage and Amperage being produced at that second. An example of this is a car alternator, the more current it produces, the more horsepower it requires to drive it. I'll post a formulae later today.

(2) The second way is a Prop Dyno. They used these back in WW1, to test the output of an engine, after they were assembled. Basicly the Generator mount is built to rotate along the propshaft axis. It uses the standard arm fixed to the generator mount, the load cell or fish scale is mounted to the arm. The torque measured is the torque applied to the generator by its propeller.

There should be more info about the prop dyno on the net, but very little about the alternator dyno.

Hope this helps

Bill

Beau Schwabe

Capt,

What you are describing is a "Reaction Torque Sensor"... the big problem is that it still needs to be calibrated.· By placing a constant or known electrical LOAD on the output of a motor or alternator used as a generator, the measured voltage on the output is proportional to the applied torque you are rotating it with.· The high dollar compact reaction torque sensors use strain gauges and slip ring clutch design to achieve a similar result.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Capt. Quirk

Here are 2 links http://www.clcombat.info/dyno.html· &· http://www.aalmps.com/dyno.html·for what Beau correctly calls "Reaction Torque Sensor" Both are done without expensive sensors.

On the "Alternator Dyno", the output of your wind turbine measured in Watts or Kilowatts (@ a rpm) easily converts to SAE horsepower and than can be converted to SAE torque. Or in SI, torque can be calculated in Newton-Meters.

Bill

littlerich

Thank you all for your thoughts, I appreciate them

Rich