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HomeAircraftHelicopterMain Discussion › bell crank servo arms vs direct to swash
10-24-2013 05:21 PM  4 years agoPost 1
waheed1998

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baltimore,md

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just a newbie seeking to learn.anybody can help me,I want to know is there a difference in flight feel in bell crank servo arms vs direct to swash.Is the cyclic response faster or you just don't feel the difference and it depends on servo torque.School me please.

anthony jackson

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10-24-2013 06:21 PM  4 years agoPost 2
unclejane

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santa fe, NM, USA

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None whatsoever that you can detect. My Whiplash is a DTS and my 700 E uses the Align bellcrank system - can't tell the difference between them as far as precision goes.

My personal preference is the bellcrank system because it's so much stronger than DTS allowing the use of cheap servos, but DTS is easier to setup and maintain... So it's a pick-your-poison sort of thing.

LS

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10-24-2013 06:47 PM  4 years agoPost 3
dodgeboy

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slidell, LA

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Well said. i would also off that usually in a crash the servos in a bell crank system will usually be fine as in the DTS will strip gears more often than bell crank systems. another thing is in bell crank systems, the servos are mostly mounted inside the frame, which is better protection. im sure you will find people on both sides. its a never ending debate

Empire hobby, Gaui USA, OMG servos, Cyclone Blades

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10-24-2013 06:55 PM  4 years agoPost 4
whoamis

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san francisco, ca

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Just got my first bellcrank (Raptor E700) after all direct (TRex, Protos, Logos).

I dig it. Lots of stuff moves when you wiggle the sticks. It certainly offers the heli designer more control over response curves, but I can't say I can tell.

People say the Raptor has a notably precise feel, but it's my first 700 and I'm a duffer so I can't speak to that.

Set up for servo/swash center is actually easier on the Raptor (servo collars) but that glorious feature only matters for about 10 minutes during the build.

The canopy color probably matters more in the end.

oops, bounced it!

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10-24-2013 07:33 PM  4 years agoPost 5
Supertoyz

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Colchester, VT

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I've got both designs as well and agree with all of the posts so far. Can't tell a difference in flight but I prefer the bellcranks. Easy to setup, especially those that use the centering rods, servo protection and I just think it looks cool. I also seem to find the servo's stay cleaner in a nitro machine when they are hidden up front well inside the canopy where they are in a bellcrank system.

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10-24-2013 07:46 PM  4 years agoPost 6
McKrackin

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Lucasville,Ohio

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i would also off that usually in a crash the servos in a bell crank system will usually be fine as in the DTS will strip gears more often than bell crank systems.
The reason for that...

In a crash,the blade absorbs most of the impact.

The remaining energy is transferred to the pitch links which absorb more of the energy.

The remaining energy is transferred to the swash plate which absorbs more of the energy.

The remaining energy is transferred to the links below the swash plate which absorb more of the energy.

NOW...in a bell crank system,there are several more parts that are going to sequentially absorb more energy and pass it along to the next part. Several more steps than a servo to swash set up.

I literally never use the word literally right.

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10-24-2013 08:36 PM  4 years agoPost 7
RCHSF

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NC

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Very well explained Mckrackin. Thanks

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10-24-2013 09:01 PM  4 years agoPost 8
Flying Brian

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St. Clairsville, Ohio

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Yeah, ask him how he knows. ......just razzing you Buddy....

"I just don't Listen" "

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10-24-2013 10:00 PM  4 years agoPost 9
unclejane

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santa fe, NM, USA

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Another reason servo damage is minimized with the bellcrank setup is the push-pull system on the servo-to-bellcrank. In a crash, no or very little side loads are placed on the servo output shaft. So generally, the servo will be jolted in rotation only, just stripping the gears. In a DTS, the servo output shaft gets slammed sideways in addition, so there you have both stripped gears _and_ smashed up bearings/case.

I've had more crashes with bellcranks, admittedly, but the servos there usually survive or nearly do, even in my normal horrific, post-hole-digger rekit-level crashes...

