450 DFC Head Design Disadvantage?

[helicc16]

I've crashed two of my Align Trex 450 DFC with the main blade striking the ground. Both times, at least one cyclic servo is busted-- usually the ELE servo. And during the most recent crash, my Trex 600 DFC, one of the cyclic servos sustained some damage,too. I had thought that with metal gear servos, I would not have to replace servos any more.

Based on what I've read about the DFC head, any slop between the head housing and blade grips or teetering movement of the feathering shaft will transmit the force right down to servos, making the servos more vulnerable to impact force during crash. In my case, this has been true.

I am not good enough to benefit from DFC heads, yet I now have to face the fact that I need to prepare to replace servos after each crash.

Please share your thoughts.

 

[pvolcko]

Yes, DFC will result in more forces being applied to the servos directly. Shorter blade links (and usually beefier too) result in less flex and more direct exposure to forces. DFC usually also means direct-to-swash servo configurations, especially on newer design helis. This is good in that it is less part count and easier setup, but it exposes servos to forces more directly and such setups require higher cost, high torque, high speed servos which means more cash out the door to repair/replace. Such setups also either require or recommend metal servo horns, eliminating the last sacrificial part before you get servo damage.

I actually don't know if it is so much the DFC head that's the disadvantage as is the direct-to-swash servo setups. I tend to blame the direct-to-swash setups more than the head configuration, at least when talking swash-driver style flybarless vs dfc. Flybar heads are another deal with lots of protective linkage to dissipate forces before they get to servos, but also complex to setup and full of parts to replace in crashes.

 

[helicc16]

Thank you, Pvolcko. Very good info.

By "direct-to-swash", I think you meant DFC and regular flybarless heads. But I don't remember replacing any metal gear servos when I crashed my FBL helis. Maybe I didn't crash them good enough

I wish they would have come out with plastic servo horn that is stiff enough for DFC but can break before the servos did. I'd much rather replace the former.

Please reread the next-to-last line of the original post. I forgot to put a word in there, making me sound cocky.

Being arrogant is not who I am.

 

[coolgabsi]

Well direct to swash doesn't have to be necessaryly a setup for dfc (direct flight control)

My vibe has a push pull mechanism but that increase part count, reduces total torque and more slop .. But I got the true dfc head in it ... Tracx.


Yes that is a disadvantage of dfc. You'll transmit more forces to the swash in flight and on un scheduled landings lol.

The best thing is to hit THold. And make it come down easier.

More dfc head had been around, there a lot of difference and disadvantages of this design coming forth. The first thing being no flap room for blades. The dfc was a copy of the tracx design with Delrin tubes.. That allowed flapping room and not rigid linkage .. While keeping swash perfectly centered to the grip arms.

Align made it metal and called it dfc. It's the latest and greatest and people love it, sponsored pilots fly it cause they have to

But see that SAB just came out with a non-DFC head upgrade getting rid of their dfc linkages on goblins and going to swashdriver and swash link type head for fbl?

Why .? They realized the disadvantages.. The slop issues and all.. And decided it wasn't good for their helis

I am in no way bashing dfc heads that they are bad or awful. I know tons of people here own that and ill get hosed for doing that, and any way doing that is not right. But just pouring out that yes

Swash servo gears breaking is one of the few disadvantages of dfc.


And no dfc isn't always direct to swash..

450pro flybarred is direct to swash too

Fly safe!! have fun!

 

[Tony]

Yup, DTS just means there is a single, short linkage from the servo arms to the swash. There is a kit where I can put that on the 600, but I'm thinking against it.

What Gaba posted above is very true. When you hit the ground, the blades are going to fold, then the helicopter is going to twist on top of the blades. this is going to cause the blades to force the linkages from teh grips, straight down to the swash, then into the servo that is trying it's best to hold it's position. And the motors on these servos are MUCH stronger than the gears.

Will taking the DFC head off stop you from stripping gears? NO, very simple, NO. You want Proof? Look at all of the people that are stripping out servos on the 450 Pro V2. This is NOT a DFC design, and still strips servos. DFC has nothing to do with it stripping servos.

So what are the advantages of the DFC design? a 1-2cm lower blade height, making the heli rotate a bit faster, putting the CoG closer to the center of the heli making it more stable. There are less parts to go wrong with the reduction of the top ball link. It looks amazing on a heli. There are also bearings in the linkage that attaches to the grips making it much smoother on pitch changes.

The disadvantages of the design are, you are using the grip linkage arms to drive the swash. This is putting unneeded stress on the blade grips. I noticed this as soon as I saw the design and it took a long time for me to warm up to it. But, if you have a dirty swash bearing, you are likely to destroy the link thus making the heli fall out of the sky after doing some really badass 3D lmao. Lets face it, people don't clean their bearings like they should, and most think the swash bearing doesn't need cleaning, but it does.

IMO, the lower head and badass looks make up for the pitfalls of the head. Do I think SAB made a mistake not going with it? Nope, they went to a tried and true design that works and has worked for years. I'm talking since the 60's and 70's when helis first started flying. Yes, they used washout arms with radius arms on them that drive the swash, but it's the same design. They just didn't have the gyros to take that flybar off.

The short answer to this is the DFC swash did NOT cause the servos to strip. Even if you had the 3G head on the heli, or a head with swash drivers, you still would have stripped the servos. It's just that you might have the option of bending the crap out of the linkage thus saving the servos whereas the DFC has a very strong linkage. It's 6 of 1 and a half dozen of the other...

 

[pvolcko]

Yeah, I've stripped one (and borderline on a second) servo on my 300X which is not DFC, but is direct to swash. Where non-DFC will save you is that the blade links will bend or the links will pop off the blade or swash ball, instead of staying rigid and attached and directing it all through the swash and to the servos. So, I think DFC does play a bit of a role in some of the stripped servos in that it will increase the likelihood of it happening.

But the big culprit, I believe, is the direct to swash setups that are coming out now coupled with the push toward more compact control and head designs which reduce link flex and breakage and instead transmit through to the servos.

But I also have relatively little experience at this. Maybe stripped servos have always been an issue and I have no historical context to set me straight.

 

[stokke]

I have no idea if the DFC head is to blame, but I have take out a bunch of servos on my 450. If I crash, I always assume at least one servo is gone...

 

[helicc16]

Wow! You guys have sure done a lot more research on this than I. Not only do you know the subject matter, you can explain it pretty darn well.

We all seem to agree that this a trade-off for simpler parts and sleeker looks. Well, time for me to start stocking up servos because I know I am going crash a lot. It's ridiculous that the replacement gear set cost more than half of the price of a new servo.

Thank you for sharing your insights.

 

[heli-maniac]

i run the dfc head on my 450 and 550
the 450 has ds415 all meta gear servos and the 550 has ds615 metal gear servos
i have crashed both of them and destroyed the blades and havent hurt a servo
the dfc links pop off the swash in a crash if they are put on correct at least that is what i have found