ace0811

Is the use of a servo programmer mandatory to get digital servos to work properly. I just insalled 5 brand new hitec digitals in a new plane. When I move a stick and let go, the control surfaces return to a different position everytime, up 1/8" from center. This makes it impossible to trim the plane and almost impossible to fly smoothly. Since this is my first experience with digital servos I have no Idea what is required. Some of the trouble shooting I've done is to make sure there was no slop in hinges or linkages. Its all tight. Then I thought it might be worn out sticks on my radio but none of my other planes do it. I find it hard to believe that I just happened to get 5 brand new defective servos(not gonna rule it out though) Any Ideas out there? PLEEEEEZ[]

The Ghost

Digitals will do that with PPM recivers, You need a PCM reciver and no you don't need a programmer to get them to work right.

Cheers

Rcpilot

My Feedback: (78)

Sell your Hitec digitals and buy some JR digitals. Problem solved.

I'll bet you bought the 56xx series of hitec (5645 or 5625). Am I right?

All those are is a pumped up 645 or 625. BOTH of those servos are well known for not centering worth a c**p.

I crashed a 25% aerobatic plane because my Hitec 625 MG servos wouldn't center. I moved the aileron to the right--and the right aileron would go up. But, when I released the stick, the servo would return to center and then stop with the aileron abour 3/8" LOW. They were going beyond center before they stopped. Move the stick left--and the right one goes down. But, on the return trip--it's hung up 3/8" HIGH.

Same thing with left aileron. Move stick left--and left aileron goes up. Release stick and left aileron returns to center and stops 3/8" low.

Same thing with the elevators.

These servos just don't center good. Not at all.

Pumping them up with digital circuitry doesn't make them center any better. It gives them great holding power. But, it doesn't improve the centering.

Hate to be the one to tell ya. But I ain't lying. I'm telling you straight.

If you bought some other series of Hitec digitals (5945 5975 whatever)--then I still say that you can eliminate your problems with JR servos.

Hitec makes some decent servos. Unfortunately--their digitals and their 6xx series don't center very well.

Ernie Misner

Huh? Why don't they pull the bad servos from production... quick?!

Ernie

ace0811

you guessed it, 5645's. So i guess I'll go ahead and get different servos. If I were to try a PCM reciever do I need a radio that is PCM also or will my Futaba 6EXA (which i think is just FM) work ok?

Gringo Flyer

My Feedback: (18)

You have to have a PCM tx to use a PCM rx. If your radio is both you should have a menu that allows you to switch between the two.

ace0811

Thanks for all the input folks. I think I have a plan of attack now. GET DIFFERENT SERVO'S

MikeMayberry

My Feedback: (1)

There are many factors here and the statement that all digital will do this unless you use PCM is not even close to being true. Also the statement that switching to JR will make all your problems go away is a stretch as well... that is one mans opinion. JR does not even offer a servo to compete against the 5645 so you will have to spend twice the money on their servos. Hitec offers high end servos for higher prices too that will inprove performance. The 5955TG servo costs the same as the JR servos and is now being touted as the best of the best by giant scale pilots who are just looking for the best their money will buy. Do a search on this to see for yourself. The 5645's are one of the most popular servos on the market for a reason... they offer good bang for the buck.

Now... let's try to solve your problem instead of just assuming the servos are junk.

How is your linkage set up?

How long is the horn and where is the linkage attached?

How much travel do the surfaces have and where are your EPA's and Dual Rates set?

These are factors that will affect the servos ability to center the surface. Yes some servos center better than others but these servos should work for you as the do for many thousands of others.

If you have a long control horn of the servo mounted on the outside hole, even a small amount of movement will move the surface a long way... if you then use the EPA to reduce this throw you will affect the resolution. You need to utilize the entire throw of the servo to get the desired movement. This is where 3D throws will have an affect on the centering and it is best to go with a coreless motor servo for more precision.

If you want to talk about this in person, give me a call; I'll help you get it set up right.

Mike Mayberry
Hitec RCD Inc.
(858) 748-6948 x 302

exeter_acres

My Feedback: (2)

I use 5645's on my Showtime (among other planes) and the centering is spot on...

(and I love my 5955's too!!)

MustangFan

In my opinion ... You don't need different servos.

I have used the 56XX series servos - the entire year actually... purchased at the beginning of this year.
They worked well on my Warbirds , PW Extra and SUKOI (sp ?)

Have you tried them yet ... or are you basing the opinion on the slam stick test.

Try this, Move the stick full up ... release the stick as you normally would ... check center ...do again .. check center ... Bet it's the same.
You may have a slight different center moving the stick down, then releasing ( called deadband ).

Realistically ... this has not caused ME any problems flying ... if I was competing ... maybe ... but probably not ... most just adjust stick inputs as required to fly the plane.

