HI all, I"m at the stage in wiring my BVM F80 and would like to know your favourate way of running two servos for the elevator, is it
A -------- Y harness
B---------Buffered Y harness
C--------- Matchbox
D -------- slave the other half of the elevator
Thanks Rcpete

If you have the channels D. If not....C.

I would not use a matchbox on the elevators or the ailerons.

JMP T 33 uses a Y harness........A
Semper Fi
Joe

either use a Y harness, or dual channels with mixing in the radio, but DO NOT use match boxes on control surfaces ie; elevators, ailerons, flaps.


mark

a simple reverseing y is the best and easyest way to go.it has a pot for centering one to match the other and nothing to go wrong,have used them for years and never had a problem

Mark Bob-O,

Why are you saying not to use match boxes on control surfaces ??

3dd,
What type of reversing "Y" are you using?? i have had trouble with some not centering after being set.
V..

The best reverser I used in the old days was Andy Low's at electrodynamics, immune to temperature differences, it is all digital, only thing I saw was that it was an 8 bit system (255 positions) and most PCM radios are 10 bit (1024 positions)...big whup I don't need 4 times the precision to fly bad.

Otherwise those reversers are bulletproof, no temp problems whatsover.

Those Expert things are analog I believe, temperture adjustment is why they have that centering pot to begin with, no? :-) They belong in the round storage bin, with some other stuff ;-)

Mr. Matt...I think you may be the smartest guy in the room sometimes. Not in an Enron way, in a good way. That driving with your feet thing cracked me up.

I had wondered why that Expert Y-harness with the pot on it always needed adjustment, now I know. I mussed with it for a long time, then consigned it to the scrap bin, I had never figured out why my trims were always changing and needed adjustment. Thanks.

PS I now carry precision 1032 bit black trash bags in my field box to put my wrecks in at the end of the day.

HI all, I just bought 2 of those Expert Y harnesses today, I guess they will be going back to my LHS.
I tried to slave my elevator on AUX 4 but did not like the results, the elevator on that side was slower and had a stepped motion.
So whats wrong with a matchbox.
Rcpete

No problem at all with the REGULAR Y-harness, only the one with the little pot with the reverser in it.
On the subject of Expert brand stuff, as an aside, some of it is REALLY cheaply made, double check that all pins and sockets are inserted into plugs, that everything is soldered, and all that. I have gotten some bad items from them, but that is reflected in their very inexpensive prices. I won't fly with one of their switches anymore, they are just not made well enough to make me happy. Food for thought.
Any way you can just flip one servo over? Saves the reversing problem. I did that on stabs for a big jet, with no issues.

as for the matchbox's? this is all 2nd hand info for me, do a search here in this jet forum, there has been many topics about the matchboxes. about 1 1/2 years aog, i started work on my kangaroo, i saud i was using matchboxes on the elevons, i had many replies saying get rid of them( not reliable) can fail. but is ok to use them on rudders and rudder / nose wheel. as for the exact reason, i am note really sure, but many have said not to use them on control surfaces such as, ailerons, elevons and elevators, so i removed them, then sold the jet to purchase a scale bird

like i has said , all that info is 2nd hand. do a search and read for yourself

mark

FWIW, my Yellow F-15 and my 1st isobar both had Matchboxes on the Elevators and both flew absolutely perfect with no trim adjustments. I've read a couple of threads about people saying not to use matchboxes on primary control surfaces, but the thing was designed for any control surface, so in my mind it's got the same likelyhood of failing as an 8411 or any other servo.

That being said, nothing beats just buying a reversed servo or sending one in to get reversed. Some people do it themselves, I just send it in. As far as ganging two servos together, in my experiance, the matchbox is bulletproof.

my .02

Sean

Pete, I believe (and I may be wrong), that channel 9 and 10 (aux 4 and 5) on the 10X are at half resolution. Try using those two channels for something that you won't care is at half resolution....like the gear or brakes. Try using aux 5 thru 7 for flight controls.

I'm sure a JR guy will chime in but I think that's the reason......

Pete, how are you? I always separate the elevators to two separate channels on my JR 10X and do the same with the ailerons. Then use the matchboxes on the flaps, rudders, steering, etc. One way to get one more channel if you need it is to use single channel operation for your turbine also. I think you have jetcats if I remember?

BTW are you going to Bardstown, KY this year? Gary

Pete:

There have been reports of a couple of matchbox failures on Giant Scale birds.......BV started recommending not using them on ailerons or elevators after his buddy Kemp Gallineau lost his Bobcat at liftoff due to a matchbox failure on the split elevators.....the common failure mode in the reports was signal in, but no signal out to either channel......rare, but it does happen.........if this failure mode happens on rudder or flaps, i.e. no signal output, then the surface should go to neutral trail, hopefully not fluttering, and the plane remains controllable.......at least so goes the logic.......obviously, a scenario can easily be constructed where the logic fails....i.e. a Bandit cruising at 200MPH that loses a rudder servo......chances of catastrophic failure of the bird due to flutter are very high........

