Building a Trex 450 Sport (Part Two)

In part one of this series, I covered what you will need to get started building the Trex 450 Sport RC helicopter. Now that we have all the items necessary, it's time to discuss the actual build process.

The first thing I did was to get a copy of the instruction manual for review. It's available online here. The manual is not a step by step set of instructions like you might expect. It does however provide exploded diagrams of the helicopters sub assemblies as well as important notes. There are also explanations of electrical component programing along with basic set up and safety information. You will want to review all this info prior to starting your build.

The next thing I suggest you do prior to starting any part of the build, would be to watch Finless Bob's instructional videos at HeliFreak. Start with Bob's Heli Skills and Set-Up Basics. Watch the following video titles as there will be information that you need to know in order to build and set up your model.


Ball Links 101 (20 MB)
BEC 101
Blade Balancing 101 (30 MB)
Blade Tracking 101 (35 MB)
Brushless motor and ESC 101
CCPM Setup Part 1 (58 MB)
CCPM Setup Part 2 (58 MB)
Dual Rates 101 (71 MB)
Exponential 101 (45 MB)
Gyro 101
Gyro Gain 101
Pitch and Throttle Curves 101 (58 MB)
Servo Wires 101 (41MB)
Soldering Deans Connectors 101 (30 MB)
Thread Lock 101 (15 MB)

The next set of videos that you should watch are from Ashley Davis at helituning.com. These videos cover the actual build of the Trex 450 Sport. I would watch them each all the way through then refer back to each as you are building your model.

T-Rex 450 Sport Build Videos
Rotorhead Build
Frames Build
Tail Boom Install
Main Gear, Head and Tail Install
Electronics Install & Finishing Off

The build will basically be done in sub assemblies. The head, frame, tail and electronics. Then you will need to set-up the head, program the speed control and gyro. I began by dry fitting the entire helicopter short of installing the electronics. This gave me a feel for the order in which I needed to install components before I did final assembly. Only then did I apply thread lock to all components. As far as using thread lock, watch Bob's thread lock 101 to see how it should be applied. Bob covers the different types of thread lock but I've found that the Sport only requires that you use blue threadlock on all metal to metal screws. (also checkout my threadlock post) The kit comes with a small bottle of thread lock, but I've heard many Sport builders say that it's not the best quality, so I suggest you do as I did and buy a tube of Blue Locktite #242. This worked very well for me and you can still remove a screw if you need to. If you run across a stubborn one that doesn't want to come undone, just apply heat to it for about 60 seconds with a hot soldering iron and it will come right out. When using the self tapping screw that go into plastic you will not want to use locktite. These should hold ok as long as you don't over torque them and strip the plastic. If you make a mistake and strip one, you can apply a very small amount of CA or super glue to the threads to secure them.

Once I was familiar with all of the components. I went back to the head assembly and checked each screw for thread lock. This is very important as I found several screws that had absolutely no thread lock which would surely have lead to a crash. Another thing I did with each screw was to clean it with denatured alcohol to remove any residual oil that might have been left over from the machining process. The oil can have an adverse effect on the thread lock. I would take a paper towel saturated with alcohol and grab the threads of the screw, then using my hex driver, I would spin the screw in the paper towel while pinching the threads with the soaked paper towel. I repeated this process until no more residue showed up on the towel. Then I made sure the alcohol had dried before I applied Locktite and torqued the screw down. Be careful not to over tighten the screws as you can break them. You want to apply just enough pressure to secure them and leave the locktite to do it's job keeping it from vibrating loose.

Also at this point you will want to watch Finless Bob's video on the Trex 450 Pro head build.

Pro Head Build Part One
Pro Head Build Part Two

While these videos show the head build for a Trex Pro, the head is very similar to the one on the Sport and Bob gives some great info in these videos. Pay particular attention to the part where he shows you how to grease the thrust bearings as mine were totally dry and required I repack them. Another note of caution, when you assemble your control arms for the head, notice that there is a small letter "A" die cast into the ball link. Be sure this "A" is facing out when you attach the link to the ball. The reason being that the side opposite of the "A" has a slightly larger diameter. If you accidently get the "A" facing in, the link can break or pop off during flight. This would cause a crash.

Building the frame would be next. Again, watch the helituning video for this as he does a good job on building the frame. Ashely mentions it, but I want to stress the importance of sanding smooth all the edges of the carbon fiber frame. The stamped edges are very sharp and can easily cut wires if not smoothed over. Use caution when sanding the CF as the fibers can irritate the skin and respiratory system. I suggest you use a dust mask during the sanding process and be sure to clean the frame parts after you are done. I would also do any sanding and clean up prior to installing the motor as you don't want fiber to get inside it.

One thing I want to point out is that the 450M motor that comes with the Sport is called an "outrunner". This was not the typical small electric motor I was used to seeing. The outside of the housing spins around the armature on the inside. Strange I know, but it works great. You just have to be careful and keep all wires and your hands away from it. You also want to take a dremel tool and grind a flat spot onto the motor shaft where the pinion grub screw will land. This is not shown on the plans, but greatly increases the holding potential of the screw. To keep metal particles out of your motor, poke the shaft through a plastic bag so that the bag covers the motor during the grinding process.

Take note of any screws that the manual refers to as "self tapping", these will be screwing into plastic and you don't want to apply thread lock on them. You will also need to take care to not strip the plastic by over tightening them. If you do happen to strip the internal threads, yo can apply a small amount of CA glue to the screw threads to secure it.

One modification I made to the frame was to replace the stock gyro tray with a lexan tray made by Rick Lohr at Clearly Superior Products. This provided me with a flat surface that I could use to mount my receiver under the gyro which was farther away from the motor wires and ESC. I found out the hard way that about radio interference when I crashed because of a glitch caused by the motor wires being to close to the receiver. Since using Rick's tray, I've had no more interference problems.

After the frame has been assembled you will want to attach the landing gear. Be sure to apply a small amount of CA glue to the skid pipe end caps before you pop them on. Another tip is to soak the rubber landing skid nuts in soapy water so that they slide on nice and easy. As they dry they will secure themselves in place.
Unlike the plans, I put the nuts on the inside of the skids so they would not over time work their way off the ends of the skid pipes. You can see this in Ashely's video.

Assembly of the tail and boom is pretty straight forward and is well covered in the helituning videos. One item that is easy to over look on the tail is the slide shaft bushing. This must be cleaned and thread locked or your going to learn how to do rapid piros way before you are ready to handle them. Not a good thing! Check out this post for a full discussion on this subject.

Here are a couple more items you need to look at on the tail. I've found the boom has a tendency to slip back into the blocks causing the belt to loosen. Some have taken the boom blocks and sanded the inside flats so that they grip the boom better, but I just wrapped a single layer of 2" wide clear tape to the end of the boom where it enters the block. This easy fix seems to have corrected the problem. Another note of caution, the tail belt can be installed backwards. The tail rotors should turn with the leading edge (fat edge) going up into the main rotor wash. If you notice this is backwards when you spin the main rotor clockwise, you have the belt turned in the wrong direction. The belt and rotors should spin freely, if not, something is wrong and you need to find out what before you fly. To see just how freely it should spin, check out Finless Bob's maintenance video.

Once you have the tail assembled, It's time to mount your servo's and electronics. I must say this would have been extremely difficult without watching Finless Bob's CCPM set-up videos. Watch them over and over if necessary as you heli will not fly right without getting this part right.

I will cover more on my experience with setting up the head, ESC and Gyro in a future post. Until then I will leave you in Bob's hands.


Part One of this Series