hank01

Problem:
Severe Hitec HS-81 servo chatter combined with slow return to the neutral position or failure to return to the neutral position.

If you own a Hitec Eclipse 7 then you already know that the preprogrammed crow mix is only available in glider (GLID) mode and that the glider mode will not work for other aircraft as the throttle is either on or off, there is no other control over the throttle. The plan is to have crow mixing in ACRO mode. With the programming described below the flaps are controlled by CH5 and operated with the landing gear switch. The landing mode is programmed to raise both ailerons when flight condition ST2 is activated by flipping the Flt. Cond. switch forward. So, to turn on the crow mix, the Gear switch is flipped forward to lower the flaps and the Flt. Cond. switch is flipped forward to raise both ailerons. It works but the servos have this nasty chatter as the attached video demonstrates. I'm not sure if the servo problem is a servo problem or if it's a programming problem or a wiring problem or a problem with the BEC or Rx.

About the video:
0-15 seconds illustrates the servo chatter with the flaperon function operating. 16-29 seconds shows the flap operating with the chatter and 30-39 seconds shows the flap servo chatter with slow return to the neutral position after turning the flaps off.

Video link: http://www.rcuvideos.com/item/8K3JWSYYTDWN0B1H

Hardware:
Servos: Hitec HS-81; 2 aileron, 2 flap
Two 24" aileron servo extensions
Two 12" flap servo extensions
BEC: Atlas switch mode 8-42V
ESC: Atlas Black 45A w/internal BEC disabled
Battery: RC Battteries lipo, 3s 1800 mAh 20c/30c
Motor: Atlas AM2921/11 outrunner (.40 sport)
Tx: Hitec Eclipse 7
Rx: Hitec HPD-07RH QPCM

Rx channel assignment:
1- Right aileron
2- Elevator
3- Throttle
4- Rudder
5- Left flap
6- Left aileron
7- Right flap

Programmed mixes:
PMX1- RT ail/RT flap mix (L/U 60%, R/D 60%) Master CH1, Slave CH7
PMX2- RT ail/Left flap mix (L/U 60%, R/D 60% Master CH1, Slave CH5
PMX3- Left/RT flap mix (L/U 100%, R/D 100%) Master CH7, Slave CH5
PMX5- Elev/ail mix (L/U 100%, R/D 100%) Master CH2, Slave CH6

Preprogrammed functions enabled:
Flaperon mix (FLAPN) using the default settings
Flight condition (FLT.C) ST2
Landing mode (LAND) where elevator (CH2) is set to 5% & aileron (CH6) to 80%
Sub trim (S.TRIM) and endpoint adjustment (EPA) set to align and synchronize the control surfaces

Other info:
The wing servos are brand new and chatter regardless of the mode of operation or mix selected and frequently fail to immediately return to the neutral position. The control surface hinge material is strip CA, it's a little stiff but still soft enough to allow the control surfaces to sag under their own weight. It doesn't matter if the motor is running as the servos still chatter if it is. Battery charge also has no effect as the servos chatter the same with a fully charged or a partially drained (motor has cut out) battery. Tx proximity also has no effect as the servos chatter when the radio is as close as 2 feet or as far as 20 or more feet away from the Rx. All programming setup so far has been with the Tx antenna fully extended and no less than 8 feet away from the Rx. The servo wires run separated in the wing but cross over each other as they pass through the wing root and into the Rx compartment. Transient signal perhaps? Any other ideas?



Hank

Dorsal

My Feedback: (17)

The first thing I would suspect would be the hinges on those surfaces. The HS-81 is only rated at 36.10 oz-in @ 4.8V, so it doesn't take an extremely stiff hinge-line to make them chatter, stutter and jerk, especially near zero. Remove the servos and work those hinges until the surfaces will flop up or down from their own weight. Then test them again.
The last RTF I bought had a taped hinge line, but the LE of the aileron was not straight, so when they taped it to the wing, it forced the wing to have a slight bow on one side, upward as I recall. The net effect was like an oil-canning, where the surface would NOT sit in the neutral position and the servo had to fight to stay at neutral. I had to remove the aileron, sand the hinge-line straight, then recover and re-attach it to the wing. It works perfectly now.

hank01

Thanks for the input Dorsal. I took your advice and brutally worked the control surface hinges until they went totally limp. I guess you could say that they were beat into submission. I checked the hinge lines and they are spot on without binding in any position. Everything was hooked back up and the chatter is still there. To take this exercise one step further, I disconnected the push rods from the control horns on all four surfaces and taped the surfaces up out of the way. Even with no load on them, the servos still chatter and hesitate to return to neutral. Looks like the next step is to pull the servos and hook them up to a different Rx and see how they behave with it.

gyrocptr

My first guess is EMI from your switching-BEC and from all of those long servo extensions (long wires act like receiver-antennas). If your present servo extensions have side-by-side, parallel wires, try changing to servo extensions that have twisted-together wires. Also, ordinary (24 gage) wire is getting marginal with the 24 inch extension length. Perhaps those 24 inch extensions could be changed to 22-20 gage, twisted-wires.

Sir Raleigh

I'm going to suspect a dirty potentiometer in the servo.

Check out these sites:

http://www.rcyachts.com/Build/servorepair.htm
http://www.m3sc.org/glitching.htm
http://www.m3sc.org/servo_pots.htm

hank01

Thanks for the input guys but it looks like it's time to >sigh< contact Hitec. I pulled the servos from the wing and hooked them up to another Rx that uses a different Tx. Guess what? They worked perfectly. The servo lead question was answered by pulling the Hitec Rx, ESC, BEC and battery harness from the model and plugging the servos directly into the Rx. On the bench, the servos act just as they do in the wing- chatter city. The external BEC question was answered by unplugging it and re-enabling the Atlas internal BEC. Lots of chatter, even more so than with the external BEC. So, through the process of elimination, the problem is reduced to either the Eclipse 7 radio or the Hitec QPCM receiver or both. Can anyone disagree with this? The radio, along with the servos, receiver and spectra module is less than a month old and everything was bought brand new. How frustrating can it be?

jdetray

There is a Hitec support forum [link=http://www.rcgroups.com/hitec-multiplex-usa-169/?daysprune=-1]here[/link]. It might be a good place to post your problem. I've received responses from Hitec support people on the forum.

- Jeff

hank01

Thanks Jeff. A post is there plus I e-mailed the schmear to service at Hitec. I'm hoping that there is a speedy response from them.

Hank