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Old Dec 29, 2010, 01:36 PM
<>< AKA W4BPS
USA, TN, Tullahoma
Joined Dec 2001
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Question
3421 vs 94820

I have been thinking about trying the Airtronics 94820 when I need another 3421.. They are just about 1/2 the price. Very close in size and weight..Any one try the 94820s? Any comments? Brian
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Old Dec 29, 2010, 02:50 PM
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San Diego, CA
Joined Aug 2004
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Brian, they are FANTASTIC servos. Compared to the 3421, they are a touch slower, but a touch more powerful when you compare the specs. For a long time, the 3421 was my favorite servo. I say this as an Airtronics team pilot, so you know I shoot straight. That being said, I don't use them anymore. They are a bit too expensive and too thick. There are too many other great choices.

I used to use them in the fuse for my tail servos. They are still an awesome choice. But they are too strong, so I choose a faster, smaller servo. Hopefully a cheaper one too. For the longest time they were my absolute servo of choice for the flaps in my large TD ships, and my B planes if I could fit them. There is the trick, "IF" I could fit them. That is where the 820 comes in. If it fits, it is a great alternative. Especially if you are a flap abuser. If not, there are a bunch of great slimmer choices. I still like the 94761 for everything in my gliders.

Also, check out the 809 servos for ailerons, and V-tails. They are really small and light. I haven’t used them yet, but Daryl likes them.
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Old Dec 29, 2010, 04:53 PM
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3421 has it's place as Dave says "they are FANTASTIC servos" I like the speed and power of the 3421 and this is a contest PROVEN servo.. If you have the room 3421 all the way

sj
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Old Dec 29, 2010, 05:05 PM
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Joined Jul 2007
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Flyin' Brian, its simple. The DS3421 is a JR servo, the 94820 isn't. Not much more to say. Remember, a few bucks saved on a $2000 airframe is chump change and increases risk. Go with the best.

JT
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Old Dec 29, 2010, 05:16 PM
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Melbourne, Australia
Joined Mar 2005
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I'm a big fan of the airtronics servo. Never used a Airtronics 94820 I assume they are the same as the 94761 with different gearing for more torque. I have only ever sprung for one 3401 (i think the model before the 3421) and its awesome on the full flying elevator of my big bird. But I'm still paying it off.

94761 proven on all surfaces to over 300mph in ds conditions give me some faith that just because they are half the price they are not half the quality.

I think tight slop free linkages and good geometry are more important than which servo you buy.
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Old Dec 29, 2010, 06:12 PM
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Harbor City, CA
Joined Oct 2003
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It's considerably thicker than a 761, though.
But now that more planes are using RDS, if it fits between the skin, it fits. No issue of the servo arm and flat covers when using RDS.

It might have to get tested on flaps if I ever build myself a bagged Supra, if it will fit.
If not, it would make one heck of an elevator servo I would think.

R,
Target
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Old Dec 29, 2010, 06:57 PM
<>< AKA W4BPS
USA, TN, Tullahoma
Joined Dec 2001
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3421

I have one coming in the mail JT. Thanks. I do really like the 761s over the 368s. I was just looking/asking around. Brian

Quote:
Originally Posted by jtlsf5 View Post
Flyin' Brian, its simple. The DS3421 is a JR servo, the 94820 isn't. Not much more to say. Remember, a few bucks saved on a $2000 airframe is chump change and increases risk. Go with the best.

JT
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Old Dec 29, 2010, 07:01 PM
<>< AKA W4BPS
USA, TN, Tullahoma
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Thanks Dave for your comments..

Great flying BTW. Congrats. Brian

Quote:
Originally Posted by djklein21 View Post
Brian, they are FANTASTIC servos. Compared to the 3421, they are a touch slower, but a touch more powerful when you compare the specs. For a long time, the 3421 was my favorite servo. I say this as an Airtronics team pilot, so you know I shoot straight. That being said, I don't use them anymore. They are a bit too expensive and too thick. There are too many other great choices.

I used to use them in the fuse for my tail servos. They are still an awesome choice. But they are too strong, so I choose a faster, smaller servo. Hopefully a cheaper one too. For the longest time they were my absolute servo of choice for the flaps in my large TD ships, and my B planes if I could fit them. There is the trick, "IF" I could fit them. That is where the 820 comes in. If it fits, it is a great alternative. Especially if you are a flap abuser. If not, there are a bunch of great slimmer choices. I still like the 94761 for everything in my gliders.

