Longhshot 4 DLG - Buildthread

[Craftydan]

First off, yeah, you'll want to brace the servo in the pocket regardless of how you run the linkage. Launches are terribly stressful on everything in the airframe, so best to lock everything down. Try to not add much weight as you do, but make sure it doesn't move in the bay.

Also, if youre going to top drive, make sure you keep at least 1/8" gap between the servo horn and the end of the pocket. If not, flush is fine.

Second, I'm not sure how the longshot wing is built out but you may or may not be able to do a top drive forward of the main spar. If the spar goes all the way through the wing, top to bottom (good chance of that) you're stuck. You don't want to make a hole in your spar for a linkage. You need the strength.


IF there is a gap in the spar, and it's wide enough to run a linkage through, you're going to cut a channel inside the wing, passing through this gap.

To borrow an image from silver sky tantan's blog:



This is what you're shooting for.

Go ahead and beef up that servo pocket, but before you mount the servo, well need to cut that channel alligned on the end of the servo. Allingment goes (from inboard to outboard) servo horn, control rod, control horn. You'll need to mount (but not glue) the servo in its pocket, and Mark on the opposite side of the wing where the rod will come out (tape is your friend, as is backlighting the wing).

Once this point is found, cut a channel in the top skin NO MORE than an inch forward. This is just an exit tunnel. You'll then use a heated wire to melt a channel in the foam, aiming for the outboard edge of the servo horn. Once that channel is cut, the stressful stuff is over. Cut your control horn mount outboard of your rod, dry fit everything, then bend the control horn to fit. Tape the servo, run your wires through the wing and mount the servo on the rod upside down. Add epoxy to the pocket (a little dab will do ya) and roll the servo down into the pocket -- the servo horn should be on the rod before you epoxy and as you drop it in the hole, it should stay there. Tape it down and let it set. Then mount the control horn on the rod, add epoxy and fold it into this pocket.... And you're done.

I know, easier said than done, and you MUST be careful around the exit tunnel or you'll damage the glass skin, but the results of burying the linkage like this is amazing.

A good vid that visualizes most of this process:

 

[vipero00]

Top Drive Horn Lengths and aileron throw.

Crafty Dan,

I'm trying to work out the geometry so the 1st thing I need to know is how much throw for the ailerons? Andrew Newton in his V2 DLG build Part 4 gives a range of +15°/-45°. It looks like most of these top drives use much shorter servo horns and the hole to hinge distance is smaller as well for the aileron horns. How much angular throw can I get out of one of these servos?

Thanks for the thoughtful responses to my questions.

Norm

 

[Craftydan]

How much? As much as you can get.

From servo to servo it will change. On the servo side, the Hyperion DS09's I use give about 140° of throw at the servo horn, but more traditional servos (which generally aren't recommended for other reasons) are closer to 60°. One nice feature with the DS09's and other mid-to-high range digital servos, you can electronically adjust the throw and center of the servo within that maximum range, but on mine I've limited to about 110° throw biased slightly to re-center the spline to accommodate the limits on the mechanical linkages. Not sure what the KS-47MG's can do in angle, but they are analog, so no reprogramming for them.


It is beneficial to have it biased down so you can get maximum down flaperons. +15°/-45° does not sound unreasonable . . . but it's no better than +45°/-45°. In the latter case you'll tend to limit upward travel (just because aileron throws that strong are wasteful), in the former, you'll need a bit of differential to ensure the aileron throw remains even as the servo rounds the circle at "neutral surface" while still allowing the flap throw can drop all the way to the bottom. Also, more than 45° down doesn't hurt, so long as you still have sufficient up and you're not tearing up your aileron hinges, control horn mount or servos.

As for sizing a top drive, you need the servo horn to be as short as the horn will allow to keep the linkage inside the servo bay. Typically it's a new hole drilled into the horn just outside the horn's spline cuff. Drill it out from the underside of the horn (use a bit smaller than your rod), then ream it out for a close fit. As long as the rod is pressed in from the top side of the horn, the rod will ride around the spline/screw from above. You then match the control horn to that -- just a bare few mm's above the aileron skin. I think mine sit at ~3mm above the aileron skin. You don't need much. You'll then use the radio as best as you can to drive the flaperons down as low as they can go when you want to stop, and have good reasonable aileron travel centered on the wing, not on the servo.

 

[ItsNotTooWindy]

Nice build thread, and thank you Crafty Dan for the video on the aileron servo install. My Longshot 4 is on its way! I am on a budget, my TX is the older version DX8 Spektrum, and I will be using a Lemon RX DSMX 6Ch Receiver w/ Diversity Antenna. Which servos should I get, and which battery will work for me? (I am not 100% sure if this RX will work with my TX?).
Thank you in advance, for any assistance.

 

[Craftydan]

Hey INTW, Welcome to the Forum!

Sorry for the late reply . . . a little under the weather at the moment

As for your radio, they should bind up just fine, and the Lemon RX should still run fine with either a direct 1S or 2S pack. The battery you pick will depend more on your servos and weight-and-balance, so I can lead you to find your optimal one, but I couldn't tell you directly.

