Axius CP Build: A Genius CP / Axe 100 CP Hybrid

Many of you have seen my experimentation in using components made for the Axe 100 CP as replacements for their counterparts on the Genius CP. This was an effort to find a source of replacement parts readily available over the counter vs long wait times for Walkera parts from the Internet.

Well, since Tower Hobbies cut the bottom out from under the Axe 100 CP prices to make room for new Brushless/Night Fly versions, many of us find ourselves buying a complete heli with charger & batteries as a BNF for less than $50, or as RTF for less than $90.

As I've said before; at that price, it's cheap as parts, plus you get two batteries and a decent little charger along with.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCPGV

http://www3.towerhobbies.com/cgi-bin...?&I=LXCPGU&P=M

I've bought 2 of these and 1 Axe 100 FP; I was curious about how a Flybarless Fixed Pitch heli might behave. After building an AnyLink module for my Turnigy 9XR, I found that they all fly very similarly to the mCPX brushed version right out of the box; even the FP as long as one is only doing hover flight. The Axe 100 CP is a rebranded Nine Eagles 125A with different firmware; chassis parts are available for that model much cheaper than from Tower or HobbyTown, although of course, not near as conveniently as getting them over the counter.
As I have recently hacked my 2nd remaining Genius CP and finally resolved the 6-Axis Gyro issues; I decided that now was a good time to take that knowledge and see if I could apply it to a NEW platform. And so, the Axius CP hybrid is born.



The donors:

On the left my old Minius CP, which, while a superior platform to the wet-noodle chassis of the Genius, still didn't resolve its Bat***** Crazy demeanor. The resultant catastrophic crash wiped out half the head, swashplate, tailboom and skids. I still haven't rebuilt.

On the right my second Axe 100 CP. Brand new out of the box, never flown. As good as the Axe 100 CP can be for a starting point.



First off; a side by side comparison of the mechanical foundation:
The Axe 100 CP and the Genius CP both have the same basic configuration; servos arranged in the same geometry, head geometry the same, and the tail boom is a plug-in replacement, aside from this issue: the motor plug is reverse polarity from the GCP.



This trend continues with the servo plugs; ground and signal are reversed as well.




In fact, pretty much everything on the GCP is Bass-Ackwards except the battery plug. I changed the Axe batteries, mainboard and charger to match the dozens of other batteries (GCP and others) that were the same polarity as the GCP. I didn't need the ticking time-bomb of 4 reverse-polarity batteries just for 1 model in my flight kit. Whether you reverse the polarity of the GCP board or the Axe batteries is up to you; the GCP batteries won't fit in the Axe battery box so you'll need to plan on using the Axe batteries for this mod. Also, remember that since we are swapping the brains of the Genius into the body of the Axe, you'll need to use your Walkera Devo transmitter, NOT your Axe transmitter.

For your reference; the Axe battery box inside measures 6mm H x 17.7mm W x 27.4mm deep.





Swapping the pins on the servo plugs and the motor plugs is easy; just slip the point of an X-Acto knife under the plastic retainer tab and lift a little to release the pin...




... then swap them around and plug them back in. Easy-Peasy. Don't stab yourself with the X-Acto knife; blood all over the connectors makes them harder to identify.





This is what your servo & motor plugs should all look like once you're done; note the positive wire in the middle of the servo plug doesn't get moved.





Now we have the connectors fixed so it all plugs in right, time to install the GCP mainboard and test. After much trial & error with my hacked GCP, I discovered that the MB needed to be tilted approximately 2mm higher on the port side with respect to the floor of the chassis than the starboard side. It needed almost no angle from front to back.

Knowing this, I decided the simplest solution might be best; I cut approx 6mm off of the front of the existing 2mm thick mounting foam, and stacked it on the port side. As you can see, I also had to cut a recess out to make room for the big yellow capacitor on the bottom of the GCP MB.





While I'm busy fiddling with other bits, I'll put a leftover bit of the backing paper from Peel & Stick Velcro on the gummy bits to keep them from getting fouled & losing their stickiness.





GCP MB all mounted...





...and side by side with my hacked GCP for comparison. Looking GOOD!





All plugged in & ready for a bench test; note that I color-code my plugs for convenience sake. It doesn't matter what colors you use for what; just be consistent. I don't even see colors there anymore; I just see ELEVATOR, AILERON & PITCH.


[youtube]http://www.youtube.com/watch?v=BsHGSr-npHI[/youtube]


As you can see the servos all work, but they all work backwards; now we have to reverse the servos internally in order for the Gyro & FBL processing to work correctly. Investigation compared to a generic servo of the same type shows that the HeliMax servos are wired the same; it is the GCP firmware that is configured reverse of the norm. Yet ANOTHER WAY the GCP is Bass-Ackwards!


