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Author Topic: Question - Rubber streatching affecting torque reading.  (Read 228 times)
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ghcrash
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« on: October 25, 2017, 07:16:40 AM »

I've never used a torque meter but I know a couple of guys who use a torque meter instead of counting turns.  Their theory is that winding to a specific torque is much easier, and accurate,  than counting turns, especially when the turn count gets above a couple of hundreds.  So I'm thinking about getting a torque meter and I'm wondering if how much the rubber is stretched affect the torque reading, and, if so, how much.

Does the amount the rubber is stretched affect the torque reading?     Do you get the same reading if the rubber is stretched three times its length as you would get if it was stretched 3.5 times its length?   (Same number of turns.)

If the torque reading varies with rubber stretch,  how much does it vary?     How much will the torque reading change between the reading taken with the rubber stretched 3 times in length compared to  3.5 times it length? 
 
I fly mostly indoor duration (Easy-B, Ministick, F1D) and am getting tired of counting 1000+ turns but I would like to understand the factors that can affect torque readings  and the use of a torque meter.

    Thanks
        George
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piecost
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« Reply #1 on: October 25, 2017, 08:24:26 AM »

George, i am not an expert on winding, so others may offer a more authoritative answer, but you should have docked the winder onto the stooge as you reach maximum torque. The winder to meter length on the stooge is equal to your motorstick length..therefore, it is consistent every wind and equal to the torque of the motor on the model.  It is this final torque that is important. Any error in torque reading during winding from variations in stretch, due to how quickly you are coming in, are not important.

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ghcrash
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« Reply #2 on: October 25, 2017, 10:11:48 AM »

 I learned something already.

Keep it coming.

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Olbill
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« Reply #3 on: October 25, 2017, 10:26:36 AM »

You need to count turns as well as use the meter. My method (probably not the best):

7x stretch at beginning. Wind in 60% of calculated maximum turns. If you can see your meter at full stretch you can wind to 60% of max torque. Walk toward dock while putting in remaining turns. Try to reach maximum calculated torque when you reach the dock. Stop occasionally and test the tension on the motor. If it feels stretchy then you've come in a little too fast and you can pull it back a bit. Once you're done winding you can back off turns to desired launch torque.

When you are comfortable with this technique (or whatever technique you decide to use) you can vary it to suit your own thirst for knowledge.
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vintagemike
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« Reply #4 on: October 25, 2017, 01:17:17 PM »

Many years ago Pete Giggle used to lay a string out from his winding jig, a number of knots tied along it told him how far in he should be for a given number of turns, said it was more consistant
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piecost
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« Reply #5 on: October 25, 2017, 01:24:05 PM »

That is really helpfull Bill. I will modify my technique. Do you manipilate the rubber to ensure even knots and avoid bunching?
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lincoln
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« Reply #6 on: October 26, 2017, 03:28:08 AM »

Many years ago Pete Giggle used to lay a string out from his winding jig, a number of knots tied along it told him how far in he should be for a given number of turns, said it was more consistant
I recall that Ray Harlan uses a strip of paper with markings on it. Ray is more organized than I am, which may be part of why he flies so much better than I do.
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Olbill
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« Reply #7 on: October 26, 2017, 12:10:44 PM »

That is really helpfull Bill. I will modify my technique. Do you manipilate the rubber to ensure even knots and avoid bunching?

I don't usually do anything to a fully wound motor. For an event like F1M where you use all the energy you can get in the motor I might try to smooth out the knots a little after the motor is on the model but this can risk a motor break and a lost model.

For events with a lot of backoff like A6 and LPP the big problem is keeping the motor from bunching on the rear hook. To try to minimize that problem I drag as much of the knotted motor as I can to the front of the model before launching. This doesn't completely cure the problem but it delays it so that maybe you can get in a good flight time before the CG shifts to the rear. There may be a slight benefit in a more forward CG during the early part of the flight to slow the rate of climb.

This info about A6 and LPP assumes that you're using long motors (20" to 22") with sleeves and have a solid lockup of the motor to the prop hook with the sleeve going over the prop hook.
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