Hi Guys,

Alot of guys have been asking for some pics. I'm using a new direct drive system on my new Carden Yaks for this season. You can see the system at DurantDirectDrive.com for more info.

System is slop free, with no parts to fail (i.e.control horns or ball links). Very good system and can be installed in any airplane, even after the plane has been covered.

Rick

I saw a system similar to this a couple years ago on a plane that flew during an intermission at an SAE heavy lift competition in Fort Worth. Was this you?

My only question about the system is what are you losing, if anything, when it comes to having no mechanical advantage with the absence of different size servo arms and control horns? In other words, are you getting just as much power to the surface with a direct connection?

Gary H.
Rantoul, Il

i believe you lose power. The machanical connections add leverage force.


Tony Fandino

Yea u lose ton's of power. Would probably work okay on a 35% but not much bigger.

-Kelly

This setup seems as god as it gets for 3D planes where lots of throw is needed. As for IMAC, not an advantage IMO. Since most can't afford to have one plane for freestyle and one for sequence flying, I think the setup should appeal lots af poeple. I explain :

If a standard setup gives 60 degrees of surface movement and 60 degrees of servo movement then the direct drive system is as good if not better since the aforementioned advantages.

If a standard setup gives 20 degrees of surface movement and 60 degrees of servo movement (like in IMAC only planes) then the direct drive system is not better as the standard setup offers MUCH more resolution.

There isn't any loss of power. This setup is currently in a 42% Ulimate, that has been put through everything possible. No flutter, no blow bye, a solid setup. It does knife edge loops all day long, and how ever many you want to do. If this was a loss of power setup. The rudder and everything else would be flatting out! Right! This plane and the other 2 Extra's on the website are also flown in IMAC. No problems. They fly very well, I have flown all of them through the Unlimited sequences and some of the old TOC and Masters Unknowns that I have.

When I get my Yaks together, I plan on running torque test against standard and direct drive setups. I'll post the findings.

Gary-- I wasn't fly the Yellow Extra there, I was flying the red one.

Rick

One potential benefit of this system would be that you lose the nonlinearity associated with our current arm/pushrod/horn setups. With zero expo on a direct drive system, the surface should move exactly linearly (at least as linearly as the servo being used). Most people would probably still use some expo, but if nothing else it may make it easier to compare expo values between setups which may have different length pushrods, servo arms, control horns, and different control horn locations relative to the servo.

Baron

As true as could get .

We now have super duper torque servos (5955) but we still need super duper precision servos. If I had all the money in the world, I would still not use this setup on an IMAC only plane as the resolution would still not be there.

I don't have all the money I would need so I must settle for a single plane for 3D and IMAC. I feel the need for precision in my sequence flying but I have to live with that since my plane is setup for 3D...

For when the ultra precision servo [:@]??

Very cool idea I was just first concerned about the mechanical advantage issue. On my 42% 260 I have one 9152 per stab and at 140% i'm at 45 degree's of throw and some high speed I can get it to block back a little. It's ingenious and has many benefit's and if you don't notice any blowback, which definetly depends on the servo then it's definetly a cool idea. It's just hard for me to imagine loosing what extra torque I have left on my elevators.

-Kelly Gerber

Hey guys,

You've all got really good points and valid concerns. I worried about the same things when I first came up with the idea, but the system proved to be even better than I hoped.

Mechanical advantage was a necessity in the old days, when servos were weak. As servos improved and Quique showed us what can be done with 60 degrees of throw, the need for advantage went out the window. If your servo requires mechanical advantage to move your surface, you probably need to upgrade your servos. Plus, remember that a linkage becomes less efficient as you move away from center, whereas Direct drive maintains 100% efficiency at all points of motion. However much torque you have at the servo shaft, you get more of it to the control with direct drive.

Resolution is the next issue. You are all absolutely correct about gaining resolution with a reduction linkage - in theory. If you use leverage to reduce your motion by 1/2, you should double your resolution. But, this logic neglects the deficiencies inherent to a linkage setup. Linkages have a small amount of play. If they had no play in the joints, they would bind - and any play is a loss of resolution. Add to this the deflection you get from the rubber servo mounting grommets, the deflection from servo arm twist, the deflection from the control horn...well, let's just say you are loosing much more resolution from your linkage than you realize. Increasing the amount of leverage just increases the forces imposed on the linkage, and that makes all of the deflections worse.

When you add it all up, you lose all of the theoretical resolution you thought you were getting from your linkage - and then some! Direct drive does not suffer from any of these resolution robbing problems.

Hope this helps...John

Good points!

I can add that on my planes, the main source of slop is from the metal gears of the servos. I also use the 5955 and this one is about as good as new and has not developed slop over the entire season I flew with it. I use Du-Bro giant scale horns and H9 titanium pro-links with ball links (very standard setup) and I can't notice any slop. There MUST be some, but I can't see it...

