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Author Topic: rubber manipulate  (Read 738 times)
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ClaudioF1B
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« on: December 23, 2017, 11:12:11 AM »

Dear. Merry Christmas and a Happy New Year for everyone !!! I have had a discussion with a model airplane friend about the preparation of the rubber to make the skeins for our F1B. I particularly weigh the rubber once I cut it and then wash it in warm water to remove the talcum that it has, once dry I assemble the skeins to later lubricate them and store them. What procedure do you do? It would be very helpful to know if I am on the right track. Greetings and Thanks Claudio!
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lincoln
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« Reply #1 on: December 24, 2017, 08:26:45 AM »

Also keep cool and away from ozone, which you can get from sparks. For instance, from old furnace motors.
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Tmat
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« Reply #2 on: December 24, 2017, 01:22:29 PM »

What procedure do you do? It would be very helpful to know if I am on the right track. Greetings and Thanks Claudio!
Claudio,

I only sometimes wash my rubber. I have not found it to be any benefit other than a very small weight loss after washing which could be used as additional rubber (a few 10ths of a gram).
The first thing I do is to remove 29.3 gram pieces of rubber from the box until I come to a "splice". This is a small black mark in the rubber where pieces have been joined to make a longer piece.  From splice to splice I call it a "segment". I keep all of the motors from each segment together. Rubber varies from batch to batch of course, but it also varies across segments. Both in energy storage capacity, and it can vary in maximum stretch length and therefore max turns, torque etc.

I weigh the rubber on a mechanical gram scale (some people use digital). Then I make up the motor to LENGTH. Not # of strands. It is a big topic which we could discuss at length. Once I have a motor made up to the length I think it should be, I do a pull test (36 kg pull) hold for a minute, then pull a 2nd time and hold until the rubber stops relaxing. Then I check the total pull length. Using a simple formula I estimate the max turns.
Then I let the rubber sit overnight. I lube the motor and do a basic torque test by winding. first to 250 turns and I check the torque, then I unwind to 150 turns and check the torque again. I have some torque targets that I am looking for. The torque test looks at the approximate cruise energy available in the rubber. If the torque is too low at the final 150 turn test, I know that this rubber "Segment" needs shorter motors. If the torque is too high, the motors could be made longer. Thus I find the optimal length and therefore max turns for that segment of rubber this way.

I hope this helps!

Merry Christmas!

Tony
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F1B guy...
But don't hold that against me!
ClaudioF1B
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« Reply #3 on: January 02, 2018, 05:59:16 PM »

Thank you very much tony for the information, it has been very helpful.
If you can pass me the formula that you use to calculate the turns, it would be of more help
Regards, Claudio
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