This article is a comparison of the X400 and the T-Rex in stock form. I should make it clear that this article covers the T-Rex 450X not the newer XL. I will update this article at a later date to compare the new XL T-Rex. The purpose of this is to highlight the areas where these helicopters differ and what if any advantage this gives one model over the other. I'll work through the main components systematically making comparison and offer opinion based on having built and flown both these models. I am a huge fan of the T-Rex, which catalysed the motivation for creating TRexTuning and I want to make it clear that in writing this article I am taking a non biased view of the capabilities of both the T-Rex and the X400. OK introductions completed, on to the first element : Rotor Head The T-Rex uses a double dampened head to provide a fairly stiff level of damping, this new design being based upon poor tracking capability in the original single dampened head. The X400 has a single dampened head much like the original T-Rex, so far I have not experienced any difficulties with tracking on the X400 and this may be due to other components commented on later. The blade grips are secured to the head using a allen bolt which screws into the feathering spindle by contrast the X400 has an external threaded feathering spindle which uses nyloc nuts to bolt the blade grips in place. The T-Rex design allows for a fairly traditional design blade grip that will fit most aftermarket blades. In contrast the X400 blade grips are very wide to accommodate the tooling required to tighten the nyloc nuts retaining the blade grips onto the feathering spindle. This means that after market blades require some significant sized spacers to fit. The T-Rex as standard uses 315mm wood blades, the X400 uses 280mm wood blades. Here the advantage to some extent sits with the X400 as blades designed for the Zoom/Shogun will fit and are in abundance. The T-Rex blade market is still maturing and blade choices are somewhat more limited. The T-Rex also places greater power requirements on the motor due to the larger rotor disk, meaning that motor choice is more restricted and amp draw requirements for lipo's will be higher. In return the T-Rex can provide a more powerful vertical performance. The stock flybar mixers and control arms on the T-Rex are a weak point in the T-Rex design and many of the tracking problems exhibited by the T-Rex in stock form can be tracked back to these components being too sloppy or bending under load. Additionally the flybar control arms were renowned for stripping when tightening the grub screw onto the flybar. The X400 uses a seesaw assembly which is free from slop and works extremely well. The X400 mixer arms also have better bushings allowing for a tighter slop free control mechanism. In this area the X400 is better designed. The same is true for the washout arms, the T-Rex again suffering from poor bushings and lateral movement in the arms introducing slop to the control mechanism. The X400 again is much tighter in this area and has slop free controls and bushings/bearings with better tolerance. The original T-Rex swashplate is again not a strong point and subsequent metal/plastic designs suffered from swashplate separation. It's early days with the X400 swashplate but for the moment it appears to be a more capable design using anti-rotation pins to stop lateral movement of the swashplate. The T-Rex has always used an a-frame elevator assembly to control swashplate lateral movement. Both designs give adequate protection. Ball links on the T-Rex have gone through multiple revisions, the current version being about right in terms of fit and finish. The X400 ball links are of similar quality to the current generation of T-Rex ball link. Lastly the major difference in the two heads is the flybar and paddles. The T-Rex uses a very light paddle making the machine very cyclic sensitive but at the same time very 3D capable. The X400 uses weighted paddles making for a very stable machine in the hover but less 3D capable. In flight the T-Rex has sensitive cyclic and collective controls and it can be difficult in stock form to keep it all together in one place at a constant height. However for 3D capability all these characteristics allow for a lively performance. In flight the X400 is very stable, has progressive collective and seems to float rather than dodge up and down like the T-Rex. The T-Rex is far better suited to an expert flyer, the X400 is far more suited to a beginner. Of course the flybar on the T-Rex can be weighted to slow the response to be like an X400 and similarly different paddles can be put on the X400 to create a T-Rex like performance. The one area that I particularly like is the progressive and floaty feel of the collective on the X400, I'm not sure how this could be emulated or achieved on the T-Rex. Rotor Head Summary Component T-Rex X400 Preferred Design Rotor Head Hub Double dampened Single dampened T-Rex Feathering Spindle Internal threaded External threaded T-Rex Blade Grips Narrow Wide T-Rex Mixer control arms/seesaw L shaped control horn Seesaw assembly X400 Flybar Mixer Arms Sloppy bushing, bendy plastic Solid, tight control X400 Washout Arms Sloppy bushing, lateral movement Solid, tight control X400 Swashplate Numerous problems OK X400 Ball Links Several revisions, now OK OK Both OK Flybar Light paddles, sensitive, 3D Weighted paddles Beginner : X400 Expert : T-Rex Collective Response Sensitive, very up and down Floaty, smooth X400 Cyclic Response Sensitive Stable Beginner : X400 Expert : T-Rex Main Frames The main frame design on the two helicopters