Thinking outside the 6s box, my 12s Rex550 build


My reasoning and concept behind the 550e
The purpose of this heli in my fleet is to be the biggest one. I have no room in my life/house/car for a 600 or 700. I also needed this bird to be affordable and yet well thought out. This is where the concept of using a pair of 500 sized packs (6s 2650s in my case) to power the 550 comes in. It allows me to share packs between my 500 and 550 in order to limit both the number of packs I own and the number of different sizes.

Now I could have simply built a stock TRex 550e and used the stock power system but as most know the stock Align stuff is often not the best choice. It does work for many pilots but I wanted to use something different. This is where my 550e starts to deviate from the norm.

It comes down to this; instead of running the stock 6s power system off a pair of my 6s packs in parallel, I would replace the motor and esc in and run a pair of my 6s packs in series. This creates a more efficient and elegant 12s power system and effectively halves the the system currents, replacing the 40A average seen by most 550/600 owners running 6s with a much more reasonable 20A average. Likewise it halves the potential 150-200A peaks, making them much more reasonable at 75-100A peaks.

For more info on HV power system, see my article HV Power Systems, why they are better

Choosing the components
The 550e only comes as an ESP Align kit that includes the airframe, blades, motor, esc, servos and gyro. I planned to use the airframe, blades and servos, but everything else would be replaced. I would put the unused kit items to work elsewhere or sell them. In the end the shopping list looked like
  • Align 550e FB kit
  • Castle Creations 60A HV esc
  • Scorpion 4025-630kv motor
  • Western Robotics High Current bec
  • Spektrum AR6200 rx
I sat on the idea for about a month, trying to save up for it, and then just could not help myself. Out came the credit card and soon I had a big box sitting on the workbench, filled with a big pile of parts that would soon be my new heli.

Putting it all together
It took me about 4-6 hours per day for 3 days to put it all together, and get it wired and set up. I ran into a few kinks along the way, outlined below, but overall it was a pretty simple built and setup.

Whittling on the frame
I knew from the beginning that the Scorpion motor would not fit in the bird without trimming the frame. What I didn't expect was how little I would have to trim. I had seen several photos of trimmed frames, many of those were for the Neu motor which requires a lot more trimming, but the Scorpion only required the inverted "T" to be removed on each side. I used some of the bottom plate mounting parts to clamp the frames together in order to do them both at once.

The soldering
Wiring up the power system was fairly simple. I used a different way of doing it from what most will use. Instead of using a 12s bec run off the main 12s pack, I used a lower voltage bec and ran it off only 1 pack like shown at the bottom of my HV article. This not only gives more options for the bec but also allows me to power just the receiver for setup, leaving the esc underpowered for safety.

Once I got the soldering all done, I got everything installed in the heli and started the radio setup. That is where I ran into my first kink.

The kinks
Every project will have its kinks and hiccups, and this one was no different. Here are the problems I ran into when putting together the 550e.

Kink 1: The WR High Current bec comes up a little short for the high current draw of the DS610 servos. During the initial servo setup I found that my AR6200 rx would randomly start blinking. It took me a little while to find the culprit but I finally figured out that if I made a quick movement on the cyclic stick, it would start to blink. More testing showed that by simply pulling the cyclic back to the lower left corner and letting go, causing the cyclic servos to bounce, would drop the voltage on the bec to as low as 2.5V and cause the rx to reset. I talked to WR and they pretty much said that the bec is to small for my application. The bec was replaced with a LiFePO4 receiver pack for good measure.

Having setup the heli, I was ready to setup the esc and so I went to install the motor and pinion only to find kink 2.

Kink 2: The stock Align motor has a 6mm output shaft, so the pinions that ship with the kit are for a 6mm shaft. The Scorpion 4025-630 ships with a 5mm output shaft. I had 2 options, I could buy a 5mm pinion or I could buy a 6mm shaft. I ended up doing both but used the 6mm shaft in the end.

With the esc and radio setup, I went through the whole bird one more time to make sure everything was good to go and this is where kink 3 was discovered.

Kink 3: The Hyperion VX 2600 6s packs are an odd shape. This shape works well on 500s but it makes a pair of them just a little too big to fit under the stock 550e canopy. I tried several placements and orientations but could not find one that would work. Using the lower position for the battery mount will likely allow the packs to fit but then I will have to trim the frames and I do not want to do that. I have some Nano-Techs coming that should fit without issue. For now I am just flying without a canopy.

Setting up the CC ICE HV 60
I have setup many CC escs, so this part was actually pretty easy but many have a hard time with it, so let me go through the steps I use.

