Help! Simple Cub servos

[tcalico]

In the build video, it would appear the elevator and rudder servos are mounted on opposite sides of the fuselage from the side the control horns are mounted on each control surface. I can clearly see the rudder servo operating on the left side when Josh test them with a radio. This however, makes the control rods cross and touch each other. That does not seem right to me, the rods stay on the sides where they good through the fuselage slot then they will not interfere with each other. What sides are the servos supposed to go?

 

[donalson]

very common to cross and touch, won't hurt anything... also it should make the push a bit more direct and prevent the pushrod from bending when it's pushing (although the difference would be minuscule)

on the other hand... I and some others have mounted the servos in the back for balance reasons (using the C pack and mounting the battery under the pod up front/in front of the landing gear slot)... when I built mine I installed the servos only after balancing them with the plane ready to fly weight (motor, prop, lipo, rx etc) except the servos... I taped the servos in location to verify a happy balance... also let me get away with using spare push rod ends lol...

 

[tcalico]

Thank you for the advice and photos. I'm building a 3 channel trainer Cub with the B pack and probably just a 1000 3s battery, so I the CG should be ok. Later, I do want to go 4 channel, and then step up to the bigger C motor, so I'll keep in mind the tail mounted servos. I see the wood stick reinforcing the elevator too in the photos, that I will add that right now.

The Simple Cub looks pretty tough with the doublers in fuselage and it fits the power pod perfect. I have built and crashed a Dusty Crophopper, broke the wing right off on the maiden but I feel doublers would help that design have more strength between the wing and power pod. I also feel that I need more "flight training" hours with something like the Cub, before I try a 4 channel low wing plane again...

 

[basslord1124]

Yeah that shouldn't affect anything if they are touching. Like donalson, I moved my servos to the rear. Shorter push rod runs. My long pushrods ended up being too flimsy anyways so it all worked out. Plus, after thinking about it, like donalson said, it helped with balance.

 

[kilroy07]

This confused me too at first.
Also if you run them straight you might see binding against the fuselage.

Another good reason to move the servos to the tail might be flex in the rods. In my last build I used pretty beefy push rods because I noticed some flexing in the rods (there are other ways to correct this however.) Just be sure to check CG if you do move things around.

In most of the newer kits you see the servos near the tail, I would expect if/when they update the cub you'll see them moved.

Let us know how it works out!

 

[CarolineTyler]

This confused me too at first.
Also if you run them straight you might see binding against the fuselage.

Another good reason to move the servos to the tail might be flex in the rods. In my last build I used pretty beefy push rods because I noticed some flexing in the rods (there are other ways to correct this however.) Just be sure to check CG if you do move things around.

In most of the newer kits you see the servos near the tail, I would expect if/when they update the cub you'll see them moved.

Let us know how it works out!

I ran the pushrods through thin carbon fibre tubes to remove the flex in the pushrods

 

[kilroy07]

I ran the pushrods through thin carbon fibre tubes

Ah, to be so lucky to have some CF "just laying around"...

Great Idea, thanks for the tip!
(Do you use Z bends on the ends then or linkage stoppers?)

 

[CarolineTyler]

Ah, to be so lucky to have some CF "just laying around"...

Great Idea, thanks for the tip!
(Do you use Z bends on the ends then or linkage stoppers?)

I bought it in error....came in useful
I use linkage stoppers at the servo end because I am rubbish at doing mm accurate z-bends ... LOL

 

[dayve]

Plastic coffee stir sticks also work well for push rod guide tubes. They're no CF tube, but they're WAY cheaper.

 

[donalson]

Plastic coffee stir sticks also work well for push rod guide tubes. They're no CF tube, but they're WAY cheaper.

I was going to toss this fact in but see you already did ... the coffee straws work well... there is a reason FT uses them... you can also use a fe zip ties, make sure they are tight but not so tight the pushrod binds... snip the left over at an angle... about 1/4 of an inch or so... push though the foam then hot glue into place... to this in a few locations if it's a long run...FT has used this method on some planes as well... but for most the coffee straw is a cleaner way of doing it.

 

[jpot1]

Big fan of the zip tie approach - see below on the boom. Due to length there are actually four zip ties, only two visible if you zoom in.

 

[kilroy07]

I've used zip ties for the FT Flyer, Tiny Trainer and Bloody Wonders, works great for those.
I find for the bigger planes though I need to beef up the rods.

I like how in the newer kits they have shifted the servos aft (like the mustang...) I'm building a couple of Cubs with the servos moved aft, we shall see how they balance.

 

[donalson]

Big fan of the zip tie approach - see below on the boom. Due to length there are actually four zip ties, only two visible if you zoom in.

View attachment 110777

so what is this thing... looks like a mid engine nutball of some flavor?

 

[Tri Blades]

My Dad has built two of these cubs and has ended up puting the rudder and elevator servos down by the tail. This didnt seem to change the cg much either. I have flown the cub both ways and can see a difference in the control surfaces from the rod flex. All personal preference.

 

[jpot1]

so what is this thing... looks like a mid engine nutball of some flavor?

Found over in rcgroups and tweaked a bit for DTFB, it’s called a Geobat. Bunch of guys at the local club call it the flying donut. Actually flys well and does good high alpha.

https://www.rcgroups.com/forums/showthread.php?1386754-Geobat-Foamie-RC-Flying-Saucer-With-Plans