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RE: ds821 dx7 servo defect - 1/9/2007 2:57 PM   
dsnyder



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Status: offline 		I've used them in 100 size aircraft with great results. I'm very impressed with the servos personally.

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RE: ds821 dx7 servo defect - 1/9/2007 3:53 PM   
hrosee


 

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Status: offline 		Danny,

I have too. I had them in two 125 size planes and they worked great.

But a Helicopter is not a plane and has more vibration. I never said they wouldn't work in planes.

The just don't seem to be able to stand the vibration of the 50 size Heli.

Have you flown they in these type of aircraft?

Harold

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RE: ds821 dx7 servo defect - 1/10/2007 2:17 PM   
dsnyder



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Status: offline 		I haven't flown them in a heli as of yet, haven't built a heli of that size since they have come out personally. However I'd say for a 50 size heli it depends on how the heli is flown as to the suitability of the 821 servos. For hard 3D a higher end servo may be a better option, but for most average pilots I don't see a problem with using them.

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RE: ds821 dx7 servo defect - 1/10/2007 2:23 PM   
hrosee


 

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Status: offline 		Danny,

I guess we will just have to agree to disagree.

I am not a 3D flyer by any means and have just been flying Heli's for a year.

I had 4 of the 821's go bad in Raptor 50's. At first I thought maybe I did something wrong in the mounting but then I saw several reports of the 811's and the 821 failing in 50 size Heli's.

They are just not strong enough for that application. It's not a big deal. You just get a servo that is stronger.

Anyway, thanks for taking your time to reply. Based on the information presented I think everyone will need to make their own decision on what application the 821/811 servo is best for.

Harold

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RE: ds821 dx7 servo defect - 1/10/2007 5:27 PM   
camgab



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Status: offline 		Danny

I have also a problem with servos .
I bought recently a new XP7202 Heli system with 4 DS821 (72 oz/in)servos
I mounted 3 of new servos on my old Ergo 46 CCPM system.
After 15 flying (sport flying, hovering, traslation ), the pitch servo stopped working. Unfortunately, I lost the control and broke the Ergo.
I think that the servo could have been failled so I had to switch it for a new DS821 .

Again, after 10 flying (last sunday), the new pitch servo stopped working, and broke the heli too.
Previously, I had used 3 NEH531 (50 oz/in) on CCPM without trouble.
I am not an aerobatic flyer right now, So I think that I never put the DS821 to a high stress
on purpose.

I´ve just wanted to tell you another problem with them .



Gabriel

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RE: ds821 dx7 servo defect - 1/15/2007 12:29 AM   
ScaleKing



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Status: offline 		Last month a friend of mine posted a cmplaint that I had with the DS821 Servo. We never really got a direct answer. But I can see here that even the helis are having problems with them. I have had three of them break (at the output shaft) before the model even took flight. I replaced the gears in all three

Last week I took my Hanger 9 182 Skylane out for the madian flight and everthing was fine. The next day not soo good. My elevator servo (which had just been replaced with new gears) broke sending my NEW BEAUTY into the ground.

I don't think that these servos have rated correctly. My 182 has the G26 evo and so it has power but it is a far cry from 3D so what is the problem? Now I have to go out and buy another fuselage, rudder, elevator. I never got to land my plane twice and now I am out of pocket another $500.00 plus the parts that I need no one has in stock so I am grounded until March.

Kindly let me know if I need to upgrade my 182 to higher end servos.

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RE: ds821 dx7 servo defect - 1/16/2007 2:17 AM   
Jack Skip


 

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Status: online 		I did some measuring on the servos today and think there may be a problem with the servo screws supplied with the DS821.

From what I have seen the servo output shaft shears off at the top of the servo, where the output shaft exits the servo. I have seen this now 4 times on 4 servos. The break is clean and level with the top of the servo. The break leaves the servo arm cavity filled with the broken output shaft. The servo screw does not extend down past the broken portion of the servo arm. The screw clearly does not provide any help to the strength of the output shaft.

The servo screw supplied, with the servo arms supplied, reaches the top of the servo. This would mean that only the servo outrput shaft is providing any strength. None from the screw.

