SEN issue 1123 - 17 August 2007

Table of Contents - SEN 1123

  1. Muncie FAI Invitational Aug 24-25
  2. NFFS 2007 Sympos Available
  3. F1A LiPo - Bauer
  4. Magic and LiPo - Morrell
  5. LiPo - Linkosalo
  6. 2007 Huron Cup

Muncie FAI Invitational Aug 24-25
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The Chicago Aeronuts will host the 47th annual FAI Invitational contest at Muncie on Friday and Saturday, Aug 24 and 25. Mini events start at 2 pm on Friday. F1ABC on Saturday 8 am. Concurrently, there will be Rudy Kluiber's "Nats One-Design Extravagava" on Friday as well as the COFFC AMA meet on Saturday and Sunday.
Do not let the word "Invitational" put you off....this is a contest open to all for America's Cup points as well as nice engraved glassware to third place. Full details can be found on the NFFS website master calendar.

Chuck Markos

NFFS  2007 Symposiums now available.
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The 2007 NFFS Sympoium publication, edited by David Mills, is now available from NFFS Publications Services, PO Box 1775, Albany, OR 97321. This is the 40th anniversary edition and packed with both technical and popular features. The usual Hall of Fame and Models of the Year are included as well as a good selection of Nakashima cartoons. Cost is $30 plus $5 for postage in the USA.  Overseas shipping is more. Please send either check or money order.  Contact <This email address is being protected from spambots. You need JavaScript enabled to view it.> for details.

Also copies of the BMFA FF Forum for 2007 are still available for $25 each.

Bob Stalick, NFFS Publications Services

F1A Li-Poly cells
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I couldn't resist replying to EoB's request for a battery discussion.  I love the LiPo batteries because they contain about 3 times more energy for the size and weight as compared with nicad or ni-mh, and also because they retain their charge while sitting on the shelf during storage.  Since nicads will lose their charge when sitting around for a few weeks they must always be charged immediatly before flying which can be some work especially when multiple models are involved.  My routine with the Lipos is much easier.  I recharge all my gliders AFTER a day of flying and then they are all ready to go at a moments notice for the next flying session.  There is a small self discharge rate of maybe 1% a month, but is usually negligible and for big contests I will sometimes give the main glider a quick top off.
Nearly all F1A flyers use two Lipo cells in series which gives a voltage of 7.4V, 8.4 max which then must be cut down with a regulator.  I don't like this because the regulator wastes power, can add noise, and adds complication which decreases reliability.  So I use a single rather large Lipo cell, in the 250 to 500mAh range.  Fully charged it is 4.2V which will drive the servos well, perhaps only slightly slower than a 5 or 6V system.  The large LiPo has excellent current sourcing characteristics which compensates for the lower voltage, and with my timer running 4 servos the voltage never drops less than 4V even after a full day of flying.  Also the larger cell should do better in cold weather which is the downside of using Lipos.  However some timers may demand 5 or 6V so the single cell may not be an option.
Regards, Ken

Magic Comment or what's under the Kilt

I use 1 80 to 125 ma LiPo in my F1B models. An 80 or 90 is more than plenty for a day's contest flying plus test flights and fly off. My  experience is that the lower internal resistance of LiPo batteries by comparison with most NiMH means that they deliver higher current so the servos go just as well. On the current Black Magic timers all have a voltage regulator so you can use 2 LiPo cells and the timer will be protected. But the voltage to the servo and buzzer is not regulated. This means that they get the full battery voltage. Some servos will take the 8.4 volts but not all. Note that in the past some people used a 9 volt battery with my timers and it worked fine but when they switched to LiPos it fried the servos, this is because the LiPo will deliver much more current.  There are people who make a battery pack with a regulator to cope with this. We have a new model timer in the works that will work with either one or two cell LiPos and protect the servos appropriately.

My personal preference is the same as Ken's and I like the LiPO technology.  Clearly I hear the argument from people who say what just one LiPo does not have enough kick to move the servos fast enough for thier more macho style of flying. And that's one of the reasons why we will come out with the new model timer, just for you macho F1A guys out there.

As with any battery it is very important to treat it with respect. With the low internal resistance of a LiPO it can deliver a very high current, which when mis-directed can cause a fire. Also the typical plastic bag packaging can suffer mechanical damage if parts move around inside your ariplance or you have a hard landing so make sure the battery is mounted properly. Those tabs are very fragile and there must be strain relief so the leads do not break off. Finally be sure to use the proper charger. Because LiPos are used in many small modern devices there are chip sets that make building a smart charger very economical. There is a wide range of chargers available, particularily from the indoor and park flyer R/C community.

So EoB you won't have to reveal what's under your kilt, or however a resident of Scotland indicates his machoness, the new magic timer will accomodate you.

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I've been using lipolys to power a F1B timer for a few years now, even in the frozen lake conditions where we fly in Finland. I use 2-cell in series battery, and a regulator to drop voltage to 5V. I think there are reasonable step-up regulators in the market now, so even 1-cell use would be possible. But not unregulated, I'm afraid. I tried that, but few servos work on 4 volts, and most of the battery capacity will be wasted as servos definately do not work when going below 4V.

