R127DF and Hitec Digitals, save your plane and read
 

Hey Guys,
I don't know if you have seen my annoying threaads of glitches on my DP Ultimate Biplane but I have finally figured out some vital information for my future planes and yours too. I was running digitals on my 127DF when I got glitches. 2 years later I decided to try to conquer this issue (which today I did) and figure out whats behind it.

I was able to duplicate this multiple times on different 127DF rx. I would load the digital servo and in a few seconds or minutes the whole airplane would twitch violently than go back to normal. Sometimes it twitches every few seconds. Crazy stuff. I switched to a 138DP rx and i was unable to reproduce this issue. It is almost like the 127 is unable to deliver the neccessary volts to the digital servos.

Please stay away from the 127DF after you get away from straight four channel setups. It nearly cost me my DP bipe when it gave the airplane more than a 3d rate full of down elevator on landing! Just wanted to state my findings. Please let me know if anyone else has had this issue. Thanks

RE: R127DF and Hitec Digitals, save your plane and read
 

The 127DF is a standard PPM/FM rx and the 138DP is a PCM with failsafe features. The PCM rx will mask all glitches due to its error checking. In some cases this is good. In others, this can sometimes create a false sense of security. There is a chance the 127DF glitches are just a warning to real external issues. It is hard to know for sure.

RE: R127DF and Hitec Digitals, save your plane and read
 

I am pretty sure its not external glitches. Because I could duplicate it at my house far away from the flying field. And it would only glitch when under load when i would hold a control surface against center (such as high speed forward flight or rotation on take off) never just by itself. I also flew the same equipment (minus the digitals) and the rx didn't glitch at all. I was also able to duplicate this glitch on more than one digital servo indicating it wasn't the servo. I too was thinking it could just be PCM (which i hope it isnt) and thats why I posted this, to see what you guys think. Thanks.
Adam

RE: R127DF and Hitec Digitals, save your plane and read
 

Perhaps the Hi-Tecs are an issue, but I've been flying several 127DFs with Futaba digital servos for several years. I fly these airplanes aggressively, though not 3F (flip flop flying), hovering, etc. I have helicopters for that sort of thing. I have yet to see any problems with these airplanes.

Another possibility is your battery isn't strong enough. It has been shown in some helicopters that certain NiMH batteries indeed do NOT have enough voltage to reliably move digital servos under a heavy load; such as 3F "flying". As far as I'm concerned, the jury is still out on this one, but there are enough experienced guys who believe it for me not to dismiss it out of hand.

However, I do NOT think your problem is directly attributable to the R127DF receiver. Try a large-capacity ni-cad battery and run your test again.

RE: R127DF and Hitec Digitals, save your plane and read
 

I agree. Glitch problems are often external from the Rx. A battery pack that is unable to deliver peak currents (high torque servos can be demanding), antenna routings that are impacted by nearby servos or wiring, metal-to-metal isues, long servo wiring, etc, are just a few of the gotcha's that will create glitchy situations. Usually a PCM Rx will just mask these so that you cannot see the real problem.

RE: R127DF and Hitec Digitals, save your plane and read
 

A light bulb just went off in my head.

I too had glitch problems with a Hitec / Futaba marriage in my Aeroworks X300L Profile. I swapped out just about everything and never did fix the problem. "The light bulb"!!! The two separate RXs I ran with were both Futaba R148DFs. I had to go with this RX because of the side connectors -- top connector RXs would not fit in the wing root with all the wires going to the control surfaces. It never dawned on my that there was an incompatibility issue -- I always assumed the glitching was caused by the long extensions on my tail surface servos (no choice giving the distance they had to travel) so I tried to elliminate the problem by twisting the wires and replacing all the servos with the new styles that came standard with twisted wires. I don't think I ever tried a Hitec Super-Slim RX instead of the Futaba R148DF -- I have them in my inventory and they would have been a suitable replacement. Its been a while since I've flown that bird because I broke the fuse in two pieces (engine problems and pilot dumbness) and haven't gotten around to repair it.

This was the configuration I was running:

Aeroworks X300L Profile (80" wing span)
Moki 180 -w- Mejzlik 19x8 prop

* 3500mah NIMH 6-volt RX battery through an MPI switch.
* Futaba R148DF 8-channel RX
* (2) Hitec HS-5625s on the airlons
* (2) Hitec HS-5625s on the split elevator
* (1) Hitec HS-5645 on the rudder
* (1) Hitec HS-425 on the throttle.

http://www.cma1193.com/MbrHgrPics2003/hilleyJ2003g.jpg

RE: R127DF and Hitec Digitals, save your plane and read
 

I am running a 2700 mah nimh 6V battery. I have checked metal to metal contact, i don't have any long servo leads to the digital servos. I have tried a large capacity nicad batt and the glitch still occurs. It could be feedback from the servo that the pcm rx is covering up. I think i am going to purchase a better rx from futaba that isn't pcm and see if it will do the same. That is really the only definite way. Thanks for the input so far. :) I also disconnected the voltwatch I was using because I suspected that it may be a possible cause as well.

