Pilot44

My Feedback: (20)

Bill,

Ok, just got the RCV 91CD's in. This is the drive washer, looks like will work OK as per your drawing.

Sent you an email as well.

Jim

MLDELARUELLE

Hello,

Can you tell me if it's recommended to use digitals servos ?
Or analogics servos are good with the twinsync.

If some brand/ref are recommended, please, let me know.

Thanks a lot
Regards
ML

yl5295

My Feedback: (1)

It is not necessary and kind of a waste to use high speed digital servos. The throttle response on all engines I or beta testers have worked is slower than a standard servo. If you use a fast servo and have a very fast or slow throttle response you may have to using a timing setting other than 2 for glow or 4 for gas. Fatory default is 4 for the timing curve that is programmed by rotary switch position 4. The only downside to have the device set too slow is time to sync is longer than it could be. However setting it too fast will cause throttle oscillations.

Acetronics

Hi, Bill

May be we could just recommend "good" servos with limited deadband ( read good return to the asked position ... )

Ahhhhh ... What is a good Servo ????

See here a really serious bench testing of common servos : http://osegouin.free.fr/servo/servor...2_nov_2006.zip

I Know ... It's in French !!!

Alain

Pilot44

My Feedback: (20)

Good question, I'm researching which servos would best serve the sync system and throttle control, digital, analog, what??

Anyone have ideas as put forth by alain? As I read Bill's statement, any decent digital not being hi speed would work well, digital only as centering is probably more accurate than analog. Other than that, I can see slower, the better, allows the sync time to do its thing.... But, that is just conjecture, I have no real time experience on the subject to date. Everything is on its way to me. so soon, I hope.

Jim



Jim

Pilot44

My Feedback: (20)

[quote]ORIGINAL: yl5295

Repeat, deleted

Robby

My Feedback: (18)

Guys,, do as Bill suggested.. Use a 'normal' servo...
I tryed a FUT3004 and I tryed HS225 and I tryed HS525...
The 3004 were the best.. I do use the 225 when I need a
smaller servo as limited by space.. I ended going back to
the 3004 servos on the test plane..

A faster the servo usually will cause oscillation, which
is one servo reacting then the other reacting causing the
motors to not sync as quick...
The unit itself has a real fast reacting time so as Bill
said to use a high speed digi servo is useless..

Just make sure the servo end points are set to a
MINIMUM of 100... The more the better.. The larger
the end point number the more preciese the servos
will be..
While trying different things I set a low end point..
I started out with a 40 low side and a 65 high side..
Major oscillation thru out the throttle range.. Then
after talking with Bill on this changed the throttle
linkage so that I would have a larger end point number..
I now have it set at low of 125 and high of 130...
Throttle response is great, sync'n is fantastik all
thru throttle range.. And,, zero oscillation at any
throttle setting even if I jam the stick <which I do often>
(BTW, I use a Futaba 9Cs)
So,, the larger the end point, the more precise the servo,
even a 10$ servo.. So save the good servos for the control
surfaces..

yl5295

My Feedback: (1)

Like Robby said... buy the best servos you can for less than $8. Centering/accuracy is not important either. It is a closed loop system and will sync the engines even if the servos are inaccurate. During development I just used double sided tape to mount servos to the test stand. Some times a servo would come loose from being fuel soaked. It would sync the engines with the servo being loose, vibrating and moving arround.

If you use a really fast servo and get oscillations you just have to slow down how fast the TwinSync moves the servo by changing the timing in the programming mode with the rotary switch in position 4.

The most important thing like Robby said is to extend the endpoints as far a possible. What you want is 100 rpm change for 1% servo movement rather than 500 rpm for 1% servo change.

Bill

Acetronics

Hi, Bill

Here ... I do not agree with you !!! [&o]

I do not doubt the twinsync will try to compensate for a "bad" positionning of the servos .... as you raised up, the close loop control is here.

Note the problem is not due to positionning precision ... but to the Dead Band ( an analogic servo amp. must ...) .

in terms of current draw that won't be so easy as the "bad" servos will start to move for a more than significant positionning error. just like with worn servo pots. so, servos will go too far, and then back again ...

