Until know, no problems in both a F3J Esprit and a Corrado II, both 6 servos, and no problems in a Raptor (heli) either (5 servos). The gliders use analog servos, the Raptor Futaba 3151.
Should I worry ?
Thanks,
Stefan.
----- Original Message ----- From: "Jim Laurel" <[EMAIL PROTECTED]>
To: <soaring@airage.com>
Cc: "James R MacLean" <[EMAIL PROTECTED]>
Sent: Sunday, April 17, 2005 9:07 PM
Subject: Re: [RCSE] battery choices
James,
Actually, sailplanes can draw quite a bit of power, especially 6ch planes with digital servos. I have long been convinced that the reason for many crashes is due to catastrophic voltage drop-offs caused by high current loads. If you've ever seen a plane that was thoroughly preflighted, linkages checked, etc., zoom straight into the ground on launch, you may have seen this in action. Usually, people blame radio interference but never think to look at their batteries, because in the post mortem, the pack seems ok. However, how many people think to check their packs under load?
I have measured loads as high as 6amps on an Icon fitted with 3 DS3421s and 3 DS368s. Packs made from AA cells were fine in the days of RES planes with analog servos and light wing loading. But today's high performance molded planes with digital servos are far more demanding on the power source. High loads caused by hard winch launches, aggressive landings, and fast flying can easily cause a high impedance AA pack to suffer a voltage drop long before they are fully depleted. Cell capacity is only one part of the equation and, unfortunately, the only number that most people look at.
For today's high performance molded sailplanes, we need battery packs that can deliver high current right up to the edge of depletion without dangerous dips in voltage. Look to the kinds of low impedance cells that people use for motor applications. Here are some examples of the low impedance cells that I am using in my planes:
F3J Icon: Sanyo CP1700 Sub C Nicad Graphite Electric: KAN 1050 2/3A NiMh Tragi: GP2000 4/5 A
--Jim Laurel
On Apr 17, 2005, at 11:41 AM, James R MacLean wrote:
Its too windy to fly here on the east coast of Florida, so maintanence
time. (Yes, I know, what a wimp. I can and have flown contests in pretty
bad wind but why risk a plane when there will be better days soon.) The
question is about batteries. I need to replace a number of sailplane
batteries. They all hold a square pack of AA size. It appears to me
that there are only two packs which make sense: the 1100MAH NiCd and the
1650 NiMH. Both are nearly identical in cost, weight and size. I have
the appropriate charger which is rated for either and does a good job in
a reasonable time. Both cells are made by Sanyo which usually means
excellent reliability and service life. Sailplanes generally don't draw
extreme servo currents so I expect the hydrides to be sufficient in that
respect - the nicads are usually superior in high current applications.
What do you think? Any data / experiences to suggest the better choice?
Thanks for your thoughts, Jim MacLean
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