I prefer a straight shot from RX to elevator servo, using a reversed servo and a simple Y-connector(no adjustment pot) where necessary...slight asymmetry in speed, centering or endpoints is rarely noticeable since we are not usually doing precision F3A serobatics with our jets.....I have found that it is easier to find a near perfectly matched set of 8611's compared to the older 8411's....if I have enough channels, to keep things simple, I prefer using separate elevator channels on split-elevator birds.......although this is getting harder on our jets with crow setups, bomb drops, and smokers.....

Tom

well i have the one from maxx hobbies and one from cermark and one expert,haven't used the expert yet but no problems with other two at all

I use Hitec Digital Servos along with their HFP-10 programmer to set EPA's and servo direction.

Marl

ok, here is a set up, and i am going to switch to a dual servo set up, i have Skymasters Bae Hawk, as of right now i have 1 8611 on the elevator, and the elevator is a full floater set with the rod connecting direct with each other, i am going to order another 8611 reversed, and just add the servo with a y harness , so now i will have over 500 oz torque, i saw the same set up fly yesterday on another jet, same as mine, single servo, same jet, and the elevator failed on test flight

mark

Single servo on a Hawk is not acceptable and, if I may say so, told you guys so on the Hawk thread some weeks ago. That loss was totally avoidable. My Hawk has twin 8511s, and has beautiful, solid, pitch response, and that is recommended now on Skymaster's website. I also recommend mass balancing the stab. With this set up my volt logger records minimal voltage drop on the Rx bus during a flight, an indication that the servos are not being hammered.

And sorry, Tom, BV is wrong, in my opinion, to actively discourage, without qualification, Matchboxes, they are great devices, its the way that they are used which needs clarification. In the Bobcat application if using a matchbox, it would be best to route ONE elevator servo via the matchbox and the other direct from the Rx so that if a Matchbox fails, and none of my 15 have, then the directly powered and signalled servo remains active, and if pitch response is diminished as result of a matchbox or the other servo should fail, you still have pitch control remaining, particularly if you have a higher rate available by selecting another flight mode. This is the way I have set up my FC Mig 29 with two ganged servos on each stab. Same for ailerons. But , sure, if you dont NEED to use a Matchbox leave it out, match servos via the tx software and totally remove the chances and consequence of failure.

We have the hardware and software available to make our jets safer and less vulnerable if we choose to find out how to use our radios to their full power.

Regards,

David Gladwin.

Pete, I think the main point that most of the guys are trying to make here is that if you do not need to add additional parts in line with your control surface servos then it is best not to do so.

An aeronautical engineer who is a friend of mine told me one time that the probability of failure on an aircraft is "the sum of its whole number of parts". In other words, the more parts the higher the probability of failure and therefore adding a matchbox increases that probability.

Quite simply, by using the matchbox there is an opportunity for it to fail and without it there is not, no matter how reliable they are reported to have been in the past. The same applies to servo reversers and any other item you put in line with the servos. Connecting the servos directly to the receiver by using either a second channel, a simple Y-harness, or a reverse servo (which only cost another $10) is the most reliable way to build your jet.

The main reason I like to split the elevators (on separate channels) is so that you can accurately match the servos to each other during the servo travel. It results in a much better flying airplane.

Just as a side note, I do use matchboxes for non flying surfaces also and I do agree that they are very reliable units but keeping it simple is still the best method!! Gary

David:

No real disagreement with your safer setup for the Matchbox......I know guys here using that method......I still keep MB's off my elevators and stick with closely matched servos, one reversed if necessary, with a simple Y or 2 channels if I have them to spare.....as far as the other surfaces, I use MB's only when absolutely necessary.....just another potential failure point, IMO....

While I have seen allot of jets saved after failure of surfaces other than elevator, essentially all of the elevator servo failures on jets that I have witnessed have ended in disaster....one exception being my friend who saved his Eurosport at Superman 2003 after one of his elevon servos broke loose, leading to loss of both roll and pitch control on that side...the generous sized fin/rudder saved the day, but the pitch/yaw-roll coupling was hairy.....

Tom

I believe you are right, Tom, ANY extra part is a potential failure and the consequences of that failure must be considered. BUT my experience of Mtachboxes has been total success and gave made the rigging of the complex wing (two LE flaps and One TE flap) on the Mig 29 simplicity itself instead of the previous nightmare !. Any comments Doug Cronkite ?

Problem with failures in models is that we are ALWAYS very close to the ground giving very little time to analyse and correct a problem, before the, almost inevitable, impact !

Of course the forthcoming 16 channle JR radio will solve the problem at a stroke !*

Regards,

David Gladwin.

* I wish, but wishes have beeen known to come true !