Servo problems.

[Peter Futers]

NO buzzing very straight rod, just tried plastic clevis to servo, clevis on rudder  wood,

fault applies with bec or 4,8v from external source 

 

losing my patience with this fault.

 

in many many years of building never had this agro . 

Thank you all for the suggestions as to the problem

tried them all (except trying a new servo)could not get my head round the fact that only happened when connected to rudder.

so rummedge the sevo box found a Corona cs-929mg new in box fitted today works fine.

thank you all 

Peter 

[Chris Walby]

Rather late to the party and no idea if this helps, but my son had an aerobatic model that had flown many times and passed all of its pre flight checks on the day in question. Just after take off it became almost uncontrollable, however he did manage to get it down in one piece.

 

Back at the bench all worked as it should, but with the canopy off I kept prodding around with my finger until just applying a little pressure to an aileron extension lead produced full deflection of the aileron from one extreme to the other. This was quite random and the TX stick input would cause normal operation although overridden if the servo extension plug/socket was flexed.

 

Unplugged and reinserted the servo plug and it never did it again. I can only put it down to a poor signal connection in the servo plug/extension lead.  

[Simon Chaddock]

Whish is why I avoid using extension leads particularly on the elevator with every wire joint soldered and preferably just a single plug onto the receiver.

The same applies for the wing servos unless of course the wing has to be removable but even than only one extra plug and socket for each servo.

 

If a servo plug and socket is going to give trouble it will be the ones that have to be connected/disconnected every time the wing is mounted/removed.

[Martin McIntosh]

Happened to one of my models more than once, with electric power to start with, overvoltage from the BEC being the cause. When the voltage stabilised after a minute or two it was OK.

Changed to i/c power but retained a UBEC to stabilise the 6.6V from the LiFe pack and the problem returned. Lowering the UBEC output from 5.5 to 5V did the trick. Some servos do not like even a tad over 5V.

[Martin Harris - Moderator]

JR?

[Paul De Tourtoulon]

On 28/04/2024 at 20:43, Peter Futers said:

Corona cs-929mg new in box fitted today works fine

I use a lot of the 929/939 analogic ones, but now and again they do fail, I have one the buzzes and jitters on my Tiger Moth aileron,

it's raining again today and tomorrow, so maybe I will change it.

[Paul De Tourtoulon]

Fed up with Tv, done it,,,

 

 Ps Corona 939mg.

 

Funny, but how did I miss the plank of wood with copper wire tied to it to pull the servo wire through ?.🤢

[Martin McIntosh]

M.H.,

Strangely not JR in this case. They are HiTec 82 mg`s. Never had any problems with them in the past on other models.

I also use a lot of Corona 939`s both analogue and digi. Due to availability at the time my Super Aeromaster wings have two each of normal digi and HV. The speed is the same in each case on 6.6V so I think that the HV ones are just regulated down.

[Cuban8]

On 28/04/2024 at 20:02, Chris Walby said:

Rather late to the party and no idea if this helps, but my son had an aerobatic model that had flown many times and passed all of its pre flight checks on the day in question. Just after take off it became almost uncontrollable, however he did manage to get it down in one piece.

 

Back at the bench all worked as it should, but with the canopy off I kept prodding around with my finger until just applying a little pressure to an aileron extension lead produced full deflection of the aileron from one extreme to the other. This was quite random and the TX stick input would cause normal operation although overridden if the servo extension plug/socket was flexed.

 

Unplugged and reinserted the servo plug and it never did it again. I can only put it down to a poor signal connection in the servo plug/extension lead.  

I've come across problems caused by poor connections in servo extension leads quite a few times in the past where I've plugged a  couple of shorter leads together to make a longer one - not ideal, I grant you and I avoid doing that now. However, my theory is that where an extension connector is plugged together and then not regularly taken apart,  the contact can degrade over time, for whatever reason and give odd servo problems. Exacerbated by by poor plating on the crimps when buying cheapo leads?

