Re: Re: Double strand motors?

From: William Gowen <wdgowen_at_gmail.com>
Date: Wed, 04 May 2011 13:26:43 -0400

What I meant by "little difference" is that in my testing I haven't seen
results that clearly indicated a difference. I have seen differences but
not consistent differences. My F1M WR and my F1M USIC site record were
both done with 3 strand motors but I think it was the rubber and the
length that made those motors special rather than the number of strands.

There is a major advantage to multi-strand motors - you can use off cuts
of rubber that otherwise may not be suitable for anything else. Most of
the F1M motors that I made for Kent were from a bag of scrap rubber.

On 5/4/2011 1:18 PM, Mark F1diddler wrote:
>
>
>
> --- In Indoor_Construction_at_yahoogroups.com
> <mailto:Indoor_Construction%40yahoogroups.com>, William Gowen
> <wdgowen_at_...> wrote:
> >
> > John, Phedon, Mark, Dave, et. al.
> >
> > ...*IF* the question is "will an *equal cross section* motor of more
> > strands have different characteristics than the *same cross section* of
> > motor with fewer strands" then the answer is there will be little
> > difference.>>
>
> Bill, it's possible everyone here was thinking per the above. But to
> say "there is little difference" still implies there is *some*
> difference, and that's where (the practical) disagreement exists. If
> there's ANY difference, that could be important to the original
> poster. And sorry, I immediately regretted saying "rubber testers
> treat stretch ratio THE SAME as turns per inch." Of course it's not
> "the same" but a function of, along with cross section. We've all seen
> the formulas where torque varies with the 3/2 power of cross section,
> and turns vary with (I forget) 3/2 power of length/square root of width.
>
> Back to original question: Evidence exists on both sides if one
> accepts all published claims as "evidence."
>
> From Don Ross FF "Rubber Powered" book, quote, discussing his turns chart:
>
> "Note that it appears as if 8 strands of 1/8th rubber can be wound to
> the same number of turns per inch as 4 strands of 1/4 inch, but this
> is not really so. It is a close approximation. You can probably get
> 5-8% more winds in an equal weight of smaller rubber."
>
> From Model Aviation, March-April 1979, Fred Pearce, "Rubber."
> "Would you get more or less energy by using an equivalent skein of
> many smaller strands? It has been hypothesized that a larger number of
> smaller strands to the same cross section area would enable one to
> store more energy" ...snip, Bob Champine experiment, etc ....
> "No appreciable difference in torque or energy storage was evidenced.
> Thus, the only trade-off in using different widths of rubber, other
> than to get the proper cross-section, is that smaller sizes tie easier
> knots, but they also offer more edges in a skein to get frayed."
>
> I believe the Fred Pearce article more than the Ross Book in this
> matter, and the reason I prefaced with, "Opinion," previously.
> MB
>
>
Received on Wed May 04 2011 - 10:26:55 CEST