torque calculator

[dbailey]

Coach Brian,

I just finished watching your motor winding video and had a question. Where did the torque you were winding to come from? I have found the Max Turns Calculator, but have not found a torque calculator.

[coachchuckaahs]

There is not a torque calculator that I know of.

My method is to watch the torque meter while fully stretched. Initially the torque will slowly climb. When the torque starts climbing quite rapidly, that is your signal to move in. Now continue to wind as you walk in, with a goal of reaching 2X the observed sharp rise in torque.

If you are winding correctly you will reach the desired length as the torque reaches this number and as the turns reach near max. If you come in too quickly, you will find that you need to add too many turns at the end, and this is a recipe for disaster. You cannot add many turns at the end when fully walked in, as most of the rubber is sequestered in knots. You will find the torque rises quickly and the rubber breaks. If you walk in too slowly, you will reach max turns before getting all the way in, and the rubber will fail as you try to add more turns to complete walking in. If you stop winding and simply walk in you will find that "grapevines" quickly form.

So there is no one torque to wind to, but rather a recognition from experience where to be on the torque curve vs the wind count and vs the walk-in position.

Generally, whether you are short on winds or over-wound, the rubber will break at a similar torque, and this can be recorded as the breaking torque. However, the torque is rising fast at this point, and getting an exact number may be hard.

For the 1/8" rubber, you should be able to get to somewhere over 2.0 oz-in, up to maybe 2.5. A safe goal might be 2.0, with slightly higher for an aggressive goal. Getting here at the goal winds and the goal length is the crux of much practice to learn a "feel" of the rubber.

At the other end of the spectrum, for F1D we generally use 0.030g/in, or somewhere around 0.050" rubber, and we max out between 0.5 and 0.6 oz-in. Even small mistakes in winding at this level can cause you to miss 10% of your goal turns.

Your rubber limit will also be affected by any micro-damage to the rubber, like from sharp O-rings or from poor knot-tying, or even thickness variations in manufacture.

How close you go to breaking will depend on the exact competition. In SO you have 10 minutes to get 2 flights in the air, so you probably cannot afford more than one broken motor in a session. Therefore you will want to be more conservative on your max torque. When you unwind to launch torque, you will have a few winds less than optimal, but you will get your flight. In F1D, it is not uncommon to break 5 or more loops preparing for an official flight. It is critical to max out the turns. We typically see 1200-1400 turns depending on the prop, rubber, ceiling height, and that lasts for 25-29 minutes. Missing just 50 turns will shorten your flight by a full minute! So we are working in the tail end of the statistical strength of the rubber, and thus multiple failures are not uncommon.

Coach Chuck

[dbailey]

So if you misjudge the walk-in, do you just unwind and try again? What is the best way to unwind/walkout to not damage the motor?

[coachchuckaahs]

If you have wound hard, then you have affected the motor. Each motor only has so many hard winds in it, and generally you want to compete on the 3rd or 4th wind.

This is more of a learning experience to get it right every time. Lots of winding experience.

But, it you grossly mis-wind, you would have to unwind completely and start over. In a SO contest, with only 10 minutes for 2 flights to start, it is unlikely that it is beneficial to take this time. This assumes a flight around 3 minutes, a wind time of 2 minutes, and a transfer and launch time of 1 minute per flight. That would mean the first flight launches at the 3 minute mark, and lands at 6 minutes. Assuming you wind while it is flying, then the second flight can launch around 7 minutes. This leaves a 3 minute window for an extra wind, which I would rather leave for rewinding if you potentially break a motor.

Once you have the feel of top winding, then a missed wind will not be off so far as to require a rewind. It may not be optimal but it will be close enough. In F1D, a missed wind will likely result in a broken motor. If the wind is instead low, then re-winding with a fresh motor is likely the answer, but we have generally unlimited, or nearly so, time for flight prep in that kind of flying.

If you are grossly under-wound, you can try pulling outward again and then continue winding. However, you will only be able to pull back out a little bit. If the winds were short at full stretch, there is no way to get them in without starting over.

Coach Chuck

[dbailey]

I was asking more for practice/testing, but that is super helpful for the competition strategy part.

So what does the "life" of a motor look like?
1) gets cut from stock as an oversized length (I believe you mentioned a specific length somehwere) and weighed to identify its average linear density and inventoried.
2) gets trimmed to desired loop length * 2 plus .25inch for the knot
3) gets tied into the loop with orings
4) gets wound to X% of calculated max winds and flown for testing
5) gets wound to Y% of calculated max winds and flown for testing
6) gets wound to Z% of calculated max winds and flown in competition.
7) gets wound to Z% of calculated max winds and flown for next round of testing.
Note: "gets wound" steps also include lubrication with silicon oil.

What are X, Y and Z?? Do you only test/optimize with one %max winds motor?


DB

[bjt4888]

We wind a series of test flights on a particular 2025-26 heli motor like this. First use, stretch 5x-6x relaxed length and wind to approx 75-80% breaking turns but definitely not more than 1.8-1.9 in oz max torque. Objective is to break motor in and not stress it too much as the important uses are 2-4. Second use: stretch to 7x relaxed and

[bjt4888]

We wind a series of test flights on a particular 2025-26 heli motor like this. First use, stretch 5x-6x relaxed length and wind to approx 75-80% breaking turns but definitely not more than 1.8-1.9 in oz max torque. Objective is to break motor in and not stress it too much as the important uses are 2-4. Second use: stretch to 7x relaxed and

...(continued) wind to approx 83-85% of breaking turns (use the NFFS calculator) and 2-2.1 in oz max torque. Third use and thereafter still stretch to 7x: first inspect the motor for abrasions (near the knot usually, if any). If there are any significant abrasions, use slightly lower max torque and max turns numbers (like 2.1 in oz and 2-3% fewer turns). If abrasions are small or zero, the third winding and thereafter can be 85-90% of breaking turns and 2.1-2.2 in oz max torque. When we get close to 90% and get 2.2 in oz the FFM heli flies about 2:43-2:49 in 7.5 ft ceiling for us.

Good luck

Brian T