Imagino que aplica tanto a la version Electrica como a la Nitro. Fuente: http://www.rcprecisionheli.com/index.php/site/article/Converting_a_T-rex_600_to_Achieve_Better_ContestFAI_Flying_Characteristics/ Converting a T-rex 600 to Achieve Better Contest/FAI Flying CharacteristicsBy: Norman Davis
I would like to take a moment to thank those that have helped me through this project. First, Erich Freyman and his willingness to answer many questions. Also, I want to thank Scott Gray for taking some brief time out of his busy schedule to assist my understanding of FAI set-ups. I am new to this style of flying, well, even fairly new to RC helicopters, and I could not have done it without this help and advice. What you will see comes from people like this, mixed in with my own ideas maybe, but I can not take claim to many of the principles involved.
I have also analyzed and researched these changes as much as possible. To do this I modeled the entire head assembly in 3D using Pro Engineer, and made the assembly interactive as the real head unit would operate by servo input. I used this assembly to analyze many angles, flybar ratios, pitches, etc, etc, and even charted the pitch motion curves of each one. It took me a while to get this assembly to correlate with real world movement, but I believe what has been developed is fairly accurate.
First, a lot of this information is somewhat reliant of helicopter weight and disc loading, or, in other words, the amount of weight per square inch of disk rotor area. The 600 was primarily designed for 3D and made to be as light as possible, but this should be increased. My particular helicopter, with the aluminum frames, comes in at about 8.5 lb. This gets the disc loading higher for this style of flying, and makes it more stable in a hover.
Now, I will discuss several topics that are key points to this conversion starting with the flybar all the way through motor choice. I hope you enjoy.
FLYBAR - The flybar provided with this kit is 400mm long. I would suggest experimenting with a range of 380mm to 400mm depending on the length of your flybar paddles. I am using Rotor Tech’s paddles on my project ($69). These paddles are great, thin, efficient, balanced chord-wise about the feathering, or pitch axis, and seem to be well designed for aerodynamics. Another plus of using this paddle is that it has allowance for quite a bit of flybar insertion. The Align manual calls for 125mm between the flybar cage to the inside edge of the paddle. I screwed these Rotor Tech paddles on until that measurement went down to 113mm, effectively shortening the 400mm flybar by 24mm. This is a really easy way to experiment with flybar lengths, as, if 113mm does not suit you, simply loosen the allen screw to the paddles, adjust to a new length and retighten.
I’m also using the extra weights that came with these paddles. The paddles themselves weigh 18g; with the extra weights it puts things around 26g. In addition to that I am using an extra set of slip on K & S weights ($15), which I have not measured, but my estimate would be that I have a little over 30g on each end of the flybar. I plan to stay in the 30-35g range on each side.
The other thing I did after I had everything mounted on the flybar, on the helicopter, and the paddles set to 0 degrees of pitch, was to balance the system on the helicopter. This was done by disconnecting the links for the flybar and the SF mixing arms. I didn’t worry about disassembling the flybar cage to remove the links. I just disconnected them from the washout arms and let those two links hang downward evenly, or, in other words, straight up and down. I moved one set of weights on one end just a little until the flybar was balanced about the tilt axis. Then, to balance the flybar about its pitch axis, I just rotated the weights so that the allen head pointed in different orientations. The allen head in the weight is usually denser than the weight itself, so rotating that allen head position will indeed balance the flybar about the pitch axis. BE SURE to do this with the AC and/or fans in your home turned off. Since the paddle will be attached to the fly bar they would catch any air current and throw off your work, and, at that point, would make balancing the system pointless.
This may sound like a lot of work for a flybar, but remember, the flybar is a main “gyro” for the whole helicopter excluding the tail, so it is important to massage it the best you can.
SWASH – The swash that came with my T-rex 600e worked fine, and certainly did its job reliably. However, in an attempt to remove as much lash as possible and make for more precise flight characteristics I knew it needed to change. In my case, this involved changing to a Quick UK swash ($69). This swash is a quality piece for sure, and uses four allen set screws to preload the bearing.
