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Digital Servos and Battery Requirements

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Old 07-28-2005, 08:24 AM
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Nickolas
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Default Digital Servos and Battery Requirements

Hi,

What kind of battery (Voltage, capacity, type) should I use in a model that has 5 digital high torque servos +1 for throttle and intended for aerobatic/3D flying type where the flight loads are quite high?

Looking forward to replies regards,

Nik
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Old 07-28-2005, 11:20 AM
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Default RE: Digital Servos and Battery Requirements

Any 4.8 to 6v will do. Use 1800ma or higher. And fast charge after 3 or 4 flights if you are flying hard. Dennis
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Old 07-30-2005, 08:42 PM
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Default RE: Digital Servos and Battery Requirements

I use a 6V 2000mAH pack on my edge with 5 digital servos, no dramas.
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Old 07-31-2005, 09:48 AM
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Default RE: Digital Servos and Battery Requirements

Much more important than the battery is your wiring. Use heavy gage wire, high quality switches (heavy duty) and gold plated connectors. Shy away from extensions if at all possible, the added loss in these can cause all sorts of problems in systems requireing high peak or surge currents like some high torque servos do.
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Old 07-31-2005, 12:37 PM
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Default RE: Digital Servos and Battery Requirements

6.0V batteries are best for performance and power. Adequately sized batteries are paramount to realize desirable results. The demands of Digital servos can be a problem with high resistance batteries. Battery mAh capacity is only part of the picture as the capacity is not indicative of the ability to provide power under load.. The best bang for the buck IMO are the low IR 1950mAh NiMH's.

As mentioned HD switches and components, minimal connector count and wire length.

Rodney

Did you mean to suggest "equally important" vs. "more important"??? I'd prefer the correct battery over standard wire sizes and components any day of the week
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Old 07-31-2005, 04:12 PM
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Default RE: Digital Servos and Battery Requirements

Michael, equal is probably a better word, hard to say which is more important. For high current servos, I prefer NiCads over NiMh as they usually have a lower internal resistance and, in these bigger planes, the small additional weight really doesn't hurt that much. I see more problems caused by inadequate wiring than by batteries.
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Old 08-04-2005, 12:07 PM
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Default RE: Digital Servos and Battery Requirements

I've often wondered why RX batteries don't have larger leads on them.[:-]

I use all HD switches, leads, and niMH batteries. Always 6V. I'll use a 1650mah in a 40 size plane with coreless or digital servos. I'll usually use a 2000mah+ in anything over 25%.

I know it reduces power to the servo, but I still use extensions. I'm just not comfortable soldering new leads on brand new servos.[] If I have to run multiple extensions in the wings on a larger plane, or out to the tail servos, I'll put the heaviest extensions in the RX, and then use a smaller extension out to the servo. I think that helps reduce the voltage loss.

So, we're dealing with HD 22ga. servo extensions on just about ALL my planes, and the switches and batts are good sized.

How come there is always a little bity wire on the BATTERY lead?? I would think that this small lead would be the restriction in the entire system.

If you're using digitals, and pulling down lots of juice from the battery, you want a larger RX, and all the other things--switches, leads.......whats the deal with the battery?
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Old 08-04-2005, 03:38 PM
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Default RE: Digital Servos and Battery Requirements

Larger battery capacity does not always equal larger peak current delivery. Some AA cells are rated at more than 2000mAh but cannot deliver the short peak current that high-torque digitals demand. One cell I like to use for smaller airplanes is the 2/3A 1200mAh, commonly used to power 1:18 scale RC cars. Some of them can sustain 25A of continuous output. I've used 5cell packs made of these 2/3A cells to power up to 50-60cc class airplanes.
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Old 08-07-2005, 02:27 AM
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Default RE: Digital Servos and Battery Requirements

Assuming you are using normal heavy gage servo extensions and wire... the restriction is not in the wire. The problem is with the factory JR/Futaba connectors. Good factory connectors will work very well for a time. Wear from plugging and unplugging and charging through the switch and continuous charge/load rates higher than about 1.5 amps does the damage to the conectors. A worn connector can only take a little over 1 amp before heating up. Heat is caused by resistance. Keep in mind, if you are not using a Power Box you are putting the total load of all the servos through relatively small traces on the RX PC board.

