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Hitec 5645 servos, Are they good servos?

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Hitec 5645 servos, Are they good servos?

Old 11-07-2007, 09:45 AM
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LostMyPlane
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Default Hitec 5645 servos, Are they good servos?

building a Extrem Flight 74" yak 54 (brillelli combo) should come out about 12 to 13 pounds, has anyone had any problems with Hitec 5645 servos? The manual from EF suggest these and I know they are a great company, but someone told me they "Think" they have centering problems. If anyone knows these servos please let me know.

Max
Old 11-07-2007, 09:54 AM
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rcdude7
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Default RE: Hitec 5645 servos, Are they good servos?

I have some in a 28% WH extra. They do not center as well as the more expensive Hi-tec servos. If I were flying IMAC, I would probably go with something better. For $45 ea. what do you expect?

BTW, there is a forum just for servos and other radio gear, you might get a better responce over there.
Old 11-07-2007, 10:00 AM
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LostMyPlane
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Default RE: Hitec 5645 servos, Are they good servos?

thanks...was looking for a forum about servos...will look harder. Will mostly fly it for sport 3Ding. do you think the better servos are called for?
Old 11-07-2007, 01:43 PM
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hvac
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Default RE: Hitec 5645 servos, Are they good servos?

i have them in my 30% Yak, on the wings and elevator. they have developed a lot of slop and one of the aileron servos stripped. i would recommend Hitec 5955's all around. Maybe a little overkill on your plane, but you can use them on anything. I have one on my rudder. Very good servo.
Old 11-07-2007, 01:53 PM
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Rcpilot
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Default RE: Hitec 5645 servos, Are they good servos?

It's the same servo as a 645 non-digital. Those don't center worth a darn.

All the 5645 is--is a digital circuit board. That's got nothing to do with the actual POT that centers the servo. I wouldn't use them if you expect any type of precision.

I'm a JR guy, so I'll stop telling the truth about those Hitecs now. Don't want to hurt anybodys feelings.

You want a servo that centers? Buy a JR or Futaba.

You don't need digitals on that airframe. It's only 74" And you don't need metal gears either. Thats a "trend" thats caught on in recent years. Do you know what the guys were flying on their 35% birds 15yrs ago? Standard nylon geared servos. They just used 4 of them on a rudder and 2 of them on an elevator.

If I was going to rig that 74" plane with a gas engine, I'd put JR4721 coreless servos on it. They are 120oz torque and will center everytime. Use a 6v battery and you got a 150oz coreless servo thats just about bulletproof on a smaller airframe like yours.
Old 11-07-2007, 06:15 PM
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Jake Ruddy
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Default RE: Hitec 5645 servos, Are they good servos?

Spoken like a true JR guy - he forgot to mention than JR cost an arm and a leg for gear replacements which JR need constantly
If you want a good servo, good centering, and don't have to replace gears every 60 flights you buy Hitec 5955s like most Hitec and all the JR guys who woke up do

Sorry RcP I couldn't resist



The 5645s are known to have a centering issue... personally it's not as bad as some make it out to be. If you are just knocking it around and doing sport flying then you will be fine. If you want precision flying you need to move up to the 5885. The issue is that if you are going to spend the money for 5985s then you might as well spend the extra $20 to get a 5955 so that in a year you dont have to spend $17 for a new gear set.

Lets not forget with 5955 they are usuable in every airframe you grow into as time goes on.

Hope this helps
Old 11-07-2007, 07:21 PM
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KenLambert
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Default RE: Hitec 5645 servos, Are they good servos?

I have them on 3 planes wh edge, wh ultimate , laneir 87" edge and haven't had any problems I don't fly Imac but I do 3d and just plane ol fly they work fine for the money in my opinion
Old 11-07-2007, 07:29 PM
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Panzlflyer
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Default RE: Hitec 5645 servos, Are they good servos?

Buy a JR
The last one I had died within an hour from new.
Buddy of mine has flown 2 35% with 5645s in the wings without issues for at least 2 seasons. They arent the best but then again they dont cost that either.
Old 11-07-2007, 09:50 PM
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Default RE: Hitec 5645 servos, Are they good servos?

