3D printing Widgets

I do not have the option of exponential on my current Futaba T6L Sport. I never quite got the hang of Klippies T6EX menus. So calm light finger motions are my preference for now. I might be forced to re-consider.

I have a copy of the manual. It tried to explain but my brain cells just didn't seem to absorb. Perhaps if I gave it another try it would make more sense

And here is another tiny printed beastie that saves lots of frustration and ripping into the depths of models....

-Jon

Some of my models mount the elevator servo on the tail and others have the elevator servo in the body of the fuselage. The latter case is helped with the occasional guide for the linkage wire. Callipers on the boom and wire and an offset opinion are needed. My preference is a friction fit on the boom so that these guides can be positioned where they will do the most good.





As usual, a zipped version of the freeCAD file and an STL can be found below. The boom is 8mm and the wire channel is 2mm. -Jon

To save weight at tail I attempted to rig a spring pull for the elevator using some bent piano wire as the torsion spring.

After many tries I ground to a halt. The 'spring' was either so stiff that the servo struggled to hold or it was not enough to pull the elevator to its full extent. Then Tony suggested I try a rubber band as the spring. I have scores of those, of all sizes and strengths (I got in the habit of picking up what the post leaves on the street).

So I printed another horn and mounted it opposed to the control horn, found a small print that I had used to fix a band to and gave it a try.

The clip is short, rather than upload to Youtube I am attempting to add it as an attachment.

And that didn't work (.mp4 in not allowed and it was a tiny bit over 2MB). I could see and play it in the preview but not after submission.

Would the administrators chat amongst themselves to see if it would be possible for the site to host SMALLish .mp4 video files (say less than 20MB) for quick shorts? It would be nice not to have to rely on YouTube.

Anyway here is the YouTube link.... -Jon

To clarify - the linkage wire is about half the diameter as I usually use - it has almost no push capability. It's a limp noodle. It probably should be fishing line or some other non-stretchy fibre.

Well spotted on the angle of the servo arm. I agree that the servo arm needs to be rotated.

One of the new bits of information on a first flight with a new wing is to get indicators of stall speed. And finding that out higher up would have been preferable. -Jon

I hate giving a servo any more work than the minimum required to move the surface against the air stream.
That includes stiff hinges, friction in the linkage and worst of all a spring return. If the spring is set to give the same effort as the servo does the other way then the load on the servo is doubled.
Do without a spring return and you can use a smaller lighter servo and still achieve the same force on the control surface.

My 'go to' if a servo right at the tail is not possible is a pull/pull arrangement using mono filament nylon fishing line. Yes mono filament is a bit 'stretchy' but I use that feature to tension the lines slightly at the neutral position so there is no 'slop'. I then arrange the horn positoin such that as the surface deflects the tension is reduced. At full deflection the 'give' line is virtually slack so I know all the servo force is being used to move the suface.

On my lightweight planes I am quite happy to use 5lb line. It is cheap, weighs nothing at all and its breaking strain is 3 times the maximum pull a 5g micro servo can deliver.
The elevator pull/pull used on the sub 200 g Cheetah powered RC foam glider.

The 3.7 g servo arm and elevator horn are obvious enough but you are hard put to actually see the 1.7lb lines unless you get a 'glint' from a light source.
However I do still prefer the elegent simplicity of a servo adjacent to the control surface it moves with a short simple link.

I appreciated the comments. I have revised the design:
Band on the bottom to address Tony's ' you want to fail better'.

I found a much finer wire for the pull (my earlier comment about the original wire being a lesser diameter was incorrect).

I think I found a combination that results in less overall travel for the elevator which might result in a less skittish flight.

I centred the servo - actually that servo is one Tony sent me from SA and this is the 3rd fuselage it has been associated with - does have a hum even when not stressed. I might need to retire it because the arm is fitting less well and will need checking after each flight.

I shifted the COG forward - it is now 45mm in the 155mm chord.

I take the comments about servo stress with a spring pull. I was intrigued about whether there was an alternative to a torsion spring. The band is slightly adjustable. I like the idea of a push-pull - it is simpler - but there is no clearance for that with the pusher prop.





The video is:

Reading the comments again...

I do have variants that use a wire linkage from the fuselage to the elevator control horn. And that works ok and the little printed wire-guides help. I also have mounted the servo at the tail with a short linkage and that worked well for me - and there is a portion of the community that avoid servos at the tail. Exploring if there are workable alternatives is an interesting excursion. In the end this latest variant might not save all that much weight. -Jon

After a few weeks of Zoom workshops and a much needed holiday I am getting back to AeroModellers....

This 3D printed widget is a prop saver for a Flight Text 1806 motor which has a threaded shaft arrangement which is problematic for prop savers. I haven't found any for this type of motor shaft. And although I would use it in a pusher, such an inflexible mounting will shorten the life of my props given my models don't have landing wheels.



So open up freeCAD and get working. It was constrained by the length of the shaft, the size of the retaining nut and the need to keep it from unraveling if torque was applied quickly. Here is the design I came up with...



And a preview in the 'slicer' software...



Here it is tightened down on the threaded shaft and with the band-bolts in place.



And with the printed prop in place and using an 'O' ring. I used M3 bolts (the bolt hole is sized to self-thread a M3).



Here is the STL file. It takes about 10 minutes to print. 2 perimeters, 25% gyroid fill, 4 layers top and bottom.



Here is the freeCAD file. It should be straightforward to tweak the parameters for a different threaded shaft or a different thickness.


Enjoy, Jon