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Author Topic: Indoor motors  (Read 495 times)
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ironchefmpls
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« on: April 28, 2020, 12:50:26 AM »

Hi everyone,
I have a question for the more experienced indoor flyers. I built a Scraps from the J&H kit. It came out pretty heavy and very ugly. I'm guessing it's over 600 mg sans rubber. After trimming, the once straight wing spars came out in shapes ranging from hockey stick, banana, and compound fracture. There are all kinds of issues. I'll post a picture for everyone's amusement.

It does fly ok. I got it flying level in 5-7 ft dia. circles in the living room. I have 2 motors made from the 0.025" strand that comes in the kit. Motor #1 is around 150 mg, at 5 inches. It caries the slightest amount of tension installed with zero winds. It was an ok starting point, but started to want to climb out of the house at 600-700 winds. Motor #2 is 340 mg, around 10 inches.The best flight was around a minute on 1500 winds with #2. The heavier, lower torque, longer running motor was apparently key. My question, is is there a Don Ross type chart out there for indoor motors? I'm looking to see how many turns motor #2 can take, or better yet how a motor of arbitrary size can be wound. Thanks.
Jeremy
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USch
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« Reply #1 on: April 28, 2020, 05:51:16 AM »

For calculating the max. turns go to the Plan Gallery and make a search at "rubber calculator" and you get 3 as shown in the included pic. I used the May 1999 from frash and had good, near results. I never tried the other two, but normally the plan gallery contains only trusted information, thanks to our beloved administrators  Grin Grin Grin Grin Grin

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Re: Indoor motors
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Olbill
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« Reply #2 on: April 28, 2020, 09:42:02 AM »

I would imagine the question is for Tan SS rubber. It takes much higher torque but less turns than Tan 2 rubber. I don't know if anyone has worked out an exact formula for Tan SS. I put some fudge factors in the formula in my flight data spreadsheet to get an approximation. I'll try to post it after morning chores.
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Olbill
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« Reply #3 on: April 28, 2020, 11:26:37 AM »

For TanSS (no scientific basis for this - just adjusted Tan2 formulas a little) (and I'm not sure if all the parentheses are in the right place)

Turns
=(45.67*L*SQRT(1/N/(W/(L*N))*0.95

Torque
(W/L/.11)^1.5

L = motor length in inches
W = motor net weight in grams
N = number of strands

For motor 14" long weighing 1.5g
max turns = 1856
max torque = .96 in-oz
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ironchefmpls
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« Reply #4 on: April 28, 2020, 01:11:13 PM »

Thanks for the help. The spreadsheet on the plan archive gives 2300 turns for a max. It does indicate Tan2 whereas J&H probably supplies SS with this kit. It looks like the loose rubber they sell is SS. I'll see what the formula below gives.
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ironchefmpls
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« Reply #5 on: April 29, 2020, 08:30:58 PM »

I made a video of this little guy flying last night. Excuse the Corona mop hairdo. The stalling was probably due to the rubber bunching at the back. This flight was after 1700 winds and an unknown amount of unwinds after a failed 1st launch. (I restarted the timer, so the 1:18 was legit)

https://youtu.be/e50VHuJSnjY

The weight on this without the motor was a portly 930 mg. Before the motor unwound from this flight, the rubber broke. Probably a nick, not over winding.

Cheers!
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bjt4888
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« Reply #6 on: May 26, 2020, 06:53:30 PM »

Good job. Fun flying during Coronavirus.

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