How about directly bonding the servo to the control surface?

[tim hooper]

Gents,

I have it in mind to revamp my Highlight E400 glider. I want to ditch the 9 gramme servo's from the nose (and their respective snakes), and instead, inset 6 gramme servos into the tail surfaces.

Nothing new about that, I know. So how about mounting the servo's so that the output shaft centreline co-incides with the hingeline, thus allowing the bonding of the servo arm to the control surface itself? (See the sketch to see what I'm blithering about.....)

Pro's;
No slop/flutter.
No excess weight.

Con's;
Accuracy needed in assembly.
Centering & throws TX controlled.

Any thoughts?

tim

[balsaman]

I have seen that done before with ailerons. The servo was inside the fuse with the arm outside fixed somehow to the aileron. I think it was a pattern ship. I don't see why it wouldn't work.

If your throws are small though, the servo ATV would have to be way back on the transmitter. This does not take advantage of any "mechanical advantage" we can attain using conventional linkage. ie.inside hole on the servo arm, outside hole on the control horn.

Eric

www.e-zflight.com

[markwild]

Tim,
The downsides of doing that are that even though the weight is less, having all the weight at the tail instead of near the CG would likely mean that you'd need to add nose weight for balance. And, since the nose is probably closer to the CG than the tail (let's assume a third of the distance) you'd need triple the weight in the nose.
Also, you do lose some flexibility in adjusting control throws, but that's less of an issue if you have a computer radio.
You'd have to be real precise in mounting, because if you're off by even a tiny bit, your elevator won't move smoothly.
--Mark

[Sparky Paul]

The moving of weight to the tail has been mentioned.. also the inertial effect should be considered.
Once a manuver has begun, arresting it will be more difficult.
For a thermaller this might not be a problem, but for a manuverer, it would show up in overshoots and extra oscillations.
I've seen a couple of microAVs that use this method, BTW.

[tim hooper]

Thanks for your responses lads!:)

The rearward CG shift shouldn't be too much of a problem; with the Cosmo g/box & 12" prop hanging on the nose, the model tends to be noseheavy anyway. Currently the battery pack is stuffed back down the fuselage as far as it will go, but will be able to move up to 4" forwards once the nose-servo's are ousted.

As Paul says, the inertial shift shouldn't be a problem either; this is a gentle thermaller and not designed for snap manoeuvres (not intentionally anyway!)

As the v-tail is removable on this model, I'll need to find a tiny 4-pin plug/socket to mount in the extreme rear of the fuselage to allow disconnection.

The only real problem looks to be the accuracy needed in the construction ie. getting the hinge line to marry up with the output shaft - if that proves to be beyond my meagre skills, then I can always mount the servos within the fixed portion of the tail and use short pushrods to the ruddervators.

I've attached a pic of the current layout.

tim

[vintage1]

Originally posted by tim hooper
Thanks for your responses lads!:)


The only real problem looks to be the accuracy needed in the construction ie. getting the hinge line to marry up with the output shaft - if that proves to be beyond my meagre skills, then I can always mount the servos within the fixed portion of the tail and use short pushrods to the ruddervators.

I've attached a pic of the current layout.

tim

I would be temopted to do two things - first of all leave the servo loose until the hinges are settled, and then pack around it and glue it in to get alignment right. Getting neutrals right should be ok with computer and v-tail mixing. Just use trims and store them.

Adjusting travel is the real bugaboo, as has been pointed out.

IF your travels correspond with servo movement - fine! otherwise I wouldn't :-)

[tim hooper]

After looking at the model, and assessing the situation carefully, I chickened out and mounted the servos in the fixed part of the tailplane.

I'll sort out some little pushrods tomorrow; it's been enough of a strain thinking through the 4-pin plug thing for one day.

tim

[Duke58]

I replaced the old standard servos and pushrod system on a 20 year old scale glide that was "hanging around", on this 112" plane the servos were moved to the wings and tail and T-tail, just short ball linkages.

The weight savings over all was significant even after rebalance, the servos for the rudder and elevator weighed less than the old pushrods, at this size model the inerita was not affected.

The old Kestral is a real good flyer again , even better than ever.

I just recieved some of those hidden acuators for a new model and I am anxious to see how they work.

I can see maybe someday when servos will be made for direct hookup with an output like the acuators and a setscrew for centering, would you buy one? :) would you even hesitate?

Tim ,I was looking forward to seeing what you were going to come up with, ah there's always next time.

Earl