It's *not* the pot that centers the servo, the pot is only a feedback device that the amp uses to determine the position of the servo output.

The centering is down to the type of motor used and the deadband provided by the servo amp.

HS5645 servos have a pretty standard pot that is used in a *lot* of different servos (some very good, some not so good).

The real reason a 5645 isn't as precise as a coreless digital such as the 5945 or 5955TG is that it has a wider deadband and the 3-pole motor has very significant "lumps" in its torque output when expressed against the rotation of the rotor. ie: at some positions, the motor produces a *lot* of torque, at others it produces a lot less.

This means that if the commanded position corresponds to one of the "low torque" positions of the motor armature then it may not actually reach that position. It's also common for servos using cored motors to be designed with a wider deadband (ie: accuracy) to avoid them "hunting" back and forth. This is because the armature of a cored motor is *much* heavier than that of a coreless. It Simply can't start and stop quick enough to hold a very precise position without overshooting and oscillating back and forth. If you want to se what happens when you try to use a very tight deadband with a cored motor look at the TowerPro MG995 -- it's not pretty.

The *least* important aspect of a servo's centering is the pot itself I'm afraid.

But, back to the original poster's question...

The 5645 is a good mid-range digital servo. No, it won't center as well as a 5945 or 5955 coreless servo but it's a lot cheaper.

For most fliers (short of competiti9on IMAC) its resolution and accuracy will be more than adequate.

I have four HS645 servos on the ailerons of my aerobatic (Extra 330L) gaser (2 per surface) and they work perfectly well with no centering problems -- the digital version (5645) can only be better. About the only bad thing I'd have to say about these servos is that they are way too slow for my flying style on 4-cells and just "adequately fast" on 5-cells or A123s. (6-6.6V).

There is a lot of "religion" in RC gear but I buy mine solely on what represents the best price/performance ratio.

I have Hitec transmitters for my beaters, a JR transmitter for my good stuff, receivers by Berg, LightFlight RC, Hitec, JR, and Polk, some Hitec servos, some OEM'd BlueBird, some Futaba and some JR.

I'm totally agnostic and brand disloyal so I like to think that my comments are totally objective.

JR servos are fine, but in the larger ones they just seem to chew gears at an alarming rate. It was for this reason that I went for HS5955TG servos for my gaser and I've not been disappointed.

Futaba servos are fine, but the price performance ratio (in the 120=150oz/in metal geared range) just isn't there.
Old 11-08-2007, 08:21 AM
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Default RE: Hitec 5645 servos, Are they good servos?

X-Jet

Excellent explanation of how a servo works, I have a 645 on the rudder of my 82" gas Extra and its works, 4" servo arm and turnbuckles rods on both sides of the rudder so its a true push pull system, I do not notice any cerntering problems at all, and I use 5955's on my bigger stuff, the only difference I can notice in flight is the speed of operation, what more can I say.

Futaba: difficult to get discount on high end servo's although very good quality.
JR: don't want to swap out gears at the end of every season.
Hitec: 5955's for $89 at Troybuilt models, I am from the UK and buy from TBM, price can not be matched in the UK.
On smaller stuff,
Hitec 645 for rudder and 625's for the other surface's
Futaba 3152 good quality fast strong servo.

All the above is IMO and has worked for me.

Mike
Old 11-08-2007, 09:19 AM
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Bob Pastorello
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Default RE: Hitec 5645 servos, Are they good servos?

xjet - EXCELLENT servo post, and right on the money. Brand loyalty means nothing if performance or cost/value compromises must be made. I also have run the 5645's (GP Ultimate, 50cc gasser, all four ailerons) and they were WOEFULLY inadequate in terms of speed, even on 6v system. There just is NO comparison in performance between a 3 pole motor and any flavor of coreless.

I used to be a JR 8611/8411 junkie, like many.

Converted to Hitec 5955 TG's after less than 10 flights on a 30% Yak with new 8611's developed gear slop - BAD.

