GOLD NUGGETS Revised version from INAV #104
It's Easy to Calibrate Torque Meters

Eighteen months ago I quickly learned that I needed to communicate with others to improve my flying abilities. 

At first, rubber sectional area, weight and length fed to me by other fliers were enough to keep my planes in the air. The torque meter was simply a hook for the other end of my rubber loop and the dial graduations provided a means to prevent over winding and breaking the rubber once I figured out where on the dial it usually broke. I began collecting rubber, and the different batches responded differently in turns, energy, breaking point and flight times. The torque meter was growing into the second most important piece of equipment I had - and I couldn't communicate intelligibly with anyone about rubber or energy. Cross section, length, turns, and weight weren't enough to be able to fly the torque dependant classes like EZB or F1-D. 

I needed to be able to read my meters in standard measures of force. For me this was inch-ounces of torque. After pleading my case, solutions were numerous. Some still insisted I didn't need to know. Another suggested finding someone with a correctly calibrated meter and couple the two…Hum? Build a new one based on wire diameter, length and graduations from web sources. I had perfectly good meters and a ton of data based on those meters graduations. And, I learned mathematically calibrated wire, based on physics beyond me, didn't produce correctly calibrated meters. I contacted Jim Jones, the manufacturer of my meters. He gave me the information I needed. 

Simple. Anyone can calibrate any meter, even a rusty torque wrench. All it takes is 15-minutes, a couple strips of 1/8-inch hard balsa, some modeling clay, thread and a scale. This is also about the only accurate way to calibrate a torque meter for the majority of fliers. Every meter needs to be individually calibrated. 

The only caveats are that the indices (dial face graduations) be the same angle for 360-degrees and the force not extend beyond 360-degrees. Greater stress will damage the tension material's structure (usually music wire) and subsequent readings will be in error. 

For convenience, I will use inches and ounces, and my Jim Jones meters. My meters have eight standard, numbered graduations in 360 degrees (0 is also 8) and ten fractions between the numbered grads. Here is the procedure to calibrate. 

Two strips of hard balsa about 1/8 inch square exactly twice the length in inches as there are the number of graduations are needed. It's 16-inches for my meters. Mark the exact mid point of the strips. Glue the two strips together keeping glue away from the center. The center is slipped over the meter's hook, between the strips, and centered on the torque wire shaft that the pointer is attached to. Glue a strip of thread to one end of the balsa lever so it hangs over the end. Weight in the form of clay will be attached to the thread to make the arm turn 360 degrees and hold the pointer on zero. 

Mark the zero point of the meter when it is at rest (with no load). If the pointer is adjustable, set it to zero. If the meter is home-built, with no zero adjustment, the pointer is on the zero setting; mark it as zero and determine the number of equal graduations you want, remembering to make the lever arm twice the graduations, in length. Don't get carried away, ten is plenty. You can tick intermediate fractions for more accuracy. 

Force the balsa arm over the hook and center the mid-mark on the shaft center. Wedge the arm so it won't slip or move on the hook shaft. My meters rotate clock-wise for indoor flying. The right side of the balsa balance arm has the thread. You probably will need to add weight to one arm to balance the pointer at zero (at no load). Rotate the meter in the opposite direction the pointer will turn for readings. When you add weight it is best to have the "weight arm" ultimately at horizontal when the pointer turns the full 360 degrees. Weight or clamp the meter down. 

Twist the arm with the thread in the direction it should read. Add clay weight until the pointer rests on zero, 360 degrees. Remove and weigh all the clay from the thread. As necessary, convert the weight to ounces. 

This weight is the inch-ounces for one graduation. To get the actual inch-ounces of torque, multiply the dial reading by this weight. For example, the weight required to read number eight (360 degrees) on my Jim Jones "A" meter at eight inches is 0.0963 ounces. A torque reading of 6.5 on the dial face is: 6.5 x 0.0963 = 0.6256 inch-ounces (in.oz.). This meter is used for mini-stick, A6 and EZB. A meter reading up to 1.0 inch-ounce will handle nearly everything flown indoors. If I had a home-built meter, I would add the actual torque directly onto the dial face. As it is, I memorized the factor and multiply. 

Now, I can communicate with the rest of the world, know what total energy my rubber has, wind my EZB's to .12 inch ounces and fly competitively. 
hbm, 10/14/01.