Quick question for you Bobcat owners: which servo are you using for the Ailerons, the digital 8411 with 155oz of torque or the digital with the nylon gears (8411SA). I have the XL and my "Servo 101" education between the two is not the best. Thanks, Ken H

I have 8411's in my XL, simply because the 8411SA's were not announced until after my BobCat's 40th flight.
Either would be satisfactory. The durability of the gears in not the question; the holding torque and power are the issue, as the BobCat has large ailerons.
Use either one. I don't think that I could tell the difference.

Harley Condra
BVM REP
RAM REP
Buy American!!!!!!

Has anyone else had any problems with the JR 3421's on the rudders? The first BC I built toasted 2 3421's at superman last fall, we swapped those out and flew about 50 or 60 flights on those, then yesterday both went **** up at the same time. THe aiflure is particularily disturbing as it throws the servos hard over to one side.

David Reid

265 flights on my original 3421's on the rudders. 3421's installed on the elevators since flight #21, no problems. What size battery are you using, David?

Thanks for the reply Harley, concerning DavidR's question what are you using for the rudders in yours? I was going to follow BVM's recommendation with the 3421's and I have some on order. I also have 4ea 8231's that I am not using and their torque is 88oz as compared to 65oz on the 3421. They are larger and advertised as "dual wide spread" on the bearing. Again my servo 101 is not up to "de-ciphering" the difference. The big question is, if the 3421's are having failures what replacement would you suggest? I believe I saw an earlier post with the 3301 recommended for the rudders along with the elevators. Thanks in advance. Ken H

Tony,

Both Vernon and myself are using 5 cell packs. I have not had a problem with mine but they were the replacements I got from Horizon. All 4 of the servos that failed were purchased at the same time. Both servos are set up on a Y harness and are going through a JR 450 gyro. I have not seen any technical spec that says not to use them on 6V so I am assuming that is not the problem. I also set the servos up where the linkage is giving the optimum mechanical advantage. FWIW yesterday these servos failed when testing the smoke system on the ground. The first failure also occured with the plane on the ground, and the second failed sometime in the flight. In all cases the servo failed hard over.

Hi David,

I had that exact failure on my Bobcat just last Friday - both hard over. Fortunately this happened as I prepared for my next flight, rather than during flight. When did yours happen ?

I took the beast home and pulled brand new 3421's out of their packing, only to find problems with these new ones too. Out of 6 brand new servos that I had available, one moved occassionally but not very often, and another is completely dead.

Re Tony's question about battery - I'm running a 5 cell 1800. Initially this was unregulated and typically sat at about 6.6V at the battery, and obviously less at the servo. After I cycled the RX battery though, it's voltage increased to about 7.1 V peak, so I decided to add a regulator (6V) before putting the battery back in the aircraft.

Of course, although the on-board failure happened within a regulated setup, the servos that failed in the aircraft had by then already been subjected to an unregulated 6.6 V previously, so it could be that the voltage was too high and affected the first 3421's...

For the replacement servos though - I actually found these failures while testing on the bench with just 4.8V - so there's no way that the brand new servos were toasted by the setup - they were just flat out bad right out of the package. That surprised me really, as I've been using JR equipment for about 15 years now, and only once previously found a failure on a brand new item - so to find 2 out of 6 to be bad right out of the box worries me a little.

IIRC, there was also a discussion on 3421 failures (either here or on the jets list) a few months ago. I seem to recall a number of replies from people who had switched to a mini airtronics servo...

Regards,
Gordon

I threw out the battery question because with a 6 volt pack, and the constant servo movement caused by the gyro on the rudder, you may be harming the servo. I suspect that if you go to a 4.8 volt pack, you will see no more problems.

You have to keep in mind that putting a servo on a gyro causes that servo to see a lot more small movements. Constant back and forth will greatly increase the current draw of the servo. Another question, are you reducing the sensitivity of the gyro when the gear is up? If you're leaving it at high sensitivity throughout the flight, the servo will be under that higher load the entire flight. With my BobCat I use 100% gyro gain with the gear down, but only 20% gear up. I am also using Duralite batteries which supply about 5.8 volts. As I said earlier, 265 flights on a 450 gyro with no problems.

Gordon, please return the bad servos to Horizon with a detailed note on the problem. I will also contact them and let them know of the issue. BTW, a 6v regulator is still a bit high. I would go to a 5.2v system.

Hi Tony,

Yes, I do have the gyro gain dialed down for gear up - in fact, I duplicated the settings which you were generous enough to share with me while I was prepping my Bobcat.

I have already returned the two newest servos to Horizon, with an accompanying letter explaining the problems, and that these are "brand new" (bought about 3 months ago actually, but only taken out of the packaging last week). The other two will follow shortly (I did the return in two parts simply because of the delay in finding receipts for the additional servos).

BTW, the "used" servos had 37 x six minute flights on them, and possibly as much time again while on the ground - so about 7 1/2 hours total running time.