Step 1: Connect the esc to a computer and program it. During this step every item on every screen needs to be looked at and adjusted as needed. My initial setup looked as follows

Heli, Governor mode, Set RPM
Motor/gearing = 630Kv motor, 8 pole, 16T pinion, 170T main gear
Auto-rotation enable = checked
Gain = 15 (default)
Initial spool-up rate = 5 (default)
Head speed change rate = 12
HS 1 = 2000
HS 2 = 2100
HS 3 = 2300 ("Info" red saying 97% throttle needed)
Motor timing = 5 (default)
PWM rate = outrunner (default)


I also setup the ICE logging screen to capture everything except the ripple and throttle input.

Step 2: Initial radio setup and setting the end points. Set throttle curve to be a linear 0-25-50-75-100 curve. Reduce high/low throttle end points to about 60. Power heli with throttle stick in high position. Raise the high throttle end point until esc beeps and then go 2 more clicks. Place the throttle stick in the low position and raise the low throttle end point until it arms the esc and then go 2 more clicks.

Step 3: Setting up the "Auto bail-out feature". Turn on throttle hold in the radio and set the value to 50%. Then set the normal throttle curve to 0% flat. Next with the motor disengaged from the main gear, power it. Spin up the motor in idle-1 until it is at full speed. Now click on throttle hold and then start lowering the throttle hold % until the motor dies and then go down 1% more.

Step 4: Setting up the throttle curves. The normal curve needs to have a 0% somewhere on it to arm the esc. I prefer to set it to 0% flat. The idle-1 and idle-2 curves can be set to either 25% flat, 75% flat or 100% flat in order to run the specified head speeds in the Castle software.

Lastly here is the way I fly this setup. Get the heli ready to fly by installing the packs in their proper location and connect one of the 2 packs to the esc. Turn on the radio and power the rx on the heli. Let it connect and check that everything it functioning. Then with the radio in idle-1 and the throttle stick centered, plug in the other pack. The ICE esc will beep 12 times and then stop. Put on the canopy and carry the bird over to the pad. Making sure th.hold is off, switch the flight mode to normal and let the esc initialize. Then switch to idle-1 or 2. Fly around. When I want to land I just throttle hold as normal to kill the motor. If I need to bail out of the auto then I just switch throttle hold off. If I auto successfully and let the blades spin down, then I switch to the normal flight mode, switch throttle hold off and switch back to idle-1 or 2 for a normal spin-up.

The end result
I weighed the heli and the numbers are 2390g (5lb 4.2oz) without packs and RTF weight of 3180g (7lb 0oz), with a pair of Turnigy Nano-Tech 2650 25C packs onboard. That equates to a disc loading of 2.86kg/m^2, or on the high side compared to 600n for example.

The end result of this build is a very solid and easy to live with heli. The 12s power system is working as expected and the numbers from it are very good. During my first 21 flights the highest amp draw I have recorded is 67A, with an average of about 18A. These are good numbers and what I was aiming for when I built the heli. And it will only get better if I crank the head speed up or go to 550mm blades.


A few things I learned from this project
Every project teaches us something and this one was no different.

The most interesting thing I learned on this project is that there is a better solution than using a bec on larger birds. I had high hopes for the WR bec and my wiring design and it worked great in theory but it turned out the bec was just too small and it was one of the larger models available! In order to go to a higher WR model, I would have had to spend twice as much. That is when a friend pushed me to try one of the new Hyperion LiFePO4 rx packs. I bought one of the chubby 1700mAh 2s models for $30 shipped, $20 less than the bec I bought btw, and made up a wiring harness for it. Now I have a pack that gives me about 10 flights of solid power and removes the ever so prevalent fear of a failed bec. It also solved my voltage drop issue and now nothing I do causes the rx to reset. Call me impressed.

This is the first heli I have used the mesh servo lead covering on and it will be my last. The stuff is a pain to install and a pain to deal with once installed. I will go back to my previous method of using regular shrink tubing to cover the wires. It leaves the wires a little more stiff but it is a more straight forward way of covering the leads and I think it is nicer in the end. I may redo my leads with shrink tubing if I get bored one day.


Flybarless conversion
The 550e flies pretty well with a flybar but like everyone else out there, the time has come to upgrade to a FBL setup. After my Vegas experience, I knew it was time and so I spent the cash. I also made the decision to just buy the good stuff the first time out ... here is what I learned.