There are several reasons to reverse the servos internally:

1)
Cost vs Convenience. It's true that several vendors offer linear servo reversers for approx $2 each; I have spent some time searching and still cannot find one that come with the 1.25mm pitch Micro JST-SH connectors used on these servos. Spektrum offers a micro linear servo reverser that would be great to at least try, except they chose to use 1mm pitch micro connectors which aren't compatible with anything else. (Of course) This means just as much soldering as if one simply reversed the servos.




http://www.horizonhobby.com/products...FSfl7AodTn4AOw

2)
Weight. They weigh .6 gr each; but there are 3 of them. By the time you solder bigger connectors on each end, more like .7 or .8 gr each. Now we're talking 2.1-2.5 grams added to your AUW.

3)

Lag. I don't know how much lag the signal processing will inject into this circuit; but any amount is mission critical. As a pilot you'll probably never notice a few milliseconds lag in an Aileron servo's response time; but in a FBL servo's control circuit, those milliseconds can make a big difference. Maybe when I break a servo I'll try making a reverser that fits to see if it makes a difference; right now, I need this thing working so we can see results. I know how to reverse a servo, and I know it won't impair the performance of my heli.





The servos are easy to remove; once you take out the single screw in the canopy yardarm, rock it, servos and all, back a little to clear the retaining tab on the main mast. Now you can lift the yardarm/servo retainer off of the tabs on the servos.





The Elevator servo is held on by this plastic bracket; there is a screw here and directly opposite on the other side. Make note of the orientation; there are indexing pegs as well which you'll be able to see once you lift the bracket off the chassis. Now, carefully remove all the wires; it's a good idea to take pictures before you do so you know exactly how to reroute the wires when it's time for them to go back in.

The next few images are a side by side comparison with the HobbyKing HK-5330 1.9gram servo:





As you can see, the HeliMax arms fit right on the 5330 shaft...











...and here I've taken the top cover off to show identical gear trains between the two.





To do the work we want to do, you only need to remove this single screw...





...and release this tab on the other side under the servo wire.





Here you can see even the same Single-chip servo controller on both units; really, only the colors have been changed to protect the profit margins. HobbyKing's servos are now shipping in white instead of that skeevy orange color. Slightly less skeevy looking; though a little screen-printing might make them not look so uber-generic.





To reverse the servo, we need to swap two wires to reverse the potentiometer signal...





...and two more wires to reverse the motor direction. Make sure you don't have any bare wire hanging over the edge that butts up against the motor; they could short out against the metal motor shell.





Make sure you don't lose this little bit of plastic insulator; it lays on top of the potentiometer.





If you do (like I did on one), you can make a new one out of a scrap of blister-packaging plastic. Dimensions are 5mmx 6mm.





Once you slip the control board back in place, make sure to carefully route the motor wires as shown so they don't get cut by the servo bottom case when you put it back on. Note that the servo pigtail wires are soldered so they face towards the inside of the servo case; fold about 3mm or so of the servo lead over itself before you install the bottom shell. This is done to act as a strain relief. Make sure you don't fold over so much that it lays on top of the transistor there; it might cut the wires if pressed against the case.





Here you can see the wires routed properly through the channel in the case made for them...





...and here you can see the insulator in place between the controller and the potentiometer. If you look closely, you can also see the little bit of servo wire folded over itself as a strain relief.




If you've done it right the servo wire should look nice & tidy like this. Also make sure you get that locking tab snapped back in place properly.




A quick test with just servos plugged into the Genius MB show they don't center to exactly the same spot as the Axe MB either; but once the arms are moved a couple clicks, they're pretty close to 90°.

Be sure you have your trims and subtrims in the Walkera TX all set to ZERO before you start and main & tail motor wires are unplugged.

Remember that your reference point is THROTTLE stick exactly at midpoint, FM (Flight Mode) switch at "IDLE UP" or "STUNT" mode with THROTTLE HOLD OFF. Keep the RX & TX powered up all the time you are making these adjustments.

Make sure you have the GCP MB set to "SETUP" mode. (DIP SW 1 set to OFF) If the servos move when you move the MB, you're NOT in setup mode. Rotate the servo arms as needed to get them as close to 90° as possible. Install the screws in the arms; ELEVATOR & AILERON servo arms point to the right; the PITCH servo arm points to the left. Now it's time to reinstall the servos.





Make sure to route the servo wires like this before you install the canopy yardarm/servo retainer; the plugs won't fit through after.






