Trying to get 2 Hitec 5645's digital servoes to work on a y harness for split elevators. Nothing happens if both servos are plugged into harness. Disconnect either and the other servo will work. System works fine with 2 none digital servos plugged in. I'm using an Eclipse 7 tx.
Thanks for any help.
Brian

brian,
You need to use the radio to reverse one of the servo's or get the hitec programmer and reverse the servo. You cannot get your setup to work with a Y harness. If you don't want to get the programmer return the servo to hitec and let them reverse it for you. Once this is done your setup will work fine.

I had the same problem with digitals, went with a seperate channel, has something to do with the digital servo electronics. I also had a problem with a servo reverser on a digital servo.

Vince

I have several GS models with as many a three HiTec Digital servos wyed to one servo extension with know problems.

Are using a buffered, boosted or amplified wye? A servo reversing wye?

Why not use the TX and program a channel to run the second elevator servo?

Bengen,

I experienced the same problem. See my posts on "Ask Mike at Hitec, on 5-26-02".

I could make it work on individual channels but not with a Y on one channel. I tried with an amplified Y and it worked with no problems. I believe it is the problem of the combination of the loading of the Hitec digital servos on the Multiplex receiver. I could get two standard Hitec servos to work on a standard Y, but not two digitals.

Also, when I connected a digital and a standard servo on a standard Y, only the digital worked! Go figure.

Has anyone else had this problem on the Multiplex 12 channel IPD receiver?

Thanks for all the replies. Gotta love these forums.

Gill,
I tried using a standard and digital together this morning and only the digital moves same as you experienced.

I have reveresed one of the servos with the Hitec programmer.

I'm using standard y harnesses. no buffers, amplifiers, reversers.

I could use 2 channels but don't know if the trim will work for both servos with the Eclipse At this piont looks like I will find out today.

I'm using a Hitec Supreme FM/HFD-08RD receiver.

BENGEN,

Until now I thought the problem was mostly the Multiplex receivers ability to drive the multiple digital servos. Mike at Hitec wasn't aware of the problem. But now that I see you are having the same problem using a Hitec receiver then maybe Mike should become aware of the problem or should do a little investigating.

I am using 11 Hitec digitals, 56xx and 59xx in a Super Reaper and 7 of the leads are about 48" long. I am going to fly this first with a rear mounted Moki 1.35 prop engine. I'm considering using buffers on all the long leads to insure a good signal to the servos and to help prevent any possible interference pick up, especially when I install the future turbine.

Has anyone had experience using the dual series hex inverter logic noise buffers
( www.uoguelph.ca/~antoon/gadgets/noiserx.htm ) ?

The CD4069 circuit is good for 4 or 5 cell applications. The 74HC04 and 74HC14 versions are best if used only with 4-cell.

BTW, are any of you (with this problem) using 5-cell packs? If so, throw a 4-cell pack on the Rx and see if the "Y" connected digital servos work better.

Thomasb,

I have only used 4 cell battery supplys and intend on using only 4 cells in flight, except perhaps two 4 cell units in parallel.

Have you used the circuits as presented in the Tony van Roon article? Any problems? Do you know if this circuit is essentially what you get when you buy a buffered extension or Y?

Several years ago I used the CD4069 to buffer some servo signals. Worked fine for me. I have no doubt that it will cheerfully restore operation on your ganged Hitec digitals.

Be sure to build it to withstand the rigors of the model aircraft environment. Do not under estimate the harsh vibration levels that some models exhibit. Do NOT use a socket on the IC (as tempting as it may be). If building circuits like this is not your cup of tea then run down to the RC hobby store and buy a factory made solution.

There are several designs out there. This is just one low cost way to do it.

I am going to have to try an duplicate this problem. So far this seems to be a problem that is experienced with the 56** series servos, I have seen no mention with the 59** series. I am aware that all the HiTec digitals are using the same digital amplifier's, I think it would be safe to rule out a difference with the amps. The 56** are 3-pole motors and the 59** are coreless motors.