is both very different and very similar. It is different in that the T-Rex uses a plastic molded frame consisting of two halves. The X400 uses a metal frame consisting of four pieces. There is an upper frame in two halves and a lower frame in two halves. The T-Rex has no provided space for a tail servo, which is mounted on the tail boom via brackets. The X400 has a inboard tail servo mount on the upper main frames. The servo is more exposed on the T-Rex in a crash. In terms of rigidity the X400 is a much more solid platform than the T-Rex with no flex or bend in the frames. The T-Rex servo tray and frames will bend and flex under servo movement. The X400 frames would be very hard to modify, the T-Rex frames are very easy to cut and modify for things like home spun CCPM conversions. I have yet to assess crash durability of the X400 frame. The T-Rex frame is relatively resilient in a crash providing it hasn't been lightened or modified. Both helicopters use a collective seesaw to provide collective pitch changes and this is where the designs are similar. The X400 seesaw is extremely well designed and free running in its bearings. The T-Rex design is less well executed and requires attention from the builder to get smooth bind free running. Both frames provide similar levels of space for radio equipment and accessories. The main shaft on a T-Rex can flex in the main frame bearings, this is totally solid and unmovable on the X400. In terms of cost it is cheaper to replace the T-Rex frames than the X400 frames. The X400 frames are lighter than the T-Rex frames. Main Frame Summary Component T-Rex X400 Preferred Design Frame design Plastic, two halves Metal, four pieces X400 Frame flex Some flex No flex X400 Weight heavier lighter X400 Ability to Modify High Virtually none T-Rex Space OK OK No preference Crash Durability OK unknown TBC Cost Low Medium T-Rex Protection of radio gear Medium High X400 Main Gear, Landing Gear, Canopy The main gears on both machines are of similar build quality and durability. They have different numbers of teeth but the gearing from the main gear to the tail is almost identical at approx 1:5 Both machines feature a a one way bearing for autorotation and a driven tail during autorotation. Landing gear on the two machines is almost identical apart for the mounting. The T-Rex has a vertical bolt through mount where as the X400 has lugs on the landing gear that bolt horizontally onto the frames. The T-Rex mounting being stronger. The T-Rex canopy is made of a fairly brittle plastic, the X400 uses a different and much more malleable plastic. I believe the X400 canopy may well be more crash resistant due to this. Main Gear, Landing Gear & Canopy Summary Component T-Rex X400 Preferred Design Main Gear OK OK No preference Landing Gear Vertical mount Horizontal mount T-Rex Canopy Hard Plastic Soft plastic X400 Tail Boom and Tail Rotor Both machines tail boom and tail rotor mechanisms are almost identical. There are a couple of differences. The T-Rex uses a carbon rod for the tail pushrod, the X400 uses a metal rod. The X400 has a solid one piece control horn that connects to the blade grips, where as the T-Rex has a rather sloppy rotating ball link assembly. The X400 uses a control horn with both a bearing and ball cup to control the tail rotor pitch changes. The tail pitch slider on the X400 has a ball on it that locates into the control horn cup. The T-Rex has a less high quality control horn using a peg that locates into a hole in the plastic control horn to effect pitch changes on the tail rotor. The T-Rex mounts the servo on the boom, the X400 mounts the servo on the rear main frames. I know from bitter experience that the boom mount is an exposed location for the servo. The overall gearbox assembly is identical on both machines. Tail Boom & Tail Rotor Summary Component T-Rex X400 Preferred Design Tail control rod Carbon rod Metal rod T-Rex Tail control horn Bearing and peg hole Bearing and ball cup X400 Tail pitch slider Three piece, rotating links One piece X400 Tail servo mount Boom Main frames X400 Overall Conclusion The T-Rex from Align provides a cheap and very 3D capable machine from stock. Parts availability is good and the market for the T-Rex is more mature. Building a T-Rex requires a lot of care and attention and there is some degree of slop in the control systems. Additionally the bushings and bearings are not all a good fit or produce effortless free movement in the control horns. The T-Rex is highly configurable due to the plastic frames and modifications are easily achieved. Parts are also very cheap. The X400 from ARK also provides a cheap but less 3D capable machine from stock. The X400 is much more stable than the T-Rex and therefore more suited to a beginner pilot. Building the X400 requires less attention in getting the controls free from binding and the whole control system is much tighter and slop free. Bearings and bushings are a good fit and the whole control mechanism is smooth running. The X400 is not highly configurable but it does have a lower all up weight than the T-Rex, negating the need for adverse frame lightening methods. Parts availability is not so good but will get better with time. Repair costs are likely to be slightly higher than the T-Rex. The X400 is overall a higher quality kit and it's flight characteristics are more predictable than the T-Rex, particularly collective control which is superb for a micro helicopter. The T-Rex is more of an experts machine and with some modification can be made to be as good as the X400 in terms of it's control mechanisms but this is at extra expense of upgrade parts.