Howard

My Feedback: (55)

I am trying determine the differences/advantages of one servo (JR DS821 vs Hitec HS-5475) over the other for general use in larger sport planes - such as powered by 120 FS. I have reviewed the numbers for each and on the surface the JR has higher torque, it is faster, less expensive, but only has one ball bearing vs two for Hitec. I don't know how to compare parameters such as centering and hunting because I don't find any information available in that area. Hitec comes with a generous number of large servo arms, does JR also provide the large arms or are they the standard size? Are both servos programmable? Should I consider the Hitec HS 6635 as a possible solution? I have pretty much decided that I do not need MG and that the filled nylon gear train is a good compromise for my use.

I am not a 3D flyer and don't need the the fastest, most powerful, baddest servo but, I want to move toward better and tighter flight surface controls and think that digital servos will help. I am certainly open to other recommendations based on your experiences and preferences. The only thing I do not want to do is simply buy at the overkill level - it is not a budget issue, it just seems to make sense not to kill piss ants with sledge hammers. When you are a hammer everthing looks like a nail.

One last question - is there any known differences between the JR or Spektrum version of the DS 821?

Thanks

Howard

BarracudaHockey

My Feedback: (11)

Same thing. Check the classifieds, the helicopter guys stay away from the 821s and they are always selling them cheap when they buy dx7s. I think Esprit Models does the same thing.

Howard

My Feedback: (55)

Is there a solid reason as to why the helicopter guys don't want them? I did get some sound advice from a very reputable retailer that, at this level of servo, the JR DS821 was a better product than the HS-5475.

BuschBarber

My Feedback: (2)

I more often use Hitec servos. Their Return and Replacement service policy is great and I think I get good value for the price.
The only plane that I had JR 821 servos in was a H9 P47-150 powered by a Fuju32ei gas engine. The 821 servos were used for Ailerons. I am also using a Spektrum AR9000 Rx and an XP9303 Tx with a Spektrum module.

I bought the plane Used, two years ago. I do not know how old any of the servos are. I switched from 72Mhz to 2.4, last year. A few weeks ago, I was flying and suddenly the plane rolled from the straight and level 180 deg to the right. No other control surface was involved. I dropped the gear and landed. I replace the AR9000 with another one, repositiond the main Rx in the plane, and put a 36" extension on the one Remote Rx. I flew the plane again with no problem. The next flight, I had exactly the same problem. It just rolled 180deg to the right. No other symptoms. I did range checks and found no anomolies. I replaced the 821 servos with some Hitec 645MG servos I had and I have not had a problem since. A friend put the 821 serovs on a Servo Exerciser and could not get them to faulter.

Just a note. Hitec Digital servos can be programmed, with a Hitec Programmer. Some Spektrum digital servos can be programmed with the Spektrum programmer. Jr and Futaba servos cannot be programmed and require a Matchbox type device to Match multiple servos on the same channel.

Other than the 821 serovs, the P47 has some ST128 serovs and 791 Retract Servos (the most torque of any Retract servo) and I have had no other problems with JR servos. It may have been the extensions that caused the problem. I switche from 821 digital to 645MG because that was all I had and I did not need the extra speed or torque. I have to use 5v battery because the 791 serovs jitter at 6v and Horizon says they are not 6v rated.

BarracudaHockey

My Feedback: (11)

They have some issues with vibration. Since helicopters vibrate quite a bit we stay away from them.

They (JR/Spektrum) says they aren't to be used for larger than 30 size nitro helis, and the most popular size nitro is 50 so there's a lot of them floating around for sale.

Howard

My Feedback: (55)

Gentlemen:

Thank you both for the feedback.

Howard

GJr.

My Feedback: (3)

I thought I remember reading that Horizon does not recommend using them on planes much larger than 120 size. But, I think for most sport purposes they are fine. I believe another concern with heli use was when connected to a gyro. A gyro can be hard on servo motors with constant movement and holding commands.

BarracudaHockey

My Feedback: (11)

They are too slow to use on a gyro.

It states not to use them on any thing larger than a 30 size nitro or 50 size electric helicopters or 120 size airplanes. Its right there on Spektrum and Horizon's web sites.