I've found issues manifest themselves as slow movement, oscillating around centre before settling and much reduced torque felt when a finger is used to resist output arm movement. Waggling the stick and exercising things for a while tends to clear the problem for a while, but it'll be back. Cleaning the dodgy connector solves the problem although I've usually changed out the connector to be on the safe side. Encountered the issue in models stored indoors as well as those kept  in my unheated garage.

Not unusual to get this type of problem in other kit where unseating and reseating PCBs can solve a lot of 'funnies'.

 

[Paul De Tourtoulon]

14 hours ago, Martin McIntosh said:

They are HiTec 82 mg`s. Never had any problems with them in the past on other models.

I have, all binned long ago.

[RottenRow]

22 minutes ago, Cuban8 said:

I've found issues manifest themselves as slow movement, oscillating around centre before settling and much reduced torque felt when a finger is used to resist output arm movement. Waggling the stick and exercising things for a while tends to clear the problem for a while, but it'll be back. Cleaning the dodgy connector solves the problem although I've usually changed out the connector to be on the safe side.

Precisely my experience too.

 

The exact symptoms depend on the type of servo, and which one (or more) of the three wires in the connection becomes poor.

 

Brian.

[Cuban8]

A weird one that I had quite a few years ago concerned some mini servos that I bought from the Nationals. Can't recall the make now but they were of a make distributed by one of the big suppliers. When connected up to my Futaba gear and about every fifth time the system was switched on they'd all burst into oscillation about their centres until quickly switched off and on again where they'd perform quite normally.

Just about subsitituted and swapped everything to pin down the problem but they just didn't like my Futaba gear. In the end I put them to one side and substituted them for another brand and just put them in my parts drawer for another day.

FF a few years and I got my first 2.4 Ghz Spektrum and tried the old servos on that.......no problem at all no matter how I tried. Fitted them in a little foamy type thing and flew it for ages before selling it on to a mate.

[Andy Stephenson]

I had a similar issue with JR mini servos on a Futaba PCM receiver, The servos would jitter when switched on but as soon as I moved the stick they would perform normally.

[Martin McIntosh]

That reminds me of a problem I came across concerning the Rx signal wire voltage level. I bought some more of the HK MCA series retracts but when connected to any Orange Rx they did not work, earlier ones having been fine, but were OK on JR/Spektrum.

I checked the signal levels on a `scope and JR`s were at 5V but Orange only 3V which was now not enough. The retract amps must have had a component change for some reason. I do not have any Futaba gear so cannot comment on it but there may be a similar problem with that and some servos.

[Andy Stephenson]

I've come across this signal level issue before, most receivers put out servo pulses at somewhat less than the battery voltage, in some cases as low as 2.8V. This could be the cause of some of the problems noted here.

[Martin McIntosh]

Glad that someone else has observed this Andy, it could well be the cause of many issues.

[PatMc]

8 hours ago, Andy Stephenson said:

I've come across this signal level issue before, most receivers put out servo pulses at somewhat less than the battery voltage, in some cases as low as 2.8V. This could be the cause of some of the problems noted here.

If you're refering to the OP's problem, why would connecting the push rod trigger the problem ?

[Andy Stephenson]

1 hour ago, PatMc said:

If you're refering to the OP's problem, why would connecting the push rod trigger the problem ?

It could be metal to metal noise or it could be a voltage drop in the power cable whilst the motor is running, not allowing full drive torque causing an under damped situation due to the extra inertia/resistance of the linkage. I have observed this situation when a battery is about to go flat.

[PatMc]

42 minutes ago, Andy Stephenson said:

It could be metal to metal noise or it could be a voltage drop in the power cable whilst the motor is running, not allowing full drive torque causing an under damped situation due to the extra inertia/resistance of the linkage. I have observed this situation when a battery is about to go flat.

I don't think so.