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EXI 450 Pro Review 

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This bare bones ARF kit comes pre-assembled (requires electronics) in 3 versions. Torque Tube version and Belt version. and Sport Version.  The sport version is like the Belt version but with plastic fins, plastic tail servo holder, cheap plastic canopy and a one piece landing gear. Note that the Sport version DOES NOT have the upgraded head and tail design so those benifits DO NOT translate to that helicopter. I recommend the Pro Belt version over the Sport version for just a few extra $$ unless you already have EXI 450 or Align SEV2 spare parts that you want to use. Note that there are SOME advantages to the TT version such as not having to ever worry about a belt slipping in the air during flight, but the advantage the belt has is that it will be less expensive to rebuild in a crash. Most crashs (and many simple hard landings) will damage the front drive gears of a TT design. So if you are flying over clumpy grass or fear a hard landing or crashes, one of the belt designs may be a better choice.

Initial impressions are good. The head like the Trex 450 Pro is elongated for better stability and a larger rotor disk when compared to a 450 SEV2 (or the EXI 450 SE Carbon).  
Some differences between the EXI 450 Pro and the Align 450 Pro I have so far seen are:
  1. Landing gear is not one piece (I like this better so you can replace only the skid strut that breaks in a crash).
  2. Flybar appears to be shorter (200mm) than Align 450 Pro (220mm).
  3. Rear Servo support is metal instead of plastic
  4. Boom support Knighthead are metal on the EXI vs. Plastic on the Align.
  5. Mainshaft is one single diameter piece and uses a collar on the EXI vs. Align has the collar machined into the shaft and then is supplied with shims. 
Head:
The play in the blade grips is very minimal. All the linkages up top except the longer tracking linkage are fixed length to speed up head setup. I can confirm that the lower washout arm to the swash has dual ball bearings (2 ball bearings per arm) and are secured with 2 screws into an insert just like the Align 450 Pro is designed. The initial run of kits were shipped with a missing piece to the flybar paddle. An email from Xheli was sent to me to warn me so I'll build with a spare set of paddles. They temporarily halted shipping of new orders until the component arrives.

Tail:
The tail is a direct clone of the Align 450 Pro. The Tail servo tray is size for a Mini servo (not micro servo like the Cyclic servos). If you want to use a Micro servo, you will have to fabricate your own adaptor using spare carbon fiber sheet, Fiberglass sheet or thin metal.  Fiberglass sheet is used on circuit boards and can be found at Radio Shack often or cut up a spare computer board or something similar. During flight tests using a Futaba S9257 tail servo and Futaba GY520 gyro, I found the tail solid as a rock. There is very little play in the mechanics which makes the gyro and tail servo work less. I also found the vibes in the tail and Torque tube LESS than my friend's Align 450 which had a DS520 and GP750 combination. Mine performed much better than his stock Align 450 Pro.  The Torque tube is more efficient than the belt. You can see this if you spin the mainblades, the TT will allow the head to keep spinning. Belts have more friction and stops your head sooner. This gives you an extra 5% or more of power and flight time.  The draw back is if your tail blades hit something, you bust the front gears often.  So when you land in the grass, do it gently or try to put a board out for you to land on where the tail is extended over the air more.  I had a hard landing once where I did not set my timer and came in quickly. I tore up both front gears instantly. If you don't care to deal with the cost of the torque tube, you can get the belt version for a little less.  I have several belt driven 450's and they perform reliably so long as you do a little mod with tape on the boom (See #8 on my 450 Tips and Tricks page)

Build:
Like any ARF kit Align, EXI or other, you should re-loctite all Metal to metal screws using blue locktite. Follow an Align 450 Pro manual for the build and setup.  Finless bob on Heli freak has a good build video. CA glue the TT bearing inside as per the Align 450 Pro Manual is especially important.

Flight test:
The helicopter is very stable for a 450, the most stable 450 I own now.  With the wider rotor disk and the elongated mixing arms in the head, it removes some of the slop factor in the head. It does not make my 450 fly like a 500 but it is leaps and bounds above a $39 plastic EXI.  Flip rates are good and even better if you upgrade even to the $10 CF blades at Xheli. A 30C battery is good to have for powerful punch outs and extra UMPH in case you need to bail out of trouble.

Components:
You can get all the electronics you need to build the helicopter over at Hobbypartz. If you want to go with Hitec servos, I recommend the following online stores: servocity, helidirect, Amainhobbies.

Here is a list of some Youtube vidoes that are very helpful to the first time builder.
Pro Build Video 1
Pro Build Video 2
Pro Build Video 3
Pro Build Video 4
Pro Build Video 5
Pro Build Video 6