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DS821 Servos

Old 10-26-2006, 01:11 PM
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RCdude13
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Default DS821 Servos

I am about to purchase 6 JR DS821 servos for a quarter scale biplane. I just wanted to get a vote of confidence from you on these servos. I assume you have had no problems, complaints or concerns about them...right? I know that a few of the JR Sport hi-torque servo's had a problem which has since been remedied. What's your opinion on these rather new servos?
Old 10-26-2006, 06:10 PM
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RVM
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Default RE: DS821 Servos

I'm not Danny, but I would tell you that I think the DS821s are the best servos in their price range, period. As long as you don't need metal gears, and the size and weight are acceptable, then you will love them. 1.5oz in a standard sized, digital, composite geared, high-torque, reasonably quick servo manufactured by a top company is hard to beat for $30.
Old 10-27-2006, 08:40 AM
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Default RE: DS821 Servos

We haven't had any reports of problems with them at this point. I've got them in a couple of models and am very impressed with them. They perform very well and have been working trouble free.
Old 10-28-2006, 03:01 PM
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Default RE: DS821 Servos

Thanks RVM and Danny...I was impressed with them as soon as I read the specs. My new bipe will be using these new JR servos.
Old 10-30-2006, 09:46 AM
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Default RE: DS821 Servos

Good to hear! Enjoy!
Old 12-10-2006, 07:36 PM
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Jack Skip
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Default RE: DS821 Servos

Maybe you guys can help, being JR knowledgable.

I am putting together a Hangar9 Cessna for a friend, using the JR DS821 servos. So far 3 of the servos have broken the output shaft. Twice on the rudder and once on the elevator. The first time the rudder one broke I replaced it with a fresh DS821. This time the rudder servo broke. Shortly after that the elevator rudder broke. With the first one breaking I thought it may have been just a bad servo. BUt with 3 breaking, there must be something else going on.

I am puzzled and would like to find out what the problem is. Not sure if it is a set up problem, or a batch of faulty servos, or what. He baught the servos about 15 months ago, but they have not been used in anything yet. The linkages move freely without any binding. The failsafe is set at center. The throws are not extreme and within the range of free motion. The plane has only been on the building table and outside once for engine break in. The arms have been snugged down to the output shaft, but not overly tight.

Any help or suggestions would be most welcome. We need to find and solve the problem as there are another 5 similar servos in the plane. My friend definately does not want totake it up until this mystery is solved.



Old 12-11-2006, 10:52 AM
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Default RE: DS821 Servos

Was there any binding or anything that could catch and restrict and bind up the servos? It may be best to send the servos in for a check up.
Old 12-11-2006, 10:59 AM
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Jack Skip
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Default RE: DS821 Servos

Thank you for the quick response.

No. There is no binding or restriction of movement. But the output shafts are cut clean across, level with the top of the servo. The broken piece remaining in the servo arm.
Old 12-12-2006, 08:33 AM
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Default RE: DS821 Servos

Hi Danny, I switched over to JR some time ago and am loving it. I have the new 7202 and 790 and 770 rec's. The 821 servos are great!. I have many hours on them in a Waco Bipe 60 w/91 4S, twist 40 w/ 61 4S and Sukhoi 60 w/90 2S showing no wear that I can see or feel, and I am not eazy on them. I run 2000 mah batterys in the planes. Now a question for you, can I run a 6 volt pack with the 821's?, and what would the torque be at 6 volts?, and would it shorten the life span?.
Old 12-12-2006, 09:54 AM
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Default RE: DS821 Servos

Yes, they are fine to use on 6V. 6V will shorten the life span slightly as with any servo, however this is not significant.

Specs
Type: Digital Hi-Torque
Torque: 72 oz/in @ 4.8v, 88 oz/in @6v
Speed: .19 sec/60 deg @ 4.8v, .15 sec/60 deg @ 6v
Dimensions (WxLxH): 0.74"x1.50"x1.47"
Weight: 1.5 oz
Bearing: Single Ball Bearing
Motor Type: 3-pole ferrite
Gears: Composite
Application: Standard size-digital servo upgrade for sport pilots
Old 12-12-2006, 03:51 PM
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Default RE: DS821 Servos

Thanks for the response, I wanted to try them on a ShowTime 90 at six volts, weight will be about 9 lbs. and they will be fast enough.
Old 01-13-2007, 07:18 AM
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Jack Skip
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Default RE: DS821 Servos

I will ask again. Is the DS821 suitable for the Hanger 9 Cessna?


I have been reading other people are also having problems with DS821 failures. Is it due to using these servos in the wrong application?