My regulator is MAX1659. Max 500mA (peak 1A), over-current protected. Nice chip for F1B, but probably too small for F1A. I'm working on a F1A version of my timer now, it will have the MAX for powering the processor, and another Micrel 3A regulator @ 6V for servos. Should suffice!
In my F1B I first used a single-cell 145mAh Kokan, then tried 2-series 60mAh Kokams. Bad experience with those, I had a cell totally fail on me (voltage dropped to zero) twice, and another case was in flight, after the climb sequence but before DT. Luckily the wind was low so I tracked down the model and got it down from the tree.

I then changed to 90mAh E-techs, bought from Bob Selman. These have been working ok, but they do not seem to be available any more. I have some new type and larger cells waiting for trials, also plan to order some cheap cells to test from UnitedHobbies (in China).

The larger the cell, the better. In addition to having more spare capacity, the larger one outputs current better so servos work stronger under higher stress. Also in cold, the larger cell is not pushed as much, so it survives better and gives better current for flight. Even though lipos are not specified for freezing conditions, the ones that I have tried have worked ok down to -20C, which is the temperature limit for flying here in Finland.

I have been charging my batteries with a Orbit Pocketlader, in series, have not used a balancer so far (but have checked with a multimeter every now and then that the cells are in balance). I have been working on a 2-cell balancer based on a design found in the Ezone discussion; I want to have a spesific 2-cell balancer, as the commercial 2 to 3 or 2 to 5 balancers seem to be so bulky. I guess any decent lipo-charger should be ok, lipo charging algorithm is so straightforward that any charger intended for lipos (not a nicad one) should do fine.

Magic Comment on Tapio's experienes

I agree that the 60 MA Kokams are not so reliable.

On the other hand I have used a number of small servos in my F1Bs including GWS, Cirrus and Dymond with one cell. I must admit that I do always verify the voltage at the end of a day's flying but it is under 4 volts and the servos still work.

Huron Cup 2007

Overcast skies and a breeze from the south greeted the competitors for the mini FAI classes at 8 a.m. Saturday.  Absence of strong lift enabled the completion of all five rounds by one o’clock, followed by the now traditional barbecue prepared by my Patty.
Good flying in some rather strange conditions brought the three event winners 4 out of 5 maxes. The rain came about 3 o’clock and lasted about an hour, followed by a freshening wind. At 6:30 it was decided to postpone the usual evening rounds and begin the large FAI classes at 7 a.m. on Sunday instead.

The next morning, wind from the west meant flying downwind of an area of rolling, dense forest giving very difficult conditions.  Everyone coped well with the tricky air through most of the first 5 rounds, however, the leading F1A flyers Kyle Jones and Jiri Horak found the turbulence too much in the 7th round and this allowed Svetan Svetkov and Bob Sifleet to slip into the top places.

The last rounds also decided F1B; John Clapp and Aram Schlosberg losing much time due to malfunctions. F1C flyers Frank Schlachta and Gil Morris decided to call it a day when the wind increased after the 5th round and settled their tie in an amicable manner. Everyone else voted to continue flying and some even stayed to practice after the competition was over.  Hope to see you all next year!

Jerry McGlashan

F1G                                         Total
Charlie Jones       USA  120 108 120 120 120 588
John Clapp          USA  120 120  87 120  95 542
Tom Ioerger         USA  120 113 117  65 118 533
Paul Crowley        USA  102 120 120 116  34 492

F1H                                         Total
Kyle Jones          USA  120 120 108 120 120 588
Bob Sifleet         USA  114 120 120 102 120 576

F1J                                         Total
Gil Morris          USA  120 120-    120 120 480

F1A                                                 Tota
Svetan Svetkov      BUL  120 120 106 120 120 110 120 816
Bob Sifleet         USA  120  99 120 120 104 120 120 803
Jiri Horak          CAN  120 120 120 120 120 120  57 777
Kyle Jones          USA  120 120 120 120 120 120   0 720
Leslie Farkas       CAN  120 120 108  66 120 120  46 700
Vidas Nikolajevas   CAN  120 120  87-   -   -   -    327

F1B                                                 Tota
Ladi Horak          CAN  120 120 120 120 120 104 120 824
Aram Schlosberg     USA  120 120 120 120 120  24 120 744
Ron Felix           USA  120 103 120  56 120 120  99 724
John Clapp          USA  120 120 120 120  20  91 120 711
Charlie Jones       USA  120 120-   -   -   -   -    240
Tom Ioerger         USA -   -   -   -   -   -   -   -
Paul Crowley        USA -   -   -   -   -   -   -   -

F1C                                                 Tota
Frank Schlachta     CAN  120 120 120 120 120-   -    600
Gil Morris          USA  120 120 120 120 120-   -    600
Srdjan Arambasic    CAN   65  26  25  24-   -   -    140


Roger Morrell