In normal operation, once the plane is trimmed for straight and level ... have not seen any bad tendency's.

redfox435cat

needing pcm reciever to use digital servos is BS. In fact there is no differance between PCM and PPM recievers. the only thing PCM does is hold position or go to a predetermined position with the loss of signal. There is no differance in the way the signal is broadcasted or decoded. It's still an FM carrier in (PPM it is a digitally replicated FM carrier) with a 1-2 ms digital pulse signal riding on it that tell the position of each channel


as far as the digital servo thing. It's the servo. I've never liked Hitec anything. they have always been the cheap altiernitive with the quality to go with it. People swear up and down about the quality. the only thing I see better in quality is thicker rubber gromets. Inside they'er junk. There bare basic HS 311 is OK for basic use like retract air valve or throttle. I've had 3 Hitec micro servo flat fail, and have had the same bad centering with the digital servos.

If you have JR stuff get JR digitals If you have Futaba Stuff get Futaba Digitals. I got 10 futaba 3151's and they are great low level digital servos.

MikeMayberry

My Feedback: (1)

To simply lump all Hitec digital servos into one catagory and to immediately say the servos are no good is very shortsided.

Here's some interesting reading.... while is it targeted to the car guys it still applies to the aircraft market as well. http://www.hitecrcd.com/servotech/performance.htm

Here's some other interesting reading as well... http://www.rcuniverse.com/forum/m_3597179/tm.htm

I'm still here to help if anyone wants it... I'll keep my body armor on though!

Mike.

mglavin

My Feedback: (31)

A digital servo, any digital servo is better than its analog counterpart. It’s simply the nature of the digital amplifier that makes all the difference, better precision and more power again will be realized as compared to an analog counterpart. That said digital servos are comprised of the same components as there analog cousins less the amplifier in play. Cored motors verses coreless motors are another determining factor for realizing increased precision, speed and repeatable results all else being equal.

The qualities of the components servos are comprised in Hitec’s circumstance are as good as there OEM counterparts in nearly all cases. All this stuff is out sourced there are only so many variables available to manufacture these components, either the components meet or exceed the OEM requirement or not. The specifications of the individual amplifiers are the only significant OEM variable IMO. Hitec digitals all use the essentially the same digital amp tuned to motor specific variables of each servo. Engineers plastic, assembly techniques and technology are all basically the same gear-train alloys and plastic formulations are proprietary. Electric motors and potentiometers are sourced too, in fact ALL Hitec Digitals use the same high quality feedback potentiometer as JR uses in there high end digitals. JR’s refitted top cap and re-powered 8611A uses the same motor and vendor Hitec specified from the gate for the 5955/5995TG servos.

Hitec digitals are shipped with the deadband parameter set to "2" of 9 possible settings. With a Hitec Hand-Held Programmer one can lower the deadband to 1 of 9. This will increase the servos ability to offer better repeatable results.

The 3-poled cored motor of the 5600 series digitals is not as precise as a coreless motored digital servo. A coreless motor can infinitely stop and hold the position commanded of it, whereas a cored motor will always rest or stop between the poles, therefore precision is a factor of same. That said a Hitec 645MG high power sport servo with a the atypical metal gear-train tolerances and cored motor maybe more powerful than other standard servos its still a standard servo on steroids with like precision and deadband. Moving up to a Digital 5645 will garner increased precision and power but its still a cored motor unit with metal-gear tolerances…

PPM does off some degree of precision not afforded 1024 PCM systems. It’s a numbers game. There are 1200 steps plausible with our TX’s, our radios typically have a MAXIMUM pulse width swing of 600 micro-seconds either side of center. 1024 PCM modulation utilizes 1024 steps while PPM utilizes 1200 steps total swing. Additionally as mentioned previously EPA, travel volumes or end-point percentages drastically affect the steps available for control responses. LOWER percentages numbers with MAX throw setups throw out hundreds of finite control step positions, thus causing coarser or notchy control response. Another variable is the trim button response of the TX in play, some are programmable parameters (i.e., high end TX’s) while others are fixed values, what this means is trim value for each step might be 5 micro-second as compared to a more precision setup with 1 micro-second response.

mglavin

My Feedback: (31)

While I agree one does not need PCM equipment to use any servo, there are huge differences in an analog RX as compared to a PCM RX.

There IS a difference in the modulated signal of PCM and the subsequent decoding of same. Yes its all done with an FM carrier. Previous to being transmitted PCM is encoded at the TX and decoded at the RX, whereas PPM is simply comprised various or multiple channel pulse position data hopping a ride on the carrier.

ace0811

OK Folks, problem solved!! Apperently (I'm still a beginner) when you have a really long servo horn and you have your plane set up to get upwards of 60 deg of travel on all control surfaces, the tiniest amount of servo movement is amplified by the time it actually gets to the control surface, DUH! By moving the pushrod in a couple of holes, closer to the pivot point of the servo, the amount that the servo didn't center by got significantly smaller, to the point I hardly noticed it and the plane flew normally. The drawback is I also got a significantly reduced amount of throw. All this, combined with the fact that I have a bottom of the line radio (Futaba 6EXA entry level computer radio) ended up being the culprit. I barrowed a Rx and Tx from a buddy which was a Futaba 9C and without changing anything in the set up of the plane the problem completely went away. I guess my 6EXA is ok for .40 to .60 size planes with analog servo's. Since I'm uprading the type planes I'm flying, I'll just have to upgrade my radio too! I never would have been able to figure all this out without the help of everyone who responded to this thread. Thanks everybody. The support is greatly appreciated.