Also, check out the 809 servos for ailerons, and V-tails. They are really small and light. I havenít used them yet, but Daryl likes them.
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Old Dec 29, 2010, 09:12 PM
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San Diego, CA
Joined Aug 2004
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They are not in the same case as a 761. They are far thicker than the 761 but they have crazy power. Spencer, wold record holding DS pilot/designer/builder has been using then for the flaps in his recent DS ships. It should be noted that they are .050" thicker than the 3421.

Quote:
Originally Posted by Swoopdown View Post
I'm a big fan of the airtronics servo. Never used a Airtronics 94820 I assume they are the same as the 94761 with different gearing for more torque. I have only ever sprung for one 3401 (i think the model before the 3421) and its awesome on the full flying elevator of my big bird. But I'm still paying it off.

94761 proven on all surfaces to over 300mph in ds conditions give me some faith that just because they are half the price they are not half the quality.

I think tight slop free linkages and good geometry are more important than which servo you buy.
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Old Dec 30, 2010, 01:29 AM
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Guys in some applications the 3421 is shorter in height than the 820 - I ended up using the 3421 just for this reason, and only this reason. Both are good servos. One thing I noticed is that no-one has mentioned that Airtronics ae manufactured in China, and most JR units are not. Don't know if that matters for product consistency and quality these days.
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Old Dec 30, 2010, 08:17 AM
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Melbourne, Australia
Joined Mar 2005
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Quote:
Originally Posted by djklein21 View Post
They are not in the same case as a 761. They are far thicker than the 761 but they have crazy power. Spencer, wold record holding DS pilot/designer/builder has been using then for the flaps in his recent DS ships. It should be noted that they are .050" thicker than the 3421.
Thanks tor that. I'll be giving them a go in the next wing that think enough to try them in.
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Old Dec 30, 2010, 12:40 PM
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United States, CA, Midway City
Joined Dec 2003
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The 94820 is slightly thicker than the 3421 as DK points out. Also, from the mounting lugs to the servo arm, height is the same. From mounting lug to bottom of servo, the 94820 is about 5mm taller.

Drive both near the limits of torque rating, the 94820 produces less heat.

The speed of the 94820 unloaded is about .188sec to turn 60degrees (6.6v) vs .135 for the 3421 (6.6v).

I don't think the 94820 is best for ele. That would have to be the JR DS3417 or the Z3650 (speed = .095, 6.6v), imo.

The gear slop out of the box in the typical 94820 is 1/2 that of the typical 3421. The 94820 is probably the better servo to use vs the 3421 for flaps if it fits. The speed of the servo is not as important here because the ail is most likely slower in deployment anyway due to geometry of linkages if set up optimally (ail servo travels 3x that of ail deflection).
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Old Dec 30, 2010, 12:48 PM
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United States, CA, Orange
Joined Oct 2006
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Quote:
Originally Posted by fnnwizard View Post
I don't think the 94820 is best for ele. That would have to be the JR DS3417 or the Z3650 (speed = .095, 6.6v), imo.
You mean DS3517, right? There is also now a HV version that is designed for unregulated LiXX packs - the DS3717.

Tom
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Old Dec 30, 2010, 12:54 PM
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United States, CA, Midway City
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Quote:
Originally Posted by tewatson View Post
You mean DS3517, right? There is also now a HV version that is designed for unregulated LiXX packs - the DS3717.

Tom
Correct Tom. 3517. too many servos to keep track of .
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Old Dec 30, 2010, 03:50 PM
<>< AKA W4BPS
USA, TN, Tullahoma
Joined Dec 2001
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Thanks

Not only are you one great guy, your also a bundle if information. ... Brian


Quote:
Originally Posted by fnnwizard View Post
The 94820 is slightly thicker than the 3421 as DK points out. Also, from the mounting lugs to the servo arm, height is the same. From mounting lug to bottom of servo, the 94820 is about 5mm taller.

Drive both near the limits of torque rating, the 94820 produces less heat.

The speed of the 94820 unloaded is about .188sec to turn 60degrees (6.6v) vs .135 for the 3421 (6.6v).

I don't think the 94820 is best for ele. That would have to be the JR DS3417 or the Z3650 (speed = .095, 6.6v), imo.

The gear slop out of the box in the typical 94820 is 1/2 that of the typical 3421. The 94820 is probably the better servo to use vs the 3421 for flaps if it fits. The speed of the servo is not as important here because the ail is most likely slower in deployment anyway due to geometry of linkages if set up optimally (ail servo travels 3x that of ail deflection).
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