Now, I just save my nickels and buy the 5955 for any application, just because of the gear train.
Old 11-08-2007, 09:34 AM
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mrbigg
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Default RE: Hitec 5645 servos, Are they good servos?

The cheaper servo's have cheaper componets and you can't expect top of the line performance at midgrade price levels. That's what I was told by a manufactuer's rep in a forum here a while back.
Old 11-08-2007, 01:12 PM
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bbagle1
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Default RE: Hitec 5645 servos, Are they good servos?

Don't know if thiis has been said yet but if you have access to a hitec servo programmer you can set the deadband to zero and it really seems to help these servos. Mins centered much better after I programmed them.
Old 11-08-2007, 01:35 PM
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Rcpilot
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Default RE: Hitec 5645 servos, Are they good servos?

XJet, I disagree with you about the pots. They DO have an effect on the centering of a servo. The pots in the lower end Hitec servosd are known to be poor quality. I guess thats why Hitec replaced the pots in the 645 servos I had. They wouldn't center and I sent them to Hitec for service. They all came back with new pots. Perhaps Hitec doesn't know how to service their own equipment?

You guys are all slamming JR about gear problems. I've been running the same 8411 servos in a 50cc airframe for 4yrs and I haven't needed to replace the gears. They are as tight as the day I installed them--some 450 flights ago.

But, thats not the servo I recommended to him anyway. I recommended the 4721 coreless. Those are nylon gears and they don't wear out in a season. I've got about a dozen of those servos in various large models and have been flying them HARD. Not a single gear related problem from any of those servos in 3 or 4 yrs of flying in 50cc size planes.

I never said they were cheap. I just said they would work.
Old 11-08-2007, 01:51 PM
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Bob Pastorello
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Default RE: Hitec 5645 servos, Are they good servos?

rcpilet - I think if you polled giant scale fliers, you'd find that your experience is really unique and not anywhere near the 'norm' that most folks have suffered with JR metal gears. Experience varies between users; that's what makes discussions good things to have....MY experience taught me quickly.

Your experience has been exceptional, and that's a "good thing".
Old 11-08-2007, 04:21 PM
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Default RE: Hitec 5645 servos, Are they good servos?

My vote is also a no to 5645. Very pool centering. Have sent two to Hitec for repair and both came back the same. I would not even use them on non giant-scale applications.

5945 and later models are good though. Futaba servos (e.g., 9101 9202 etc nylon-gear ones) are also good on centering.
Old 11-08-2007, 04:46 PM
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Jake Ruddy
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Default RE: Hitec 5645 servos, Are they good servos?

I think aerobob pretty much hit the nail on the head there...

I am surprised Pat Roy hasn't chimed in.. he has flip flopped back and forth between the 2 companies and is now running 5955s for the reasons being discussed.
Old 11-08-2007, 04:57 PM
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MikeMayberry
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Default RE: Hitec 5645 servos, Are they good servos?

The digital circuit does make a big difference in the centering ability of this servo vs. its analog brother. In my experience they felt very similar to the analog/ coreless 945MG servo (now 985MG) in the air.

The JR4721 in certainally a valid option, but for that price you could go with the 5985MG or 5955TG which offer even higher performance.

Most people feel the 5645MG's work very well in sport/3D models, but if you are looking for an ultra precise servo then you should opt for the 59XX series.

Mike.
Old 11-08-2007, 08:01 PM
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Default RE: Hitec 5645 servos, Are they good servos?

Why do I have to pull 4 8411s and put in gears in less than a year?

Putting any nylon gear servos in control surfaces of a gasser is a no-no
Old 11-08-2007, 09:23 PM
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Default RE: Hitec 5645 servos, Are they good servos?

It depends a lot on vibration. Soft mount your engine and you will save a lot of gears. Also static balance your control surfaces will help.
Old 11-08-2007, 10:08 PM
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XJet
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Default RE: Hitec 5645 servos, Are they good servos?


