Any DIY cure for Servo Glitching?

[Bearded Flyer]

I know that many people are using these servos with no problems but I have some (4) Hitec HS55 servos which cause glitching on a range check of 15 paces. I have already sent 2 back due to glitching but the replacements are no better. They have been bought from 2 different suppliers.

Background:
Tx's: Hitec Optic 6 & Hitec Ranger III Sky 35Mhz channels 64 and 69
Rx's: Hitec HFS-04MG & Hitec Electron 6 channels 64 & 69
Servos: Hitec HS55 and Multiplex Tiny S
Power: Futaba 4-cell NiCd
Glitch Checker: DIY PIC based LMA and Glitch Checker

All tests are done using only the above hardware which is not installed in a plane. Any combinations of the above using 1 or 2 of the Multiplex servos result in a successful glitch free range check at 30 paces. Any combination using 1 or 2 of the Hitec servos result in glitching at 15 paces. If I do not move the servos, or 'excercise' one of the channels without a servo attached, then there is no glitching recorded. There is no discernible voltage drop in the servo power line whilst moving the servo. I have used a IPD Frequency checker whilst 'exercising' the Hitec servos with a manual servo 'mover' with no hits on the frequency checker.

I have tried the following with no improvement:-
1) Capacitor across power and ground wires of servo plug
2) Diode in signal line

Is there anything else anybody can suggest (except using alternative servos) that might help solve the problem?

Thanks
Richard

[Hell-e-Guy]

Have you tried warping the servo wire around a ferrite core?
It makes a simple common mode choke....looks like all you tried to do is suppress the differential noise.

[meteor]

As a note to non-tech types, Servos don't "glitch"...

They simply react to a 20ms PWM (50Hz) pulse with an on duration between 1ms and 2ms. No signal, no movement. (if you power the servo without a signal wire attached, does it move erratically??)


Sooo... Look elsewhere, like the receiver or transmitter, for the source of unwanted movement.

As above, do you record a glitch if you pull the signal wire from the servo? (a test to see if somehow you have the servo feeding back noise to the receiver...)


I'm sure if you try them in alternate (non-Hitec) equipment, and they will magically stop "glitching"! ;)


Also, when you say a glitch was "recorded", does it manifest itself as a visible movement, or is this an analysis of the PWM signal to the servos?

You may simply have too much emphasis on technology, rather than on basics.

One or two out of spec, or sync, pulses over a matter of a few seconds is trivial, and very "liveable". No servo on earth can react fast enough to respond to one errant pulse, followed by the correct pulse train to cause a significant departure from control.

[Bearded Flyer]

Thanks for the replies,

Hell-e-guy - I have tried a ferrite bead tonight and I have also tried wrapping the servo lead in aluminium foil grounded to the -ve terminal of the Rx. Neither has cured the glitches.

meteor - The glitching in the model was so bad that the motor would start at random whilst moving the control surfaces. As I am now trying the servos out of the plane with no horns attached I cannot see, at 15 paces, whether they are glitching or not, hence the checker. The checker records between 30 an 70 'hits' in about 20 seconds. A hit is a pulse that is either missing or falls outside the normal range. If I could guarantee that another make of Rx would cure the problem I would buy one. I have used mainly Hitec equipment to try to keep glitches to a minimum.

I am tempted to try some HS56's but I think that they may be HS55's in a fancy case with stronger gears. The Multiplex Nano S also appears to be the same 'guts' as the Hitec.

Richard

[meteor]

Hmmm...

I'd suggest a very methodical "build-up" test, by eliminating as many components as possible, and add them back in until you start to see the problem.


As before, the first easy test is to connect the "bad" servos with their signal lines pulled, with other two "good" ones under test to see if it's a super-basic noise issue. (not very likely)

To further test, you can also do neat things like power the servos from a seperate battery, to see if it's a receiver power feedback issue. (Common ground, seperate positive supplies. I've done this for high-load servos, as to not tax the BEC and risk the aircraft...)

You comment about the glitching occurring only during movement could be very telling, as it suggests some sort of receiver power issue. (the servo is drawing too much current?) Perhaps you have a bad filtering cap in the receiver?


I'm sure if you test all the possibilities, the issue will come to light.

[Trevor_G]

Sounds like a power problem. Could be bad cells. Maybe the charger is faulty and the battery is not properly charged.

If they are old cells could even be black lead.

Try measuring battery voltage while you are moving the servos.

[Magrat]

This any use?

http://www.rcgroups.com/forums/showpost.php?p=5650249&postcount=11

[Gary Warner]

If it's the 55 servos causing the problem, it should be reproducable in my shop. I'll give your setup a try in a few days and report if I see the same results.