RE: R127DF and Hitec Digitals, save your plane and read
 

Hilleyja and Zope Pope,
One thing to watch for if you get glitching problems is the voltage at the servo. You can NOT do this with a meter or a voltwatch. Now here is the hard part....the only way you will see quick voltage drops is with a scope. A meter or voltwatch will give you an average and it is much too slow to give you good data on glitching. I know everyone doesnt have a scope in the shop but it is very interesting to see what goes on if you can get your hands on one. Another interesting place to put a scope is on some of the low cost switches being sold. You can see a significant voltage drop when all the servos are moved under load but for such a short time that you would never see it with a meter.

Pete

RE: R127DF and Hitec Digitals, save your plane and read
 

My thing is if its a voltage drop issue, then why does it only happen on a ppm rx and not my 138DP rx? I am also running a heavy duty MPI switch with the voltwatch built in.

RE: R127DF and Hitec Digitals, save your plane and read
 

also modeltronics. Checking the voltage at the servo, what will this tell us? Will it be able to tell us if a servo is bad and causing the glitch?

RE: R127DF and Hitec Digitals, save your plane and read
 

Watching for a voltage drop with a scope at the servo will give us an idea of what the servo is seeing at peak load. To some point as the voltage starts to drop the current required to provide the needed torque goes up. Now the second thing that can start to happen is you can get a voltage drop at the battery (more prevalent with NiMh batteries because of the higher internal resistance).

Next...another very interesting place to look at with a scope is the switch. Just because a switch is called heavy duty does not tell us the contact resistance and the current carrying capacity of the switch. A voltage drop at the switch for even 100 milliseconds can cause the discriminator or the decoder in the receiver to do a lot of strange things...glitching can be one. This can be very different from one receiver to another.

Another place you will see voltage drops is on the contacts of low cost extensions. There are some on the market that skip the gold plating to keep cost low. Using servos the require higher current with these just make the problem grow.

You will not see any of this with your voltage watch. Even if we could I know my eyes are not quick enough to see a 100 millisecond voltage drop on one. They are very good for showing the average condition of the battery.

Your problem may not be any of these things...just something to look at and think about.

If you lived closer I would invite you over to look at your system on my scope.

Good luck, I hope you can solve the problem.

Pete (HiTec service center)

RE: R127DF and Hitec Digitals, save your plane and read
 

wow, mucho info. Anyways, I have decided to send my servo in to service and maybe they can check it out on a scope as I am convinced it is either the rx or the servo. I replaced the rx, so now I just need to find out if the servo is fine. I will let you guys know what they tell me. I am just going to replace that servo in the meantime and see if that helps. Thanks

RE: R127DF and Hitec Digitals, save your plane and read
 

I had pretty much the same problem with a 127DF on a DP Edge 540T with 5945's on the elevators and 8611 on the rudder. I had a 6 volt battery. When the rudder was deflected 1/2 and I held it there, it would just bump once or twice and stop. It didn't do it at neutral, only under load. Then I plugged a 5945 elevator servo into the rudder channel and same exact thing on that elevator half. Then I started to see the elevator channel doing the same thing. It turns out that it seemed to get worse near the 3rd and 4th channel of the rx. I tried different tx's and the same exact thing happened. I replaced the rx with a brand new 148DF and the problem is completely gone. I am using the same battery and extensions as before. I'm glad I found this in my basement.

I have the same model rx in a CAP232 25% with (5) 5645's and there is no glitches at all. Not sure if it's just some rx's or maybe I damaged this one, not sure. The one I'm having problems with was in a crash (not a bad one though, more like a hard landing). I used it in a Funtana 40 for many flights with no problems so I think it's the high current digitals that it does not like.

Joe

RE: R127DF and Hitec Digitals, save your plane and read
 

Joe, that is the exact same problem i have. I am glad someone agrees and I am not crazy! :)

RE: R127DF and Hitec Digitals, save your plane and read
 

I have also experienced servo glitching using Hitec digitals with a Futaba reciever in my 1/4 scale Extra.

I have not flown my Extra in quite some time due to this problem. I am getting ready to buy the electronics for a Comp-Arf 2.3 and I am having a difficult time that Hitec digitals are the way to go because of this problem.

I have considered using JR8611's but the servos have a reputation of developing slop, Futaba does not seem to have the power and torque in their servos that I would like. (the physical size of the servos is an issue for all control surfaces except rudder.

Hitec has the servos I need and would like but then there is that servo glithing issue!!!

Keep posting your information as I am very interested in any information that could shed light on this problem.

RE: R127DF and Hitec Digitals, save your plane and read
 

has this servo glitching occured at all with the hitech rx to hitech servos does anyone know ?