Tell me if your close loop will compensate for non-linear servo behaviour like this one.

The test for the servo is to move -very slowly- the stick, and look for the stick position change needed for the servo starts to move ...

Alain

yl5295

My Feedback: (1)

Alain,

Yes the Twinsync will compensate for non-linear servo movement. All servos have some amount of dead band. If the deadband is greater than .01ms (10us) then you will loose some accuracy. Most expensive coreless digital servos have about a 1-2us deadband. Most of times the RF link between the TX and RX introduces 2-10+ us of jitter frame to frame. So you want a servo with a deadband of 10us or less. The twinsync will correct for servo positioning error but not servos that jitter due to a worn or dirty pot or overshoot and correct.

Also if you do the test you talk about, do it without the TwinSync installed. The twinsync makes the servo output a little notchy due to a high deadband and filtering on the throttle input. It has to do this so frame-frame jitter from the receiver is not sensed as a throttle stick change. A throttle stick change disengages the syncronizer, moves the servos, then rengages the sync unit.

However, the resoloution of the TwinSync is better than 1% driving the servos but you can not see it until both engines are running and it is controlling the servos. Try running it with the best servos you have and the worst and report on the difference. I am willing to bet what you will find is you will have to slow down the timing with fast servos and speed it up for really slow ones to get the best time to sync. In the end I think you will find the entire system performs the same because throttle response time and your endpoints (higher is better) are the limiting factors.

(I have about 250 assorted servos. I did bench testing during development with everything from Futaba 9452s (0.07sec/60 deg) to some really old 0.4xsec/60deg Kraft servos). The 9452s are amazing servos. They are so fast you can visually see stick bounce if you turn loose of the spring loaded transmitter stick.

OK... I've given out enough trade secrets...

BillS

No experience with digitals but I spent almost half a day attempting to get analog servos to return engines to the same 5,000 rpm high idle setting. With some disappointment I finally settled on a 5,000 to 6,000 rpm high idle range. The experiment had nothing to do with Twinsync but was for engine out simulation.

Conclusion was that analog servo return to position was not very accurate. The spring preload barrel rotation and short throttle rotation arm does not help accurate control of engine rpm at idle setting.

After taking a second look the carburetor barrel rotation will vary between engines from about 50 degrees to about 70 degrees. Most servos will rotate 90 degrees at 100%. A longer throttle barrel rotation arm and 140% travel (or maximum) using all the servo rotation should assist Twinsync in more accurate speed control with any servo. The change will probably also help my initial return to same rpm problem.

Bill

Acetronics

Hi, Bill

Thanks for the explanation. I keep in mind that servos must follow the stick movement as closely as possible without any "hicks" or jumps from a position to another.

May be one day, I'll try the twinsync with two of my KPS 12 Servos ... as there is some clearance in the "lack of bushing" ( LOL !!! ) ... the deadband, seen from the control surfaces is quite astonishing
Some nostalgy of the on/off R/Cs ... may be.
I Still Own an operating KP4B " Series 70" set, I got directly at the factory ( 4 th of the series !!! )

<< OK... I've given out enough trade secrets...>>
... yess, you gave here lots and lots of info [:-] .... shhhhhhtttt !!!!

Make me think it's better to have the Engine RPM following "linearly" the servo position ( think to OS .61 SF and RF W/Pump series where very little RPM difference inthe second half of the carburettor aperture ...). Just play on the servo and carb arm angles for that.

That also follows what Robby said some posts upwards.

And so did BillS !!!

Thanks once more

Alain

Mustang51

My Feedback: (25)

I am going to use this linear servo set-up. I think you guys should consider it.
When it comes to what I'll have wrapped up in my CBA P38, I won't skmp on what is arguably one of the most important components in a R\C airplane, the radio system(servos).

http://www.e-clec-tech.com/lisekits.html

-M51

Acetronics

Hi, Mustang

Why lose torque in such devices as most of your driven surfaces ( or carb drum ) have an axle-to-turn-around movement ??? ...

just give an exponential movement !!! ) to driven things ...

