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Thursday, September 11, 2014

Screaming Into The New Age With Hitec's HS5087MH

When the MXS came on the market, it offered such incredible mind blowing performance that it created it's own little cult of devotees. The big draw was it's huge elevator and short tail moment, which delivered incredible pitch authority. Walls and parachutes were the sickest things we had ever seen, while snaps spins, and tumbles were much crazier than we were used to.

Even crazier was that the MSX is still super stable and does superb precision work as well. In it's own way, it's performance balance is as perfect as the Extra EXP's, though a bit on the wilder side.

Part of this additional performance came from the MXS using the slightly larger, more powerful, higher torque Hitec HS85MG on the elevator (as opposed to the smaller HS65MG). This made elevator stalling and blowback a thing of the past. Add to that you can get longer arms for the HS85MG servo and lots of us were getting 88 degrees of throw!

From there, many of us also outfitted our 48" Extras, Edges, Lasers and Yaks with HS85MGs on the elevators.

Enter The HV Dragons
In the four and a half years since the MXS first debuted, power systems and especially batteries have become much more powerful. The planes not only accelerate faster, but they go much faster too, and carry much more force and momentum, through hard maneuvers. Now the beloved HS65MGs that we use for the ailerons and rudder were starting to show it's age a little and riding on the cusp of being marginal for these planes ..... at least those that were being flown insanely hard.

As you may have read in Testing: Hi Tec's New HS5070MH Servos , it seems like 7.4 is the way the industry is going to go.  After testing the HS5070MH in a 48" Edge, I became convinced this is what you need if you are going to really ream out a 48" EXP. We were simply trying to demand too much performance out of those tiny HS65MG servos, and the only way to get it is with higher voltage.

While the new HS5070MH drops right into the servo opening for an HS65MG,  this creates a bit of a problem for MXS owners, because that plane comes out of the box set up for the HS85MG on the elevator. The HS85MG will eventually burn up on 7.4 volts ..... not the kind of excitement you want considering we are talking about the elevator servo, so we needed another solution.

To go to high voltage on the MXS (and perhaps other EXPs that have been set up with HS85MGs on their elevators), Hitec also offers a high voltage version of their HS5085MG. This new servo is the HS5087MH.

HS5087MH Specifications

Motor Type:3 Pole Ferrite
Bearing Type:Top Ball Bearing Support
Speed (6.0V/7.4V):0.17 / 0.13 second
Torque oz./in. (6.0V/7.4V):50 / 60 oz-in
Torque kg./cm. (6.0V/7.4V):3.6 / 4.3 kg-cm
Size in Inches:1.14 x 0.51 x 1.18 in
Size in Millimeters:29 x 13 x 30 mm
Weight oz.:0.77 oz.
Weight g.:

Again, this is another drop-in deal. It appears to have been made from the same case as the HS85MG, so if you are flying any plane set up for the HS85MG, this servo will just drop right in and even the screw holes will be the same.

All of my 48" EXP elevators are set up for the HS85MG, and I was a bit distressed to think I was going to have to build a whole new hangar of planes to go to 7.4 volts. With the combination of the HS5070MH for ailerons and rudder and the HS5087MH for the elevator, I just change servos and bump up the voltage.

Just My Luck
Honestly, right now is a very inconvenient time for me to be building planes, but just my luck ...... I happened to have a new MXS sitting around that I had built up while recovering from a recent illness. I stripped out the HS65MGs I had installed on the ailerons and rudder and replaced them with the new HS5070MH servos. For the elevator, I bought a brand new HS5087MH and it dropped right in.

A nice surprise on this model is that the servos dropped right in with no modification necessary at all. On my Edge, I had to space the servos out a little or they would bottom out. The MXS fueselage is wider at the rear, which helped give the servos a little more room, and apparently the MXS wing is thicker where the servo mounts. I encountered no problems at all. Hopefully this means the wings on the Laser, extra and Yak will take this 5070 with no modification. We will find out soon because I am converting the whole fleet.

Again, I used a Castle 10 amp BEC to power the servos, but this time I went with 7.4 volts instead of the 8 volts I used with the Edge. 8 volts was simply not necessary, so there was no need to tax the system that hard.

Set Up
Since the plane was already set up for Hitec servos, the servo arms already on the plane work perfectly. Just my luck, all I had to do was change the servos out and tinker with the sub trims a little.

I had previously flown this plane about two or three flights just to check it out and it was fine, so I knew we were starting with a really good platform.

If you compare any of these photos to my previous MXS articles, you will see nothing has changed. Since dimension-wise the servos going into the plane are essentially the same servos that are coming out, nothing on the setup changed

OK, maybe something a bit different this time. The MXS has such great rudder authority that I did not use the G10 arm extension this time.  Instead I used the standard single arm that comes with the servo. With the G10 arm I had my endpoints at less than 100 and at full right rudder the control horn was still hitting the side of the fuselage. With this arm, I peg my end points out at 150 (All Futaba has) and the control horn is about 1/64" from the fuselage at full deflection.

Well, you knew we were not going to change anything here. I did not want to give up any of the MXS' signature insane pitch authority, so we went with what we know works on this plane.

Unfortunately I was not happy with the servos arms we were using previously. They tended to develop slop in the spline and could wiggle around on the servo output shaft. This is not good for a lot of reasons, so I have switched over to Hi Tec's PN55709 servo arm for the elevator. These arms fit better and stay tighter than what we were using before.

This is the longest single arm in the pack, and it gives us the exact amount of throw as we were running before. On the old arms we would have to cut the last hole off the arm, because otherwise it would hit the bottom of the stab, but with the PN55709, you just take it out of the pack and put it on.

We got pretty much what we were expecting. Like on the Edge, the 5070MHs performed extremely well without a hint of stalling or blowback. I'm now seeing that I was getting some of that with the HS65MGs because the high speed roll rate has become blinding. I couldn't keep up with it before, but now it's just crazy.

With the HS65MG previously on the elevator, we were getting really good pitch authority at high speed, and that's remained unchanged with the HS5087MH. I don't think we were getting any stalling before, and now with the 5087 we definitely are not. I don't think pitch authority has become any better because it was always really solid, but on high voltage with the 5087, the plane feels much better in high rotation maneuvers like a parachute and or wall.  It just feels more solid and confidence inspiring.

The MXS seems to snap and tumble with a little better authority, which I think comes for the 5070MHs being much stronger than the HS65MG, which were made marginal by higher performing airframes like the EXP series.

I think for the vast majority of people the HS65MG and 85MG will still be fine, but for the extreme of the extreme, I find these servos are going to be essential. Since these 7.4 volt servos are a bit of overkill, I expect them to have not only typical Hitec durability, but maybe even better reliability because they aren't being punished to their limits like we were doing to the 6 volt servos.

Knowing this project was coming up, I set both my 48" MXS aside, and I really missed flying them. Now that the MH servos are here, I'll be flying this one every day, so stay tuned for more on these servos and, of course, more video.

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