!!!WARNING!!!
This is a very, very long post.


Parts list: (see pic)

Main motor: KB20-40-17L 3400k from United Hobbies

Tail motor: AMMO 12-30-4110 from Tower Hobbies

Main ESC: H-Wing Pentium 18amp (HW P18A) from U.H.

Tail ESC: H-Wing Pentium 6A /.8bec/6g Speed Controller (HW-6A) from U.H.

Programming Card: OEMRC P-Card for H-Wing ESC’S

Gyro: Futaba GY240


Misc. Parts:

From Tower Hobbies: HPI cone washers (LXN050), Hitec 24 “extension wire (LXHZW3), GWS tail housing (LXHHE4), Custom Works cone spacers (LXNUA4)

From Radio Shack: Radio Shack's Normally-Closed momentary micro switch (275-1548).


The Build
OK here we go! As you know taking the blades off helps a lot. Or you can take off the whole rotorhead. The easiest method I’ve found to do this is to pop off the flybar links at the swashplate and remove the head bolt (see pic). It’s only 3 points and the head will then pull off in one piece. Now that access is easier I moved on to removing the main motor, 3-in-1, and tail motor. Taking the tail boom off makes this easier too.


With the motors out I then removed the pinions. I used a GWS micro-heli pinion remover (see pic). It worked well on the main motor, but I had previously pushed the tail motor pinion on further to increase clearance between it and the tail rotor so it didn’t work there. I used some small diagonal cutters and pried it off carefully. It came off pretty easy so no big deal. Putting the pinions on the BL motor was easy enough too. On the tail motor I did cut about 1-1.5mm off the end of the shaft with a Dremel again to maintain clearance between the pinion and tail rotor.


I took a measurement from between the OE motor’s can to the bottom of the pinion so when I re-installed the pinion on the BL motor it would be centered vertically with the main gear. My pinion was a bit off so I adjusted my measurements to center it. To install the pinion I used a piece of hard wood. Since the shaft protrudes past the gear I also drilled a hole in the board for shaft relief. With that I was able to press the gear on. The tail can be done the same way.
I’ve also heard C-clamps work very well too.


When installing the main motor I had to file the slots in the frame to get the screws straight going into the threaded holes in the motor. I used the original 2.5mm x 5mm cap screws with the HPI cone washers (see pic). They worked great. The washers don’t bend or cone. They come pre-coned. On some motors the side of the washer may have to be filed to clear the bearing housing on the motor (see pic). It depends on your motor. Here’s a word of caution on threading in the screws. Do not use a ball type hex driver here. I used a 2mm Integy driver from Tower (LXKTJ2). It’s just too easy to cross thread into the aluminum housing of the motor. I also made sure the wires were toward the rear of the heli. Once you set your mesh tighten her up and that’s it.

OK, now onto the tail motor. Using the OE tail housing it’s a simple bolt in procedure.


I didn’t go that route. I used a GWS tail housing because it’s beefier (see pics). It doesn’t have long slots for the motor screws like the OE housing so the motor fits very securely. In fact with the pinion installed it took some work to get it in. The GWS housing also has a different offset from the OE housing so it requires a spacer (see pic). A Custom Works cone washer worked perfect (see pic). With the smaller part of the cone against the bearing it only contacts the part of the bearing that’s spinning which is good.


My tail motor came with 4 screws. I thought they were a little long so I cut off a millimeter or so just to make sure they don’t contact the windings.


OK, so now the tail motor is mounted in the housing. At this point you need to salvage the old tail shaft or get a new one. When putting the tail shaft into the tail housing make sure the threaded hole for the boom screw lines up with the bottom of the tail housing like on the OE housing. I dabbed a little CA on the tail shaft to keep it secure in the housing. I added a step here using a modified Wal- Mart knitting needle (more on this later) I had to reduce the diameter of the tail shaft so it’d fit inside the needle (see pic). The needle has thicker walls.


Then I test fitted the shaft in the boom (see pic). I also wanted to make sure the tail shaft/boom screw didn’t protrude into the hole, but it did so I ground it down till it was flush. Notice the pattern yet. I’m paranoid about electrical shorts. At this point it’s nearly ready to go into the tail boom, but before that the motor still has to be wired.