Rock the servos & retainer into place under the locking tab; make sure they're tightly in place before you install the one retaining screw. It will fit with very little force; if it doesn't, look for a pinched wire in the way.





A little extra time spent here carefully routing the wires through the provided retainers will save you a lot of headache with wires ripped off by servo linkages later. Ask me how I know.





Okay; now it's time to trim out the servos. AGAIN:

Be sure you have your trims and subtrims in the Walkera TX all set to ZERO before you start and main & tail motor wires are unplugged.

Remember that your reference point is THROTTLE stick exactly at midpoint, FM (Flight Mode) switch at "IDLE UP" or "STUNT" mode with THROTTLE HOLD OFF. Keep the RX & TX powered up all the time you are making these adjustments.

Make sure you have the GCP MB set to "SETUP" mode. (DIP SW 1 set to OFF) If the servos move when you move the heli, you're NOT in setup mode.

The Walkera Devo TX doesn't permit you to set subtrims on the individual servos; instead, it sets subtrim on the ELEVATOR, AILERON & COLLECTIVE PITCH virtual channels. First, get the amount of offset equal between all three servos by adjusting first the AILERON SUBTRIM so that rear two servos are equally off-center. Then, balance those with the front servo by adjusting the ELEVATOR SUBTRIM so that you can get all three servos the same amount away from 90°.





Now you can adjust the COLLECTIVE PITCH SUBTRIM to bring them all up (or down) to 90°. I know it's hard to tell from the photo; but trust me, they're all pretty close to dead-on. Don't worry if you don't get it right on the first try; just do it all again starting with the AILERON SUBTRIM. You'll get closer every time until you have them right.





Now it's time to level the swash. AGAIN:

Be sure you have your trims in the Walkera TX all set to ZERO before you start and main & tail motor wires are unplugged.

Remember that your reference point is THROTTLE stick exactly at midpoint, FM (Flight Mode) switch at "IDLE UP" or "STUNT" mode with THROTTLE HOLD OFF. Keep the RX & TX powered up all the time you are making these adjustments.

Make sure you have the GCP MB set to "SETUP" mode. (DIP SW 1 set to OFF). If the servos move when you move the heli, you're NOT in setup mode.

There are lots of tricks and tools for this; but thankfully the Axe has plenty of room at the floor of the chassis to be able to just measure with a ruler at all three swash balls. I wish Walkera had thought to do this. Adjust your lower links so that the swash is level; then adjust all three an equal number of turns so that so that your blades are at zero pitch.

Now, time for a second test of the servo action:


[youtube]http://www.youtube.com/watch?v=d40CsW_iEJA[/youtube]


As you can see, all the servos operate correctly, and the blades are at zero pitch (this is the easy way to determine zero pitch on a FBL heli; both blades side by side at 90° from the rotor head). Time to see if it flies!

[youtube]http://www.youtube.com/watch?v=-rILhMpjeLU[/youtube]


As you can see, the 6-Axis Gyro is working better than with my hacked Genius CP (See my other videos for a similar bench flight with a homebrew adjuster mechanism). I'm VERY pleased with this; the stability and self-correction are everything I hoped for when I bought my first Genius CP 2 years ago. I was ready to kick it to the curb a dozen times; had I guessed that the fix might be as simple as raising the port side of the MB 2mm I'd have been loving my GCP all these years. I've been flying my hacked GCP for a couple months now; I think I'll rebuild and get rid of the adjuster mechanism, that way I can put a normal canopy on it.

My experience here, and the reproducibility of the same issue and the same fix, indicates that this is a single, simple fault in one axis of the 6-Axis gyro which anybody should be able to replicate. My advice, if you want to use 6-Axis mode, is to just TRY adding 2mm of sticky foam to the port side of the MB as I have done. If it doesn't work perfectly as it has now twice for me, I'm willing to bet it at least gets everything close enough to get it perfect with subtrims. I know a lot of folks have spent a lot of time chasing vibration as the culprit here; my experience indicates that vibration is an issue best cured at the source by making sure your rotating mass (head, motor, gears and blades) is properly balanced, rather than trying to fix the mounting so it is more vibration resistant.

Summary:

Aside from EVERYTHING being reverse-polarity on the two, I think that the combination of the Axe 100 CP chassis and the Genius CP mainboard results in a heli that is superior to either original craft. The Genius chassis is terribly designed; it is not nearly rigid enough because they tried to use the same flexible plastic as they make skids out of so it could be all one piece. When loaded heavily from aggressive pitch-pumps and similar acrobatic maneuvers on the bench, I could see the main motor deflect as much as 4mm in all directions, and it deforms easily from motor heat.

