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Digital Servos and Nicads

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Old 05-23-2005, 05:24 AM
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Thomas Cummings
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Default Digital Servos and Nicads

I keep coming across mentions that Futaba digital servos are to be used with nicad batteries only, not li-po or nimh. However, I cannot find anything regarding this in the manual that came with my radio (7CAP) or on Futaba's website. Can someone point me to the offical word?

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Thomas
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Old 05-23-2005, 07:30 AM
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LSP972
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Default RE: Digital Servos and Nicads

This has been one of those rumors, myths, whatever you want to call it, for some time. IOW, you won't see anything "official" on it.

Here's the deal:

Fact One: NiMH batteries do not put out as much amperage as ni-cads. They have more capacity, but not as much "grunt". This means that, under heavy load, the voltage supplied by a NiMH cell can drop significantly- much more so than a ni-cad.

Fact Two: Certain devices, such as the Futaba 401 gyro, have been proven to re-set (and cause crashes) under load when the supplied voltage drops below a certain figure.

Fact Three: Digital servos use quite a bit more battery power than standard, or analog, servos.

Fact Four: The majority of people who have (or THINK they have) suffered from this phenomena are folks who do a lot of extreme flying- 3D, if you will. These wild gyrations really tax a model's servos/electrical system to the limit.

Supposition One: Since these 3D guys tend to be very enthusiastic and vocal, we hear a lot about what happened to them. Some of them are automatically assuming that NiHM batteries were the cause of their woes, and are therefore to be avoided. If one hears something long enough, you can start to believe it.

Supposition Two: Dura-Lite, or other li-po/li-on whatever will cure all battery ills. You can make up your own mind about that one...

Basically, there might be something to this, at least as far as NiMH batteries go. But is it the heinous problem some make it out to be? Personally, I think not.

For the past two years I have been flying a 55" biplane with four digital and one analog servos on a 1650mAh NiMH pack, with absolutely no issues. The model is flown aggressively, but NOT wildly.

If you like to flip, flop, and thrash your model about, then you might take heed to this. Otherwise, I'd use an appropriate-size NiMH battery with confidence.
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Old 05-23-2005, 09:57 AM
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Default RE: Digital Servos and Nicads

It was more of a problem with the first generation of NiMH that hit the streets. Newer batteries from reptulatable manufacturers, this shouldn't be a problem.

Lots of info at http://www.rcbatteryclinic.com
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Old 05-23-2005, 12:52 PM
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Default RE: Digital Servos and Nicads

Check this thread out.
http://www.rcuniverse.com/forum/m_29..._1/key_/tm.htm

We are discussing something similar with NiMH and digital servos. NiMH can kick out enough amps if you use quality cells, but most manufacturers, even quality ones, have super high impedance which limits the amps it can put out. go to www.hangtimes.com and read their faq. They have some good info on batteries. RC battery clinic is another good site.
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