skywarrior

Hi
I owned a Skymaster hawk for one maiden flight due to the failure of the elevator servo HSR-5995TG.
This servo was chosen because it claimed on the box to deliver 24kg @ 4.8 volts and 30 kg @ 6 volts. It was chosen instead of 2x JR 8511 @ 15 KG each being the normal set up used by many on this model. The reason was to eliminate one servo weight ( I wa electing for a lightweight engine and fuel installation) and reduce the risk of bad servo matching.
I ran the systen at 4.8 volts through a "Powerbox system" with 2x 2100 Li poli packs for power supply. The model crashed due to lack of elevator power, it failed to pull up on the first turn although when crashed it was all functioning electronically and was therefore subject to a pits autopsy by many well known top modellers and shop owners. The elevator moved in proportion to the stick but did not have much power when held back by hand.The voltage was measured at the servo lead junction to the servo and it was 5 volts !
I susequently did my own torque test useing hand weights and setting the output take off on the servo arm to 1 cm ( ie inside hole) It picked up 11 kg and failed @ 17 kg. This is far short of the word on the box ie 24kg @ 4.8 volts. which is what it says on the box.
The response from hi Tec was:

Quote

"The 8511 is the same servo as the 8611A in the USA and it appears to have a rating of 15 kilo at 4.8v where the 8611A has a higher rating only due to the different testing method. The 5995/5955 are only slightly more powerful than the 8511’s, not over double as you indicate. It would be advisable to use two 5955’s for better performance but one is marginal. "


Here in the UK the JR importer Mc Gregor states the 8511 digital Jr servo will give 15 kg if using two of them that make 30 kg. The Hi Tec HSR 5955 box says 24kg @ 4.8 volts for one servo NOT two.

Anyone had any similar problems ? Or is this a case of it does not do what it says on the box ?

XJet

When it comes to the power and speed of servos I take *all* manufacturers claims with a grain of salt.

Hitec make some damned fine servos and the 59xxTG range are currently acknowledged as the best in their class -- but I believe (and independent tests prove) they're not as powerful as claimed. I gather that Hitec have a servo torque-testing base on the moon, right next to JR's similar facility :-)

I've got some TG5955 servos but I bought them beccause I wanted a geartrain that would wear out in a high-vibration environment (like a big gaser) -- not because I believed the outrageous torque figures being quoted.

Despite the fact that I could (if the manufacturers claims are to be believed) use just one for my elevators, I'm going to use two -- because there's no such thing as "too much control surface power".

I note that you've said you've got 5995 servos -- aren't they the robot ones?

Don't forget that there are a number of other factors which could have affected your installation:

1. was your linkage stiff enough for the flight loads that were exerted on it? (this includes the stiffness of the elevator itself -- if the horn was in the centre, can the ends blow-back with a high amount of aerodynamic pressure while the centre remains correctly elevated?

2. are you using greater than 100% EPA/ATV? I believe that Hitec recommends against the use of excessive transmitter EPA/ATV with these servos and that they can go to sleep for a second or two if overdriven in this way.

3. could you have a faulty unit?

4. was the 5V you measured sustained under load?

5. Hitec say that the quoted torque figures are "peak" or "instantaneous" or something. The point is that the servo will begin to reduce the drive to the motor if it detects that things are getting too hot. This means that its *sustained* torque is no where near the claimed figure -- but at least it wont burn up like the JRs have been known to.

I think it's about time we started a "honesty in advertising" campaign aimed at *all* servo manufacturers -- not just Hitec.

lrb75

My Feedback: (12)

The hitec 2006 catalog states 250inoz (18kgcm) of torque at 6v and 333inoz (24kgcm) of torque at 7.4v If you only had 5V then you won't even have 18kgcm of torque as you experienced. The 8611a has 260inoz ~19kgcm of torque @ 4.8v according to the horizon hobby website and the 8511 15kgcm. At best if the box was correct you only had 24kgcm of torque. Either way you didn't have as much torque as the recommend setup.

skywarrior

Hi there and thanks for the reply. I enclose a shot or two of the current Hi Tec catalogue which is self explanatory. Maybe they have changed things lately but this is the info I worked to as published.

skywarrior

Hi just a note to say that I agree that if anything comes of this thread it may be that manufactures will publish a more honest or at least a specification that we can all relate to our hobby more easily. For instance most modellers might think that the test rig I have shown above is what they think to be a fair representation of the servo application for an aircraft set up.