HOWEVER... the head and servo geometry are great, and the MainBoard IS pure GENIUS despite the poor manufacturing execution. We are just now seeing similar flight-stabilization gear from the big names; while I've seen a couple that were close to as good, I still have yet to see anything BETTER than the Genius design which is now over 2 years old.

Whether you choose to build on the Axe 100 CP, Mini CP, or Genius CP platform is up to you; personally, I love the Genius for its brains, not its body. I think either the Mini CP or the Axe 100 CP / Nine Eagles 125A is a much better chassis; that was why I built my Minius CP in the first place. It had the best of both: a really great, rigid chassis, and even BETTER servo/swash geometry (The same trilateral design as the Goblin) and the same great, rugged head as the Genius. If I'd only known how to make the GCP MB work right, I'd probably have never stopped flying it.

Pros:

1) Cheap servos. HobbyKing has the 5330 currently available for +/- $3.30 from the US warehouse and the International warehouse; you can buy 4 for the list price of a GCP Walkera servo:

http://www.hobbyking.com/hobbyking/s...dproduct=33312

http://www.hobbyking.com/hobbyking/s...ec_0_17kg.html

2) Parts available over the counter, not just via internet. Of course you can buy them cheaper online; but when you're broke down you can go to your nearest HobbyTown and get parts. Most "Local Hobby Shops" that stock the Axe 100 CP as part of their partner program with Tower Hobbies will also keep at least the common fail parts in stock.

3) Better chassis than the GCP: More rigid, separate skids so you don't HAVE to patch with hot glue all the time. We all know you will anyways; but you don't HAVE to.

4) CHEAP AS DIRT. Where else can you buy a 6CH FBL Microheli, complete with 2 batteries and a charger for under $50? NEW, I mean, and not out the back of a white van?

5) Upgrades: Bling it on, baby. All the new CNC bling for the Axe 100 SS/SSL fit the Axe 100 CP. I'll let you know what else fits the platform as I find out myself.


Cons:

1) Canopy. It breaks easily like the original GCP Canopy did, and it's expensive at $11-14. The Axe 100 FP canopy costs $8-9, but you have to move the grommet holes. You CAN buy the Nine Eagles 125A canopy for as little as $4-5 online though. However, the Axe 100 SSL canopy is pretty sharp looking at $11:



http://www3.towerhobbies.com/cgi-bin...?&I=LXDHFT&P=M

2) Tail rotor: Whose brain-fart was it to price a single tailrotor at $5.49? Buy the KBDD ones for mCPX for $3 a pair and fuhggeddaboudditt.

3) Upper links (swash to blade grip): They break. A LOT. Buy them in mass quantities. They're 4/$3 at Tower; you can buy the Nine Eagles ones online at 4/$2. I suggest buying 10 packages at a time if you can get a quantity discount. On the plus side; if the links are breaking, you're probably not going to break servos as much.

4) Batteries. Your GCP batteries won't fit; you're stuck with the Axe 200mAH batteries. They're not bad, and they're not expensive. HOWEVER... the Axe 100 SS (The new brushless version they're clearing the Axe 100 CP out to make room for) has what looks to be a larger, longer battery box in the skid to accommodate their 400mAH battery. It also looks like the new skid should bolt right up to the Axe 100 CP chassis. I'll let you know when I have it in hand.

5) Too many itty-bitty helicopters: You know you're going to buy two or three at that price; hell I did and I'm so cheap I make a Scotsman look like Hugh Hefner. (It's the Welsh dwagon in me.) Your wife will threaten you with bodily harm and your fleet with two-fisted flyswatters. Be warned.

Resources:

The Nine Eagles 125A part list, with part numbers for reference so you can Google prices, is here:

http://www.nineeagle.com/part_detail...029454145.html

The Axe 100 CP Parts list is here:

http://www3.towerhobbies.com/cgi-bin...I=HMXE0821&P=Z

The Axe 100 SS/SSL parts list is here:

http://www3.towerhobbies.com/cgi-bin...I=HMXE0824&P=Z


And eHirobo's 125A V2 (Night-Fly Version) parts page is here; it also appears to have a lot of Nine Eagles part #s:

http://www.ehirobo.com/shop/Nine-Eag...654/index.html


Well; that pretty much covers it for now. I go to my Flying Club tomorrow night; hopefully I'll have a chance to get some decent video of it flying in 6-Axis mode. I'll update here as I have more news; there's still a lot of stuff I want to try out. I really like this platform; I think it has a lot of potential.


Tags:

Genius CP, Axe 100 CP, Flight Test, 6-Axis Gyro, Axius CP Build, Heli, Microheli, Helicopter, RC, Radio Control, Flight, Flybarless, CCPM, 6CH, Collective Pitch