Alain

PS: your shop exhibits ... respectable costs !!! ... and I respect them too much to buy something there !!!

sj3cub

My Feedback: (9)

Hi Bill, I sent you a e-mail about a sync unit and LED display purchase.

Regards,
Scott Morgan

Mustang51

My Feedback: (25)

[sm=72_72.gif]

Blade47

Bill!

Just In case you are not getting my Email ..just wanted to let you know I have sent in my IC for a update...Let us see how long it takes the Dog Team to get there and back

yl5295

My Feedback: (1)

Got it and will be watching for your IC.

jfail1

My Feedback: (2)

I have been using the TwinSync for about two months now and today it saved my plane. I have two planes using the TwinSync, a Hobbico TwinStar with O.S. 25's and a CMP C-160 with O.S. 32's. This morning I was getting ready to fly my TwinStar when I had some trouble in the pre-flight check with the left engine. It seemed to be loading up kinda bad. I re-adjusted the high and low end and all seemed well. I rolled onto the runway for take off and all still seemed well. As I accelerated, both engines came to full power and I rotated for liftoff. Immediately after lifting off the left engine quit. The plane started to roll over but almost immediately the right engine throttled back and I was able to regain control and land the plane. On further examination it was found that a hairline split was present in the fuel line from the needle valve to the carb thus causing the engine to lean out and shut down. Long and the short of it is the TwinSync did exactly what it should do by throttling the running engine back to help regain control. If it had not been for the TwinSync I probably could not have realized what happened right after lift off and reacted quickly enough to gain control and save the plane. I replaced the fuel line and two more flights were without incident. A great product!!!

Acetronics

A great conceptor too ...

Alain

tomlee

My Feedback: (1)

Just ordered one of your units for my Nitroplanes Cessna 337. I am using Magnum 70 4-strokes.

I am wondering if the twin sync will work on an OS 240 twin? Or a Magnum 160 twin?

yl5295

My Feedback: (1)

It should be fine. Customers are running it on .25 glow to 62cc gas.

Acetronics

Hi, Tomlee

The use of a twinsync on a "push pull" is interesting ... let's see.

What if your rear engine overheats and looses RPMs ??? [:@] ( a common feature of ' 337 models ...).

The Twinsync will reduce the global available power, ... instead of letting the front engine pull your plane to bring it back to the field.

Same thing if the front engine looses RPMs.

You'll have then to disengage the Twinsync to keep on flying !!!

So, conclusion ... the twinsync doesn't help you at all for this plane configuration ...

Keep it for " side by side" Engines config.

And do not forget to give a strong cooling to the rear engine ... With or whithout the twinsync.

Alain

PS for Bill ... : in this figure, a device that slightly opens the needle valve would be THE best solution ... ( another goodie from you ??? )

yl5295

My Feedback: (1)

I would disagree Ace. The primary function of the TwinSync is to synchronize the engines so that make that perfect harmonic sound. That would be desireable on a 337 as well as other planes. The latest software has a mode 6 now to disable the idling the running engine in the event one dies. This is for planes like the 337 and the Ziroli DC3 (i.e. planes that fly well on one engine).

I do have an idea for controlling mixture. TBD.

Acetronics

Hi, Bill

Ok for the sound

But, in that particular case, the "hot" engine generally doesn't die ... the twinsync is supposed to regulate ( Ok ??? ) and will reduce both engines, and in that case, ... the overheated engine runs better when closing the throttle.

We'll have a big " RPM Oscillation" on BOTH engines ... if we do not manually reduce the Stick demand. If that case, the speed ( read wing lift ) given by two slowered engines will be far less than that with a live engine at it's full RPM's and careful piloting.

We still have to disengage the sync to get a safer flight ... even and overall if that makes the hot engine stop.

I personnally experienced that figure some years ago on a single engine plane ... while flying back to field just one or two feet over some corn heads ... and engine RPMs widely oscillating.

Nervous breakdown was very close !!!

Back to our subject ... the best we could do here is to idle or stop the rear engine ... cause there is very very little chance the "hot engine" propeller speed gives more airspeed than the flying speed. ( the "pushing engine thrust " comes < 0 !!! = propeller only drags )

Hope my explanation was not so dark ...

Alain