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Nov 02, 2008, 01:45 PM
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It's Here! T-Rex 250 Build Thread

Well here it is, Align's first venture into the micro helicopter market, the T-Rex 250. I have built a few micro helis in the past years, but having flown just about every T-Rex Align has put out, I am very anxious to get my hands on this little guy. So between trick-r-treating and entertaining guests at the house, I managed to put this little heli together and document as much as possible. Hope this will be of some help for those who are interested in this heli, or just seeing what is available in the micro heli market.

When UPS delivered the box, I was surprised at how small it is. It looked almost like one of those box that T-Rex 450 canopy comes in. Take a look at the size relative to the T-Rex 500 box in the photos below.

There are three type of T-Rex 250 kits:
Standard - kit with motor and ESC.
Combo - standard kit plus three DS410 digital servos for cyclic.
Super Combo - combo kit plus GP-750 heading lock gyro and DS420 rudder servo.

Opening the box revealed parts neatly packaged in number plastic bags. Main frame is already pre-assembled and sealed in a plastic bag, as well as the head and tail assembly. The nicely painted fiberglass canopy is wrapped in thin layer of protective foam, and then covered in plastic. Following the tradition of all T-Rex kits, Align included tools which have proved to be very helpful in building and repair of their helis. In the case of 250, they included a pair of micro hex and philips drivers with nicely anodized aluminum handles. The size 0.9 micro hex driver is a very important tool, since I don't have one this small in my tool box, and 90% of the T-Rex 250 build depends on it.

Two sets of main blades and tail blades are included for different flight characteristics. There is a pair of 205mm tapered blades, and 200mm straight blades. According to Alan Szabo Jr. test reports (courtesy of Align forum), while both blades poses good flight characteristics, the 205mm tapered blades are more suitable for high head speed, high power 3D flights with increase agility and responsiveness. Similar increase in flight responsiveness can be noticed from the 40mm tapered tail blades. I will report back with some actual field tests of both sets of blades later on.

For those familiar with the T-Rex line, this little heli would be no stranger. Almost everything from head to tail is a shrink down copy of its larger siblings. Just like the more recent T-Rex kits, most of the pieces come pre-assembled in 3 major component groups: head, frame, and tail assembly. The pre-assembled pieces reduced the assembly time considerably. However, as with any pre-assemble pieces, I always disassemble and check for the presence of thread locking material. Other than the obvious places where dis-assembly is required for parts fitting (tail boom clamp, fly bar cage, etc), I'm glad to report thread lock was observed in all places.
Last edited by Steph280; Nov 07, 2008 at 12:35 AM.
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Nov 02, 2008, 01:45 PM
1.21 Gigawatts!
Steph280's Avatar
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Head Assembly

The head comes sealed in a plactis bag already assembled as shown in the photo below. All you have to do is build the flybar cage (don't forget to pop on the link) and assemble it onto the head with flybar attached. Then comes the painful part: threading on those tiny ball links. Just clamp the link rod with a plier, and then thread them on with your hand. Do not crimp the plastic links with plier during assembly, as it could cause damages to the link. The head assembly took no more than 15 minutes, with most time spent on those links.
Last edited by Steph280; Nov 02, 2008 at 06:11 PM.
Nov 02, 2008, 01:46 PM
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Frame Assembly

Just like the head assembly, the carbon main frame came pre-assembled out of the bag as shown in the photos below. The frame is the typical double stacker carbon plate design found in T-Rex 450's. Combined with machined aluminum standoff, the frame forms a very rigid structure to withstand the force exerted by aggressive 3D flights.

Not much needs to be done with the main frame. The assembly starts by mounting the 3 cyclic servos with the included screws and plastic threading nuts. It's a little tricky to hold the plastic nuts inside the frame due to space restraints. Make sure you work on a towel or area where a lost screw is easily locatable, since they are extremely small.

Then the head is inserted into the frame's main bearing block through main gear. Unlike the traditional through the shaft bolt method of fixing the main gear, a tiny screw is threaded from the end of the shaft at bottom to hold the assembly together. The access hole on the bottom frame plate allows this to be done with ease.

The typical proven T-Rex landing gear design is utilized in the 250 kit, but in a much smaller scale. Nevertheless Align has included the same end caps and rubber stops with this kit. The skids are held in the plastic bows with drops of glue.
Last edited by Steph280; Nov 02, 2008 at 03:35 PM.
Nov 02, 2008, 01:47 PM
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Tail Assembly

Next comes the tail. Again the tail assembly is pre-done at the factory. Thread the belt through the tailboom, and install the tail assembly onto the boom. There is a small plastic piece on the tail assembly clamp area which needs to be removed during assembly so the tailboom can slide in. The notch on this plastic piece prevents the assembly from rotating on the tailboom. Once fitted, the horizontal fin mount, pushrod guide, and rudder servo mounts will be fitted onto the tailboom. I don't know how many time I forget this step and had to remove the tailboom.

