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recommended battery for 7 servos

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Old 11-30-2005, 02:07 PM
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aars
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Default recommended battery for 7 servos

I've been a regular RC pilot using 4 to 5 servos; therefore I always use the standard Rx battery (4.8V , 600mah). Now, I am building a plane which will use 7 servos: 2 ailerons, 2 flaps, 1 LG, 1 engine, 1 rudder, 1 elevator.
For what I read, I should change the battery for a more powerful one. Is this true? What would be a recommendable battery amperage? Should I increase the voltage too? is there a formula according to the number of servos?

Finally, should I increase the wire gauge to 22?

Thanks for the advice
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Old 11-30-2005, 03:55 PM
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Red B.
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Default RE: recommended battery for 7 servos

It depends.
In my Sig Somethin Extra, modified with flaps and indipendent elevator halves, I use 8 Hitec 225 servos (2 flaps, 2 ailerons, 2 elevators, 1 rudder and throttle with a JR 600 mAh 4.8 V NiCd Rx battery.
With this set-up I can fly for two hours with capacity to spare.

Your milage may be more or less depending on what servos you use, the linkage and your flying style. I would consider it prudent to go for at least a 1000 mAh battery, just in case...

I strongly suggest that you use a separate battery for the landing gear servo in order not to drain the Rx battery if the l/g binds during retraction

/Red B.
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Old 12-01-2005, 08:50 AM
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Default RE: recommended battery for 7 servos

Thanks Red for the advice!!

You mentioned a separate battery for the LG. Is this also recommendable with pneumatic LG?

If so, can you tell me how to connect the battery to the LG servo? I’ve never done something like that.
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Old 12-01-2005, 09:49 AM
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Default RE: recommended battery for 7 servos

For pneumatic retracts there is no need for a separate l/g servo battery. I was thinking about mechanical retracts for some reason. Sorry about that.

/Red B.
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Old 12-06-2005, 09:45 PM
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Default RE: recommended battery for 7 servos

I thought I would add my experience since I have often wondered the same thing. I have a KMP Hurricane (72") with a gas engine (Roto 25) that has seven Futaba standard analog servos (2 ailerons; 2 flaps; 1 LG--air; 1 elevator; 1 rudder) and I have been successfully using the standard Futaba 600maH pack for a long time. I measure my voltage after charging and before flying and then after I get home from flying and I always start with about 5.7 volts and end up with 5.3 volts after four flights, which typically includes about 50-60 minutes of receiver "on" time. My type of flying with this plane is smooth, scale like flying with basic maneuvers, so I never jerk the plane around or make large control surface movements. I have considered going to a higher capacity pack, e.g., a 1000 or 1100 maH pack since they are relatively inexpensive, but just can't see the justification since I have yet to get any lower than 5.3 volts. I have been charging these packs overnight using the standard Futaba wall charger at 60maH. Good luck with your decision.

-Ed
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Old 12-07-2005, 09:11 AM
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Default RE: recommended battery for 7 servos

Thanks for the advice Flyfast1!!

You mentioned you are getting 5.7 to 5.3V out of your battery. Is this from the standard battery of 4.8V-600mah? or did you changed your battery to a 6V?

thanks,
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Old 12-07-2005, 12:13 PM
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Default RE: recommended battery for 7 servos

Yes, it is a standard 4.8volt pack from Futaba, 600maH capacity, the one that came with my transmitter when I purchased it. Immediately after charging using the standard Futaba wall charger (4.8v charger), my pack reads about 5.7 volts. I get the exact same readings on another Futaba receiver battery in another plane--same battery: 4.8 volts; 600maH capacity. At one point I put a post in the battery forum about this because I was surprised that it charged up so high. I figured a 4.8volt pack would charge to 4.8 volts. Someone replied showing some type of charge diagram from Sanyo who makes the batteries and each cell does charge up higher than 1.2 volts and 5.7 volts for the entire pack was not uncommon.

-Ed
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Old 12-07-2005, 12:51 PM
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Default RE: recommended battery for 7 servos

The battery size will vary a lot depending on if the plane is set up with huge 3D throws or just normal precision throws. For 3D you'd need at least 1000mah and I'd go with 1500+ mah so I can fly all afternoon on a single charge. Also depends how many flight you want out of it without recharging.
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Old 12-07-2005, 02:29 PM
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Default RE: recommended battery for 7 servos

Hi,
I have 8 servos in a 4 star 60. 2 on ailerons, 2 on added flaps, 1 rudder, 1 elevator, 1 throttle, and one on an added tow hook release for towing gliders. I was useing a 1000mAh bat for the longest time and got plenty of time on it. Recently I switched up to a 2200 mAh batt. I have not had the chance to fly it with this battery pack but im sure it will last me all day!
Hope that Helps!
Jon
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Old 12-08-2005, 11:56 AM
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Default RE: recommended battery for 7 servos

I actually have 8 servos, not 7 in my Hurricane--I forgot about the throttle servo.

I guess what can be taken from this thread is that it depends on what type of plane and flying are done and how many flights one wants in a flying session. For my warbird application, the control surface movements are small and slow--I aim for smooth flying. I also have a 4*60 with the same battery and have experienced the same voltage levels. I do some aerobatics and IMAC basic routines, but don't go all out all the time. So, for these planes and setups and this type of flying with up to four flights per session, the standard 600maH pack seems fine. For applications where the throws are greater or the style of flying is using the servos a lot more or where more than four flights in a session are desired, it probably makes sense to consider a larger capacity pack, perhaps a 1000maH pack. This is also with standard analog servos. If you start using digitals that generally consume more power, then upgrading the receiver pack makes more sense.

Good thread, interesting topic.

-Ed
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