With the screw full seated into the servo arm and output shaft there is another 2.5mm available. The funny thing is the depth of the output shaft is close to the length of the servo screw provided. But it does not account for the thickness of the servo arm. I think somebody goofed when packaging the servo arm screws.

I used a regular #4 corse thread screw and ground it down to just fit into the servo output shaft and it is 2.5mm longer than the supplied servo screw. This takes the servo screw down below the top of the servo and will surely help provide strength to the output shaft.

For the 4 servos I have it cost me $0.20 and a few minutes with the dremel to make the longer screws. I don't think I would put these sevos into a big plane, but now with the longer screws I feel comfortable enough to try them in a small 40 size plane.

So. Questions abound now.

What length screw should be used with the DS821 servos?

What size planes are they intended for?

What size helicopters are they intended for?












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RE: ds821 dx7 servo defect - 1/16/2007 3:08 AM   
n3cal



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Status: offline 		I have the DX7 Heli Version which came with 4 DS821 Servos. My original intent was to use these servos in my Raptor 60 Heli. From what I read on this thread that may not be a good idea. I've been running the same Futaba S9020's on my Raptor 60 for the last 4 years with no issues. The Futaba S9202 specs (76 oz @ 4.8V) are pretty close to the DS811 specs (72 oz @ 4.8V). The only thing that irritates me is these servo's come with the Heli Version of the DX7 and the manual does not mention anything at all about the servos or any limitations. So I too would like some answers to Jack Skip Questions. Thanks.

Best regards,
Cal


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RE: ds821 dx7 servo defect - 1/16/2007 3:16 AM   
Ken6PPC


 

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Status: offline 		Jack, how long are your servo arm mounting screws? I just measured one of mine from a DS821 that I bought as a separate purchase (NOT as part of a system), and it is 0.2962" long, including the screw head. (7.524mm)

quote:

ORIGINAL: Jack Skip

I did some measuring on the servos today and think there may be a problem with the servo screws supplied with the DS821.

From what I have seen the servo output shaft shears off at the top of the servo, where the output shaft exits the servo. I have seen this now 4 times on 4 servos. The break is clean and level with the top of the servo. The break leaves the servo arm cavity filled with the broken output shaft. The servo screw does not extend down past the broken portion of the servo arm. The screw clearly does not provide any help to the strength of the output shaft.

The servo screw supplied, with the servo arms supplied, reaches the top of the servo. This would mean that only the servo outrput shaft is providing any strength. None from the screw.

With the screw full seated into the servo arm and output shaft there is another 2.5mm available. The funny thing is the depth of the output shaft is close to the length of the servo screw provided. But it does not account for the thickness of the servo arm. I think somebody goofed when packaging the servo arm screws.

I used a regular #4 corse thread screw and ground it down to just fit into the servo output shaft and it is 2.5mm longer than the supplied servo screw. This takes the servo screw down below the top of the servo and will surely help provide strength to the output shaft.

For the 4 servos I have it cost me $0.20 and a few minutes with the dremel to make the longer screws. I don't think I would put these sevos into a big plane, but now with the longer screws I feel comfortable enough to try them in a small 40 size plane.

So. Questions abound now.

What length screw should be used with the DS821 servos?

What size planes are they intended for?

What size helicopters are they intended for?














< Message edited by Ken6PPC -- 1/16/2007 3:17 AM >

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RE: ds821 dx7 servo defect - 1/16/2007 3:20 AM   
Jack Skip


 

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Status: online 		Please do not get me wrong. I just received the wonderful gift of a DX7 radio package (from 2 friends and my wife). The radio exceeds my biggest expectations. It is super fast giving that 'connected" feel with the plane. It releives me of the fear of a newbbie shooting me down by mistake. It has model lock. And a host of other great features. Plain and simple, it flies great.

My concern is there may be some "mistake" in the servos that come with the radio. Not a mistake with the radio.

I think the guy given the task of measuring for the servo arm screws messed up and did not take the measurement with the servo arm attached.

I also think people are extecting too much from these servos based upon the reported torque numbers.



Bump again on my questions.

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RE: ds821 dx7 servo defect - 1/16/2007 3:30 AM   
Jack Skip


 

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Status: online 		Hi Ken,

Its been a while since I was up in Ohio. Hope winter is treating you well (build time).