For the tail motor wires I used the Hitec 24” servo extension for the wiring on the tail motor it’s a snug fit through the tail shaft, but it’ll go (see pic). I fed just enough wire through the tail shaft from the “boom side” to make the connection to the motor. I did it this way so I wouldn’t have to pull the whole length of wire through the tail shaft. I then desoldered the connectors and soldered the Hitec servo wire directly to the motor. After determining proper length I resoldered the connectors on the Hitec servo extension wire (see pic). I then pulled it through the boom using fishing line. It’s tight to get the connectors and wire down through the hole between the main gear and boom without taking out either the servos or main-gear (see pic). You may want remove to either or both of them out to make it easier. You could also solder the connectors on after the wires are through the boom and around the bend.


Now we move on to the ESC’s. This is pretty straight forward as you can see from the pics. First I soldered the motor connectors on to both ESC’s. Then I soldered the battery wires from both ESC’s onto a common connector. I used a Dean’s Ultra Plug. For mounting I used 4” zip ties for the main ESC and double-stick foam tape for the tail ESC. After that it’s a matter of hooking up the motor wires and Rx connectors. Don’t forget to disable the tail ESC’s BEC (see pics). I cut the negative and positive wires out completely. The only down-side is now I need to use the BEC from the main ESC to use the program card with my tail esc. To rectify this problem I took a Y-servo harness and cut out the white signal wire on one side (see pic).


Now I have had some little problems pop-up.

First the main motor didn’t seem to work right. It seemed like a pole on the motor was burnt out. It turns out the “Super-Soft” start option on the ESC doesn’t have the power to start the Axe’s heavy (compared to a propeller) rotor. Took me a while to figure it out, but resetting the ESC to “Soft” start solved the problem.


Problem number two. The tail ESC wouldn’t arm. Turns out the GY240 and ESC don’t like each other. As close as I can figure these particular ESC’s need to power up and receive a signal from the Rx at the same time. The gyro initialization caused a problem. After some experimenting I found that if I interrupted the Rx signal between the gyro and ESC after the gyro armed the ESC would beep a “no Rx signal” code. I discovered that if I unplugged the ESC from the gyro then plugged it back in it would arm. Cool! However instead of pulling it apart every time I installed a normally closed momentary switch to temporarily interrupt the signal (see pic). It worked out well. Now I wait to arm the tail till the body is on and the heli is ready to fly.


The only catch is that the throttle must be at zero which means the gyro has to give a 0% throttle signal. If the heli has been turned counter-clockwise then it will not have 0% throttle.
So I just to turn it clockwise till the servo armed. The other thing I did with the tail ESC is set 0% throttle at mid-stick instead of far left. Not bad considering that none of this stuff was designed to work together.


Anyway that’s my Axe CP full BL conversion. I hope you found it helpful.

... and yet even more pics!

Wal-Mart Tail boom

This is the Wal-Mart knitting needle-to-tail boom mod. At three or four bucks for two of them it’s a great mod. It’s also fairly straight-forward. Just pop off the buttons and cut to size. I did this with a Dremel and cut-off wheel. The hole from the tail shaft screw is 5mm from the edge. The hard part is grinding or sanding down the tail shaft evenly. I did it with a Dremel and used a screw as an arbor, but putting the tail shaft in a drill would probably work better. You could also have a machine shop lathe it down. Going that route I’d bring a couple tail shafts.

Aside from that I changed out some of the Axe’s hardware too. I changed the head button screw to a Dubro 3mm x 6 flat head screws (Tower Hobbies-(LXFRJ8). I thought it looked better . I also did the popular cap-screw mod on the blade grips, but they hit the blades when they folded forward so I went with Heli-Max 2mm x 5 button head screws (LXLBR0) and Heli-Max 2 x 4 x 0.3mm washers. The washer’s slightly smaller outer diameter allows it to only contact the inner race of the bearing. This helps alleviate that “sticky collective” problem the Axe sometimes exhibits after a changing a broken blade grip. The lower profile bolt no longer hits the blade. The Button head does require a smaller size 1.27mm Allen though as you can see. Though this size is rare it’s SAE counterpart isn’t, usually listed as .05” or .050” it’s the same exact size. I use Integy 0.05” drivers (LXKTH7) and they work great.

Well that’s all I’ve got so far so good luck and happy flying.

My flight report

The tail has a lot of power. In fact I recommend the AMMO 12-30-3850 if you’re going to a BL tail motor and maybe even a DD tail if you’re not worried about bending the motor’s shaft in a crash. The 3850 is actually the one I meant to get. I have to pay closer attention when ordering .

The head speed is way up. It’s too high actually. It’s 2880 rpm in a hover and 3000 rpm at full throttle. The thing is a rocket. I’m still using the stock Tx so I don’t have the luxury of Throttle/Pitch curves therefore I can’t optimize my set up. Even if I could optimize the curves I’m nowhere near the skill level to take advantage of 3000 rpm.

