Torque Meter

SOCoach
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Torque Meter

Postby SOCoach » February 11th, 2010, 2:18 pm

I've coached Science Olympiad for 15 years and we've been fairly successful at Wright Stuff, but we've lacked consistency. I've heard other coaches talk about using a torque meter and I've looked at the plans to build one several times. This year I have a couple of kids very interested in flying planes and a parent who is willing to help build the torque meter. Can someone on this board give me some insight as to how to use the meter and go about helping get better times?

Thanks!

baker
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Re: Torque Meter

Postby baker » February 11th, 2010, 3:57 pm

http://www.indoorspecialties.com/articl ... 0Meter.pdf Easy to build, works really good, don't get hung up as to whether it's calibrated. Just use the dial as a reference...

http://www.modelflight.com/torque.html Another design, seen it, never used it..

SOCoach
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Re: Torque Meter

Postby SOCoach » February 11th, 2010, 4:21 pm

Thanks . . I think that is design we are going to try and build. My biggest question however, is how exactly does the torque meter help. I am assuming torque is a more useful gauge in determining the power of a rubber motor than number of winds?

baker
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Re: Torque Meter

Postby baker » February 11th, 2010, 4:47 pm

As a motor, rubber band is used it gets weaker. 1500 winds just doesn't produce the same flight anymore, well maybe 1550 might get you the same as a brand new motor. So measure what a new motor gives you, maybe 2.5 on the dial, doesn't matter 2.5 of what it's just a reference number you want to come back to. But...maybe a .125 motor is too much energy but it gets you up to the ceiling, well try a .085 motor and wind it to the torque of what the .125 motor was. Now you get to the ceiling but most important, you have a ton more windings on the motor than you had on the .125 motor. This equals more flight time. but this all works with trim for drag, proper pitch of props for proper prop speed (say that 3 times) so you don't eat up all you windings too fast, and selecting the proper size motor for the ceiling your work with this day. A stop watch is the most important tool to tell you how well your doing...

jander14indoor
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Re: Torque Meter

Postby jander14indoor » February 11th, 2010, 7:29 pm

Torque meters have all kinds of uses, though baker hit a couple of the big ones.

Part of what makes this event interesting is the nonlinear storage and release of energy from a rubber band, and if you don't measure the torque you can't see and manage that.

Without a torque meter, you can learn to trim a plane, and get it to fly fairly long, but you really can't best match rubber to prop to plane. You also lose a LOT of learning opportunities.

With torque you can introduce work, energy, and power to the discussion. Work is energy which is force times distance for linear systems, or torque times turns for rotary systems. For a nonlinear rotary system like a twisted rubber band, its the area under the torque-turns plot!

Start plotting those for your motors. Plot them on wind up vs wind down. You'll find a big difference due to hysterysis. You have to put in way more energy into the system than you ever get out. You can also start making clear why its so important to wind past launch torque in low sites and unwind back.

You can start making clear how your rubber band is a fuel tank AND an engine. The width of the band is your engines ultimate power, but the area under the torque winds curve is its fuel capacity. Are you flying at full capacity? Can't tell without a torque meter.

And so on.

For specifics on practical use, search this years discussions, AND last years. Ask more specific questions, etc. We'll be happy to answer.

Jeff Anderson
Livonia, MI

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Re: Torque Meter

Postby calgoddard » February 11th, 2010, 10:01 pm

Baker raised a few issues that I wanted to address.

First, you should only vary your motor width a couple of thousandsths of an inch at a time, e.g. from .095 to .093, not .125 to .085.

Second, if a given torque on a .125 motor just gets your plane to the ceiling, the same torque on a .085 motor would produce a drastically different result. Your plane would probably not make it to the celing, but even if it did, you are probably going to end up with many unused turns. You would have a poor cruise and a rapid descent with an under-sized motor.

The same torque for the same motor width will get you to the same height if the original torque for that motor got you to that height. In other words for a given motor width, assuming the motor is not fatigued, you can accurately predict climb and final height based on torque, and vary the winds for different performance.

Of course, all of this varies if the temperature changes. The warmer it is, the higher your plane will climb. So always mark the temperature of your gym on your flight logs.

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Re: Torque Meter

Postby calgoddard » February 11th, 2010, 10:36 pm

The Ray Harlan torque meter is a useful device.

The Cezar Banks torque meter is far superior.

It pivots and has a manual release that allows you to easily remove a fully wound motor with one hand so you can mount it on your plane even though it has no O - rings.

I have posted a picture of the Cezar Banks torque meter in the Image Gallery.

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Re: Torque Meter

Postby Dark Sabre » February 12th, 2010, 6:21 am

His image:
2018|9/Cezar_Banks_Torque_Meter.jpg

leetx
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Re: Torque Meter

Postby leetx » February 12th, 2010, 10:04 am

Here's the plan for the Cezar Banks torquemeter. It's not the best image, but should be good enough. His is on the top half of the image. I'm planning to build another meter using this plan.

Image

I've also uploaded it to the gallery.

Here are two of the simplest to build that I've come across, especially if you don't want to solder. I built ours using glue and tape. Once I had the right materials, it took me less than one hour. This is the one that I based mine on:

http://www.gryffinaero.com/models/ffpag ... meter.html

Associated tech talk on that page -- how to use a torque meter, how to calibrate: http://www.gryffinaero.com/models/ffpag ... etech.html

This last one may be the simplest of all to build, only wire and wood.

http://www.indoorduration.com/ftp/solde ... emeter.pdf

Have fun and good luck.

baker
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Re: Torque Meter

Postby baker » February 13th, 2010, 7:32 am

If you make a meter, you'll need a dial face... try this..
http://www.indoornews.com/custom/utilit ... en_svg.php


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