First I have to say I am TOTALLY impressed with your measurements. I cannot be so accurate.

using me best eye glasses and best ruler I get:

Just over 5mm of screw on the supplied screw.

About 8.5mm on the screw I made, not counting the head.



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RE: ds821 dx7 servo defect - 1/16/2007 3:35 AM   
n3cal



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Status: offline 		The DS821 servo horn screws from my complete DX7 Heli system measured 5.5mm (not including head). I can see what Jack Skip's point is. The screw might be too short.

Cal


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RE: ds821 dx7 servo defect - 1/16/2007 3:37 AM   
Ken6PPC


 

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Status: offline 		Looks like you HAVE found a difference, anyway. Mine came directly from an unopened DS821 package that I recently got from Horizon Hobby. Perhaps the ~2.5 mm difference in screw length would make or break the servos from Spectrum! I honestly don't know.

I DO know that I have put two planes outfitted with DS821 through their paces this past summer, and I was very impressed with them. Never a HINT of any problem, and economical as well. That is why I bought more for my next plane.

I used a digital micrometer to measure that screw. Yeah, it was overkill, but it was already lying there on the bench, near the servo.....



quote:

ORIGINAL: Jack Skip

Hi Ken,

Its been a while since I was up in Ohio. Hope winter is treating you well (build time).

First I have to say I am TOTALLY impressed with your measurements. I cannot be so accurate.

using me best eye glasses and best ruler I get:

Just over 5mm of screw on the supplied screw.

About 8.5mm on the screw I made, not counting the head.





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RE: ds821 dx7 servo defect - 1/16/2007 3:44 AM   
Ken6PPC


 

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Status: offline 		Whoops! Back up here! Your measurement was WITHOUT the screw head. Without the screw head, mine is about the same 5.5 mm long. I checked one that has had a lot of use and abuse, and it is about the same as well.

I don't know if the screw length is too short or not now. As much time as I have on my older DS821's, I believe I would have had a problem by now, if I was going to have one. I was NOT gentle with these!

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RE: ds821 dx7 servo defect - 1/16/2007 3:57 AM   
Jack Skip


 

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Status: online 		Thanks for the quick responses.

I guess my biggest point was the lack of screw down past the top of the servo despite the extra 2.5mm available. The break point I have seen on 4 occassions is at the top of the servo.

Seems a longer screw could have been used and may have prevented the breakage.



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RE: ds821 dx7 servo defect - 1/17/2007 2:54 AM   
Jack Skip


 

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Status: online 		No answer yet? Bump on my questions for the JR Folks.

What length servo screw is meant for the DS 821?

What size plane is intended for the DS821?

What size helicopter is intended for the DS 821?


The Spectrum radio is so SWEET I wonder why they got burdened with crapy DS821 servos?


I am beginning to wonder how long it will be before the Spectrum radio is offered without the JR servos? I'll bet sales go up when that happens. If I was at Spectrum I would think about it.

Lets take a quick pole. Who would take a Speckrum radio, receiver, RX battery and switch without the servos for $230.00?

I would. Maybe 2. Maybe 3.






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RE: ds821 dx7 servo defect - 1/17/2007 3:05 AM   
Jack Skip


 

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Status: online 		I measured some other servos I have and found them all to have screws that extend down past the top of the servo. The only servo I have that does not is the DS821. The only servo I have seen fail is the DS821.

Now. JR support is saying there is no TREND in servo failures. Please, if you have had any DS821 servo failure post it here.




< Message edited by Jack Skip -- 1/17/2007 3:11 AM >

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RE: ds821 dx7 servo defect - 1/17/2007 2:00 PM   
ScaleKing



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Status: offline 		Jack Skip

You are up early!!

I too have had problems with the DS821 servos. Three of them have broken on me at the output shaft while the model was not in flight. One broke on my in flight and ruined my Hanger 9 182.

I have not measured the srews in my servos but from what you are saying I think we deserve an answer from JR as to why these servos are assembled with shorter than usual srews?

I have posted my problem with this servos earlier but up til now I have not had a reply from a JR rep. I just added another model to my collection but I am very afraid of placing these DS821's in it. I can't afford to keep loosing models to servos!!!!!!!!!!!

