Why use digital servos in TD ships?

[oscillator]

Yesterday I was talking to a guy who consistently finishes near the top in our local TD contests and he stated digital servos were a waste of money in unlimited TD ships. He wasn't talking Oly's - but Pikes, Supras, etc. His reasoning was TD flying is very imprecise compared to say pattern flying - and when you were hunting around trying to core a thermal with the plane 1000 ft up and half a mile down wind, what good was a precision servo?

Certainly his argument has some merit - and his flying results speak for them self. Then again, there are some guys who could probably dominate with a beat up EZ glider on a worn out high start - that doesn't mean the Supra on a winch isn't more capable.

It seems obvious that a digital servo would hold a more precise camber - but I can't claim to have done scientific testing to determine the most optimum camber on my wing. Nor can I claim that 1 or 2mm of camber makes a significant difference (might, might not. Again, no easy way of conducting an accurate scientific test).

So how about it? Why do we really put digital servos in our unlimited TD ships? My honest answer? Because every one else does and because they are "better" servos. Until now I have never stopped to ponder if better gains me anything in my application.

-Mark

[gklimber]

And let the fur fly !!!

jer

[John Walter]

Digis have greater holding power and more precision. We need holding power during launches (ever seen an F3J launch on a windy day?) and high precision for camber adjustments for speed, cruise and thermal modes.

I rely on Mark Drela for the correct camber on my Supra. I can't prove the extent of performance improvement due to camber changes, but I can see the difference in the air.

I might pose the question in reverse - why would I put $20 servos in a $1,500 airframe?

[schrederman]

I guess I'd have to call upon my experience flying full-scale to answer this one. I know my trailing edge settings were pretty accurate on my PIK, and the linkages were tight. Two degrees degrees made a lot of difference at times. When I'm flying my models, regardless of what they are, I want to know where the surfaces are, and not guess. As cheap as I am, I have bought my last cheap servo. I lost a couple of models to bad servos. I'm not saying digitals don't go bad... but I am finally thinking they're better than the cheap ones.

Just my take on it... your mileage may vary.

JW

[rdwoebke]

So how about it? Why do we really put digital servos in our unlimited TD ships?

Mark,

A while back, somebody either here on rcgroups or on rcse actually did some "rough" scientific testing on a plane with an altimeter and tested a few different servos and he claimed that he could extract more out of the zoom launch with a faster servo on elevator. This probably means digital. I don't know where the post was/exactly who it was, but my reccolection is it was somebody in Europe.

So, when I put together Psyko #2, I went with a reasonably priced and quick (by the specs, but also by watching the thing it sure seems faster than my other servos) Hitec "mini" (not micro) servo on my elevator.

Ryan

[mlachow]

OK, he picked one point, flying a thermal way downwind. Now what about launch. What about landing, what about having the airfoil at the best setting during zoom or min sink when there is no lift.

And of course all the designers totally wasted thier time designing the airfoils and everything else. And especially the machine time to make a precision mold. That was a total waste.

I'll bet the faster response of a 2.4 system is also a waste on a thermal model too.

[Hossfly72]

I'll bet the faster response of a 2.4 system is also a waste on a thermal model too.


LOL, anything faster than AM is overkill if you fly the way I do!!!

[nuevo]

The launch issue has been well covered. Holding power and precision at holding that position. To me, the most compelling position for a digital is the elevator, due the precise centering and repeatability. I can give just one click of down trim and tell the difference in the airspeed when trimming.

Rudder would be the least necessary for a digital, IMHO.

That said, I've used nothing but digitals for several years now. It's like having to go back to a "regular" TV after owning an HDTV.

For each, it's a personal choice, strongly influenced by one's frugality and/or commitment (addiction) to our sport.

[Robglover]

So how about it? Why do we really put digital servos in our unlimited TD ships? My honest answer? Because every one else does and because they are "better" servos. Until now I have never stopped to ponder if better gains me anything in my application.

-Mark

Mark -

You and your buddy are correct. You should never use digital servos. Nobody else should use them either. You would be better off trying to find some really old AM radios as well. While you are at it make sure that your pushrods are a little sloppy and your hinges have some play in them as well. Your gliders will definitely fly better.

[oscillator]

I'd have to agree with the digital on the elevator for centering accuracy.

It's the wings I'm wondering about. I guess I should go measure how much better a digital servo centers than a decent analog servo. The point is somewhat academic though - since saving $20 each on 4 servos in a plane that costs close to $2k is almost moot.

Still, I have to ask myself - how much does it really improve things? I've seen more than a few high end sailplanes built up with analog servos. I always thought it was kinda silly to put cheap servos in a nice plane. I wonder if we are the silly ones just purchasing what the marketing departments sell us.

Mark (who still has all digital servos in all his big TD ships)

[Mark Miller]

I agree with Rob. Same as I see no reason to have radial tires on your car. Radials are a waste of money. Goodyear Polyglass works well for me and I'll save a few bucks to boot.