LS

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10-25-2013 01:09 AM  4 years agoPost 10
Shawn Behrens

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DEEP IN THE BOG

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Bellcranks also provide more areas for slop to develop. Also bellcranks can provide another place for tuning geometry if you can find/make different ratio bell cranks. The bellcrank designs have there plusses and minuses. Personally I have no intentions of ever going back to them but I can understand why some are partial to them.

RCROTORPRO
Compass Helicopters

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10-25-2013 01:55 AM  4 years agoPost 11
Dr.Ben

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Richmond, VA, USA

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If you want a control system that provides essentially linear collective change per unit of collective stick movement across the full range of stick travel, an appropriately designed closed loop (push pull) system is the only way to get that result unless you have a linear servo. That aside, in spite of today's extremely robust servos, direct link is harder on servo geartrains. The biggest gripe I used to have with push pull systems was the linkage set up without using subtrim or custom drilling wheels. TT made that a moot point with the quick calibration system.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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10-25-2013 09:19 AM  4 years agoPost 12
1tonv

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Pontiac, michigan. U.S.A.

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well i believe there is a difference in flight between the two. i too own 2 whiplashes and 2 trex700. the bellcranks are alot slower off center stick, while direct POPS HARD off center if that makes sence. i feel a , sort of, lagg like expo. i tune that out using daul rates but i feel the difference. with direct setup is a snap but its harder on servo in a crash. where as bellcranks usually just strip servo wheels

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10-25-2013 01:47 PM  4 years agoPost 13
Four Stroker

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Atlanta

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The servos will last about 4 times as long with bellcranks than direct. Your direct heli has more pop ? Same head ? Same blades ? Same servos ? Same dampeners ? Same TX (JKos) ?

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10-25-2013 03:34 PM  4 years agoPost 14
honda411

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Surprise, AZ USA

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i can agree with the damage to the direct swash servo setup. Had a few break after a crash. Like the setup much much more and the links are a little easier on the finger tips during the build.
But the bellcrank is way to go i think. Servos protected as mentioned above, and wont break the servo nearly as much as a direct setup.

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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10-27-2013 08:47 AM  4 years agoPost 15
1tonv

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Pontiac, michigan. U.S.A.

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All helicopters are Exactly the same, if they weren't Iwould never have posted as I am well aware of all the different variables

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10-27-2013 09:05 AM  4 years agoPost 16
Volcano

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chicago

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I hate my outrage 550 bellcrank because the elevator strips when the blades touch the ground. On my goblin I use relatively weak servo arms so they are the weak point, and less trouble to replace.

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10-27-2013 11:51 AM  4 years agoPost 17
unclejane

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santa fe, NM, USA

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Some helis put a bearing on the other end of the servo shaft to try to help support it. It's kind of a kludge, but may help with this shortcoming of DTS. I believe one of Avant's models has this and I vaguely remember seeing it on some others, tho can't recall which ones at the moment.

I'm hoping DTS eventually just dies down as a fad and we can go back to good bellcrank arrangements eventually. When building my Whippys it was kind of nice because it was so easy to setup and maintain, but it makes me a little nervous. Especially the prospect for the servos in a possible crash...

LS

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10-27-2013 12:19 PM  4 years agoPost 18
Flyagra

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Singer Island, Florida

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Tracking blades is more work with bell cranks if there is any slop. You can't just adjust on the bench with a pitch gauge and know it will be perfect - you still have to fly it and watch.

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10-27-2013 12:39 PM  4 years agoPost 19
rpat

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Weirton, W. Va.

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Dr Ben
What are you talking about when you mention TT has a Quick calibration system? Never heard of it, tell us more.

trex 700fbl cal30,minititan,, trx600fbl,trex250,logo 500,Velocity N2

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10-27-2013 02:29 PM  4 years agoPost 20
Dr.Ben

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Richmond, VA, USA

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This picture works better than words, but basically all the bellcranks can be locked at 90 degrees with an included tool, all rods except the two to the blade grip are premade and fixed length, and the included servo arms allow for centering without subtrim because they very securely clamp to also included servo output adapters.Thus the whole baseline mechanical set up takes about 5 minutes. The system is used in the E720, G4/4.1 nitro, E820, and the E700.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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HomeAircraftHelicopterMain Discussion › bell crank servo arms vs direct to swash
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