Time to add parts to the shopping cart. Let me start off with the heart of the mechanical setup, the KDE hub. It is over twice the cost of the Align hub but I wanted the quality and so it went in the cart. To that I added the 600 silver FBL blade grips, silver swash follower and 550e FBL link kit. The last piece was the big one and that was a Mini VBar. I double checked the order and typed in the credit card, it was on its way!

A few days later I held the small box with all the parts I needed to convert to FBL ... right? Not even close. I pulled out the hub and it was exactly what I expected. Next the blade grips and that is where I started to realize I would be making a second order. The grips looked great but only come with the radial bearings and not the thrust bearings!?!? For $50 I expect it to be the whole kit. I checked the parts list and they were not included. Why include some of the parts but not them all? I also found out that the brass spacers were missing as well. So far I needed to order a set of thrust bearings and a dampener kit with the little brass spacers ... but not to worry as I have those parts in my FB head, so I borrowed them and planned to make an order to replace the parts. So I tore the FB head apart and soon I had the FBL head all together ... and what a piece of art it is! I have to say I am very impressed with the KDE hub (see photo on right).

Now for the install. I pulled off the AR6200 and Spartan, and stuck on the Mini VBar. I wired all the servos to it and began the VStabi software. Aside from the binding process, which I somehow always get to work but only by playing with it, the setup went very easily ... that was until I found the next hiccup. I installed the head after leveling the swash only to find that the FBL links are made for larger balls. They would pop onto the 600 sized balls and were really loose. They fit the balls on the FBL blade grips though. After some investigation I found out that they are the 700 sized balls. I suppose they do this for strength and I am fine with that but I wish I would have known beforehand.

Okay so now that I know what all is needed, let me make a list so the next guy doesn't get surprised like I did. If you use the KDE hub then you will need the dampener kit with the brass spacers (HN6098). If you choose to use the Align FBL head (H55007A), then it comes with those parts. Next along with the main blade grips (HN6113), you will need the thrust bearings (H60001-1). Thankfully the swash follower (HN6114) parts are all there, even if they come with an unneeded washout block. Lastly the FBL links are needed (H55047) but to make them work, new balls are needed (H55060). In the end I had to spend about $30 on missing parts, not cool, and had to buy several extra pieces I can not use, again not cool.


Updates
As I learn and try new things on the 550, I will post up info here.

Sept 23-25th, 2011 - This weekend was the annual Albuquerque fun fly event. Several things happened including me passing 300 flights on the 550e, me using the 550e to place 2nd in the expert competition (sounds better that it was, I am no expert ... I just competed well across the board) and I had my first crash during a timed auto that landed in the weeds. The crash was not terrible but fairly expensive as it snapped 2 servo arms, lost one arm with servo-swash link, stripped both servos, broke both blades and stripped the main gear (tried to bail out at the last moment and failed). The bird did extremely well as always and I am nothing but happy with it, except the stripped gears ... that should not have happened. Ah well, 305 flights before the crash is not a bad number. 

Apr 20th, 2011 - I did a specific test flight on each pack I have and compared the results. The new Voltz and TP packs both did very well. During the TP flight I recorded a new max wattage peak of 4391W. The TP packs held 45.6V under a 96.2A draw ... go packs!

Apr 18th, 2011 - Flew my new Thunder Power G6 45C packs today. They are a really tight fit but they do fit. I am watching the logs carefully, as I expect great things from these packs. I will post up a flight log after they are broken in but so far they are extremely solid.

Apr 17th, 2011 - Fixed the motor. A while back I remember reading about how a user on HF had an out of balance motor similar to mine. His solution was to open it up and chisel all the balancing putty out of it. That seemed to make it much better. With nothing to loose really, I did the same to mine and it is so much better now. It is not perfectly smooth but it is a huge improvement. I put the 550e back together and made a test flight. All was better! 

Apr 16th, 2011 - 4th flight on FBL setup went really well. Still using the Express firmware but set to "Vivid" and it flew great. Then 5th flight the troubles began. On spool-up the heli would pitch forward on take-off. Very scary and not good. I believe the problem is from the vibs caused by the motor. Looking into a replacement. 

Apr 12th, 2011 - 164th flight: FBL test hover went off without a hitch. Touchy but flyable. 

Apr 2nd, 2011 - The first of the Nano-Tech flight packs died on its 69th cycle. For the previous 5 or so cycles I had only been using it for autos, taking only about 1800mAh out of the total 5300mAh in an attempt to prolong its life. Well I spend #69 flying some of the smoothest scale flight I have ever flown and when my timer went off at 5min, the pack was toast. The first of the 2 6s 2650 packs was way puffed and hot enough to start melting the Velcro. The second flight pack is still holding up but I would guess not for much longer. Overall I feel I have gotten my money out of the 2 flight packs but I think I am ready for something better. A set of Voltz 2600 35C packs was ordered to try.

