SEN issue 1133 - 16 September 2007

Table of Contents - SEN 1133

  1. The Ultimate LiPoly ?
  2. Tow Hooks from the NFFS Forum
  3. Tracker Rx Info from the South Pole

The Ultimate F1A Li-Poly ?
From: This email address is being protected from spambots. You need JavaScript enabled to view it.

Sheriff SCAT,

I promised some feedback on my experiments with Li-Polys (LP) in F1A. Well other than the fire and the destruction of my building room, things have gone well ....

OK, so I kid. I have now tried 2 cells with regulator and a single cell LP. I was recommended a iPod Nano replacement battery which is only slightly longer than the current Kokam 300mAh puppy BUT it comes in capacities upto 500mAh. I chose one at 400mAh which cost me £4 ($8) a throw which is much cheaper than a Kokam. The only difference is that the Nano battery only deliver about 1-2C but this is OK for timer use. Note that you have to do a small amount of desoldering to remove a PCB from the battery and then add you preferred wires/connector but this is simple if you can control a soldering iron.

I did an experiment with a Multiclass timer with Becker S100 servo. After 26 flight cycles (note that the servo doesn't move on circle tow) I saw a voltage drop of only 0.05v from a starting point of 4.12v. So Ken Bauer and other are correct in saying a single cell can power a timer OK. I also tried a 2 servo Muticlass set up and that worked fine and finally I've tried a 3 servo BMT from that Sheriff SCAT and that works OK but note that I haven't done the same duration tests yet. One european flyer told me he uses the Kokham battery on a 4 servo model and gets over 30 flights.

The regulator I used is a 3 component device described here :-

Whilst this is written with a RC DLG (F3K) bias it is an excellent statement of LPs and the regulators.

I see real advantages for using these batteries as have others. A single Nano battery is about 7gms with wires whilst a 100mAh Ni-MH is 17grms and falls apart after a few years. A twin LP is 13 grms and the regulator about 4grms - still very light.

I'd be happy to provide any further info that the readers of this fine organ would like.

Thanks for all the past advice and comments from flyers on this subject.


 From the NFFS Forum

Post subject: F1A hook reed switch and other hook related items


From an email from Dave Edmonson.

He has a model equiped with reed switches on the tow hook. Many flyers have
had this problem-- the model is flying well, the rudder adjustment is made
to open (widen) the glide circle and behold on the next flight the timer
does not start. This same failure mode happens with the mechanical timer
starts as well. Good thing for the "fly away logic" on our e-timers if
we launched in good air.

Reducing the glide rudder decreases the amount the hook body swings back
and so the critical point is reached that the separation between the
magnite and the switch is not great enough for the switch to open.
Here are some of the ways I've used to solve this problem.

1. Relocate the magnet; On the standard M&K (and similar designs)
the kevlar tread / epoxy can be cut with a razor and carefuly peeled
away. Rotate the magnet and use thick CA to refasten. Movement is
small- can be frustrating when it is not right. Pierre Brun designed
and makes a niffty machined piece that allows the magnet to be moved
via a set screw.

2. Biase the hook body backward by adjusting the forward stop screw and
re-adjusting the straight tow rudder (at the rudder control arm turn
buckle). It does not take much, .015-.025 inch but it does change
the hook position. Make sure the switch works in the forward
(straight tow) position.

3. Drill a new hole to reposition the rudder line to the zoom lever-
move the new hole closer to the pivot point. Requires the hook to
swing back more to get the same rudder deflection. It also
decrease the zoom rudder during launch but a bit more zoom
rudder adjust can be made.

4. Similar to shorter zoom rudder lever attach point, lengthen
the rudder control arm.

5. Replace the reed switches with the small cherry micro-switch.
I orginally used these mechanical switches and had no problems,
I switched to the reeds when Stamov and M&K showed thier use.
The advantage I thought was they were water proof. I "shorted"
a switch on a test flight that landed in a shallow puddle just
before the first round at Palm Bay years ago. Other than landing
in water, the micro switched seem a tolerate to water as the rest
of the timer system. Perhaps I fly in mostly dry Lost Hills-- .
I also could not figure out a clever away to use the reed switch
on the re-latching hook development program. Rene Limberger
did use reed switches on his Stamof hook based reltaching hook,
Victor, I now offers a similar reed switched relatching hook
(ie removed the strain gage)- dumbed the "Stupid hook".