I’m also stuck with the OE 14T pinion. I’ve heard it’s a weird pitch. Regardless I haven’t found any other pinions that will work. The run time is down about 3 minutes or so from the brushed motor set-up and I’m not happy about that either. With my pinion problem I’m now looking to go to a 2900Kv motor. I look at it this way since there doesn’t seem to be a direct correlation going from brushed to brushless I look at this first motor as a point of reference plus it was only $15. Anyway I’ll let you know how it goes when I get the new one.

Heliko - very cool man!! I may have to try this... thanks for being our test pilot

Since Helimax gave the Axe the wierdo pitch gears, wouldnt the mod described by Rollingball [link=http://www.rcuniverse.com/forum/m_5620569/tm.htm]HERE[/link] be the perfect companion to a brushless set-up?

I have already gotten the motor and speed control for my brushless set-up, just waiting to pick up a tail, tail esc, and gyro. If Helimax doesn't make a set of pinions for the Axe CP then I'm going to seriously consider the main gear mod. Not only will this open the door for easier to find pinion gears, but I'll have an auto hub to boot

Excellent write up Heliko

Thanks guys,

ATB, it would be cool to have an autorotative main gear, but I don't want to cut up my frame and at $30 for the gear it's kinda pricey. Regardless though it's still nice to have the option.

After I ordered my second BL motor a fellow RC heli pilot from RC Groups found some pinions that may work. He did the math and found that these pinions with a 0.4 module size are very close to the Axe. I think he said it's like a 0.08% difference. Here are the links to the [link=http://www.bphobbies.com/view.asp?id=V053824&pid=NGWSV058]10T pinion[/link] and [link=http://www.bphobbies.com/view.asp?id=V053824&pid=NGWSV057]12T pinion[/link] They also have 14, 16, 18, and 20T pinions, but they really wouldn't be useful to us. If this second motor doesn't put the RPM's where I want them I'll give the pinions a try.

Would installing some type of inline resistor to lower the voltage by a volt (to 10.1) lower the headspeed? I know for sure that the electronics on the Axe will work fine with as low as 5v (BEC circuit) and the motor is happy running off of anything above 7v (took a voltage reading off my stock NiMH pack after about 2mins flight time and continued to fly for another 3mins).

Or would an inline resistor lower the duration LiPo?

ATB, I'm not sure, but I don't think a resisitor would work. If you added resistance you'd decrease amperage, but voltage would stay the same. Remember Ohm's law. Amps x Resistance = Volts. I'm not sure how that would affect a BL motor. Probably not good though.

If I remember right a diode may work. I used them once for something a long time ago (can't even remember what [sm=confused.gif]) and I think they dropped 1.2 volts per diode.

The problem is volts x amps = watts. If voltage is dropped then overall power is reduced. I want the power just at a lower headspeed. Even if no other pinions work it's just a matter of finding the right Kv motor. Like I said the first motor was a reference point. I'm confident my next motor will put the headspeed where I want it. Plus I'm keeping my fingers crossed.

Nice work, you definitely need to pitch that stock TX[X(] Seems like a lot of work though, why not just get a MX400 or a better bird?

Its all about improving and upgrading!

Nice job, hope the motor swap or the pinions get you where you want to be. Let us know if the flight times come back up.

I know. I'm planning on upgrading to a 7C one of these days.

I like the Axe. I like it's size. It's a stout, simple (relatively speaking) heli. I wish I could've gotten a bare bones model though.
When I bought it I wanted a CP heli with a Hiller type head that could handle some outdoor flight. I'm not planning on any 3D at least not for a long while so a collective T/R isn't imperative. What I really like is scale. I eventually want to turn the Axe into a Dauphin with a fenstron tail. This would be hard to do with the 400. My BL tail motor will bolt right into a GWS 40 or 50 EDF and work well for the fan tail.

I'm sure I'll eventually move up to a 400, but right now I'm happy modding and learning how to fly the Axe.

Happy flying

One could also install the ARK-400 Main gear and flip the bearing if one does not want to mod the frame. Just a thought
[quote]ORIGINAL: alienteabagger

Since Helimax gave the Axe the wierdo pitch gears, wouldnt the mod described by Rollingball [link=http://www.rcuniverse.com/forum/m_5620569/tm.htm]HERE[/link] be the perfect companion to a brushless set-up?

