Re: Re: Motor weight, size density?
I've also used 4 strand motors for F1M (and 3 strand!). I size my multi-strand motors to give the same length as my successful 2 strand motors. I've seen very similar results to 2 strand motors using this method - both in motor testing and flight times.
I'm not surprised that you got much better times from 3/02 rubber than 2/99.
----- Original Message -----
From: gerard moore
To: Indoor_Construction_at_yahoogroups.com
Sent: Wednesday, June 02, 2010 6:54 PM
Subject: Re: [Indoor_Construction] Re: Motor weight, size density?
I suppose that for comparitive purposes the mass per unit length of a strip of rubber is always going to be the best ballpark figure available. Remember that the idea is to have a better way of comparing like with like as opposed to just thickness of rubber.
For the individual this still holds true, assuming that the measurement of the rubber can be made REPEATEDLY in a way that always gives the same error.
For example. Geoffrey Lefever won the 2007 British nationals F1M competition using a 1.5 gram motor made up of 4 strands. The strands were 1.1 g/m.(Feb 99) His flights were 17.17 & 18.06.
Being a novice I thought this was worth trying to replicate on my own model. Regardless of accuracy achieved by me in making up my motors (March 02) I instantly increased duration by around 1 minute to 17.40 in similar conditions and similar fixed pitch model and torque. However the turns back off to avoid the cat walk was phenomenal.
So model number 2 was built with a v/p to allow the model to be launched with no back off. Using the 1.1g/m motor as a bench mark I was able to compare other motors above and below this figure.
My best flight (19.25) was achieved with a motor made of 1.05g/m strands.
I can't say what percentage of accuracy is involved, but by being methodical I can be more sure of being able to cut some strip that will give a similar result.
I now have a model that is more efficient, as a result of comparison to someone elses and I have a better means of replicating the performance.
:O) G.
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From: Yuan Kang Lee <ykleetx_at_gmail.com>
To: Indoor_Construction_at_yahoogroups.com
Sent: Wed, 2 June, 2010 22:20:15
Subject: [Indoor_Construction] Re: Motor weight, size density?
I suppose that there are two main issues here. First, there is the issue of accuracy of the size/length/weight of the rubber strip. Second, there is the issue of comparing results with other people and with other regions/nations.
Regarding the issue of accuracy:
What is the required accuracy, 1% or 5%?
If the required accuracy is 1%, I would think that measuring the untied motor's weight and length is the way to go. Using a 10 mg scale, it is easy to get within +-1% of a 1g motor. Even better if you have a 1 mg scale. Using a ruler to measure 30" of untied motor, it is very easy to get within +-.01%.
In terms of measuring the thickness of the motor, say for .060" rubber, can someone accurately measure the width to +-1%? How?
If the required accuracy is 3 or 5%, perhaps measuring the width is okay.
--- In Indoor_Construction_at_yahoogroups.com, "Bill Gowen" <wdgowen_at_...> wrote:
>
> I agree that many people still use rubber width to describe motor sizes but there has been a lot of discussion in this group in the last few years about weight per unit length being a better method. I've forced myself to quit measuring the width of rubber. What I'm looking for now is some common ground in the weight per unit length method so that discussions of motor size will have some sort of universal meaning.
>
> Even this method isn't foolproof since the number changes after a motor has been used. I'm using the measurements of a freshly made motor or of one that has had an extended period of rest.
>
> BTW - the temperature at USIC on Sunday had the same effect on my 5/99 F1M motors as the conditions at Lakehurst last summer. At home in my 75 degree basement I can wind to .8 in-oz pretty reliably, but at USIC I blew my 4 best motors trying to reach .75. For A6 I came home with 2 left out of 8.
>
> ----- Original Message -----
> From: Yuan Kang Lee
> To: Indoor_Construction_at_yahoogroups.com
> Sent: Wednesday, June 02, 2010 4:01 PM
> Subject: [Indoor_Construction] Re: Motor weight, size density?
