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Simon Lockington Before we start, I should let you know that I'm now a sponsored pilot for Align, while I don't really think that has impacted upon my opinion of the little T-Rex, I should declare that. I had always thought mini-electric helicopters to be a bit of a waste of time. I watched experienced pilots struggle to keep their Hornets in the air much less do much interesting with them, and whenever I would talk to these guys they always seemed to be working on them. Screw that I thought, I'll stick with nitro's thanks! My local club then formed an 'interest' group of electric fliers that would organise regular indoor meets, but I never bothered checking that out, I wasn't really too interested, I was busy dealing with Sylphides and cantankerous OS 91 PS's... By now, my mates with Hornet's had finally given up and gone back to Raptors. Then one weekend it was howling with rain and Andrew and I decided to call in on the indoor electric event since there was nothing better to do. There we found a group of about 15-20 guys flying various models around in a large gym. Little helicopters were buzzing around like screaming bandsaws and I was very aware that any one of them could deliver some serious damage should it get out of control. Andrew, having earned his stripes on the battlefield with a Hornet knew a lot of the guys and machines that were flying around, I on the other hand wasn't familiar with anything that was going on, so just watched as some tiny helicopters came perilously close to people, the ground and other helicopters. I was starting to wonder if I should have bought a fly swatter along! My first real introduction to little helicopters came when one of the guys who was Mode Two offered me a flight of his blinged up T-Rex. The first impression I had of this tiny helicopter was just how stable the thing was! It just sat hovering beautifully and was very neutral in piroettes. In fast forward flight the little machine tracked around quite nicely and had a tonne of power, and didn't have any nasty tendencies that I had been expecting. Apart from craziness on this one where it either had no negative pitch or full negative which made for some interesting tic-tocs! I went away from that really impressed with little electrics. Then when I went to 3D Downunder everyone seemed to have T-Rex's. Of all the machines there, the machine that flew the most was a T-Rex. That thing must have crashed five or six times, each time minor parts were replaced and away it went again. Now it seems everyone has a T-Rex! PRESENTATION It comes beautifully packed in a nice colour cardboard box that is perfectly suited to placement under Christmas trees. Within the cardboard box is a very serious looking aluminium case that contains everything you need to build your T-Rex. Some parts worth mentioning is the two sets of rotor blades (one wood set, the other carbon) and the little blade holder. The unfortunate thing is that once built, your T-Rex won't actually fit inside that nice metal case which is a shame, although I'm lead to believe you can buy a T-Rex carry case which I think I'll have to get in the near future. As always, all the parts come in seperately sealed bags, however much of the helicopter is already built. The two main frame sections (upper and lower) and the head and tail box are already assembled. Reports on the net have told of some of these assemblies not using (or using too much Loctite), so it's prudent to disassemble these parts and check for yourself. INSTRUCTION MANUAL GETTING STARTED As the head is already fully assembled (and I mean FULLY) there isn't really a hell of a lot to do on the first page. You fit the flybar and flybar control arms and paddles. All this is really very straight forward, however just double check the measurements of the flybar length on each side. I went by the 69.4mm advertised in the manual and the flybar was not symmetrical. In the end I just made it symmetrical regardless of the actual length. I took my head apart and put the larger shims in to make the head stiffer, as well as to make sure everything had been assembled properly. The little paddles that come with the Rex are snazzy looking carbon ones that are threaded on after the adjustable weights are placed on the flybar. With that done, the links are made up and attached to the head and that's it with the head! FRAMES Fitting the servos can be a bit trying. You have to hold some 'plastic nuts' behind each frame that self tapping screws thread into. It's best to get this done before you go installing too much more (such as the mainshaft and rotorhead), otherwise you'll find it pretty frustating! I mounted my Hitec HS56's with the servo tabs on the inside of the frames and the plastic 'nuts' placed behind the plastic tabs. This in effect brings the balls on the end of the servo horns closer to the frames which makes the swashplate pushrod geometry more correct. You will notice that if you mount the rear mounted elevator servo this way, the geometry will be great, the ball on the servo horn will be dead center and all will be right with the world. HOWEVER, as soon as you move the servo horn on the servo output post, the ball will hit on the servo casing. So, what you need to do now is make the ball shorter so it can move freely without hitting the case. On the two T-Rex's I've built so far, I've done it two ways. The first time I counter sunk a indentation in the servo horn so that the ball could sit within this. I then used CA to bond up the ball and horn to get some