FYI, high strand-count wire is better than low strand-count. Electrons travel on the wire surface and not through the core.

Also, if battery internal resistance (I.R.) is an issue, which is really is not any more with newer NiMH batteries, run two batteries of smaller capacity (thus equal to a big battery) on two switch harnesses. You will get all the current 'punch' you need and redundancy too. It also reduces current load through any given plug in your system by halving the current through it.

Use 5 cell batteries to give additional voltage to deal with voltage drops caused by long leads/multiple conections. Keep in mind that a 5 cell battery will not last as long as a 4 cell of equal capacity in a given airplane. Figure on about a 20% reduction in flight time/apparent capacity. Nothing is free... but bigger batteries are cheap.
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Old 08-07-2005, 07:44 AM
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Default RE: Digital Servos and Battery Requirements

Go here and read the info near the bottom of page.
http://www.hangtimes.com/rxpacks.html
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Old 08-08-2005, 03:05 PM
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Default RE: Digital Servos and Battery Requirements


ORIGINAL: Ch0pp3r
FYI, high strand-count wire is better than low strand-count. Electrons travel on the wire surface and not through the core.
Nope. What you're referring to is called "Skin Effect", which describes the effect that high frequency signals tend to travel nearer to the surface of the conductor. This is why an RF coax cable with copper coated center conductor works almost as well as solid copper center conductor. There, however, you are talking about frequencies in the MHz range and higher. Some audiophiles claim that the same effect applies to speaker cables and line-level interconnects. I have doubts whether the skin effect applies to the audio frequency range (low kHz), but I won't argue with highfalutin HiFi gurus, who claim they can "hear" differences in all sorts of esoteric setups.

For sure though, the skin effect does not apply for DC and low-freq AC current. This is why power cables are very often solid or low strand count conductors. One may argue that for RC electornics, the "signal" lines are high enough frequency to be affected by the skin effect. Again, the PWM signals are relatively low-freq such that any effect is neglegible. Beside, the longest run in even the largest model airplane is likely less than 6ft - no where near long enough for what little skin effect there may be to cause substantial rolloff. For RC, the high strand count conductor's main advantage is flexibility and the typical higher quality copper associated with the more expensive cable.
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Old 08-08-2005, 05:53 PM
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Default RE: Digital Servos and Battery Requirements

-This is a great switch: http://www.smart-fly.com/Products/Switch/switch.htm

It has 18 gauge wire on the battery side with a supplied Dean's connector. It has to j-type connectors on the rx side.



Check out this great battery, I have yet to use up a full charge: http://www.hangtimes.com/rxpacks.html

1950FAUP Series Sanyo 4/5 'A'
Rx & Ignition pack, 5 cell

The Sanyo HR1950FAUP 5 cell NiMH 6.0v Rx pack is an exceptional hi-capacity solution to solve the size and weight dilemma faced by pilots with high speed, high torque servos in aerobatic applications that MUST keep the footprint small and the weight low. These packs provide the tremendous power required in giant scale IMAC 3-D servo applications. With impedence ratings similar to Nicad Sub-C systems this pack will develop the servo torque you need without a significant voltage drop under the load. These are Sanyo's finest High Rate NiMH cells in a pack engineered to save you weight and hand you run time capabilities that rival Lithium systems costing twice as much.

Comes with HD 20g leads and either Futaba or JR/Hitec/AirtZ gold plated connectors. Big Bird Muscle, ultra small size and weight! An excellent choice as an Rx or Ignition pack where high servo power and maximum speed combined with minimum all up weight is critical!

Single cell dimensions: .70 x 1.70in

Total pack weight inc 20g connector: 7.5oz $39.95

Internal Impedance: 5.0 mOhms
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