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Sunday, December 11, 2016

52" Extra EXP__What To Do With Your Spare HS85MGs

Doc's Disclaimer: Extreme Flight recommends Hitec HS-5087MH Digital HV Premium Metal Gear Micro servos for this plane. Using HS85MGs in this plane is something I took solely upon myself to try.

Times are tough. A lot of times you just  have to use equipment you already have, and pick your plane accordingly. However,  most of us have a few Hitec HS85MG servos laying around. This is a robust and reliable servo that is also reasonably priced. 

While not the recommended servo for this plane, the HS85MG served many of us extremely well for years in the highly popular 3DHS 51" Slick. A lot of those planes got crashed or just plain wore out, so most of us would like a nice plane to put that gear into. These servos will happily drop right into a brand new Extreme Flight 52" Extra EXP, so I thought it was worth a try.

A lot of times $100 or so is enough to keep a project from happening. I was really tight on this one, so I had to save some money somewhere. Being able to use servos I already had made the difference between flying this plane and hanging it up for display. New HS85MGs sell for about $30 apiece, or $120 for a whole plane's worth. If you add to that you won't need a separate BEC,  that's another $25 savings.

While the recommended servo for the 52 Extra is Hitec' excellent HS5087MH, the specs on the HS85MG are still really good, and judging by how well they performed in our 51" Slicks, I was sure they would be fine in the 52".

HS85MG Specifications

Motor Type:3 Pole
Bearing Type:Top Ball Bearing
Speed (4.8V/6.0V):0.16 / 0.14 sec @ 60 deg.
Torque oz./in. (4.8V/6.0V):42 / 49
Torque kg./cm. (4.8V/6.0V):3.0 / 3.5
Size in Inches:1.14 x 0.51 x 1.18
Size in Millimeters:28.96 x 12.95 x 29.97
Weight ounces:0.77
Weight grams:21.83

 The Shout Out
First, a big thank you to my friends in the Hitec service department. I tend to be a little bit hard on my equipment, so I rely on them to inspect and repair my high usage and crashed equipment. Generally Hitec inspects and cleans servos at no charge unless you have stripped gears or broken cases. Any time I am not 100% sure of a servo I just send it in, and when I get it back I know it's going to work fine.

I generally like to use new servos in any new plane, but for this one I had a handful of HS85Gs in my "serviced" collection. Hitec service has been so good that I confidently put them into a brand new plane with no worries.

So, thanks to Hitec service who helped make this project possible.

Servo Arms
For this plane I wanted to use Xcessories Light Weight 1.25" Servo Arms on all surfaces.

For the ailerons I used the inner hole on the Xcessories 1.25 arm and ran my end point controls out 125%. This is more throw than I am used to, but I like it this way. Having the additional authority at slower and near stall speeds is extremely useful. My post stall 3D flight has actually improved because of the additional control, and now I am rethinking my set up for all my planes. I will probably turn the aileron throw on my other Extras up a little too, and learn to be a little smoother on the ailerons at speed

Click To Enlarge On All Pictures
I added my now customary 25% spoileron mix and this is what it looks like: 
I was really careful with my hinging on this plane. I made sure I could get a full 90 degrees of elevator throw. I was not sure if I could get it all with the arm I had, but it was worth a try. I had to drop the servo down about 1/8" because the servo arm was just barely rubbing on the bottom of the stab a little. It was no big deal ...... I used a small straight edge and Xacto to cut the a straight line. 
I have not measured the throw yet, but I am satisfied with it! I'm pretty sure there is no more left to get.

For the rudder I really wanted to use an Xessories arm, but we don't have 7/8" arm just yet.
I used the small arm from the Hitec PN55709 set instead and it's perfect. I've got my end points turned back just a little and the the rudder almost touches the elevator halves.

ESC Installation
One really nice benefit of using the 6 volt HS85MGs is that you don't need the extra complication of a separate BEC. Not only does this make for a simpler and cleaner installation, but you save about $25 and a little weight. You just plug the Airboss in, set the timing to high, and go fly it.

Battery location
As always, battery choice is Thunder Power. For this plane we went with 4s 3300 Elite 70C series packs. Power is sick. Running the plane hard I still get 4.5 minutes, and come down with around 15.25 or so volts in the pack. this is a good margin and being nice to the pack pays off with longer lifespan.

This is where the pack ended up in my other Extra, so here is where I started. So far I think it's dead on where I like it, which is slightly ahead of neutral.

What decals?
I love this color scheme so much I didn't want to clutter it up with any decals. Of course, Old Glory will always be on the nose, but outside of that I wanted to keep the plane's appearance clean and pristine.

As of this writing, I only have three flights on the plane, but I am delighted with it. I don't seem to get any stalling or blowback at high speed, and the plane just feels really good. I did a few high speed walls and parachutes, and the servos were up to the job every time. At full speed with full aileron deflection, I have no hope of keeping up with it for more than a roll or two, so there is no stalling or blowback here either. The servos just do their job, and while that sounds matter of fact, it's actually a jolly good thing.

While the HS5087MH is a faster, stronger servo, there is still a lot of life in the HS85MG and I think they are probably fine for this plane. They are fine at least for the way I fly them. The HS85MG has served us so well in the 51" Slick and other planes that I have no concerns about their reliability at all. In fact, these have always been so reliable that I use them confidently.

We hope to be shooting lots of video with this plane soon, so keep an eye on the blog.


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