As I mentioned I have several Giant Scale models with wyes and HiTec 5945 digitals on 6volt Duralites. One model has [3] 5945's with one custom wye per stab half and the same basic setup with [3] on each wing section. Never had any problems with the wyes. I am using unbuffered plain old custom wire length tailor made wyes. One per stab or wing that allows me to connect all the servos to itself and then provide enough wire length to make it to the fuselage connection point. These are made to fit the model possibly the lack of multiple connectors and extensions is creating less resistance. I noted that someone mentioned the addition of a boosted/amplified wye solved his problem.

Well,,,

I have tried:

2 tx's - my Eclipse and a Prism 7X
2 rx's - both the same model # as above
Different freq. as I have the Spectra module
4 and 5 cell battery packs
y - harnesses from 3 manufactures 2-6" and 1-12"
5645 and 5625 servos

And in a last ditch effort tried an old Futaba "gold box" and AM receiver both 15-20 years old. WORKS GREAT...

Conclusion is that I believe it is in the receiver. I may very well be wrong but can't think of anything else. Will be talking to Hitec on Monday to let them know to make their stuff work I have to use another manufactures equipment. Really hope Hitec can prove me wrong or show that I'm doing something incorrectly.

The outputs of many receivers can only drive a 5K ohm or lighter load due to their CMOS driven servo signal. I have a feeling that the offending servos are conflicting with this limitation.

If you have a good ohmmeter then unplug the servo and measure the resistance from its ground to the control signal (across black and yellow). Reverse the meter leads and record readings both ways.

Standard servos are usually 20K to 50K ohms. What are yours?

I took another look.

First test:
Tried the Y with two HS5645MG servos- neither would move at all, not even a twitch.
Tried with only one HS5645MG on one leg of the Y- worked OK.
Tried two HS225MG standard servos, worked OK.

2nd:
Tried the Y with two HS5945MG servos- both worked OK. (I hadn't tried these before).

The tests were done with a Multiplex 12 channel rcvr on 4 cells.

3rd: Measured the resistance of various servo's inputs between the black negative and the signal wires with a BK Precision model 2845 autoranging multimeter:

HS5645MG 12.26 Megohms
HS5625MG 13.02 Megohms
HS5945MG 11.22 Megohms
Another HS5945 10.63 Megohms
A standard type servo, HS225MG 56.5 Kohms

All of the ohm readings of the digitals were polarity dependent- switch the leads and the reading was infinate ohms. The standard servo read about the same resistance either polarity.

I was surprised at the high resistance of the digitals. I thought they were loading the receiver outputs too much when two were connected. I tried the resistance readings with another multimeter, a Micronta digital model 22-185A, confirming the high ranges although not exactly the same readings.

I think I will look at the receiver outputs on a scope without, with one and with two servos to see what pulse voltage is.

Later.

Jerry,

Interesting measurements. Perhaps the digital servo uses a stiff passive pullup resistor. What is the resistance between the servo signal and the battery [+] lead (yellow and red)?

BTW, the servo pulse amplitude from my Hitec 8-Ch Supreme Rx is 3.2V (driven into a standard servo). I'm not sure how your digital servo conditions this signal. But, if it is a direct connection to the servo's microcontroller (unbuffered), then lower amplitudes would start to cause trouble.

Also, check to see if the signal's "ground" voltage rises when the digital servo is plugged in. A substantial ground voltage differential (ie, if the pulse's low edge becomes elevated above ground) will cause trouble too.

Thomas,

I will look for the low voltage part of the pulse to see if it rises. I'll also check the pulse when I load it with a regular servo to see what is happening there.

So my test (maybe later today) will be no load, single servo load and double servo load for 5645s, 5945s and 225s.

Resistance check from positive to signal wire:

5945 6 Megohm, polarity dependent ( 0 meg probes swapped).
5645 0 Megohm either probe polarity. Hey!

I'll post when I get the pulse scope data.

I only have an old analog volt/ohm meter but will second Gill's readings.