It is not constructive to publish figures based on the max torque avaialble when the servo motor is at full speed or for an breif instant. That leaves us in "Never land" as far as I am concerned and we therefore need more directly related info than seems to be available at present.
Purely my opinion and I am sure there are other views. Perhaps it would be good to here some.

Regards

dirtybird

My Feedback: (5)

Very interesting. If I were you I would sue Hitec for false advertising

skywarrior

Hi
It would be very interesting to see the spec. you quote in print and its source. Why would two sources be so different?

dirtybird

My Feedback: (5)

I checked at the Hitec web site. It still lists the 5995 will provide 333 oz-in at 6.0V and 416 at 7.4V
The best I can get out of the one I have is 221 oz-in at 6.0V. Maybe I should send it back and ask for one that will provide 333 oz-in.

lrb75

My Feedback: (12)

You have the wrong servo for airplanes. The 5995 is for special robot applications and is 180deg output. The numbers I quoted were for the 5955 which is the standard TI geared servo for normal airplane applications. People are talking about different servos. I found an old post from Mike Mayberry that says the rating for the 5995 at 4.8V would be about 270inoz of torque. Did you reprogram the servo for normal throws or did you just reduce the throws at the transmitter? Lowering the throw on the radio could possibly reduce the max output of the servo as well???

dirtybird

My Feedback: (5)

The Hitec WEB site lists the 5955 at 333 oz-in on six volts. The best I can get out of the three I tested is a little over 200 oz-in. Maybe I should send those three back, too. Come to think of it I did send one back. I burned it out trying it on 7.4 V. Hitec replaced it with no questions asked

skywarrior

Hi, this will probably answer some of your queries. However the servo was reprogrammed useing the Hi Tec programmer. All throws were below the 100% ATV max and the linkage was a refined ( no catching /no hard points / no slack ) original of the "Skymaster " linkage as used by thousands of others.




David,

The 8511 is the same servo as the 8611A in the USA and it appears to have a rating of 15 kilo at 4.8v where the 8611A has a higher rating only due to the different testing method. The 5995/5955 are only slightly more powerful than the 8511’s, not over double as you indicate. It would be advisable to use two 5955’s for better performance but one is marginal.

While the specs are similar there are a couple differences. The input is 900-2100us on the normal servos including the 5955 where it is 1100-1900 on the 5995, also the 5955TG has a heatsink case for additional cooling which improves overall durability. Basically, there should be no reason to use the 5995 when the 5955TG is available for the same price and is suggested to R/C, where the robot servo is not. Again, that is not to say that it will not work, just that the 5955TG is suggested due to the reasons I listed.



Mike Mayberry
Customer Service Manager
Team Manager
Hitec/Multiplex USA

icaro

...mmm

Sorry, but... are you shure that your installation test are ok?


Best reggards,
Luis

DKjens

My Feedback: (50)

skywarrior,
In post #1 you say the Skymaster needs 30Kg on elevators. You state that on the box of the HS5995TG, it's rated to [email protected] and 30Kg@6V. You say you ran it at 4.8V, so you say right there, that with those numbers you are 20% below recommended torque.

In post #4 you post pictures showing the HS5995TG is rated to 24Kg@6V and [email protected], where did this information come from, since it's different from what you state in post #1?
Also, your photo of you test setup shows the servo plugged into the Rx, not the Power Box. The Rx gets its power through a small servo wire in that setup, the servo in no way takes any advantage of a sizeable power bus, why even have the Power Box attached in this test if not simply as a voltage regulator?

I have never seen the HS5995TG servos with a torque rating at 4.8V. I have run these servos at 7-8V, but prefer to run them now at 6.5V, as I do with the HS5955TGs as well. I can tell you there is a substantial and very noticeable difference in the power of these servos from running them at 5V and running them at 6.5V. Running them at only 4.8V makes absolutely no sense to me, especially in a setup as yours where you use LiPos and a PowerBox.

