Search This Blog

Tuesday, January 31, 2012

More Extra__And Installing The HS85MG Servo On the Elevator

Last week I retired my beloved red Extra EXP, which has been my primary beater since wrecking my original blue Extra EXP. I have made so much progress with that plane. Whenever I would stick to just that plane for a week or so, I would always learn something new, or something I would be having trouble with would suddenly make sense.

I was so comfortable with this plane that I would try anything with it. For the longest time I thought the Edge and MXS were slightly better 3D planes, but once I started pushing the Extra deeper and deeper past the stall I learned how to get more out of her and she 3Ds better than I had ever dreamed. The learning process always seems to step up a notch when I fly the Extra.

Mostly I nailed down my precision a little better with this Extra, but I think she helped me raise my entire game. What a great airplane she was, but I had put so many hard flights on her it was time for something new.

I am especially pleased that she has a good new home with a guy stepping up from another brand, and will be flown hard daily.

Unfortunately I also trashed my blue MXS a few days later, so now I am down two planes with the flying season right around the corner, but the good news is my replacement red Extra EXP got here yesterday.

Today's ARFs, especially EXPs, are so nice and so complete that even a crash is not so bad any more. You hate to lose a good flying plane, but with a quality EXP you can be back in the air in a couple of days. Sure, some guys claim a couple of hours, but I don't know anyone who works that fast and doesn't have stuff falling off the plane.

This will be an in-progress kind of report. I may come back and update this report, or maybe even file a new one, but either way. I'll keep everyone up to date on how it's going with the latest Extra EXP build.

Installing the HS85MG Servo On The Elevator
The EXP series was designed to operate on the Hi tec HS65MG servos, but we soon found out with the quantum leap in airframe performance that we were asking too much for that servo on the elevator.  The MXS has always been set uyp to run the larger and more powerful HS85MG servo, though the Exta and Edge will benefit from that too.

The first step is to make sure that you do not move the servo output shaft forward or backwards. The push rods have a finite amount of threads, so if you get the servo in the wrong fore/aft location, you might end up with a push rod that is too long (fixable by snipping off a few threads) or too short (not fixable without a longer push rod).

Drop an HS65MG into the elevator servo hole, and mark the location of the servo output shaft on the fuselage with a magic market or felt pen. When you install the 85MG, you want the servo output shaft to line up with the mark you just make.

Next, line the 85MG up over the hole and guesstimate how much you will have to cut the opening to make the servo fit in the proper fore/aft location. As you can see, I simply laid the servo over the hole and then cut away the covering. From here we got lucky because to keep the output shaft in the same place, we just need to open the servo hole rearwards.

Now that the fore/aft location is locked in, let's drop the servo down. We do this for two reasons: first is that the servo is too wide to fit, and second, we need more space away from the stabilizer so the large Dubro servo arm we are going to use has clearance and doesn't rub on the bottom of the stab.

Here I use a straight edge to cut a straight line, and then I go back and drive the blade in deep. You can see there is a balsa block on the fuselage bottom and that needs to be relieved so the servo will sit down.

I tried really hard to get a good picture but this was the best I could do. You can see how I notched out the balsa block fuselage bottom and now the servo sits low enough. Seal all the covering edges down with a trim iron, and on mine I ran some CA in to seal the wood and lock the edges of the covering down. 

Lastly, here is the finished servo installation. You will have to dry fit the stab and servo with Dubro arm installed to make sure you have enough clearance, but I've done these before and I am confident opening the hole downward enough to get the servo in also drops it down enough.

One final trick is to push the servo as rearward as it will go in the servo hole. You probably won't get it absolutely perfect and will have a little slop, so move that servo backwards and that means you will have to turn the ball link further onto the push rod to get the elevator centered. One or two or three more threads going into the ball link is more margin against the push rod pulling out. You might even need to snip a thread of two off, but that's a lot better than not having enough threads on something like the elevator. 

As of this writing I don't have the stabilizer in yet, so I am going to cheat a bit and post a picture from my beloved and late, original blue extra EXP. You can see how important it is to have dropped the servo down because of the tight clearance the servo arm has to the bottom of the stabilizer.

I am using the longest arm in the Dubro pack, and the ball link is bolted to the second from the outside hole on that arm. I cut off the overhang of that last hole to get a little more clearance, but you can see it is still pretty tight. All my extra EXPs have been set up exactly this way and they have all flown beautifully.

No comments:

Post a Comment