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Servo question

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Old 12-29-2004, 12:36 AM
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khodges
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Default Servo question

Getting ready to build my first 1/4 scale bird, L-19 BirdDog.I'm using a std. (S3001) servo for throttle, but can't decide what I should do for the rest. I've narrowed it to:
Futaba S9001 coreless--54 oz/in torque, $30 each
Futaba S3010 std high torque--72 oz/in and one ball bearing, $25 each
Futaba S3302 1/4 scale servo--89 oz/in and final metal gear $50 each.

Size isn't an issue ,but I'd like to keep the price down as much as possible. Would the std high torque servo be big enough (torque) for this plane? I mean it's no Extra or P-47; and the 3010 has a faster transit time than the 3302. And how about the metal gear in the 1/4 servo-- what are the pros and cons of metal meshing with plastic gears. What are you guys recommending if different from these? I'd rather stay with Futaba, out of familiarity.

Gonna use one servo for elevator, one for rudder, dual aileron and dual flap.

As James Brown says so well--- HEP ME, HEP ME, HEP ME PLEEEEEZ!!!!
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Old 12-29-2004, 02:24 AM
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Default RE: Servo question

Glow or gas power?

I'd look real hard at the 9001 coreless unit all around, These servos properly setup should be fine. Since this model does not likely require large control surface deflections, short servo arms and long as possible control arms would create a mechanical advantage.

A 6.0V power system would be preferred IMO as well. Battery weight is negligible in this bird so don't skimp here, more is better for various reasons.
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Old 12-29-2004, 07:53 PM
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Default RE: Servo question

Michael-- thanks for the reply. It's gonna be a gasser, a US-41. The 9001 doesn't really have much more torque than the std servo, so I wondered if it was really enough. The 1/4 scale has plenty, and I wondered if it was excess for my needs, given the price of the servo, and the 3010 had a good bit more than std, was closer to 1/4 scale servo, but much cheaper, and the smaller size would make them easier to conceal in the wing for ailerons and flaps. I plan to mount them on their side with only the servo arm protruding out of the wing, and am even considering a totally concealed linkage, at least for the flaps.

I was also planning to stay 4.8V for lower power consumption, and was looking at 2000 mAh NiMH battery pack. What would be your recommendation for capacity at 6.0V, and do you recommend 6V for the extra torque and speed?

Rereading the post it sounds like the Goldilocks Syndrome--you know, this one's too small, this one's too large, this one's j-u-u-u-st right.
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Old 12-29-2004, 07:59 PM
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Default RE: Servo question

One other question, while I'm at it: is another reason for your recommendation for the 9001 servo due to its coreless design? What is the advantage of coreless over standard?
Thanks in advance, Ken
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Old 12-29-2004, 09:15 PM
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Default RE: Servo question

Ken

What does the manufacturer recommend for servo power?

The 1/4 scale servo would be fine, but are very heavy and way over-kill IMO. There also power hungry.

The coreless servos are more precise, typically faster and offer more power with like current consumption.

I eluded to utilizing short servo arms and long control arms, this employs mechanical advantage. If your servo is rated for 100oz-in and your pushing a .75" servo arm coupled to a 1.5" control arm you end of with a lot more servo FORCE than you began with.

100/75=133ozs Force, 133ozs. Force x 1.5" = 199.5oz-in TORQUE to the surface... MAX out your ATV and use the servos full travel arc this provides better system resolution while taking advantage of the mechanical linkage system.

6.0V systems offer more power and torque for a paltry difference in consumption IMO. I'd use a 2700mAh NiMh 5-cell battery. I'd even consider two batteries and two switches in this model. Cheap insurance IMO.
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Old 12-30-2004, 09:53 AM
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Default RE: Servo question

The 3010 should do fine. No need to go to 6 volts unless you just want to for the prestige--the Bird Dog doesn't need it.
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