strength back into it. This is OK, but I like the second way better. This time I ground the bottom off the ball and left the servo horn intact. I like this way much better. Another thing to get sorted is servo horn length. There isn't much in the manual regarding how long the horns should be, so you're left to your own devices on how long they should be. Initially I fitted the 11 tooth pinion to my motor, most of my mates here are using the 13, however it's very easy to change so I'm not too worried if I've made the wrong choice. Fitting the main mast and auto hub allows you to set the meshing required for the motor. I meshed mine up so there was a very fractional amount of back lash. I noticed with my main gear that it was slightly warped. However given the large pinion tooth area, I wasn't overly worried. I also too the opportunity to plug the servos in and configure the sub-trims to get the horns lined up correctly. UNDERCARRIAGE The skids slide into the legs and are secured with a couple of drops of CA, then the skid stoppers are attached. Now the whole assembly is attached to the helicopter with self tapping screws. TAIL ROTOR SYSTEM It should be noted that since I've built this model, Align have announced replacement parts for the HS1127 bolts that hold the tail grips into the hub. Apparently there have been a few failures of standard bolts failing. You should check with your local dealer regarding replacement parts. Fitting the tail gearbox on the boom was a bit of work. The tolerances between the gearbox mount and the size of the boom are very tight, I found I had to use a flat head screwdriver to slightly prize open the gearbox mount and slide the boom all the way in. At this stage I didn't tighten the clamp onto the boom. The tail servo mounts are then slid onto the boom and the pre-assembled boom supports are attached to the model. Now came the tricky bit, sliding the boom into the mounts. At first, I tried just sliding the boom into the mount as you would with a conventional helicopter like a Raptor. After ten minutes of getting no where, I decided to remove the mount from the frames and attach it to the boom. To remove the mount you remove the bolts holding it into the frame, plus loosen the immediately surrounding bolts. You see the mount has a rise machined into it (with the 'Align' text embossed) which slots into rectangles cut into the frames. Therefore you have to slightly spread the frames apart to free the mounting from these rectangular slots. Once you have the two piece mount free, you'll notice that one of the sides has a slot raised where the boom slots in. I sloted the boom into the mount, then ensurinig the correct orientation of the tail belt, slotted that around the tail drive pulley and then re-installed the mount. With the mount installed, I set the belt tension and tightened all the bolts before ensuring the tail fin was vertical and tightening the boom clamp. Now the boom, boom supports and fins are installed, I mounted the tail servo and began work on the tail pushrod. The instructions call for the use of a Z-bend wire attachment at the servo end of the pushrod which I was not a fan of. Instead I used a spare ball and threaded a plastic ball link onto the end where the Z-bend would normally be, a much better solution. The pushrod has a guide built into the boom support mount, however this can be a bit tight, so I ran a drill bit through it to ensure a low friction movement. The servo is then placed on the boom to ensure linkage throw is equal on both sides. I would have preferred that the pushrod be longer so as to keep the servo as close to the frames as possible. Mainly for weight distribution purposes, but also to possibly prevent crash damage. My T-Rex has a problem with the tail rotor pitch linkage that mounts on the output shaft. The bearing in the plastic housinig has a LOT of friction in it that is imposing a lot of drag in the whole system. I've sprayed some CRC/WD-40 into it and will run it for a few flights to see if it frees up. The other T-Rex that I built does not have this problem. Mechanically, the helicopter is complete. ELECTRONIC MOUNTING I mounted the gyro on top of the boom mount, however I'm going to investigate having that somewhere else to try and provide an element of crash protection. As I'm not familiar with soldering components, I had a mate do the connections between the motor and speed controller and also the Dean's plugs on the batteries and speed controller. We also used a velcro to help fasten the battery to the mounting tray as well as the provided velcro ties. Setting up the CCPM and pitch values wasn't difficult. Exactly the same as any CCPM helicopter. I adjusted the links until I got the pitch range (10 degrees each way) and geometry I wanted. I had heard reports of guys crashing when the bottom servo arm hit the main gear at extreme throws so was concious not to use too much servo travel. SETTING UP THE SPEED CONTROLLER
