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Wednesday, December 30, 2015

Tweaking out the 3DHS Extra__MURDER SHP

I've been flying the 3D Hobby Shop Extra SHP for so long that I know the airplane almost forward and backwards. I have built maybe 10 or so of them for myself and friends, and I have utterly thousands of flights on these airframes. With each new one I keep finding ways to push the plane harder and harder, and this one especially will be no exception.

I have always intended to build the ultimate SHP, but I just never got around to it. I wanted to build it with the best of everything, and with every tweak I have ever learned flying this airframe. There has always been something I wanted to try on "the next one," like high voltage servos, an all ball link pushrod system, electronic stability system (ESS), and just generally apply eight years of experience with this plane to build the best one ever. Now I have all the pieces together (except as of this writing the stability system is not here), and the time is right.

Click To Enlarge (All Pictures)

As you can see it's still an SHP, and it doesn't even look that different from my other ones. The big differences are going to be in the little details.

The Old Setup
Before this project, I think we were getting everything we could have from the plane and equipment we were using. The SHP is closing in on eight years old, though it still does the job it was intended for with remarkable grace. However, as the equipment improves you can get more from the plane.

The SHP I flew all summer used the tried and true Hitec HS65MG servos, and those were still fine. The plane still flew beautifully and was a joy to fly, though I think the newer high voltage Hitec HS5070MH servos will take the new plane to the next level.

Extra SHP__The Boomerang Returns from Doc Austin on Vimeo.

Extra SHP__The Boomerang Returns II from Doc Austin on Vimeo
The New Ride  
For starters, my friends at Hitec sent some HS5070MH servos for this plane, and those have worked so well in my EXPs that I am confident they will really improve the SHP. These servos drop right in to the existing servo opening and you don't have to modify the plane in any way, which is nice since it helps the build go smoother.

The faster response and higher torque of these servos are really nice, but the thing I like most about them is their super precise centering. You can super fine trim the plane by turning the trim adjustments down, and with the superb centering the plane really locks in. This shows up most in precision maneuvers because the better trimmed out the plane is, the less corrections you have to make. Just point it and go.

With the higher Torque, stalling and blowback are relegated to the dark ages. Now you get instant response, and full deflection. Previously the drag of the control surfaces would slow the plane and dissipate some energy before the surfaces could fully deflect, but now it's like flipping a light switch, You have the control surfaces pegged instantly while the plane is still carrying maximum speed and energy, which transforms violent snaps and tumbles into violent snaps and tumbles. 
We have known for awhile that ball link hardware is the way to go. Awhile back the SHP pushrods were converted to ball links, but only at the control horns. The SHP still uses the swivel-type connectors at the servo arm. If there is any one thing that can be improved on this plane, I think it's having ball links all the way around.

Ball links, when set up properly, work smoothly, and are drag free and slop free. With ball links you get a more precise flying plane. You get a better flying plane, and I wanted this to be the best SHP yet. This means that ball links all the way around were the only choice.

Set Up
Aileron Set Up
Astonishingly, the aileron pushrods and ball links from the 44" Slick work perfectly on the SHP.
All I had to do was turn the servo around so the output shaft is further from the control surface. This part was easy.

Elevator Pushrod
Now we get to the lucky part. I found a rod threaded on both ends that turns out to be exactly perfect for the elevator. I just spun the ball links on all the way and it works. Scratch around in your box of wire and threaded rods and you might be lucky too. If you can't find a suitable pushrod, keep reading because I had to make one for the rudder, which I will show you in the rudder pushrod section below.

This servo arm was made out of carbon fiber a few years ago by a friend. It was just meant to be a little bit of bling, and it's been on all my SHPs since. It looks cool, so why not?

Rudder Pushrod
Now this is the hard part, but it wasn't really that hard. I could not find any 2mm threaded rod, but I had some 256. It's a little too big for the 3DHS ball links, but 2mm Dubro is a little beefier where the rod goes in, and I used those. Once I had the right length figured out, I used medium CA on the rod and then slid a carbon tube over the outside. After that set up I ran a little thin CA into each end and let it seep in.

This rod was just a tiny bit too big, but if you get the right size the rod will thread into the carbon. Then a drop of thin CA on either end will secure it nicely. You can also make an elevator pushrod like this, and even the aileron pushrods. Making all the pushrods like this would be even cooler because it's carbon and it will all match. It works, but it's also cool bling.

Here you can see a set up error which I have since corrected. The rudder pushrod is on the wrong side of the control horn. As you can see, the pushrod is not properly aligned between the servo and rudder control horn, I solved this by moving the ball link to the other side of the control horn and now it is a straight shot from the servo to the rudder.

Setting Up The Ball Links 
It takes a little care to set the ball links up, but it pays big dividends. I have already covered this in another article, so scroll down to Ball Link Set Up.

For securing the ball links I depart from the hardware pack a little bit. I like to use Dubro 2mm X 12mm case hardened allen bolts. It is always easier to work with an allen driver than a screwdriver, and I've got a really nice set of Losi tools for this. I also like to use an aircraft locking nut, and then a regular hex nut on top of that and jam nut the two together. Once that is done, I apply the coup de grâce in the form of a drop of medium CA to the exposed threads. Like this, the assembly can never come apart on it's own, but by spinning the nut off it will shatter the CA and you can take the assembly apart from there.

One thing I have wrong in this picture is that the ball link is a little bit twisted. You want that to be centered on the ball so it will operate at maximum freeness. I just had not gotten to checking that yet when I took the photos.

Powering The Servos
For these servos I needed a 7.4 volt power source. The Airboss ESC puts out 6, which isn't enough. To solve this I used a Castle Creations 10 amp separate BEC. I've been running these servos on 7.4 volts (while they are capable of 8) but this time I turned them up to 7.8. With Castle's link USB program it's a five second job.