ORIGINAL: Rcpilet
XJet, I disagree with you about the pots. They DO have an effect on the centering of a servo. The pots in the lower end Hitec servosd are known to be poor quality. I guess thats why Hitec replaced the pots in the 645 servos I had. They wouldn't center and I sent them to Hitec for service. They all came back with new pots. Perhaps Hitec doesn't know how to service their own equipment?
Poor pots *can* wear more quickly than higher quality ones and that can cause centering/accuracy issues after a while -- but a poor quality pot does not mean bad centering out of the box. Believe it or not but you'd not notice the difference between a $50c pot and a $5 pot until the former started to wear.

If you have a servo that was working well but starts to jitter around center then there's a good chance that the pot is worn but if it centers poorly from new then the fault lies elsewhere.

You guys are all slamming JR about gear problems. I've been running the same 8411 servos in a 50cc airframe for 4yrs and I haven't needed to replace the gears. They are as tight as the day I installed them--some 450 flights ago.
I think most of the people reporting worn gears are flying gasers with large (aka "heavy" control surfaces. This setup can hammer a gearset and case much faster wear than when the same servo is used (say) on a warbird with much smaller and ligher surfaces that also have far less mechanical advantage against the servo.

However, it's been my observation that (for some reason) JR's gears still wear out quicker than Hitec or Futaba when used in exactly the same kind of setup and airframe.


But, thats not the servo I recommended to him anyway. I recommended the 4721 coreless. Those are nylon gears and they don't wear out in a season.
I'm sorry but your "x-spurtise" is showing again :-) Nylon geared servos are *not* suitable for gas-powered planes (especially an aerobatic ship like a Yak). The stresses put upon them by a vibrating gas engine and those large control surfaces is just asking for trouble.
--------------------------------------------------------------------------------
XJet
Old 11-08-2007, 10:19 PM
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Rcpilot
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Default RE: Hitec 5645 servos, Are they good servos?

ORIGINAL: XJet
I'm sorry but your "x-spurtise" is showing again :-) Nylon geared servos are *not* suitable for gas-powered planes (especially an aerobatic ship like a Yak). The stresses put upon them by a vibrating gas engine and those large control surfaces is just asking for trouble.
What do you think guys were using 15yrs ago when there were no digitals? Guys flying giant scale 35% gasser planes were using nylon geared servos because thats all they had. They were using 3 and 4 nylon geared servos ganged together and adjusting them mechanically. You might want to confirm that by talking to some guys that have been flying these giant airplanes for more than just a couple years.

Don't forget, the original poster is flying a rather small airframe. It's 74" and it might have a 50cc engine at best. Nylong gears will work just fine.

I installed JR8231 NYLON geared 88oz digitals on the elevators of my 80" World Models Patty Wagstaff with G62 engine. Flew it 450+ flights without a single gear related problem. Actually not ANY problems. It would still be flying today if I hadn't slowed it down too much and knocked the gear off on landing.

This MYTH that gas airplanes need metal gears is just that a MYTH.
Old 11-08-2007, 11:08 PM
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Panzlflyer
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Default RE: Hitec 5645 servos, Are they good servos?

I think they were not flying what we fly today nor were they flying how we fly today some of those sevos were twice as big with half the torque and sorry if this upset some but the World P Wagstaff is not exactly 3d by todays standards.
Old 11-08-2007, 11:37 PM
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Rcpilot
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Default RE: Hitec 5645 servos, Are they good servos?


ORIGINAL: Panzlflyer
but the World P Wagstaff is not exactly 3d by todays standards.
Never said it was.
Old 11-09-2007, 12:13 AM
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Default RE: Hitec 5645 servos, Are they good servos?

I have flow gasser with both nylon and metal gears, from my experiance nylon gears have been stripped by gasses as small as 40cc BUT "only when engine is out of tune" or unbalance prop,

the times I have stripped nylon gears on gassers has been when I am tuning the low neddle and the engine starts 4stroking hard the vavrations are so intense you will see waves in your covering and nylon gears will strip.

would I recomend nylon gears on a gasser, depends. I would use nylon gears only if i woldnt care to much about what I was flying, if its a nice new shine plane please use metal gears unless you dont care tomuch about the plane.

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