c/f

My Feedback: (1)

I can't seem to find any info on a Sport Digital that JR/Horizon had on magazine adds awhile back selling for $49....?? Does this product still exist? Price?

Thanx for info.............

R Horn

My Feedback: (2)

http://horizon.hobbyshopnow.com/prod...p?prod=JRPS811

there you go
Rich

AcroJo

My Feedback: (1)

I just switched over to the DS811 servos. These things are SICK !!!! I replaced some High Tech 605BB. I didn't know what I've been missing. Now all I need is one DS8231 for my rudder and I'm all set. Joe

Ed_Moorman

My Feedback: (1)

I have a set of JR 811 Sport Digitals and also a set of Hitech 5475 digitals. You can notice the JRs are faster and they seem just as powerful. The Hitechs do whine-loudly.

AcroJo

My Feedback: (1)

Big difference. The reason I switched was for a problem with servo drift with the one year old and two wreck Hitechs. I put in two planes before I realized that I had an intermittent radio problem. I switched to JR. To keep flying while we still had weather left I never got around to swapping out the servos for the new ones that came with my radio. Then after a while I noticed that I was constantly adjusting my elv. linkages. (Duel elv.) So I sat down and just started flapping the elv. up and down. After about two dozen reps they were off center about 1/16" The more reps, the more they would drift. Drove me nuts trying to figure if it was program mix, linkages or what. Those Digital servos fixed that and are they sweet. Joe

bentgear

I have started likeing the Hitec 5475 more than the JR 811. I have 10 of the 811's and half of them have developed the shakes so bad that one almost ripped an aileron off. I wish JR would stop trying to set the deadband to less than 1 and I think they would have a great-cheap servo. I have made sure they are not mounted too tight, that there was no slop in the linkage, that I was using 4-40 linkage, have used both 4.8 and 6 volt packs, etc.

Joe, if you compared the 605's centering ability to a pile of dog crap, the dog would win. I think that may be why they dropped it from the ine.

Ed M.

AcroJo

My Feedback: (1)

Ed, This is my first forray into the digital world and I am already experiencing the shakes. Re-did my linkage to eliminate slop but still had flutter in the elv. with the longer linkage. The only way to eliminate the shaking was to adjust my control horn out resulting in less throw and compensating with increased servo travel in the TX. These 811s are a big improvement over the HT605s but I am finding out everything comes with a compromise. So if I back off on the mount screws a bit it will help? There isn't any compatability issues with JR to Hitech? Or perhaps my problem was wear and tear. Whats the specs on the 5475s ? Ounce/inch, speed and $ Thanks, Joe

c/f

My Feedback: (1)

Shakes are not neccessarily a bad thing, I cannot put a CRC throw deflection gauge on surfaces using a JR8411's. I think you are seeing some mechanical problems you might not otherwise be aware that exist in servos with wider deadbands.

I would suggest that you attach the control clevise on the surface to be controlled at the same measurement away from the pivot line to the horn hole, equal to the measurement of the servo arm center out to the hole you are using in the arm. This will give you a 1to1 ratio of available torque versus mechanical geometry.

AcroJo

My Feedback: (1)

C/F, Thats about where I set them up at but I could not keep the one elv. servo from going nuts. It would not stop unless you grabbed it. I havn't flown with this setup, but was a bit apprehensive of that type of movement in flight. Are you saying that the servo might be bad? If I'm going to change anything then I would probably go for Hitech digitals. Joe

c/f

My Feedback: (1)

I have only used the high dollar Jr digitals in my turbine aircraft. I use nothing but Hitec 85mg in my combat aircraft so I am not bias on either brand.

Jr servos come with a 3 year warranty so that says allot to me on wether or not someone believes in their product enough to put their money were their mouth is. I will be trying the 811 for an upcoming project and will be more sensitive to mechanical geometry to avoid some issues as you have pointed out.