Now servos on a budget . . . "cheap" is relative. First off, what goes in the pod and what goes in the wing do not need to be the same, but all of them will need to be tiny workhorses. You can cut corners here, but cut too deeply and you'll feel it later. The wing servos will probably cost you the most, since they'll need to be very thin -- I wouldn't settle for any servo thicker than 9mm. So far, among the "budget" DLG servos, I've used the Hyperion DS09-AMD and the Turnigy D56LV (appears to be a rebranding of the KS HD47MG servo).


Among those two, I REALLY like the Hyperion servos -- stronger, faster, wider swing, will function farther down in a 1S lipo pack, and is reprogramable (a bit fiddly, but will allow you to digitally adjust the center, limits, deadband and speed of the servo's throw *after* it is installed). A better servo all around, but over twice the cost. The DS09-SCD version is a touch cheaper, since the gears are carbon instead of metal, but in general carbon servos are a touch easier to strip than metal gear -- your call. The SCD is also a touch lighter, so it's not just cheaper.

As for the D56LV servos . . . I'm not thrilled with them, but I'm not hating them either. They are a bit smaller, but the play in the gear train is more than I care for and the low voltage tolerance isn't fantastic -- mine will start to have trouble settling into a position (jitter and hunting) around 1/2 full on the 1S lipo -- they Hyperions are solid down to ~20% where I usually pull the pack out. On the positive side, this gives me a good "low voltage" indicator -- jittery ailerons, time to swap. On the negative side, I'm swapping more frequently than I should . . . but I can get a decent flying session out of a 1S 200mAh pack driving 3 of them (that DLG is Bank-N-Yank). A long session will need two. They're cheap, and you do get what you pay for.

Will you notice the difference? Initially, no, but as you get familiar with your bird, there's a good chance you might. If you install top drive, replacing servos is major surgery, so weight out cost-to-benefit now.


Other servos that are popular among DLG's . . .

Still in the low end of price is the Dymond D47 -- Small, good throw and torque, can't run 1S but can run 2S directly. I've never used these, but they're universally recommended as a budget DLG servo, enough so, I have no issue recommending them.

On the way up is the KST X08 servos, weighing in at $30-40, depending on the version (V5 has a wider throw and a bit more reliable). Early X08's were fragile so many builders won't touch them, but that has been fairly well addressed and for about half the price it will give you most of the performance of . . .

The MKS DS65K/DS75K servos . . . Pretty much top of the line in every way, but a set of 4 of these would nearly double the cost of your airframe. I point these out for perspective not as a suggestion, since budget, they are not. They ARE worth the price for a high end ship, but the longshot is a mid-range ship -- a good airframe in every respect, but she's probably not worth the extra cost.

There are a few other servos in this mix, more at the lower end, but these are the usual suspects.


As for servos in the pod, you aren't as limited by dimensions, but voltage can be an issue -- the staple 9g and 5g servos aren't as flexible in voltage, but they can be made to work. One of my favorite in this class -- the MG90D and MG90S are fantastic servos, but they need a regulator to run -- 4.5-6V Keep this in mind while looking for pod-servo alternatives. Also, while there may be more room in the pod for them, every bit of space you can save with a smaller servo may make it easier to mount them, and leave more room for the battery. In this case, I do not recommend the Hyperion DS09 servos for pod servos -- they are very narrow, but they're also fairly tall. I have them in my largest DLG's pod, but they barely fit -- YMMV.


So which battery? Depends on what your servos can handle. If they take a 1S pack, go with that, with a full-house glider anywhere between a 1S 200mAh pack (~2hr of flight time) to a 1S 1200mAh round-cell (roughly the size of an AA battery, and I can fly these for several 2-3 hr sessions on my largest DLG before swapping -- typically no less than a week's worth of flying). On 2S, the recommended mAh range limits will be around half the 1S range, but I've never had to size these so it's hard to give real numbers.

The servos set the voltage and the pod will set your size. Start dry-fitting your pod servos and RX and see where they mount and how much room you have left. Particularly with smaller lipos, you will want to remove them to recharge, so think about what you'd need to do to get the battery out. This alone may limit you in the thickness or length of the battery pack. Next, find the biggest reasonable sized pack that will fit that space (more mass in battery means less mass as dead-weight ballast for balance).

When you've got a setup that will work, fly for a bit and you might think of a better pod layout to make more room, or mounting point for the electronics to let you put a bigger pack in -- these tradeoffs can be done later, so long as you've got something that works now.

 

[ztoon]

Just sharing my DLG servos setup:

Zephyr (home build)
Fuselage: Dymond D47 (pull springs)
Wing: Graupner DES427BB

FW6 (pcm) All servos in pod
Tail surfaces: D47 (pull springs)
Ailerons: Graupner DES28188MG

FW4.2 (pcm) All servos in pod
Tail surfaces: Hitec HS45HB (originally rods, now pull springs)
Ailerons: Futaba S3114

Composite Versus (Hobbyking) now modified as a 'mini F5J'
Fuselage: D47 (pull springs)
Wing: Corona digital 9g (cheap, good torque but centering not good enough), tried Dymond D60 before and it was much better.

Tried 2S direct, 2S regulated with 5V BEC, now I my prefered setup is 1S direct with FrSky Rx's (D4R + X4R)