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RE: ds821 dx7 servo defect - 1/17/2007 3:26 PM   
dsnyder



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Status: offline 		The servos have the same screws as all other JR and Spektrum non-metal geared servos. There is no size model the servos are intended for, that is based on the particular models torque requirements etc.

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RE: ds821 dx7 servo defect - 1/18/2007 1:18 AM   
Jack Skip


 

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Status: online 		Thank you Dsnyder for the quick response.

But I am a bit edgy about the DS821 problems still, despite your assurances. JR is saying they are not aware of any trends of servo failure. But other threads on this forum and threads on other forums seem to contradict this. People are posting about their probelms and about calling JR support. JR support is responding to the posts. So I have to beleive JR is aware of these problems. If they are not, that may be another problem of internal communication at JR.

It would seem from other threads and other forums it is common for the servos to experience a shear of the output shaft. It also seems there has been motor burn out. It is fine to think JR will replace the gear set, but what other damage is covered? If the servo has known problems and JR does not advise buyers and users, are they going to be responsible for damages resulting?

JR response is similar in most cases with posts about how good the servo is and about good reports. Or worse yet they suggest it may be setup issues.

Now the stigma of pour servos is attaching itself to the Spectrum radio, which is a fine product. But the Spectrum is only available with the DS821 servos. So what happens if you package a great product with a lemon? Just scan the classifieds to see the long listing of DS821s for sale. We will see.

If the servo arm screws are all the same, but ony DS821 servos are seeing failure of the output shaft, then the DS821 output shaft may be weak. This would be a design weakness in the servo, not a setup problem. Why would DS821s fail when other servos have not?

I have 4 more DS821s in the box. I do not have the guts to try them, even in a trainer plane. Anyone want to buy 4 DS821s cheap?








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RE: ds821 dx7 servo defect - 1/18/2007 2:16 AM   
Ken6PPC


 

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Status: offline 		I might be interested in your servos. How much do you want for them? Have they been mounted, or are they brand-new?

BTW, I did a search in the classifieds. This is the only listing I found: http://www.rcuniverse.com/market/item.cfm?itemId=251373 I don't see that as much of a bargain, since list price is not much more than this is.

quote:

ORIGINAL: Jack Skip

SNIP
I have 4 more DS821s in the box. I do not have the guts to try them, even in a trainer plane. Anyone want to buy 4 DS821s cheap?










< Message edited by Ken6PPC -- 1/18/2007 2:17 AM >

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RE: ds821 dx7 servo defect - 1/18/2007 3:12 AM   
Jack Skip


 

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Status: online 		4 DS821s, never mounted. Make an offer.


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RE: ds821 dx7 servo defect - 1/18/2007 11:33 AM   
Jack Skip


 

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Status: online 		Ken, if you are seriously on the market for the DS821 servos check the classifieds on th eheli forums. Loads of DS821s for sale.

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RE: ds821 dx7 servo defect - 1/19/2007 5:10 AM   
dick Hanson



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Status: online 		He said -she said --I heard - etc..
second hand info is VERY undependable .
FWIW- for years - I used the JR 811 -predecessor to the 821 - on 33% models for multiple aileron servo setups
my new 50 cc powered BLING has the 4 821 servos as aileron servos - no problems whatsoever -
The servo arms used with servos having plastic output shafts - can be overloaded if the geometry of the arm connection is not proper - I don't know why or if the "failures" were a result of that type setup - But 90% of all servo problems I have seen --are a result of the user doing setups which exceed prudent linkages or linkages which exert a twisting load on the output.

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RE: ds821 dx7 servo defect - 1/19/2007 12:06 PM   
Jack Skip


 

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Status: online 		Dick Hanson, I respect your experience and knowledge and appreciate your input.

I have seen 4 of the DS821s fail first hand. I have seen the resulting damage to the model. I have taken measurements of the servo screw and output shaft. Tomorrow a friend and I will do some experiments to measure the breaking point of the output shaft. No he said she said here.

Perhaps you could provide some information for me please? Will the output shaft from a DS811 fit into the new DS821? If I could swap out the output gear to one that has proven itself stout enough I would be comfortable using my DS821s.

I wish you luck with your new 50cc gaser and her DS821s. I certainly hope not to see you posting back here about a DS821 failure causing you to crash your new baby.



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