RE: R127DF and Hitec Digitals, save your plane and read
 

Hmm, i haven't tried. I don't own any Hitec Receivers. But that would be a good check. I am going to send my servo in just to make sure its 100%. But Joe mentioned that he switched to a 148DF which is ppm and the problem went away. This leads me to think that it isn't just pcm covering it up. This is definitely a weird issue.

RE: R127DF and Hitec Digitals, save your plane and read
 

zope,

The 148DF is actually FM. You had me thinking there for a minute.

Joe

RE: R127DF and Hitec Digitals, save your plane and read
 

hey joe,
(Thats a good song), anyway PPM is FM, PCM is the digital version and what you were thinking of. So it does lead me to think it is just the 127 rx, and I can make it happen on more than one of them so I am not thinking that its just one of your rx's.

RE: R127DF and Hitec Digitals, save your plane and read
 

I was also thinking. This could also just be an issue with the 5945 servo. I can only get it to happen with a 5945 and not my 5645. Seems to match joes claim of it only happened on one of his airplanes and not the one with the 56xx servos.

Hilleyja. I think that your problem could be battery related. I just got educated by the owner of NoBS batteries on internal impendance (sp?). The digital servos could be loading the batteries too much and the voltage maybe dropping too much causing the glitch. Just a guess. Trying to explain that side as it disproves my 127 theory. :eek:

Adam

RE: R127DF and Hitec Digitals, save your plane and read
 

I got a HiTec digital servo for another project I am building and it was horrible [:'(] I put it on the elevator channel of my current plane and it worked, by design it is very rough and grindy sounding compared to my JR digital servos (obvously lower quality), I was a bit dissapointed but for the money I could live with it... I put it on the Throttle channel of the same plane and it would not work at all, or just jerk around sometimes [X(]. I put my JR digital back on that channel and it was perfect. This is top of the line JR setup I have been flying for years, and never a single glitch, but the HiTec servo glitches, doesnt work etc [:@]. I started to read the forums and read about a lot of crashed planes due to HiTec digital servos doing weird stuff [X(]

MY JR digitals cost 120 each, overpriced but they work PERFECTLY. I really wanted to use the Hitecs for 50 bucks, but I will save 70 bucks on a servo and crash my airplane, I will NEVER buy another digital Hitech servo, they are just to squirrely and unreliable.

RE: R127DF and Hitec Digitals, save your plane and read
 

I can relate to your comments for the most part but in my case I disconnected all the servos except the JR 8611 on the rudder channel and it still jumped. You're right that the JR's sound way smoother than the 5945's.

RE: R127DF and Hitec Digitals, save your plane and read
 

Sweet something else to support the theory that the R127df won't run high voltage non futaba servos. Hey Joe, what version 5945 did you have. I have 1.03, I wonder if this has anything to do with it?

RE: R127DF and Hitec Digitals, save your plane and read
 

My 5945's are V1.03 but like I said the JR 8611 did the same thing all by itself, no other servos connected.

RE: R127DF and Hitec Digitals, save your plane and read
 

Everyone has their own opinion. It’s unfortunate you've experienced a problem with a Hitec digital. These kinds of problems are not uncommon of any product. You may simply have a defective servo, an installation problem or short coming that causes the servo to act erratically. In some cases there are OEM compatibility conundrums that become apparent when different technologies are mixed. Hitec Programmable servos control signal line is bi-directional, an electrical noise problem maybe present and not realized of other digital servos. For instance many of the so called problems of Hitec servos has been traced to low quality servo connectors, extensions and wyes which contribute to electrical losses on resistance.

Some of us have owned hundreds of Hitec digitals with nary a problem. To suggest that the product line is squirrelly and unreliable is a huge misstatement IMO. After all your experience is but of one inexpensive sport digital and heresy of forum readings. Hitec sells more digital servos than all the other manufacturers combined, they can't be all that bad.

If you're going to compare digitals you might want to compare like products against one another. Your $120.00 JR servo is a premium coreless digital servo, not an inexpensive sport 3-pole cored motor digital servo. Your $120.00 JR servo is almost comparable to an HS-5955TG premium digital. Your $120.00/$50.00 comparison would be akin to an apple and orange. If you want to compare a JR sport digital (811) to a Hitec metal geared sport digital (5645) you'll be close, less the anemic power of the 811 comparatively.

The metal gear-train of the 5925/5945's has been well proven by many modelers to be as smooth if not more so and hold up to the rigors of giant scale models far better than its JR counterparts (8400 series).

How are you guys determining which is a smoother servo? Are you manually cycling them through end-points? You realize this a not a good thing to do, right? In any event Hitec metal gears are comprised of an Alumilite alloy mixture; in some cases you'll find an imperfection or miss-match which often goes unnoticed after a little flight time. The new Hitec super Titanium geared servos are the strongest, smoothest and not to mention tightest on the market at this time.