The Align links will most likely fit tightly onto the Quick UK swash balls. To solve this, once you have everything put back together, simply squeeze the link on the ball with a pair of channel lock pliers ever so lightly. Wiggle the link by hand and repeat this until the link is just loose enough to move freely. If you wish to use a link reamer tool that is perfectly fine, but I prefer to use this method as it is my belief that in conforms the plastic of that particular link to that particular ball.
Another thing you will want to check is the anti rotation post’s motion through the anti rotation guide, except for owners of the new ESP or newer Nitro Super Pro of course. Mine fit a little tightly, therefore I sanded the inside part of the slide with sand paper until the post moved up and down the slide evenly and without any binding.
BLADE GRIPS - The Trex 600, being designed for 3D, has been set up for negative delta, as apposed to a positive delta. My guess here is they did this to give it more “pop”, or quicker response, but this can also have a negative impact on stable flight on a windy day. What I did here was to simply flip the blade grips to change this delta to a positive value, hopefully making the helicopter handle wind in a much better fashion.
This modification is very simple. Just remove the head button, disconnect the links, flip the blade grips over, and reattach the head button. As a result you will also need to flip the seesaw and SF mixing arms attached to the seesaw. Reattach the links and voila, you now have positive delta.
This will also require you to reprogram the radio, but being this set-up changes more than just this, you will want to start fresh with your radio programming anyway. Now, the swash will move downward to make positive collective, and upward to make negative collective. This is perfectly fine, the helicopter does not care, and it’s the end result we’re looking for here.
WASHOUT ARMS – This is a very important modification if you have an older Trex 600. These “new” style washout arms have ball bearings at the pivot point within the arms, and they go a long way in removing lash from the system. If you have an older Trex 600e, like me, you will need to add one more spacer between one of the washout arms and the washout base to keep the system from binding and locking up on the main shaft, as laid out as an example using my old plastic parts below.
SERVO WHEELS - As far as servos themselves go, the Futaba S9452’s are fantastic. Lot’s of torque, metal gears, and good response time. But, for the servo wheels, this was a big learning for me. I would not recommend metal arms, especially metal servo arms with just two arms. The reason for advising against metal is lash. The Futaba plastic arms squeeze onto the servo, eliminating any lash, but metal arms are a slip fit, not perfect, and will just add more lash. Also, there is too much opportunity to have to use subtrims or not have everything at 90 degree angles.
I would recommend either a plastic Futaba servo wheel that you custom drill, or these 6 arm plastic Futaba wheels that I used. There are little numbers marked with each of the 6 arms, and each number corresponds to the degree of offset for that arm. Not only will the star wheels press on nicely and tightly, but you can find an offset that will eliminate most if not all need for subtrim. I had metal two arm servo horns on the helicopter before, and I must say, as cheap as it is to do, this is an important modification. The money I spent on those metal arms could have gone to something better.
RUBBER BAND MAN - You may have wondered from the previous photo what is that rubber band all about? I picked this trick up by seeing a photo of one of Scott Gray’s Sylphides. This rubber band presets the metal gear mesh inside the servo to eliminate servo lash. I tried to find a location and angle that would never allow the servo to unload the mesh and therefore open lash. This is only worth doing if you have followed the previous steps in the head, or, by that I mean the servo lash is the largest contributor to total lash of the system.
To do this modification for the front two aileron servos, I first simply put an extra couple of balls from the old plastic mixer arms into the star servo wheels as shown. I then took the long balls out of my old washout arms, and drilled extra holes in the plastic battery retainer using the existing frame holes as a pilot. I then screwed the long balls into those holes. It not only serves that goal, but keeps that battery retainer from flexing inward when you strap on the main battery.
For the elevator servo I drilled a hole in the tail block and screwed an extra short ball into it. I wrapped the rubber band around it and then around the upper link ball on the star servo wheel. If it makes you nervous to have it attached to the tail block I’m sure you can find another location. Hopefully the band should either pop off or snap easily enough in a bad crash, but if you bust the tail block out there are far bigger problems than any problem the band could cause.