Are you using stock supplied servo arms? If you were to set it up so that the distance from the contol surface attachment pivot point in the vertical plane, were a greater than that of the servo arm hole from the center, would it stilll bounce? At any point going in this direction does it stop? This kind of mechanical mis-match I have seen many times and resultant surface flutter. On a standard servo where the deadband is 5 deg off this may not show as a servo bounce as do digitals yet does not mean it will perform as needed. Another thought may be that the horn is too close to the pivot point? A robart style horn with more of a distance from hingeline could also work. I use this type pretty much as I have had some pull/pull systems flutter being too close to the hinge line.

I do appreciate the heads up info. Thanx.................

Ed_Moorman

My Feedback: (1)

Are you talking about aerodynamic flutter in the air or the servos jittering on the ground?

JR digitals, and some Hitechs, and also coreless servos will jitter around center on a 5-cell pack and sometimes with a really full charge on a 4-cell pack. If this is the case, it will go away in a minute or so. Or you can add a voltage regulator. I use one from Cermark. They are usually fairly inexpensive.

If you are talking about aero flutter, there are a few things you can do. First is to stiffen the controls. Use 4-40 rods on ailerons. If the length is more that 6 inches or so, I make a short pushrod from the fiberglass arrow shafts. The hi-dollar solution is the carbon rods with titanium ends.

Next, use the bolt-through ball links instead of clevices. These are the little gadgets you bolt to your control horn. They really take out the slop. Here's a photo on one used on my Funtana.

Third, get some aftermarket extra long servo arms. Longer arms will reduce the angular slop in the controls. Besides they give those large surface movements we all like.

4th, Seal the control surface gaps with tape or matching covering.

5th, do not round off the trailing edge of the surface. Square corners are less prone to flutter than rounded edges. The Morris TopCap ARF I have came with squared off trailing edges.

c/f

My Feedback: (1)

Ed,

What we are describing is yet a third phenom I will call "static bounce", It is particular to digital servos with tight center deadband. just placing a quarter or defelection gauge on a control surface can make them bounce uncontrollably. The fear is if it does so on the ground it may do so in the air. My contention is that an improper mechanical advantage is giving the weight of the control surface more leverage than the servo thus starting a bounce with an initial movement.

Any thoughts..............

dirtybird

My Feedback: (5)

What you are describing is called hunting. The servo deadband is set too tight. The inertia of the control system and whatever control you exerting causes the the servo to overshoot the return point and then reverses the torque but then the inertia causes it to overshoot in the oposite direction. This results in a heavy battery drain. This condition may or may not disappear under flight loads. It also could get worse and end in flutter.
One way to stop this is to open the deadband. Only Hitec servos allow you to do this.
Another way is to static balance the control surface. This could make it worse- you just have to try and see.
Another way is to lighten the control inertia. Make the control lighter.
This is a tough problem. Its caused by the tight control loop of the digital servo. The servo is OK without being connected but when the connection to the control surface is added it goes nuts. There is going to be a lot of hair pulling until we find a solution that works. Right now it seems to me that Hitec has the best solution

bentgear

c/f, what I was describing happpens on the ground, altho sometimes I can still detect it on a slow flyby. I have had it happen on ailerons, elevators and rudders. On a rudder there is no weight bias. As Ed Moorman described I have used all type ends, arm lengths, and control horns. It even happens on a 4.8 volts pack that is about to dump. I do not feel it is a battery or control setup. Some of my 811's do it on any surface and some have never given a problem on the same surface using the same control setup. At least they are not as bad as a Futaba that I have that has the shakes just setting on the bench, without an arm on it.
One thing I have found after some help from Danny (JR/Horizon) was make sure the servo case is not making contact with the mount on the sides and leave the mount screws on the looser side.

Ed M.

AcroJo

My Feedback: (1)

Gentlemen, Thanks for responding. 4/40 rods. HD ball links, saftey lock quick link clevices
(plastic w/ metal pin. Steel clevis has too much slop) and HD servo arms. Its only one servo that does it. On the bench it will shake all day. Right now to stop it the distance from the pivot point on the servo arm out is less than the distance from the surface out on the control horn. When it becomes equal or less on the horn it shakes. I may switch them around to see if its the placement or the servo itself. Also I will try to back off on the mount screws. Thanks again, Joe