Then the boom is fitted onto the main frame. Loosen up the 8 screws on the frame's boom clamps to facilitate the boom installation. Twist the belt 90 degrees counterclockwise and loop over the drive pulley. Pull tight and tighten the 8 screws to clamp the boom in place.

The rest of the steps includes the installation of boom supports and tail fins. I choose to install the tapered blades for initial flight test.
Last edited by Steph280; Nov 02, 2008 at 02:51 PM.
Nov 02, 2008, 01:49 PM
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Final Assembly

At this stage, the T-Rex 250 is about completed. Mount the ESC and clean up all the wires to ensure nothing gets caught up in rotating parts. The manual also suggests installing the receiver as far away from ESC as possible, which may not be needed with the modern 2.4Ghz receivers.

For those who has a couple of T-Rex kits under their belt, this build will feel right at home. The kit can literally be build in an evening or two, provided you didn't have to search for lost screws in thick carpet like I did. Did I mention the parts and screws are really tiny? I didn't realize I need reading glasses until I started building this heli. Luckily Align has provided a bag of spare screws/washers in the kit, just like they do with all their other kits.
Last edited by Steph280; Nov 06, 2008 at 05:27 PM.
Nov 02, 2008, 01:50 PM
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Setting Up

The thoughtful people at Align also included a spacer for use with their optional pitch gauge to facilitate measurement of pitch on those tiny blades. If you don't have Align's latest pitch gauge, I strongly suggest you take a closer look at one. Unlike other pitch gauges, this one has a fine adjustment knob to adjust the measurement in small increments. One of those "why didn't they think of that before" kind of thing.

Not knowing what to expect with this little guy, I followed the instruction manual and set the pitch range at 11 degrees +/-. I fly only in idle-up-1, so I set it with full 22 degrees and V shaped throttle curve as 90-85-80-85-90. If the linkage length suggestions were followed during the construction process, -11 to +11 pitch range would not be a problem. Align did warn that exceeding the maximum 11 degrees of pitch may result in loss of tail control effectiveness, since the startup torque may exceed the tail compensating power, causing heli to spin.

Here is a little tutorial I put together for the Align GP-750 gyro settings.

Added 11/25: Some additional photos on wire routing suggestion.
Last edited by Steph280; Nov 25, 2008 at 04:28 PM.
Nov 02, 2008, 01:51 PM
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Flight Testing

I apologize for the delay in flight report. Ran into some setup confusion with gyro, plus the shorter daylight has eliminate the possibility of after work flights.

I did do a quick hover to trim it out. Initial impression on hovering has been positive. The heli leaped off ground and settled into a stable hover. The characteristics resemble closer to larger helis than the micros I've flown such as JR Parkmite, various Hornets, and buddy's Gaui. Not much trim was needed if you carefully level your swashplate during setup. The tail responds with authority, which was a weakness I found in other micros. Gyro is a bit sensitive and I had to dial the gain down, but works really well with the DS420 servo.

Speaking of servos, I believe the DS410 are one of the reason for the well behaved hover characteristics of T-Rex 250. They are fast, torquey, and centers very well with no noticeable deadbands. Once they are available separaterly, I will give them a try on T-Rex 450's and report back my findings.
Last edited by Steph280; Nov 06, 2008 at 02:33 PM.
Nov 02, 2008, 02:32 PM
Registered User
nicely done, musta took a loong time, i couldn't help but notice your little pm says '1.21 gigawatts!' LMFAO i love back to the future and thats the best part of it!
Nov 02, 2008, 02:34 PM
Registered User
thx for the pics
go fly quickly.....
Nov 02, 2008, 02:41 PM
Put a Quark in it!
nexgen's Avatar
Kudos Steph. cant wait to get mine!!
Nov 02, 2008, 02:48 PM
Just here for the fun
I want one.
Nov 02, 2008, 05:50 PM
Plastic Buddha
aftica's Avatar
Last edited by aftica; Nov 16, 2008 at 08:16 AM.
Nov 02, 2008, 07:30 PM
Registered User
What is the auw minus the battery. What is the weight of the included battery.
Thank you
Nov 02, 2008, 07:42 PM
Registered User
S76 Mech's Avatar
Subscribed, thanks for the great write-up !!!

Can't wait till I get one of these babys !!!

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