servo questions

[olmod]

do todays sub 6 gram servos' use a moulded ceramic track feed back pot or a sprayed on carbon track, it used to be a big scource of problems.what is the breakdown of servo failures?circuit board or mechanical? the info' would be helpfull as i want to buy shortly.

[bigandy]

MOst of my tiny servo failures have been stripped gears!

Mainly my fault for hitting the ground too hard :)

Andy

[olmod]

so snap apart ball links on control surface horns are advisable on make and model ?? :D

[Dan Baldwin]

not hitting the ground works better, but I haven't quite perfected that method either.

I haven't stripped any gears yet, but I have had some Hitec servos get jittery around center because of a bad pot (I assume). I also had some old Cirrus servos put a short on the 5 volts. I had two, and they both failed the same way within a couple months of each other.

I recently bought some Blue Arrow 4.3 gram servos from Balsa Products for my Tantrum, and ended up throwing them in the trash. They had so much backlash that I couldn't even come close to trimming out the plane. I put some HS55s in the plane, and it now flys great.

Dan

[olmod]

this is the sort of info' that is worth its weight' 1st hand EXPERIENCE ;)
Happy new year . :D

[Frank Brasington]

Olmod,

Seems no one really address your question, nor can I since I'm just coming back th the hobby after a 45 year hiatus. Your qustion is most important, and yet I'm afraid the industry probably uses carbon paths, instead of cermat/plastic. NNaturally the manufacturers don't publish "dither cycle" ratings on their devices and the way I used to fly it didn't matter. Anybody got a good mighty-might motor for my gallopinng ghost single channel Rudder-Bug Jr>?

I'll be following your thread to see if anyone has looked at the feedback pot construction.

Regards,

Frank

[olmod]

Yes i also had a break,but you hooked me with the galloping ghost inquiry, i do have a brand new rand servo that i never got around to using ,it cost me a bundle origonally :( i used an old OS single chanel servo gutted and fitted with a centering spring that worked real good ,i still have my home built radio gear used for that medium ,i even made the ball jointed stick assembly :D we were giants in those days :D i find it strange no one has any knowledge about the feed back pot in todays servos' cheers. :)

[Terry S]

It would be nice to see servos with a hall effect feedback system....

Terry

[GailInNM]

I have worn out and replaced several pots in Hitec HS-55 servos. They were carbon pots. Got about 70 hours of flying a micro heli on each of them. On micro helis there is constant small movements around center if you are flying in a small area as I am. The center of the pot started getting the jitters, not serious but noticeable.

Pots have been a problem in servos since the inception of feedback proportional systems. The very early servos (1963-65) used wire wound elements which would wear through. Carbon pots were worse however. About 1966-67 several alternative methods were used. Kraft systems used a variable capacitor such as is used in portable AM radios for the feed back element. F&M systems used a variable inductor. Then the small, for that time, Cermet elements became available and the problems went away. I have not seen, but have not really been looking, Cermet elements small enough for the current crop of micro servos. It may mean that we are stuck with carbon pots for a while on them.

With microprocessor based servos, several alternative techniques are now available, including Hall efect, that were not practical just a few years ago. I suspect that we will see some of these come in to the main stream of R/C in the next few years. There are already some Hall effect devices being used in some speciality servos.

Gail

[olmod]

For bringing me a bit more up to date :) ,i remember kraft with the vari caps' and heard tell of the vari inductors but never saw one,carbon painted tracks in pots were always blamed for most servo problems back then and was a big issue,i knew the answer was the cermet pots and that is why i enquired as to what is used today in these small servos , i read reports of servos not centering ,dithering trying to find centre and running off to one end and wonder why its not being addressed :confused: ,if these servos have taken a step backwards in design in regards to feedback pots ,perhaps modelers should do a little more lobbying to manufacturers and talk about it a little more in the forums to help to rectify the problem, :)

[olmod]

tech friend called in ,he used to do a lot with servos' he told me that my recolection about cermet pots was true for a while but even those became worse and generated noise,he went on to describe what he called JC pots wich were a baked on substrate track that was like vitreous by nature and the pickup was a tiny carbon button,when dissasembling the tiny button wich was spring loaded ,quite often flew and being so small it was named the JC button because thats what was exclaimed at the time :eek: has anyone examined modern servos and had a look at whats used today???