Lastly, to my knowledge Hitec has never ever recommended these servos to be used in radio controlled airplanes. Because they will only recognize a signal from 1100-1900us, if atv is not turned down to a bit below 100%, they will react weird when moved to the "high" signal end. You may have had your elevator set to give up at the high (1900us) signal end, and if your atv was to large, then the servo will act in the following way: If moving your transmitter stick fast to that side, the servo will stop before reaching the extreme. Then, when slowly moving the stick back, the servo will first move further out towards the extreme and then start moving back to center.

One thing is that your setup may not have had nearly the torque needed, another is that the servo would have been slow and perhaps exhibited the scenario described above. I don't think anything can be blamed on Hitec, but rather a wrong use of servo and less than desireable setup.

DKjens

secretsg

In the photos you've provided they both clearly state 24kg rating only comes at 6.0v. Where did you get the 24kg @ 4.8v from?

adrenalnjunky

My Feedback: (18)

same question as secretsg here - all the pics posted of the box, and ServoCity all agree - 24Kg is listed at a 6v spec. 30@ 7.4v.

If you were regulated to 5v - then that's why you were nowhere near the 30kg mark you say your model required, and even at 6v you would have been under the 30kg mark.

mglavin

My Feedback: (31)

What size servo and control horn is utilized on the Skymaster? If the ratio is not favorable you got problems @ 5V...

JohnMac

Interesting,
Why do you feel that the SM Hawk requires this amount of power on the elevator. Mine has only one servo on the elevator, a 8511 and it works just fine. What engine are you using? How much travel did you have on the elevator? On my first flight I set elevator rates to low since the elevator movement looked to be huge. I soon realised I needed full travel on the elevator. I am Using a Wren Supersport in mine.
Regards,

John

Geistware

My Feedback: (16)

I would say if you were testing at 17kg on 4.8 volts then you were close to the rated specifications for this servo.
If anything, your test proves that the specifications are close.

skywarrior

Hi there and thanks for your interest.
I have re viewed the details of the servo and taken note of the posts in this forum and have to admit to a misreading of the spec. Yes I was wrong to say that 5volts gives 24 kg. Unfortunately I threw the box away and have had to get details from a friend who has an original box. Usually the specs are for 4.8( 5volt) and 6 volt output and I have overlooked this and read 5 volts for 6volts. I must admit to never having seen the 5 volt spec omitted from any servo I have used so far but there you are its my mistake and I must admit it.
To cover some of the points you have made I can confirm that the servo was installed in the aicraft via the Powerboxbus bar and not in the rx output shown in the pics. This however would only be an issue if my understanding is correct if the rx was unable to handle the current and went into failsafe on the bench test. This has happened to me many years ago along with many others which is why I was very keen to use the Powebox when they first arrived in UK. The advantage being that over long runs it amplifies the voltage and in larger model installtions so there is no loss at the servo. I can confirm this with others as we maesured the voltage with a meter on the crashed model ( carried like a just still breathing patient to the pits. It was 5 volts at th junction of the servo to the servo lead. My reason for using the single servo was to eliminate ganging two together as used by many others including Ali and David Galdwin (see his article Jets) my understanding was 24 kg was ample for this purpose but as we now know it was not 24 kg at 5 volts. The bench test failed around the 17 kg max and I mean max. In fact it faded to 17 Kg not stopped at kg not picking up 18 kg. Therefore I would conclude probably useful power much lower than this. I was using a Wren Super sport for power and the pilot was John Palmer who is reconised as one of the best for my test flight. The linkage was slightly modified for the better ( friction loss and robust joiner from one end to the other) I will if anyone wants to se this provide a pic. Having trouble with camera but will post it soon. The atv was set to normal 60 travel by the way.
Sum up I read it wrong BUT I still am very uncertain about the real pulling power of this servo but will be convinced by others now maybe.

Regards
David

mglavin

My Feedback: (31)

Warrior

What are the control and servo arm lengths?

Why not utilize MAX servo resolution/ATV with the appropriate servo/control arm length and make use of MECHANICAL ADVANTAGE? In this scenario you’ll be able to multiply the servos available lifting FORCE by the ratio realized for MAX servo angle…