Regarding the 6V regulator - I talked the folks at Horizon before ordering this. I was looking for about 5.2 as you suggest, but Horizon sells only 4.8, 5.7 and 6V. I did not want to use 4.8, because of the long servo extensions used in the Bobcat - despite using heavy duty extensions, the length of the wire and the number of connectors will cause voltage drop, and I have had problems in the past where (high spec) servos at the end of a series of long extensions will twitch due to the reduced voltage. So, for me the 4.8 was out. Horizon said that either the 5.7 or 6.0 regulators was just fine for use with the JR servos and gyro, so I ordered both. So far the 5.7 has not arrived (back ordered), hence my use of the 6.0.

Are you saying that the 6.0 V reg is definitely a problem, or just that 5.2 is your personal preference ?

I will look for another source that sells 5.2v regulators - but *if* 5.7 and/or 6v really is a definite problem then perhaps Horizon should stop advocating the higher voltage regulators, and consider stocking the voltage regulators that are actually correct for use with the JR systems they sell, instead of the ones that may not be as suitable.

Once again Tony, thanks for all your help and advice. One of these days I'll hopefully get a chance to repay you in some way.

Gordon

I have no proof that 6v is the definite problem. I'm only taking a guess comparing your's and David's set-up that have had failures vs. mine that has not. May very well be an incorrect guess.

You can get 5.2v JACCIO regulators from Central Hobbies.

We originally started using 6 volts years ago prior to digital servos. With digitals I do not believe we need that much voltage, but I do like the consistent supply that the regulator provides. That consistency was more important in pattern competition then in jets, but it's still nice to have. From what I have seen, 5.2 volts is plenty for the digital servos.

I talked to the Tech goobs at Horizon this morning. I asked specifically about the battery voltage issue and they told me that the torque rating of the servo is at 6 volts. I also asked would the 5 cell pack be a problem and they told me no it would not. I then asked if this has been an issue again they said no. I have not had any problems (yet, and knock on wood) with the servos in my BC but this really concerns me. My gyro, and Vernon's was set up with the same kind of rates as you mentioned Tony. Maybe not quite 100% when the gear is down. And maybe slightly higher than 20% but not much. I have seen some jittering with a freshly charged pack with a big Giles I have with 5 cell packs but so far the BC has been rock solid. I think the disccussion about the Airtronics servos centered around the 3301/3321 servos and Bandit rudders.


David Reid

Okay - understood.

I have ordered some of these regulators from Central. In the meantime I will simply watch these servos very carefully and continue to use the 6V regulator from Horizon.

Gordon

I've been running 6v in my airplanes for quite some time now, in most cases unregulated without any problems, so I don't think that's the issue.

I hate to speculate on what a problem might be because it only serves to snowball on itself I think, and leads to misinformation more than actual info.

What you guys have done is the best approach in my opinion, that is send the failed servos to Horizon Service and have them look them over. I know some of the guys in the service department fairly well, and will give them a heads up on this. Maybe there is something specific to the time frame the servos were purchased.. maybe not. I don't know.

But to answer the original question, either one will work, and I doubt there is any reason to choose one over the other for this application. Because this is a low vibration application, there is not going to be the same kind of gear wear noticed in helicopters (where the SA version originated).

Doug Cronkhite
Team JR

Ken,
I'm using the 3421's on my rudders and elevators. 49 flights so far, and no problems.
I have a JR 1400Ma 5 cell pack with Jaccio 5.2 volt regulator.
I agree with Tony F. with the concept of reducing the gyro gain when the gear is up to reduce the loads on the servo, not to mention the reduced current drain.
I cannot understand why two servos would fail simultaniously (DavidR) unless the cause was exterior to the servos, or from heat build-up. David is very fortunate that they died on the ground.
All of my extension harnesses are JR heavy duty, and only one JR amplified Y harness (rudders).
Since so many guys are finding problems with this servo, I'll keep close watch on them.

Harley Condra
BVM REP
RAM REP

This is a big concearn for me as I am just about to order four of these servos for my bobcat. The fact that they are failing at full deflection could be a serious issue since I planned on using them on elevators and rudders. Last thing I want to do is loose my plane from servo failure. I find it interesting that they all happend to fail on the ground. Was this failure as soon as power was turned on? Any suggestions on a diffrent model servo with the same specs that I could use instead???? Tony? I think that this is a serious enough issue that JR would need to find the cause for failure and report it immediately if it is a production problem! What's your suggestions guys?
Todd

Todd,

The 3421 isn't even produced anymore. The servo was superceded by the 3301 quite awhile ago. I'd suggest going ahead and using the 3301.

The failure mode of the 3421's reported here being exactly the same does suggest something in common is happening though I'm not sure I'd hazard a guess as to what without more information.

Doug Cronkhite
Team JR

Doug,

The 3321 are not produced anymore the 3421's are still being produced. The 3301 replaced the 3321.

Not all of them failed on the ground and I do not remember but I think all of them failed after the battery was fully charged. I have never actually measured the voltage after a full charge but after talking to a couple of other people today I am adding the jaccio 5.1 volt regulator. (They don't make a 5.2)


Todd the 3301 works fantastic on the elevators. I have done some high speed flight with mine and some high G turns and have not had a problem with them. Vernon and I actually flew a little "sorta" combat, dog fighting stuff, and we were really yanking on the airplanes.