It tooked me some time to resolve that the shock from the hook
relatch would cause a premature bunt start and the following e
xciting sky writing. This is what "swtich bounce" is all
about and once under stood is not a problem. This was
dicussed in SEN several years ago.

The limited range of the reed switch is its biggest draw back.
I have slowly replaced the reeds with the micro switches. It
is especial difficult for me to get a set up on F1H with
its small hook swing. It is also nice to put your ear to
the fuselage and hear the switch "clicking". I do note
that M&K on the the new impluse hook design used 2 reed s
witches and one push pad switch. It does not look easly
to replace these so I'll continue to be using them.

The black magic is equiped to use Hall effect switches.
I have never used them but they seem to be as positional
sensitive to use as the reed switches and required an
addition power wire to be used.

Vasily designed and produce a mechanism that swings the magnet
away at unlatch but I have seen several people have problems
with it-- seems like un-needed complexity to me.

General info, both the the M&K and Stamof hook forward switches
are wired the same, however the latch switched are wired
opposite opposite. Roger M on the Black Magic has "check"
box in the "More" screen to toggle between these two
wiring configurations.

One last note, be sure to keep iron particles cleaned
from the magnets. Lee Hines after returning from a New
Zealand- Austrilia trip was having the ocasional
"no-start" problem. After I pointed out the particles
that had accumulated, Lee cleaned them off, the problem
went away.

Thermals, JIM

 Comment from:


Hello Jim

I meant to say that I am using Hall effect switches. I consider that to be a
magnetic switch, not a reed.

But like you say, the problem is the same.

I have not had problems with the small micro switches, and don't like the added
complexity of the Hall effect switches.
Dave Edmonson
Comment from

Roger Morrell
The reason I provide the Hall effect switch options is because they have
the advantage of no moving parts and are less susecptible to
environment - physical damage, dust and water. The disadvantage
is that the have an extra wire. They share with reed switches that
they are harder to set up than mechanical switches.

I believe that both M&K and Stamov chose reed switches because they
felt they are more reliable than mechanical switches. This may be
due to the quality of the mechanical switches that were
available to them 15 years ago.

Roger Morrell

Now a comment from


I've used micro switch from the time of the first Bauer timer (1981 ?),
through Koster's Van Wallene, Muticlass, BMT and probably others and
never had a problem. You can get them sealed, unsealed, and in
various colours to meet your need.
More on Micro switches fro Roger Morrell
One thing that I forgot to say was that it is very important that the micro switches
be of good quality and designed for low current operation. This means that the
should have gold contacts. On the Magic Timers and any other electronic timer
the current flowing through the switch is only a few milli amps. For some other
applications, including the reset button on Black Magic I use a simple push
button switch. Some people have tried using these or some thing like them
as hook switches. They are not appropriate. The will not make a good enough
contact. The lever on the typical micro switch ensure that a good
mechanical connection is make between the timer and hook.


Good Info on Rx
From: Vin Morgan [This email address is being protected from spambots. You need JavaScript enabled to view it.]

Gooday Gregory,

The IC-R10 is a good receiver for tracker transmitters because it has a SSB/CW facility you can arrange to hear a ‘beep’ rather than just triggering the squelch as in an FM receiver. This greatly increases sensitivity because you can hear a beep tone even if it is weaker than the noise. In addition, in SSB/CW mode the receiver will not remove the signal strength information by limiting as is done to receive FM signals. This means you can get direction by observing the change in signal strength as you turn around when holding the receiver close to your body (the body shielding method). And the R10 has a very large frequency range – it will tune to any transmitter.

The Kenwood TH-F6 would probably also be good – maybe better (I haven’t tried one of these whereas I have briefly tested an R10). The Kenwood is a bit more modern – has a lithium battery for longer life, is smaller and lighter and I think it has smaller tuning steps which could be useful.

The specialized tracking receivers – like mine, biotrack etc, are probably a bit more sensitive and have better meters but usually have limited tuning range.


Vin Morgan

Roger Morrell