I have already gotten the motor and speed control for my brushless set-up, just waiting to pick up a tail, tail esc, and gyro. If Helimax doesn't make a set of pinions for the Axe CP then I'm going to seriously consider the main gear mod. Not only will this open the door for easier to find pinion gears, but I'll have an auto hub to boot

Excellent write up Heliko

Well today I had an unscheduled field test for the tail boom. Short take, I crashed resulting in some nasty blade strikes on the boom. The surprise is after a couple square hits as you can see the tail boom was nearly unaffected. My OE boom would been at a right angle. This turned out to be a great mod not only for the price difference, but durability as well. My only real damage was two more grips. This puts me around ten now I think.

How about buying a pack of those metal ball link ends (I think the correct size is 3mm). Drill out the broken blade grips and installing those?

this is a killer mod!!! Not only do you get to walk through the walmart with knitting needles wondering what people are thinking (I used the ninja story).... it also looks great and looks like it's a bit more healthy than stock!! thanks Heliko!!!!

ATB,
I already have the metal ball links. I think they're 3.8mm and they were $15 from Helihobby. I bought them during the blade grip shortage because I was desperate to get back in the air. I made that modification on one broken grip and used it temporarily until I could get new grips. The metal-balled grips are stronger without question. The reason I changed it back out to plastic-balled grips is the same reason I never went to CNC grips like many others during the shortage. The grips act as a fuse or shear-pin. When they break they saves parts further up the line, and since they're cheap and easy to replace I decided to stick with them. The crash I had was into the stairs of a deck and the damage was minimal. I believe this is largely due to the sacrificial grips.

Strat this is a killer mod, you'll really like it.

Heliko this is an awesome thread. Thanks for being the guy to do this right and document it in a way that a newcomer like myself could also try to achieve these results. You might want to try the CNC Blade Grips. I like mine. Yes they do transfer the damage, but some of the crash energy is also absorbed and dampened in the process. What winds up breaking is the seesaw instead of the grips. This seems to happen after 2 or three shall we say "hard landings". Learning nose in on a failing stock battery can result in this.

Thanks No Hesitation I glad you found this thread helpful. I may try the CNC grips one day on two conditions.

1) I stop crashing, or at least stop crashing as much and...

2) They make them in a color other than purple [:'(]

Thats why sharpies come in so many colors my friend heh heh

Oh yeah, I got 'em, they work great on the blades, but on the aluminum it rubs off pretty easy and you end up with technicolor fingers.

It's OK though as popular as the Axe is they'll soon be an aftermarket following, one of the salesman over at Helidirect told me they're already working on upgrades including CNC parts. They'd have to be crazy not to. In the automotive industry about 70% of their profit comes from replacement parts. I'm pretty sure the RC heli industry works the same way so in time we should see lots of cool stuff in cool colors for the Axe.

Heliko ill 2nd that ! No Hesitation got it right!!! i vote you our demo man! in a matter of speaking
wal-mart specials works for me, along with your nice step by step (picture text) cough cough! lol
keep it coming i went down yesterday....same thing to my grips i agree with you its a lot cheaper
replacing them then a lot of other parts! a lesson i learned is don't turn away from you heli
even if its to tell your son he can go out! is all it took for me to wind up stuck!!
in the wall of my game room!! my son asked if i was redecorating the walls! smart guy ,lol

BL update

Well I've put a few flights on the BL set-up and it's working well save for one problem. During quick or sharp rudder inputs the tail jumps around and wind seems to make it worse. This caused a nice crash the other day which luckily only resulted in a broken strut. I'm told this may be gyro resonance since the motor isn't acting fast enough the 240 is over compensating. I'm going to try a few things to rectify or at least lesson this effect such as a DD tail and tweeking the gain, but until I do I can't recommend a BL tail. []

I also found out from a fellow poster that [link=http://freestyle-hobby.com/]Freestyle Hobby[/link] has a belt driven tail in the works for the Axe so that's another option.

wouldn't a change of tail motor pinions fix that? Smaller pinion = faster spool up of tail rotor?

Im paying close attention to thids post so once i get all my BL parts together I'll know what to do =)

It's not the spool up of the tail rotor it's the lag time of BL motors. This is a hot topic right now in the RC Groups micro helis forum. It seems the 240 is an impatient little gyro. It also might be the tail ESC. Afterall it was only $16 and though it works fine it wasn't made to control a T/R. It also may have to be upgraded. I expected some difficulty with this. It'll take a little time, but I'll think I can get it to work better. Of course Tower is out of stock on some of the parts so that's going to slow things up, and the heli is down right now from the last crash so I'm waiting on other parts. Oi Vey!!