Setting the speed controller requires setting the throttle stick to various positions to tell the speed controller what value of each setting you want. Once the speed controller has recognised which value you want, it will emit a specified beep sequence to tell you to move the stick to the position you want for the next setting. The whole configuration process takes less than a minute or so. I set my speed controller up with 'Brake Disabled', 'Mid-Timing', 'Medium Discharge' and 'Helicopter 1'. SETUP As discussed, you get two sets of blades with the T-Rex, one set of woodies and a set of 315mm Carbon blades. Both blade sets need balancing, however the sets I've used have not needed more than using the Align tracking tape on one of the blades. FIRST FLIGHTS I eased the throttle up and the motor fired up. I had set the throttle curve to be a flat line at about 60% to start off with. I let the heli sit on the ground with the rotor head spun up to listen for any gear meshing noises, and ofcourse to see if anything would fly off :). Lifting into a hover the tiny heli made a move towards the towels on the washing line as Murphy's Law dictated that it would, but we got it under control easily and began examining the tracking. Finding it out, I landed and adjusted it by two turns which fixed it. Increasing the headspeed made the heli sit a bit better in hover and I also put in 20% expo which helped. There was an indoor electric fly in happening that afternoon so I quickly put the Rexy in the car and went to that. On my first flight it appeared that putting the larger head shims in wasn't a great idea as the machine was nodding quite noticeably. I was trying to work out why it was doing this now as it wasn't in the back yard, however I had changed to the longer wooden blades which would account for this. Increasing the headspeed to flying speed settled the heli and got into some forward flight to see how it handled. I was pleased to see it wasn't twitchy and tracked around nicely. The roll and flip rate was ok, but I felt it needed more. The machine is very stable upright and inverted which I really like and didn't do anything untoward through piroetting maneuvers. T-REX CRASH TESTING One blade was broken, the mainshaft bent and ofcourse the main gear. It seems the main gear is a disposable part as I don't think I've seen a T-Rex crash that hasn't broken a main gear. Also, one of the servos had stripped a gear. Upon further inspection I noticed the top mainshaft bearing was also damaged as you would expect. Everything else however, was fine! Guys flying the standard plastic T-Rex were impressed with the low damage count saying that generally on their machines, more plastic bits break (such as the blade grips). However I can't help but think that if the top main shaft bearing mount had been plastic on the SE, then I wouldn't have done a bearing... Unfortunately I didn't have the parts needed to fix the machine there so it was back to the work bench. While fixing the machine I decided to remove the larger head shims and go back to standard. I also installed the 13 tooth pinion to get more headspeed and more cyclic power. FIRST FLIGHTS PART II I flicked into Idle Up One and tried some flips and found the elevator was still too slow for my liking which was strange. Aileron however was good with a nice quick roll. The tail was also a bit slow for my liking so I decided to land and check things out. A test with the pitch gauge revealed that even though the Swashplate values were the same for both Elevator and Aileron, the actual Elevator and Aileron pitch was not the same. I had both values set at 72% and found that I was getting about 7 degrees of cyclic on aileron but about 5 on elevator. Increasing Elevator to 82% bought things even again. I'm not a fan of having such large numbers on the cyclic controls in your CCPM swashplate values, so I may experiment with lengthening the swashplate balls to get greater cyclic pitch so then I can wind these values back down. With these revised CCPM values the elevator flip rate was much better, but still not blisteringly quick which I'm a little surprised about. I'll have to get someone to tach the headspeed to see what it's pulling. The tail is a bit interesting. I'm using a GY 401 in non-digital mode with a HDS-877 servo, I'm running about 55% gain (as defined on my 14MZ) and it goes well at this setting, however during a flip or any other sudden maneuver such as a tic-toc, the tail will wag. I'm gradually reducing the gain value by two percent each time. I've also re-examined the tail linkage to make sure that's as free as it can be. I found it to be a little stiff, but widening the tail pushrod guide under the boom clamp and putting a little Tri-Flow on this and on the tail output shaft also helped. I would try running a shorter servo horn too, but at the moment I'm using the smallest one there is. I'll continue to work on this and see how I get on. It will be good to try it though on a calm day! SUMMARY I don't think it would be an overstatement to say that I do believe my flying will improve with the T-Rex simply because I can go down to the park after work and do a couple of flights of real flying (as opposed to compensating for less than great flying characteristics). Align seems to emulated the business model of Thunder Tiger (and you'd have to be blind to not realise that a lot of the design of the T-Rex comes from the Raptors) in producing cheap models that fly well that are exceptionally cheap to fix. Hence, you see T-Rex's all over the place. Align also seem very responsive to market demands as well. Apparently people were wanting to buy blade grips in single quantities rather than in bags of two and within a week or two, single blade grips were available. Certainly some lessons for the usual manufacturers in that. So now Tiny the T-Rex as I've named it, comes down to the field in the back of the car, hiding in between the Vigor and Sylphide's which tower over it, hell, even the little Raptor 50 towers over Tiny! Once I've had the opportunity to put more flights on it, I'll do a follow up article on the life and times of Tiny the T-Rex. |
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