>
>
>
>
> I would prefer to use what most people use, which seems to me to be just the width of the motor in thousands of an inch. E.g., .025" for a light EZB, .080" for LPP, etc. I talked with other experienced flyers at USIC, including my Pro partner, Tom Sova, and all refer to rubber sizes this way. In all the plans I've come across from the U.S. and U.K., rubber motors are indicated this way. E.g., ".025 x 12", ".050 1.25g", or ".042 x .055 x 15.5 1.075g" -- that is, all describe the width of the rubber in .001 inches.
>
> I only recently, about 2 weeks ago, started stripping my own rubber. There are two main reasons I am currently using g/in to measure rubber instead of using the width of rubber in .001 inches:
>
> 1. the Harlan rubber stripper does not output a rectangular cross section -- it is trapezoidal. It's difficult enough for me to measure rubber's width when the cross section is rectangular. With a trapezoidal shape, I would have to measure the long and short bases of the trapezoid and take the average. Yuck. This is the first reason I went to g/in.
>
> 2. I've found that the "thickness" of Tan Super Sport to be different than that of Tan II. For reference, I was using 04/10 TSS and 03/02 Tan II. Tan II's thickness is about 0.042", while that of TSS is about 0.046. If I strip the two rubber with the same setting, the stripped rubber has different g/in and don't perform the same. Perhaps this is a non-problem, but because I primarily use TSS, I wanted to be able to compare TSS and Tan II. This is another reason I went to g/in.
>
> But I prefer to use what everyone in the U.S. and U.K. use, if I could overcome these two obstacles.
>
> --- In Indoor_Construction_at_yahoogroups.com, Nick Ray <lasray_at_> wrote:
> >
> > I have been using inches per milligram of untied loop. I think because knots
> > are not consistent, and increase in relative mass as the rubber size
> > increases the untied loop is the way to go. The reason I started using
> > inches is because I didn't have meter stick handy. I would say meters are
> > probably better if we wanted to create universal system. I don't think using
> > grams or milligrams matters much as its just move thing decimal places
> > around. It would be ideal to use as many significant digits as possible in
> > order to get a more precise result.
> > NIck
> >
> > On Wed, Jun 2, 2010 at 1:07 PM, Fred or Judy Rash <frash_at_>wrote:
> >
> > >
> > >
> > > Bill,
> > >
> > > Thanks for all your help on many items.
> > >
> > > I think that everyone will work in grams. Probably we should eliminate
> > > ounces from AMA, NFFS, etc Indoor (and maybe Outdoor) rules whenever
> > > possible.
> > >
> > > The unit for length is harder. Most of Europe and the rest of the world
> > > would argue for meters and probably we should also. I believe that most use
> > > g/m of the untied strip. I think in grams naturally from a lot of chemistry
> > > lab time as well as model building time, but do not automatically think in
> > > meters. I can live with either inches or meters. If I use inches, I always
> > > use decimal inches. I never write down a mixed fraction. If I try CAD which
> > > I do occasionally, I never use mixed fractions there either.
> > >
> > > I would even be so extreme as to argue that our schools should teach
> > > decimal fractions before mixed fractions. This should start a strong
> > > off-topic thread. <GRIN>
> > >
> > > Fred Rash
> > >
> > > On 6/2/2010 12:41 PM, olbill61 wrote:
> > >
> > >
> > >
> > > I'm wondering if there is any way of describing motor weight per unit
> > > length that is more prevalent than others. The way I started out is by
> > > dividing total weight of a finished motor in grams by the motor length in
> > > inches. I think Kang has started using grams per inch for untied strip. I
> > > think Leo is using grams per meter.
> > >
> > > Can any others who have switched to weight per unit length describe how
> > > they do it? I'm early in the process of doing it this way and could switch
> > > to a different system without much trouble. I'd like to hear from English
> > > and European fliers also.
> > >
> > >
> > >
> > > No virus found in this incoming message.
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> > > Version: 9.0.829 / Virus Database: 271.1.1/2913 - Release Date: 06/02/10 05:57:00
> > >
> > >
> > >
> > >
> > >
> >
>
Received on Wed Jun 02 2010 - 18:24:24 CEST
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