I have a question. If you use this system and have any servo issue how do you get to the servo for service ?
This has to be one of the most interesting threads i have read in a long time. Really gets you thinking.....
I would like more data on this type of setup.


Tony Fandino

Getting to the servo is just a matter of removing the hinge pin (I usually use a single pin made of .047" piano wire for all the hinges) and sliding the servo out as you remove the control surface. To remove the servo from the control, you remove the servo shaft retaining screw and pop it off. The whole operation takes less than a minute.

Here's a neat trick for the guys still stuck on the resolution issue...I have been building two sets of control surfaces for my planes. One is undersized, for IMAC precision. The other is oversized, for 3D. Each surface is all set-up, with the servos attached. To switch from one to the other, I remove the hinges and swap the servo/control assemblies as a unit. Since I use Matchboxes, I plug the second surface into the remaining ports in the matchbox, which are pre-programmed for that particular surface. It takes about 3 minutes to convert my plane from ultra-precise IMAC to hot-dog 3D.

I've got a trick to negate the servo gear slop too...if you are running dual servos per control. It envolves intentionally offsetting the neutral points to "take up the slack" in the gears. Be very careful, though, because you can fry a servo in short order if you offset to the point that the servos fight each other. This is an advanced technique I would NOT recommend until your flying is good enough to notice the gear slop.

John DuRant

That's a cool idea, and with some recent experiences in breaking a hinge, it isn't a bad idea to have removable surfaces on normaly setup airplanes.

-Kelly Gerber

Very Very Interesting .......

This is very cool, keep the free flow thinking going. Is this the same as running a 1:1 IE 1 inch servo arm and a 1 inch horn on my linkage as far as power is concerned.

I saw a guy do something similar to this on an US 1000.

He had built a pocket in the control surface and lined it with formica (cabinet top). It was a very snug fit for a piece of piano wire. He bent an angle on the piano wire and then hooked the piano wire directly to the servo.

The piano wire slid inside the pocket in the control surface, and because it had a bend in the end--rotating it via the servo output shaft caused the control surfaces to move.

It was a very slick setup, and he had no exposed control linkages. It was all buried inside the plane.

Needless to say--the plane wasn't very draggy.

That is an adaptation of the RADS system that has been around the glider world for several years. Seems to work very well. Slop free, neat and clean.

Is there any concern about weekening the wing structure by cutting in to what amounts to an aft spar? It is my experience that the trailing edge adds some strength otherwise we would just add hard points for hinges. Please don't take me wrong, I really like the idea and may consider doing it. I would like to see it on a bunch of different designs first.

Dan

I haven't noticed any apparent weakness from cutting through the hinge line.
That is my yellow plane on his website (121" span 42#'s) and I bent my wingtube bad enough that I almost couldn't get it out of the plane, so it has been put through its paces.

You have to remember where the wingtube ends on your plane and I would recommend not putting one right at the end of it, but inside the wingtube the wingtube will take the load and the closer you get to the wingtip, there will be significantly less leverage.

I haven't lost any sleep over it

John

I have to second ricks statement about ample torque. John has a $2% ultimate and if the surfaces are drooped when he turns on his radio they leap into perfect center! His plane is 40+ pounds and has a 3w 212 4 cyl. I have seen him put it through some violent near full speed maneuvers and it is as solid as a rock.

You do not get something for nothing. With a convintional system you can make big throws by lessining your mechanical advantage and you loose torque but gain speed. You can set up a plane for presision and gain torque through mechanical advantage, but you loose speed.

I think the direct drive system is the perfect balence, and the cost is less for this system than buying HD Ballinks, titanium rods and long aluminum servo arms. It also makes the plane safer. With a convintional system you have 6 potential single point failure points the servo arm, the ball connection to the servo arm, the ball connection to the rod, the rod connection to the other bakk, the other ball to the control horn and the control horn. You only have the connection to the servo with the Direct Drive system.

Just my 0.02

I too have seen the Direct Drive on several planes competing in Sportsman thru Unlimited in the SC region. Mostly Unlimited. Never a problem. It appears to be a very clean installation and a well thought out design. I will have to consider it on my next build.

Ryan

Respectfully, I disagree...

If you are talking about a 3D setup, ok. But if we want to do precision flight, a good linkage can actually REDUCE the free play. With the Direct Drive, your surface will have the free play of the servo gears. Ok... but with a good linkage, we can make the small gear play almost disappear: the result is that the surface is rock solid with almost zero play!

How can this be done? Properly choosing control horn & servo arm lengths, no mistery. For the interested people, I posted some math formulas on the pattern forum some time ago. The drawback of course is that you loose the amount of throw, but if we are interested in the best resolution, power and precision of centering a good mechanical setup is better by definition - it's physics.

Hey Guys,

I finally got around to some more pics. I'm running a bit behind on the new Yaks. Here is the direct drive system mounted in the horizontal. It's really simple to install!!!!

Rick

Well I guess that is one way to do it. Why would you go to a system like that? Is it only to reduce failure points?