The Horizon site now shows the DS821 with "New, longer-lasting plastic gear material". When were these changes made? Can the older DS821 servos be upgraded to the better gear matrials?

If there are problems with these servos I hope that JR does not try to side step them and think modelers will forgive them. If there is a problem I think it would be better to admit it and address it. JMHO.

Old 01-15-2007, 10:17 AM
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Default RE: DS821 Servos

There has not been any change to the 821 servo, that is in reference to the gears being made from a new material vs other servos. We have not seen any trends with problems with the 821 servo.

The 821 should work fine in that model.
Old 01-15-2007, 12:23 PM
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Default RE: DS821 Servos

Hi Danny

Do you think the ds821 is stong enought for a TopFlite Giant Corsair
there is 1 servo per elevator.

thanks!!!
Old 01-16-2007, 09:26 AM
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Default RE: DS821 Servos

I'm not familiar with that model and what the torque requirements etc are. I'd contact the manufacturer for information on that.
Old 01-16-2007, 06:36 PM
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Default RE: DS821 Servos

ORIGINAL: dsnyder

I'm not familiar with that model and what the torque requirements etc are. I'd contact the manufacturer for information on that.
HI again Danny!!

In the manual they said this : "Servos should be rated heavy-duty. For flightcritical
control functions a minimum of 45 inch/ounces of
torque should be considered"
in this [link=http://www.top-flite.com/reviews/topa0410-rcm.html]review[/link] they put JR 4721 on all surface

the plane will weight 24-26 lbs

so what do you think??

bye!!
Old 01-17-2007, 10:16 AM
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Default RE: DS821 Servos

Torque specs wise the servos sound like they would meet or exceed the requirements.
Old 05-10-2009, 11:23 PM
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Default RE: DS821 Servos

I just bought a Black and Yellow Seagull Yak 54 and a 20cc gas engine. It has a 63 inch wingspan and about 9lbs. Would it be too much for the DS821's? The website from Seagull and Horizon Hobbies does not have the torque requirements for the plane.
Old 05-11-2009, 08:57 AM
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Default RE: DS821 Servos

The 821's are NOT recommended for gas and have restrictions on the size of model for glow and electric.
Old 05-13-2009, 02:38 AM
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Default RE: DS821 Servos

Thanks Zeeb. How about the 20071 servos? This is my first BIG project and would like to do it right the first time. They are over 100oz/in but still within reach of my budget. Have not bought the radio yet, so looked at the 821's because they come with the DX7. Any help on servo recommendation would be appreciated.
Old 05-14-2009, 09:56 AM
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Default RE: DS821 Servos

Hitec 5625s are what I use in my 70" Yak with 28CC
http://www.chiefaircraft.com has great prices on hitec stuff, usually cheaper than Servo City
Old 11-18-2011, 03:00 PM
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Default RE: DS821 Servos

Wow, I just had a strange series of problems.

I've had a number of DS821 servos that I never used, still brand new, they came with two radios I bought. I've been building large scale models for the past couple of years, so they didn't get used.

I was just building a Corby Starlet, and decided that the DS821s would be perfect. I installed the servos, hooked them up to the radio, found the centers, and then went about building the linkages. Once they were built, I ran the ailerons up and down. To my surprise, both splines sheared right off. I checked my throws, and I had reduced them first (learned that a long time ago), so there wasn't any reason they should have sheared. How strange.

I have DS821s on several other models, never had a single issue. I've never had a single issue with JR servos, period.

Still thinking maybe I did something wrong, I set up and hooked up my rudder. I made sure that I hooked the linkage up to only the second hole out. If anything broke, I didn't want it to be the servo this time. Set it on reduced throws, ran it back and forth, and .....there goes the spline. What in the world?

This batch is bad, no doubt in my mind. I can't take a chance on these servos. I'll have to step up to something I can be confident in. But I'm wondering if others have experienced this?

Jim
Old 11-18-2011, 05:25 PM
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Default RE: DS821 Servos

That's the most common issue with them
Old 11-18-2011, 06:20 PM
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Default RE: DS821 Servos

Yeah? I hadn't heard that before.

I can believe it now.

Jim
Old 11-19-2011, 04:53 AM
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Default RE: DS821 Servos

Absolutely. Heli specific forums are full of threads about them shearing the output shafts. The amps die too under too much vibration.

We have a simple test for them before putting them in a helicopter. Put them in a bucket of water, if they float they are safe to use.

I've had nothing but excellent results with Spektrum and JR equipment but those particular servos belong in 40 size trainers.

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