Gary
--

[Bearded Flyer]

Thanks Gary I will wait with interest. I will also follow the thread mentioned by Magrat.

Richard

[Bearded Flyer]

I have just received some J Perkins 7.5g servos which look almost exactly like the Hitec 55s but are black and ................. they DO NOT GLITCH at 30 paces :D

I will fit them today and give the plane a test flight.

Richard

[vintage1]

I am wondering if a bad batch of these has come into the UK..I've got a bit of twitch...on one too..got plenty more except replacing is a total pain..

[Bearded Flyer]

Vintage,
Interested to hear that. What does it say on the round sticker on the servo? I think, and it is too late to check, that all 4 of mine say '05 12' and that 2 have a purple sticker and 2 are green (but I could be wrong). I will check the exact markings tomorrow.

Richard

[vintage1]

Can't get at the back of mine without extensive surgery..ah well.

[Bigun]

HI all,
Just reading this thread about glitching HS55’s. I bought 4 from Wings and Wheels at North Weald a couple of weeks ago. After fitting two in an electric glider, when I do a range check there all over the place – servo arms moving by +- 30 deg or so. After trying the obvious moving aerial’s etc, I am now down to these faulty servo’s. I have tried 3 different receivers, different batteries, different transmitters, channels and locations, but the only common denominator is the HS55’s. They also seem to interfere with what ever is connected to the receiver. If I plug in a couple of Futaba 148’s the system is rock steady. Add any one of the HS55’s and all 3 servos jump all over the place! I find it hard to believe that all 4 are faulty, except if as suggested there is a bad batch around. Any ideas where to go now apart from take them back to where I purchased them from?

[vintage1]

HI all,
Just reading this thread about glitching HS55’s. I bought 4 from Wings and Wheels at North Weald a couple of weeks ago. After fitting two in an electric glider, when I do a range check there all over the place – servo arms moving by +- 30 deg or so. After trying the obvious moving aerial’s etc, I am now down to these faulty servo’s. I have tried 3 different receivers, different batteries, different transmitters, channels and locations, but the only common denominator is the HS55’s. They also seem to interfere with what ever is connected to the receiver. If I plug in a couple of Futaba 148’s the system is rock steady. Add any one of the HS55’s and all 3 servos jump all over the place! I find it hard to believe that all 4 are faulty, except if as suggested there is a bad batch around. Any ideas where to go now apart from take them back to where I purchased them from?


Nope.

Mine seemed to improve when cycled a few times. Bugger I bought 4 from someone there as well...haven't tested them yet..

[Bearded Flyer]

Bigun,

Can you tell me what the numbers are on the Blue/Purple circles stuck to the servos. This will help identify if we have a bad batch.

Richard

[Bigun]

I definatley think there is a bad batch of HS55's around. I now have 6, all with a purple sticker '06.01' on them that exhibit the same problem. I ordered two similar size servos - Sirrus SC201's and fitted them and they are perfect no problem at all. A friend of mine also bought 4 at Wing's and Wheels and he has the same problem - when the signal gets weak (15 - 20 paces with airel down as in a range check) they jump all over the place. They are actually putting RF interference on the power rails, so they also effect anything else plugged into the receiver. We have sent an e-mail to Hi Tec, will post their response, mean while I suggest that if anyone has bought HS55's recently check them out.

[Peter Seddon]

I've just put two into the wing of a Sniper EDF jet 06.01 so will have4 to give them a try.

I'm using a Multiplex IRD receiver so if there are problems when the pwm signal to the servo starts to break up I hopefully will not see that and not get the problem.

Regards Peter

[Bearded Flyer]

Bigun,

My glitching HS55's are marked '05.12' and I have 2 with purple stickers and 2 with blue. I sent the first two that I bought back to the shop and got them replaced (after the plane had crashed :( ). As the new pair that I got from them, and the other 2 from a different shop all glitched I thought that it must be my setup so I started this thread. I now have J Perkins 7.5g servos in the plane and they work without glitching.

I will be very interested when/if you get a reply from Hitec to your email.

Richard

[Bigun]

I also bought a couple of JR371's today and they also work fine - I want to go fly the plane I bought the servo's for!
Down at the club flying field there was also another guy with a couple of 55's in a new ducted fan model that was doing wierd things.
I'll post Hi Tec's response when we get it.
Cheers

[Sim69]

:( :confused: :mad:

[Hell-e-Guy]

Richard,
Can you give a link / details on your DIY PIC based LMA and Glitch Checker.
Sounds interesting.

Hell-e

[Bearded Flyer]

Hell-e,

This is the link http://www.designsoft.com.au/ahome/rc/PIC-LMA/LMA.html

Richard