Harley it was Vernon's airplane that the two failed at the same time and the first thing he chaecked was the Y harness. We have all heavy duty servo leads 22 guage servo leads and good connections that are heat shrunk. Replacement servos have already been installed and there is no problem other than the 3421's. There is absolutley no binding in the linkages or the rudders. One of the servos was making a humming noise (not the normal Digital buzz) and the other made no sound at all.

I am going to watch mine carefully and add the voltage regulator.


David Reid

I can not be 100% sure of that, for the ones that failed actually in my aircraft. I switched on and went through my normal pre-flight - checked the voltage on the built-in DVM, etc then went to check all control surface movements before start-up. When I got to the rudder check, I looked over at the rudders at the same time as I gave left rudder input.... and noticed then that they were stuck hard-over. So, I have no way of knowing whether the rudder went hard over as I switched on, or only when I fed it some input.

One of my buddies who was helping me suggested that the gyro could have been confused about its neutral if I had perhaps inadvertantly bumped the aircraft during power-on. I tried cycling the RX battery switch, but the servos did not move.

Then I switched off, manually moved the servos back to neutral, and switched the RX on again. Both servos stayed in the neutral position, rather than going back to the hard-over position they had been in previously, but they stayed neutral regardless of the input from the TX. They also did not attempt to stay neutral when some manual pressure was applied to deflect the servos - in other words after the initial hard-over kick, the servos did not move at all under their own power. However, a later test showed one servo once again moving some of the time, and then it stopped altogether again.

I think that this is a serious enough issue that JR would need to find the cause for failure and report it immediately if it is a production problem!

While it certainly was disconcerting for me (and probably David too), I would caution against over-reaction. So far, *two* JR customers have reported experiencing a similar symptom (not necessarily identical cause). That's two out of who knows how many customers.

Before I got into the software business, I used to work as an electronics test & repair technician for a British defence company. I can tell you that sometimes a series of unconnected failures can look like a pattern, without actually being one, especially when the sample space is small enough.

What I'm trying to say is that while I would hope that JR will take the time to look at the returned servos in a little more detail than they would do if the servos were sent in for e.g. crash damage, I don't think we should necessarily assume the worst... let's wait & see what Horizon has to say, and wait to see if any more people report having the same kind of problems. In the meantime, lets not panic. ;-)

Regards,
Gordon


P.S. Regarding the simultaneous failure - yes, that does suggest the possibility that the trigger, if not the actual problem, could in some way be external - anything from the battery to the gyro could have a hand in this.... but there again, the ones that failed on the bench (as I tested them before installing them as replacements for the ones that failed in the aircraft) were not connected to the same battery, had no gyro attached etc. So, speculation is probably pointless, and I'll await Horizon's response.

Whoops.. my mistake. You're absolutely correct. I got the numbers mixed up in my head.

I've sent an email off to the guys in the service department about the failures and I'm sure they'll be interested to see Gordon's servos. Might take a few days to hear back from them though with everyone in Toledo for the show.

-Doug

Thanks for the reply Harley. I will continue to plan on using the 3421's unless they are pulled by Horizon. I actually miss the 3321's BTW

Thanks Doug.

No huge hurry on the timeline - I didn't mail the first pair of servos back until Monday afternoon, and am just heading off to send the other pair right now. I figured that if I hear back within a couple of weeks, then that's a pretty good turn-around.

Thanx again,
Gordon

I want to empahasize again that all 4 of the 3421's that we had fail were in the same airframe, and were purchased at the same time. Vernon and I are both adding Voltage regulators as we think that may be the culprit.

DR

Thanks for the clarification, David--You're correct. The Jaccio is 5.1, not 5.2 as I stated. The 5.2 that I have is one from Performance Products for the Tadiran Batteries.
It is safe and sound in the cabinet, not exposed to the dangers of rampant electrons and jet fuel.
Who would fight over a lousy .1 volt, anyway.
I'm still gonna keep my eye on 'em, cuz the airplane is alot harder to come by than some #@*%^$#@!+%^#^@~_servos!

Harley Condra
BVM REP
RAM REP
Buy American when you can!!!!!!

The exact same airframe, or the same type airframe? Are both of your radio setups exactly the same (extension guage, y-harness, receiver type, battery type, etc.) or are there differences? The servos that failed were both rudder servos correct? Connected to the same type of gyro?

I want to get as much info as possible to give to the service department. The more factual info the better chance we have to figuring out what's going on.

Doug Cronkhite
Team JR

Doug,

The exact same airframe. Vernon's is the only one that has had the problems. I had 2 kits and 2 sets of servos when his first set of 3421's failed (one at a time over Superman weekend) we swapped them out with servos I had for MY bobcat that was not built yet. But.... the setups are identical in both of our airplanes.

His plane has about 50-60 flights on the second set of servos.

The servos were all purchased at the same time.