I'm gonna go check eBay for some ABBA 8 tracks for my Nash Metropolitan.

Mark

[O.L. Adcock]

Personally I don't use high quality servos because of their centering accuracy, I do so for speed and torque. I can daned sure tell the difference......O.L.

[Hossfly72]

I don't want to fan the flames or anything, but I wanted to ask a question about digis since it was here. Do you have to have a special transmitter to utilize them correctly or will any transmitter work? Also reciever? I've never had a need for super accurate centering or that much speed since I fly floaters mostly, but I'm curious.

Thanks,
Hoss

[DOWN WIND JIM]

If Digital Servos Were $10 And Analog Were $20 Would You Say:
Why Put A $10 Servo In A $1500 Plane !?

[Mark Miller]

If digital servos were $10.00 we would not be having this conversation. If analog servos were $20.00 they would not exist. The only reason they do exist is because they are cheaper. Not because they are better.

I can get you some hickory shafted golf clubs cheap.

Hoss.... Digital servos work with any transmitter and receiver. It has to do with how the amplifier in the servo processes the radio signal.

Mark

[VH-ASC]

Yesterday I was talking to a guy who consistently finishes near the top in our local TD contests and he stated digital servos were a waste of money in unlimited TD ships. He wasn't talking Oly's - but Pikes, Supras, etc. His reasoning was TD flying is very imprecise compared to say pattern flying - and when you were hunting around trying to core a thermal with the plane 1000 ft up and half a mile down wind, what good was a precision servo?

-Mark

Proves my theroy that some modelers are the cheapest people in the world! No problem to spend $1500 or more on a plane and then put the cheapest servos, batteries, hardware.. etc, in it. WHY?????

Really, at 1000+ feet how can he tell that his glider is not hunting and drifting due to poor centering? Maybe if he spent the extra money on some good digital servos he would be at the top, not hear it.

Don't get me wrong though, there is a place for analog servos too. I use some good bb Hitec isn my Sagitta 900 and they work great. My TD and DLG glider I have digitals. My DLG there is no trim cenetering issues at all.

Also with bigger gliders don't forget about the holding power of digitals. Full tourque all the time. Analog you have to deflect the arm to get full power (blowback).

Jeremy

[Bryan Quick]

Here's an analogy. If you wanted to shoot a rifle in competition using iron sights, would you rather have a rifle that groups 1" at 100 yards or 0.1" at 100 yards?

This is the same argument used in the rifle community over and over. 'You don't need a rifle that shoots better than the smallest scoring ring on the target.'

So, when you choose your equipment you must make a variety of decisions to stay within the contraints of your budget. One philosophical position states that digital servos are probably one of the cheapest areas to upgrade the quality of the entire system that comprises your gear. The other position is summarized by 'you won't notice the difference, so why bother.'

So, as was stated earlier in the thread, why use better radios and airframes if you don't take advantage of them with good servos that are as exacting as the rest of the airframe and it's components?

[Ralph Weaver]

I'm about to build an 3m E-Topaz. Obviously no winch launching. Is there any reason to think that I'd notice the difference using digitals? Maybe only on elevator? I can't think it would matter on the spoilers.

I haven't chosen servos yet and would be open to any advice.

[VH-ASC]

I'm about to build an 3m E-Topaz. Obviously no winch launching. Is there any reason to think that I'd notice the difference using digitals? Maybe only on elevator? I can't think it would matter on the spoilers.

I haven't chosen servos yet and would be open to any advice.

Ralph,
Agreed, you could use an analog on spoilers, tow release, and even rudder if your trying to keep the cost down. Remember the digital has way more holding power that may be important if your spoilers are big and used at high speeds. Other than a floater type glider I'd use digitals on the main flight controls from now on. Once you use them with a tight control system you will never go back.

Digital vs analog is like 2.4 gives you more feel than 72mHz. I thought that was total BS but a few of my friends who are long time fliers and skeptical too have said it is a very noticeable difference. Same goes for digitals.

Jeremy

[nuevo]

Once you use them with a tight control system you will never go back.
I hope this comment isn't too OT...

Any benefit of digitals is negated if you don't have a tight control system installation. That means zero slop at either end of the pushrod, no binding of the pushrod, no slop in the surface hinge, no tape pulling loose, solid servo installation, and a fully supported pushrod that will not flex when you force the surface to push against it. You can even have slop in the threads that hold the clevis.

In the last month, I helped solve some bad behaviors of a few friends airplanes that each had multiple symptoms listed above. Just sloppy linkages were the primary cause of erratic behavior on one plane.

[Charged]

Well i say why digitals are better , no doubt they arent . We had a f3j contest this weekend and two of my friends were competing ,both had Tragis with analog hs.125 or something and guess what both of them servo centerpoints went off and settings got lost . First one didnt get to the finals and other fried in the finals .So im putting digitals to my Tragi .