I have always hated running a separate BEC simply because of the extra complexity. That, and it took me awhile to understand them. I came into electric RC not even knowing what an amp was, so understanding a BEC took a little bit of experience with them. I still hate the complexity, but my soldering has gotten better over the years and now installing a BEC is no big deal. Now, it's just an extra piece.

I was also reluctant to use them because of my poor computer skills, but Castle's excellent program makes it easy. Since you can see, and check what you are doing it's easy to set it once and forget about it. You can't change the programming by accident like you can with ESC, so I like that part.

Since the BEC runs the radio, you want to keep it cool. Here you can see I mounted it with Velcro
right behind the first former and down low . It is reasonably out in the open, so cooling should not be an issue.

In the end, though, nothing is as simple, reliable and easy to use as an Airboss ESC, so I hope we see  7.4 capable Airboss ESC soon. With the current 45 amp unit, you just take it out of the package, install it, and then forget about it. It's hard to beat that for being user friendly.

Power System
There was never any doubt it was going to be the Torque 2814 and Airboss 45 Elite ESC.  I've been using this system exclusively in my 47-48" planes for the last eight years, and they have never let me down. This plane was originally designed for this power system and it simply bolts on perfectly, kind of like the plane was originally designed for it!

You can see this motor is pretty beat up. It's been around a long time and served duty in my beata Yak and my last two SHPs. Basically it has had the snot run out of it, but it still runs well enough that it keeps on chugging.

If you click to enlarge the photo, you can see I cut the switch off the speed controller (ESC), soldered the wires together and heat shrunk them, and then stuffed them into the clear heat shrink on the outside of the ESC. I do this because with a separate BEC the switch is disabled anyway. I am so used to having a switch on the plane that using it is part of my safety procedure. I cut the switch off because now it doesn't do anything and can give a false sense of security. Any time the plane is plugged in, it is live, and in this case the switch is like a safety on a gun that doesn't work. You can plug the plane in with the switch in the off position, but it's still live and can bite you. In this case it is better to simply cut the switch off so it doesn't confuse me.

I used an Extreme Flight EXP tailwheel assembly on my last SHP, and I found it to be a big improvement. I have always liked this assembly anyway, and it works superbly on the SHP. In my last Extra EXP article I showed how to set one of these up to be almost maintenance free. Scroll down to tailwheel assembly.

Wheel Pants
While not a big detail I really like the shape of the Extreme Flight wheel pant. They are a little heavier and more robust that the pant that comes with the kit, which will come in handy when bouncing the plane off the deck. The black look also affords a good place for a Thunder Power decal, which has become customary on all my wheel pants.

Normally I do a lot of business with B and E Graphics, but this project came together quickly and it was faster to go through a friend locally who runs a graphix store. The white roundels are duplicates of the ones that come with the red 48" Yak EXP, only they are made from 3M High Performance Vinyl. They are much thinner and about a quarter of the weight of the stock decals. This makes them pliable and easy to work with. 3M High Performance Vinyl is also much easier to apply with decal solution. The air and fluid squeezes out easily with a graphics squeegie, or in a pinch a credit card will work.

Custom decals are almost always better than what comes in the kit. They are easier to work with, look better, and in the event you have to remove them, come off easier too. It's just more of the best of everything. You can have anything in decals you need made by B and E Graphics. They have all the 3DHS and Extreme Flight artwork and can pop it out in a couple of days.

I only managed two short flights so far because I got to the field and discovered I had forgotten my batteries! I borrowed a couple of packs from friends and got the SHP dialed in pretty quickly. Everything worked just like I was expecting, except the servo centering was even better and the SHP is now locked in like never before. Along with the double ball link pushrods, the SHP is even more precise flying, and it was already pretty damm good.

The biggest surprise is how hard the SHP will pop in a parachute when you have the irresistible force of an HS5070MH behind the elevator. It's just plain silly. The rolls on low rate were also much faster than I was expecting because now there is absolutely no stalling, and I had to turn that back about 7 or 8% to get my customary 3 rolls in five seconds.
Snaps and tumbles are much improved with the servo's big torque and holding power. I expect it to become even more violent with the speed, power, and momentum carrying weight of a 4s 2700 packs. Right now it's just gentle and easy like the last one was on 3s.
There's not really a lot I can say after only a couple of flights on 3s power. The plane is definitely the best SHP I have built yet, but I don't think we will see the real gains until I fly it hard on 4s.

In all it was a really good first day for the plane, though the conditions were so bad we didn't even try to shoot video. It would not have been fair to the plane, but the blog this summer is overflowing with SHP videos. Until we get some good weather and new footage, you can check those out.

EDIT: Between the bad weather and backlog of other projects, it took longer than we expected to get some 4s Murder SHP 4s video. After adding the SFGs to the elevator and going to 4s power, this plane is as tweaked out as I know how to make it. You can see the power, acceleration and speed are absolutely insane. It's a bad ass little monster.

I am still planning to add a stability system, but it has been a mater of researching to find the best one that I can still afford. remember, I have a whole fleet of planes that I will probably want to convert, so $100 gyros are out of the question. I could always try something cheap, but then you run the danger of it not working so well and maybe losing the plane. I've got it narrowed down to a few choices and hope to order a stability ystem soon. Right now I am just having fun with the plane and hate to change anything because it is flying so well.

EDIT: Here's the final tweak to the Murder SHP. The SFGs on the tail are downsized copies of the original Extra SR SFG. I had a few made up at a local laser cutting shop to fit to my SRs, and later my MXS'. They add a little bit of elevator authority and yaw authority, and maybe some all around stability.


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