big_G

As a relative noobie in AMA pattern competition (2 years), my flying coach often mentions to me that I fly a little "twitchy" at times, like starting and stopping rolling maneuvers. (I have about 60% expo on all surfaces) I just bought some new servos and at 6 volts they are VERY fast. Just throwing it out there...are our servos getting too fast?...I mean, a full scale plane and pilot would be much slower on the yoke during pattern maneuvers. Slower servos would no doubt smooth the inputs a bit.

speedracerntrixie

My Feedback: (29)

I would tend to think that 60% expo is a good indication you are still using too much throw. I tried using the servo speed option on my radio once, the resolution went out the door. I would suggest dropping your expo down to 35%-40% and adjust your throws to have just enough to get you through the sequence. This may mean you will have to set up a rate switch for spins that would have more elevator and rudder throw.

mmattockx

Servo speed has nothing to do with how smooth you are on the sticks. The perfect servo would have infinite resolution and would follow the stick movements perfectly with no lag at all. If the plane is twitchy it is either set up incorrectly or you are not smooth enough with your stick inputs. I bet speedracerntrixie is bang on about the control throws.


Mark

big_G

Yea, it's probably me. I fly thumbs, and perhaps pinching the sticks will allow more precise movements. I need to give that a try.

mmattockx

Crank the spring tension up a bunch, too. Most radios are sold with the stick tension set super low and that is not conducive to precision work.


Mark

Anthony-RCU

My Feedback: (2)

Several good suggestions here but how much throw do you have?
For most pattern stuff around 12 degrees is plenty for maneuvers. If you are flying a sequence with snaps and spins then conditions will be necessary but try lower rates.

big_G

Anthony...My throws are about what the plane asks for. The dilemma is I have the servo link on the inner most hole without the ball link hitting the stabilizer opening, and the other end on the outer-most hole on the elevator horn. I already have the travel volume set at 50%. I don't want to lose too much servo resolution. I'll try raising the stick tension on the TX and see how that goes. Thanks for the feedback, guys.

bjr_93tz

The 14MZ had and I'd bet the 18MZ would have as well, adjustments for Sensitivity and Hysterysis for the inputs from the sticks. From my dim memory, the sensitivity adjustment was for slowing down how fast the changes in the stick position were fed into the servo position information and the Hysterysis adjustment was for taking the shakyness out of the stick inputs, so servo speed isn't the only game in town if stick jerkyness is something you just can't fix.

There's subtle difference between these adjustments and the servo speed adjustment which it also has.

Large amounts of expo also encourage people to stab at the sticks because nothing happens around the middle. As Speedracerntrixie has pointed out, adjust your maximum throws down to the bare miniumum you need and knock the expo back down. Smoothness is something that will come with practice if you focus on it.

speedracerntrixie

My Feedback: (29)

Maybe posting a picture of the setup. It sounds like the elevator servo is buried in the stab with the servo arm sticking out. To get less travel and be able to get your ATV/DR back up to 100% the linkage will have to go under the stab sheeting is the way I understand this. If you need to make a bigger cut out for the linkage, do so. The judges wont give a rats butt about your cutouts but they will care about your lack of smoothness. I had the same issue with my CARF Extra and actually modified the servo mount to move the servo closer to the skin and allow more of the arm to come out of the stab.

big_G

I'm not worried about cutting the skin to get a closer location on the servo arm, but the geometry is getting ugly. The stab is thin, (on a Vanquish) so not much relocation of the servo is possible.

kenh3497

IMO the 3D craze is carrying over to every aspect of the hobby. At least as far as control surface motion is concerned. I set my elevator throw so I have "just enough" plus a bit more for those OH S*IT moments on landing. Aileron throws are set so they "feel balanced" to the elevator. Rudder is set to what ever works. I resisted using expo for a very long time but now have progressed to 25% to 30%. Just enough to make the servo throw a bit more linear.

So with the above said... The MFG settings are nothing more than a starting point. I believe most of the "recommended" throws (from the mass producers) are way to much and could be cut back by 40% to 50%. Set the throws to how they relate to how you fly and what you want the plane to do.

