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Old 07-18-2002, 06:53 AM   #1
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Default Digital vs Analog servos

Does anybody have any comments regarding the advantages and disadvantages between digital and analog servos?

Thank you

Nick
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Old 07-18-2002, 06:55 AM   #2
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Digital- more expensive. higher holding power, higher power comsumption

Analog- Cheaper! but still plenty good.
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Old 07-18-2002, 06:56 AM   #3
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The digital servo has a chip that checks the position of the servo many times a second, rather than just using feedback like the analog servo.

This increases accuracy.

The digital servo's also have better speed and torque numbers as well.
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Old 07-18-2002, 07:04 AM   #4
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dtm: you mean that they don't worth the extra money

Something else too!

Some of my friends have digital servos and I have noticed that a strange noice comes from the servo even when it is not moving! What is that noice, is it normal


Thanks again

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Old 07-18-2002, 07:15 AM   #5
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In addition to the digital ones advantages metioned above, you should ad, that they got better resolution and their torque are independant of position.

If they are worth it? Well, there are good analog servos for less money. On the other hand, I believe that the steering servo are the most overlooked hop-op and also an very important hop-op. Then add, a servo can last for a long time and can be taken to other cars. Unlike car specific hop-ops.....
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Old 07-18-2002, 08:09 AM   #6
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Digital (supposedly) center better and are more precise. However, I don't use digitals in my electric car because it becomes a drain on the batt. There are some nice analog alternatives though. Right now I'm running an Airtronics 94157. It's about 2 years old (newest version is 94357) but it's still very quick and I got it for $40 so no complaints here.
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Old 07-18-2002, 08:19 AM   #7
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nnick, not necessaryily not worth the money....its just that analogy servos are really quite all right. If you have a big budget then digital is the way to go. For most purposes with a digital and analogy servo of the same spec, you will notice very little difference when running the car. I certainly cannot notice any deficency in my KO 2001 (analogy) compared to my 2143 (digital).

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Old 07-18-2002, 08:21 AM   #8
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Here is a very good explanation of the technical differences!

http://www.futaba-rc.com/servos/digitalservos.pdf
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Old 07-18-2002, 08:29 AM   #9
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nnick: that sound coming from the digital servos (even when not moving) is normal. Some digital servos are louder than other when it comes to this noise, but pretty much all of them make that noise.

I could be wrong, but I believe that noise is the servo constantly checking and re-checking and re-re-checking its center position, so that noise would be from the internal motor. If you try to move the servo from its center position while its on(pysically by hand, that is), you'll hear that noise increase, as the servo fights to keep its center position.

I get the same noise (though not as much of it) from my analog KO Propo 2173.

As for if its worth it, thats up to you. Servos like the KO 2173 have better torque and speed numbers and cost less than 'some' companies' digital models. But its generally agreed that the centering isn't as precise. Centering hasn't been an issue with my 2173, its dead on everytime. Then again this servo isn't exactly cheap($89.95), so I got what I paid for.

Generally, the digital models will run you $15-$20 more. So whether their worth that extra $$$ is up to you.
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Old 07-18-2002, 10:13 AM   #10
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That is exactly what the noise is, the servo is trying to center itself exactly precisely at exact precise center, which is generally impossible, but it tries anyway.

Many (most?) digital servos are also programmable - IF you have the programmer. The only ones that I know of that are available are HiTec's programmer (very expensive) and Multiplex (something like $80) and they only program their respective brand of servo. You can program things like endpoints, speed, dual rate, etc. right on the servo so you can set up your servo and use your controller as a fine tuner rather than to set your DR at like 70 or something - it also means that you could use a cheaper radio. . .

I'm not sure about KO, Futaba or Airtronics, though.
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Old 07-18-2002, 01:44 PM   #11
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Darkseid - Id say $89.95 is pretty cheap for the 2173, in the UK its 84.95 ($134)!!
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Old 07-19-2002, 02:56 AM   #12
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I thank you all for the info. You have been very helpfull!


Thanks again

Nick
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Old 07-19-2002, 08:11 AM   #13
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Ian S: I guess it wasn't that expensive after all huh?
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Old 07-19-2002, 09:44 AM   #14
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If you are a good driver now, a digital servo will make you a better driver.

Get a digital radio and digital servo, and you will be so much happier with your performance.

I gained so much more control and tunability by going with a Lynx 3D FM and digital servo.

Plus with hi-tecs unbreakable servo policy, you are only hurting yourself on the short and long run buy not paying a little extra for more control and much more durability.

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