Called Hitec this morning and they said they don't recommend using Y harnesses. Well then start making 15-20 something channel receivers to handle all the servos in the larger planes (40%), and radios with enough mixes to get them all to work. I told them my Futaba stuff worked fine (with their servos) and should probably switch back.

Try changing the ohmmeter scale to something that can resolve a few K ohms. The exact value may be revealing.

Thomas,

My readings were not 0 Ohms, they were infinite Ohms, no reading.

Sorry, haste makes errors in communication.

BENGEN- Are you just using a standard "Y" and no extentions? How long are the leads? Are you using a votage regulator? Have you tried different digital servos or just these two?

I would have thought this would have shown up before now if it were a problem.

You may try using another "Y" and plug the batter directly into it bypassing the the RX.

I'll do some checking here to see if we can duplicate the problem.

Mike.

Mike,

Please read my post #12 in this thread. I think it answers your questions.

Standard Y harnesses and 5645 and 5625 servoes.

Mike,

My tests were run with a 12" long Y with 20 gauge wire and a 24" long Y of standard gauge. No extra length beyond the Y's.

I have 4 5645s and 2 5625s. I tried all combinations of 5645s and 5625s in dual and single servos. All the singles worked and all the duals did not work.

I tried your suggestion of using two Ys with the battery plugged in one of the Ys and two servos in the other two plugs, still no cigar. A single works, two do not work.

I am using 4 cells, nominal 4.8volt pack, charged, no regulator.

These are the servos that were reworked by the factory so as not to lock up, or whatever. They have the sticker.

I am ready to try any other reasonable test you want to try, Mike.

Just for a data point, I use 2 5645's on a long Y to drive elevator. One of them was reversed for free by Hitec . I use a 6v pack and a Futaba PCM reciever. Works fine. Identical motion even though I haven't tuned the servos beyand what Hitec did for me.

The only time I had a problem was before I had the servo reversed. I was using one of those reversing y's, and it didn't work out. Gave similar result to those shown here.

BTW - no worries on current draw on these puppies. I just read the test results published in the sailplane column of Model Aviation from February. These things draw a rediculously small amount of current per oz-in of output. Lower than the other digitals AND regular servos tested(like, half).

While I was at the LHS this morning I tried to duplicate the problem first described, NO LUCK.

I removed a two HiTec Eclipse TX's with Spectra modules and RX's from the boxes and pulled ten 5645's from the boxes two standard HiTec wye harness's set-up the RX's and wyes and servos. No problems at all on aileron, elevator and rudder.

Everything worked fine.... The servos tracked equally across the board with ten servos and two radio systems...

Is it possible the the specifications and or tolerance's for specific components, i.e. resistors or capacitors maybe outside the desired parameters thus causing this phenomena? It seems to me that most of us using these servos are not realizing this problem and the handful that are may have equipment that is for some reason providing results that differ from the rest us...

Mike and other respondents,

Just a point of clarification. I am taking part in this discussion to help solve a potential problem. I can easily solve my immediete problem by connecting my two canard elevators in to two receiver outputs, or if I felt confident in the buffered Y, use one of those.

I am really impressed with the Hitec digital servos to this point. I have a Hitec programmer and can set the servos up to be a match for all my surfaces.

I also am impressed with the Multiplex receiver to this point. The combination of versatility of both of the hobbys latest technologies is astounding.

However, when I connect the combination in a well used configuration (two servos Y'd) and find a problem of non compatibility, I start to be concerned. Is the Multiplex rcvr a borderline unit? Are these particular Hitec servos borderline? It makes me wonder if there is a marginal specification that could drift such that a working unit today will be a non show during flight. I have too much invested to not be concerned.

So, I want to know what is happening, what is the problem. It's looking like there is more than one brand of receiver with the problem (At least Multiplex and Hitec). I have two Multiplex 12 channel receivers and they both respond the same way, same problem. And multiple 56xx servos exhibit the problem. This problem should be easy to solve.