Ken

flywilly

My Feedback: (121)

Hey big_G,
Is the photo in post #10 at maximum throw? And is the amount of up elevator throw the same?
All the points mentioned above are correct. It appears from the photo that you have more (maybe significantly more) elevator throw than you need. It also appears that to mechanically reduce the throw you will have to do some surgery. The elevator servo clevis position seems the obvious choice for change to reduce throw, but you will have to cut out the opening for the clevis bolt (and maybe the head). Lengthening the elevator horn is the other option and might require a bit more work, but could provide a little more flexibility for future throw adjustments. You definitely want to use maximum servo travel to optimize resolution and the minor amount of effort required to make the mechanical fix will be well worth it when the airplane performance impoves.
The set-up recommendations provided above are excellent suggestions. To summarize there are two basic approaches:
1) setup for optimal performance (smooth maneuvers) for everything but spins and snaps and use rates/condition for those maneuvers
2) setup for enough throw to perform snaps/spins and use exponential to provide a nice 'soft', gentle response around neutral
Use a neck strap or tray and thumb and index finger on the sticks. lengthen the sticks as much as possible (get extensions if possible) and adjust stick spring tension accordingly (Hanno Prettner was a pioneer of this set-up and he seemed to have pretty good success ). Stock spring tension is typically pretty soft; a firmly defined center stick position is beneficial, then adjust tension to personal taste.
This is all relatively easy and obvious to long time pattern fliers, less so for newcomers. Pattern fliers are pretty casual when referring to 'ideal' airplane set-up, but it is the essence of successful competitive flying.
Good Luck,
Will

big_G

Thanks, flywilly. The pic. depicts full throw, high rate (100%). Up/down appear the same...I need to verify with an angle meter. I will try to break the "thumbs" technique and implement your suggestions on the stick tension and length. I'll clearance the servo horn slots tonight.

Gary

bjr_93tz

Here are two pictures of various elevator linkages stolen from the 'net, one is from an Aries07 the other from an Asyuler 70.

The geometries aren't pretty, but small on the servo and large on the surface pretty much trumps the funny angles. However, playing around with those angles can yield results that are fairly good. Way back in the day when aileron differential had to be done mechanically, the arms/linkages weren't at mythical right angles to each other, but were at the angles they needed to be to get the desired surface deflection.

By off-setting the servo horn the right amount and changing the linkage length, you can get your surface travels pretty close to spot on with your TX endpoints within 1-2% for each side. This way not only are the maximum deflections the same, but also the small deflections at part stick.

That being said, a "cheat sheet" for an Aries07 from a respected flier gave the linkage ratios, surface deflections and TX rates, with the "normal" rates for the ailerons only 45%, so that's giving up a huge amount of resolution but the snap roll aileron rates were 120%.

Smooth Pilot

Gary,

After going through several Vanquish planes this year, I found that you do not need much throw on the elevator or the ailerons. I cannnot remmember my exact settings, but they were not much. In fact my high settings were just enough to get the job done in a smooth manner with a little extra if I screwed up a maneuver to recover. In aome cases I even used the low rate for certain maneuvers to smooth them out (loops and rolls primarily). As far as the twitchy part, I had the same problem and would gradually increase the expo and concentrate on not moving the sticks unless it was necessary to gwt rid of the twitch. It can be done, but you have to work at it. Believe it or not the Vanquish is just like the other pattern planes and quite capapble of flying by itself with just input to correct wind gusts and point it where you want. I will have another one ordered at the end of the month. See you on the contest trail next year.

Sheldon

PS: You did not mention which servos you are using, but with a decent quality digital, ball bearing, metal geared servo, you do not lose mush resolution, if any, by reducing the percentage at the transmitter. That is per Earl Haury, FAI competitor, and he explained his methodologys that he used to test the servos and it sounded good.

big_G

These are my elevator servos: http://www.servodatabase.com/servo/futaba/s9650
See you in Intermediate next year.
Gary

Smooth Pilot

Be careful. This servo has plastic gears that could become stripped with just a bump to the control surfaces or through normal wear. Again, if you look around you can find servos like the Hitec HS5685MH that is digital, has ball bearings and metal gears for $39.99. It has 179 oz/in of torque and great resolution. Another benefit they are also 7.4 volt servos, but will run with 6.0 volts. Plenty for ailerons and rudder.

Look around, it is worth it. These servos can also be found at Servo City http://www.servocity.com/index.html along with other brands.

Sheldon

big_G

I got a good deal on these servos....Those are a bit bigger than my Futabas, and I had to widen the servo opening to fit them. Did you use there on your Vanquish?...I may look for a slightly smaller alternative metal gear servo.

Smooth Pilot

Yes, and they worked superbly. The elevator servos I used were the Hitec HS7245MH. They are smaller and torque is slightly lower (89 oz/in), but still digital with ball bearings and metal gears. Unfortunately, they are also more expensive, $69.99 each.

Sheldon

Ron Stahl

My Feedback: (12)

In the words of my good friend Steve Stricker and winner of the 1996 TOC " there is no such thing as servos that are too fast, the faster the better".

Dave Harmon

Try increasing the length of the transmitter sticks in 1/4" increments.
This will really help with the twitchiness.