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digital servos

Old 06-28-2011, 06:57 AM
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miker49
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Default digital servos

i just recieved my aeroworks p-51. recomended servos are hi tec 7985 mg digital.i know i need to use mg's and high torque,but do i really need to use digital servos? 985's are the same torque and mg'ed.thanks
Old 06-28-2011, 07:02 AM
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BuschBarber
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Default RE: digital servos


ORIGINAL: miker49

i just recieved my aeroworks p-51. recomended servos are hi tec 7985 mg digital.i know i need to use mg's and high torque,but do i really need to use digital servos? 985's are the same torque and mg'ed.thanks
You do not necessarily need to use Digital Servos. I have an H9 P47-150 with a Fuji 32ei motor and I use Analog Servos. It is advisable to use Analog Servos for Flaps, especially, since they are never really at Neutral, but somewhere in between.
Old 06-28-2011, 07:36 AM
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fizzwater2
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Default RE: digital servos

Rich - what does not being at neutral have to do with analog / digital servos?
Old 06-28-2011, 08:33 AM
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BuschBarber
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Default RE: digital servos


ORIGINAL: fizzwater2

Rich - what does not being at neutral have to do with analog / digital servos?
I am not sure that is the correct explanation. I was advised, by some fellow club members who fly scale gassers and jets, that digital servos draw quite a bit of current when holding the Flaps up. Analogs are easier on the battery for Flaps, Air Valves, etc.. I am not sure where I got the idea that Neutral was an issue.

Old 06-28-2011, 09:32 AM
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fizzwater2
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Default RE: digital servos

Makes sense - digitals are somewhat power hungry, and you really don't need that on a lot of functions.

I don't use many digitals at all, but then again, I fly mostly race planes, and we don't normally have air valves, flaps, etc. I am currently building a new Q500 plane with digitals on the v-tail and ailerons, but the throttle servo will probably be an HS82MG or something like that. I would like to try the 11mS mode on my new DX8, but I'd have to buy a digital throttle servo to do that, not sure if it's worth it for what I do with a radio!

Old 06-28-2011, 10:03 AM
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Campgems
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Default RE: digital servos

Neutral in the servo is where it is not trying to move one direction or the other regardless ofwhere the stick is. It can be at any point of travel. Center is different, On flaps, if the servo is binding at full up, a digital is going to draw more current than an analog, but the analog will also draw more current if the it is stalled before reaching neutral.Just like a throttle servo that has the end points off and at full throttle is jammed and is going to draw more current. The Digitals have a better resolution at center for the most part. If you put a little pressure on the digitalservo while it is centered, you will hear it start to buzz as it if fighting to get back to the neutral condition.

After doing some testing a while back on different servos, I found that the name brand digitalservos, IE Futaba, JR, Hi Tec, etc were better at returning to center than the analog servos. The worst of the bunch I tested was a Tower Pro Digital 995 metal gear that was selling on Ebay for very little money, something like $6 each for a 100 in oz plus. It was awful. The best centering was a Futaba Rudder Servo a 9254, for a gyro. It was lighting fast and the return to center was very precise, 0.8 degrees while the Tower Pro wallowed around 2.5 degrees. Surprising that the next best was a Futaba 3004 at 1 degree.

My 2 cents worth, I like the digitals. The price difference isn't as great as it was 6 yeas back, and with the availability of the 200mah NiMh 4.8 packs at very little weight difference to a 500 mah NiCd packs of old, the extra current draw isn't an issue.

Don

Edited to correct the best servo number and to add servo types
Old 06-29-2011, 06:15 AM
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Zeeb
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Default RE: digital servos


ORIGINAL: miker49

i just recieved my aeroworks p-51. recomended servos are hi tec 7985 mg digital.i know i need to use mg's and high torque,but do i really need to use digital servos? 985's are the same torque and mg'ed.thanks
'Lemme ask 'ya one question; Which radio system are you planning on using? If you're planning on using a Spektrum/JR 2.4GHz system you'll find that the 9 channel and above rx's when used with a 2048 resolution capable tx, will produce some undesirable servo actions on power up and before the rx links with the tx if you use analog servos.

As far as this particular question, I decided some time ago not to buy servos specifically for one model since that restricts other possible applications down the road. In the case of the AW Mustang, I bought Hitec 7955' which are bigger than recommended but I can use 'em in anything I fly including GS aerobats and they're only about $12.00 a piece more than the recommended 7985's.

Some folks claim they cannot tell the difference between analog and digital servos when it comes to flight performance but I can on my aerobats. The AW Mustang is going to be my first Warbird so I can't say with any authority if that same difference can be felt on the Warbird, but it'll have the same servos I use on most everything else now in any event.

JMHO....

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