Mar 11-12th, 2011 - I attended the Las Vegas FF and only flew the 550e. While there I tried/learned a few new things. First up I installed the KDE T700 hub with an Align mod1.0 gear and Scorpion 11T mod1.0 pinion. It seems to work fine but is very noisy. Next I tried out a set of Align 550mm blades at 2100, 2250 and 2350rpm. They work well but cause noticeably higher current draws and mAh usage. For the first time I hit the LVC and logs show the Nano-Techs dropped to 3.15V under load. They are on their way out after 50 flights. Lastly I did my first inverted blade scrape! (see pic)

Nov 6th, 2010 - Schlake was in the mood to take some heli photos, so I got some nice shots. He was shooting with his 600mm f/4.0L, so no action shots but he did get me doing some low inverted hovering.

Sept 24th-26th, 2010 - This was the weekend for the 2010 Albuquerque Heli Fun Fly and the 550 was a perfect fit for it. I had a blast flying it, in fact that was all I flew. It also did awesome in the competitions, allowing me to take 1st in the intermediate class and 2nd in the drag races! I have to say it was one of the best helis there. It was not the biggest or most powerful by a long shot but it seemed to be the perfect size, big enough to see but small enough to easy to deal with. It was light and fast without having the 4min run time of the 600 electrics. It was very much on par with the 700s in terms of fun and usefulness, just smaller and it only took half as long to charge packs. The only thing I would have changed was to make it more competitive in the drag races by running a higher head speed. This year I simply ran my 3rd gov'd set rpm HS of 2450rpm. It did very well but the big 700s were just too fast. Next year I will toss on a 18T pinion and run more like 2750rpm. That will make it a very different ball game ;)

Sept 12th, 2010 - My first crash if you can call it that. I was practicing autos and the tail landed in a weed. When I spun back up the weed caused the KBDD tail blades to get in a bind and they both snapped right off at the root. We learn as we go.

Sept 5th, 2010 - Today while setting up the new esc I discovered that the Scorpion is making some serious vibs. I am assuming it is a bearing issue and have ordered a set of Boca hybrid bearings.

Aug 31th, 2010 - I found out the ICE 60HV is one of the problem escs under the recent service advisory. I called Castle and they set me up with an advanced warranty replacement. I received a new replacement esc on Friday, Sept. 3rd.

Aug 22nd, 2010 - The Nano-Tech packs work great in the heli. They run a warmer than I expected but not more so than my Hyperion packs.  I worked on ti-tocs quite a bit, so they got a tough start to life. I did log my flights (see right column).

Aug 16th, 2010 - Got the Nano-Tech packs from HobbyCity. I got the 6s 2650mAh 25C packs and they look great! They are much smaller than I expected and fit easily under the canopy. They are also a bit lighter than the Hyperion packs at 789g for a Velcro'd pair, vs 853g for the Hyperions.

Aug 15th, 2010 - I noticed that the % throttle shown by the Castle Link software was not very accurate. It warned me that I selected a head speed too high to govern properly when I choose 2300 but the average throttle shown on the logs is much lower. I ended up setting 2400 and 2500 for 2 modes and the software warned me I was over 100% at 103% and 108%. I flew both and I still haven't hit 100% internal throttle. For some reason the numbers are just not lining up. They are much closer on my other ICE escs. Either the high cell count is messing with it or the motor Kv is off.

Aug 13th, 2010 - Got the Fusuno canopy today and WOW is all I can say. That it the brightest painted canopy I have ever seen. It is actually slightly smaller than the stock canopy but once mounted it is a different shape that will allow a little more room for some packs.


The kit and parts.


Modifying the frames.

Motor clearance. There is actually much more than it looks.

Wiring up the esc and bec.

Pretty bird. Man I like orange!



Those packs just don't fit under the stock canopy.


The first log I have to show.

21 flights in (note the rx pack & Fusuno canopy)

The Nano-Tech packs fit MUCH better.

Nano-Tech pack log from Aug 22nd, 2010.

Drag racing was way more fun and not nearly as
scary as I expected.


Had my friend Schlake take some photos of the 550e
with his 600mm f4L. Here is one ...


and here's another ...

and another ;)

Blade scrape!

FBL head

FBL head installed, Mini VBar behind that.

Nice framed shot.

It fits in the bag!

A test flight on the new TP packs. Also contains the 
highest wattage peak to date, 4391W.