I got my rubber bands at Staples, and you will want to use a thin and really elastic rubber band so that is does not start to load up the servo.
The side effect of the modification is you will have to get used to the swash sinking a little when you turn everything off.
Notice I also have a little metal nut on the back side of the star wheels attaching the ball. I like to do this and put a little dab of epoxy to assure everything stays put, and accurately.
I don’t have my receipt but the cost of this modification is about $1.99, maybe a few dollars more if you have to buy the wheels.
TAIL SETUP - My goal here was to find a setup that would allow me the Bob White, aka Finless, recommended limit A and limit B of 115 in the GY611 gyro. I used a Futaba servo wheel and as you can tell by the numbers going around the center there are a lot of servo angle offsets to choose from. There will most likely be one of those that will get the wheel all centered up. The hole I drilled is 11mm from center, or roughly half way between the 10mm and 12.5mm circles marked on the wheel. I used a pair of calipers, set them to 22mm, and got everything centered up from one side to the other, which allowed me to make a drilling mark on one side.
I now have limit A and limit B set to 115, and it just barely falls short of binding at full extents.
I also used the Quick UK carbon fiber tail conversion. I think they are about $39, and will go a long way toward tail precision. I believe the goal here is to have the tail well enough fitted to be able to use the maximum gain you possibly can for precise tail holding without it causing wag. My experience, which is very limited, is the more lash you have, most likely the less gain you will be able to use. My gain is set at 32; it might be able to go higher I just haven’t tried after these modifications.
TAIL FINS - The last modification to the tail is to cover the tail fins to make them solid, as this will help with forward flight. I used some of the Monokote sticker, not the typical Monokote that would go over an airplane wing, but the stick on kind. I sanded the fins to make them smooth, put the sticker material on, cut the edges, used a covering hot iron with sock to get the sticker material to bond well and make it conform to the curves, and then trimmed off excess with a hobby knife. The cost of this modification is relatively small.
MOTOR – This is mainly a topic for owners of the older Trex 600e, but motor choice is very important. The most important thing here is reliability and minimal vibration. If you plan to compete expect to also be judged somewhat on safety and durability. It would certainly be a bad day if you were performing for the judges and your motor blew a bearing, and/or your ESC caught fire, causing an emergency auto or even worse, a crash. I would recommend at least having the new 650L and mating speed control from Align. These seem to be performing better from a reliability standpoint. My personal choice was a Hacker in-runner brushless, or specifically, the Hacker C50-11XL mated to an 11 tooth pinion. This in-runner is so smooth and silky it shows in how the helicopter hovers, and it has plenty of power. It also has performed flawlessly with no maintenance whatsoever to this point and shows no sign of problems. You will drop a few extra dimes on this motor, but in my view it is worth every single one.
CONCLUSION – I hope you have enjoyed reading through this conversion. It certainly does not entail everything regarding my helicopter or the changes I’ve made in an attempt to help it perform better, that would be a small book. That is one thing I have learned over this process: the technicalities and effort of not only your flying, but setup. If I may quote Wayne Mann, “tuning your helicopter so that it requires less work from you in flight”. However, it does contain the bulk of information you can use to help change the flight characteristics of your helicopter on a reasonable budget.
As far as the CAD analysis that I did, which required many hours of hard work, and often late at night? What I found is the head design is more or less what it is, for good and for bad. I primarily wanted to make changes to the flybar ratio, but with that change created an unwanted effect to blade pitch in certain conditions. At first I was somewhat disappointed, but in the end what it did was teach me what a good adjustable head design is. If you want the ultimate head for this helicopter; one that will allow you to make adjustments to things like flybar ratios without having a negative impact, you would want a head that has the mixer arms attached to the main grip arm like the Kasama head unit. Who knows, you may say this item in a future installment, unless I convince myself to make a JR Sylphide 50 or 90 my next helicopter………
, which is the older aluminum version of this kit, although the principles laid out in this documentation should carry through the GF/CF versions all the way to the new 600 ESP and nitro versions.
Dilber MC Theme by HarzeM modified by Madcortina