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Standard Servo vs. Digital Servo

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Old 09-14-2004, 11:57 AM
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aec12
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Default Standard Servo vs. Digital Servo

Could someone tell me the difference in a standard servo and a digital servo? In other words, what would the Futaba S3151 digital servo selling for $60 do that the Futaba S3004 standard servo selling for $14 would not?

Thanks,
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Old 09-14-2004, 01:17 PM
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Gringo Flyer
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Default RE: Standard Servo vs. Digital Servo

Drain your battery in half the time

I have four in a new plane and wow they eat up the bateries. I only have 3 flights with mine and I havent noticed a tremendous difference in flight. I am not a pro pilot either.

For me, the digital servos came with my 7C, but I dont think I would buy them apart from a radio.

Also, Tower has those servos for $39 and not $60 if you are wanting to buy some. However, if you buy 4 that comes out to $160 for another $100 you could buy the whole setup radio, receiver, servos, etc. If you really want the servos but have a radio, you could sell the radio and rx, bat, etc for $100 easy.
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Old 09-14-2004, 02:12 PM
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Default RE: Standard Servo vs. Digital Servo

digital servos are MUCH, MUCH stronger for small movements. they are basically able to use the full torque rating at any position, whereas standard servos have proportionate power depending on the distance they are off center. Along with that goes increased centered ability and response time.

Depends on the plane, on a trainer or some sport flyer plane you won't notice a difference. (btw, they should be used with a larger battery pack, those stock AA 600 mah nicad's are almost worthless for many uses)
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Old 09-14-2004, 05:06 PM
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Default RE: Standard Servo vs. Digital Servo

i think a standard servo has the same power no matter how far off centre it is. not all digital servo's suck current either. some hitec digitals use less current under load than futaba 9204's. digitals are supposed to have better centering, quicker response time and better holding power.
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Old 09-14-2004, 07:27 PM
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Default RE: Standard Servo vs. Digital Servo

ORIGINAL: locoworks
i think a standard servo has the same power no matter how far off centre it is. not all digital servo's suck current either. some hitec digitals use less current under load than futaba 9204's. digitals are supposed to have better centering, quicker response time and better holding power.
Yes, in theory, a digital servo will apply full torque and move the servo arm to the requested position then turn off so although it might draw a little more current while actually moving, a digital servo should spend less time driving the motor.

By comparison, a traditional servo (since the term digital is a misnomer anyway) will experience a reduction in torque as it approaches the commanded position and this means it may actually sit slightly off that position and continue to drive the servo-motor with reduced power but increased current consumption.

In the case of the traditional unit, this means that the overall current draw could be higher than the digital although the digital will draw much higher currents for shorter periods of time and spend more time in a quiescent state where the current draw is very low.

The secrets to reducing the current draw of your servos is to make sure your linkages and hinges are free and non-binding and don't use a servo that's really too small for the job.

I think one thing that causes a multitude of problem is that some people are reading the torque ratings for modern digital servos and thinking that a tiny digital (like the hitec 5245) can be used to replace a standard-sized non-digital. In such an application, the smaller digital has to work very hard to do the job and is more likely to draw extra current when operating against normal flight loads.
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Old 09-15-2004, 06:19 AM
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Default RE: Standard Servo vs. Digital Servo

Thanks for all the info guys. Sounds like with price considered, I will stick with standard servos.
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Old 09-15-2004, 06:40 AM
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Default RE: Standard Servo vs. Digital Servo

Forget the power, which is nice, the big thing is the centering. If you are a good flier, you can tell the difference, especially on ailerons.

As for batteries, a 1600 mil NiMH pack is the same size and weight as an 800 NiCd. And can't you get a field charger for $25 or so?
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Old 09-15-2004, 08:58 AM
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Default RE: Standard Servo vs. Digital Servo

A standard servo has an analog amplifier and the digital servo has a digital amplifier. The benefit is that an analog servo needs more error signal to get the power to the motor. Higher the error, more power applied. A digital servo can have this programmed into the amplifier so that with a specific amount of error can generate full power to the motor.
ORIGINAL: aec12

Could someone tell me the difference in a standard servo and a digital servo? In other words, what would the Futaba S3151 digital servo selling for $60 do that the Futaba S3004 standard servo selling for $14 would not?

Thanks,
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