Trex F.A.Q. Updated 4-24-2007

[vinljp]

Hi guys,

Great tips you got there, many thanks to you and Bob!

I do have a question with regards to hunting down vibrations in the heli.
Can you provide us with a step by step procedures of how to hunt down the source of vibrations?

Thanks a million !!

[superflY851]

I have a question about the three swash servos.
I have a serious problem with my three Hitech HS-65hb servos. When i get up to around 70% throttle all three swash servos start twitching. So much so that i almost crashed and am currently grounded.
I made a video
http://video.google.com/videoplay?do...53187896797115

HELP!!!

Trex450se
3 - hitech HS-65hb
futaba gy401
futaba s9650 digital tail servo
DX7
AR7000 reciever

[Cryofix]

I would ask about that in the main trex forum

[rdlohr]

Nice writeup on Spread Spectrum and 2.4 Ghz technology by kgfly:


This should help folks to get an understanding of how spread spectrum technology differs from conventional FM (PPM/PCM) radios.

* There are no fixed channels in the ISM band. It is 80MHz wide and each user can use as much or as little, divided up however they like. WiFi defines 15 overlapping wideband channels. Some video senders define just 2 or 3 wideband channels. Spektrum define 80 x 1MHz channels, use two per active link and so support up to 39 simultaneous users. XPS define 12 x 5MHz channels and support up to 120 simultaneous users. Futaba FASST is also believed to define about a dozen 5MHz channels but have not AFAIK released any details nor even a claim to the max number of simultaneous users.

* The implementations of spread spectrum for R/C all use encoding that is unique for each Tx/Rx pair (this is the "binding" process where the Rx learns the Tx's unique ID). This encoding means that even if multiple Tx operate on the same logical channel they simply look like a small increase in the background noise floor to each other. So if you were flying a Spektrum system and something else came along on both the active channels, unless it was a very powerful signal across them both, the system would just keep working with a slightly higher noise floor.

Certainly a foreign Tx can NEVER take over your model, that kind of shoot down is virtually impossible. The most that can happen, although unlikely, is that the noise floor on all channels in use on a given link gets high enough to start causing packet loss and ultimately, inadequate packet throughput, at which point the Rx will go into failsafe.

* There is no such thing as a "bullet proof" RF link, and certainly not CDMA. Any RF link can be overwhelmed by noise. Any Rx can be swamped by too much RF power, even from out-of-band. However, these new spread spectrum R/C systems provide a much higher level of robustness, noise rejection and sensitivity than the old FM (PPM/PCM) technology. We are talking about 10 to 1000 times better. So while models will be lost to R/F problems, it will happen far, far, far less often than it used to.

* Spektrum defines 80 x 1MHz channels. It uses two per active Tx/Rx and reserves 1 for binding. So you can have up to 39 Spektrum Tx/Rx sets active at a time. When Tx 40 is turned on it is unable to find two clear channels so waits until it can. That user cannot fly until some channels are cleared.

* XPS uses a different approach, with 12 x 5MHz channels. They claim to support up to 120 simultaneous users. You can see straight away that they are making use of the spectral efficiency and link security of spread spectrum to allow up to 10 users per channel without any concerns. While XPS is DSSS, because theirs is a live two-way link, the Tx monitors the R/F signal level, and lost packet count and availability of alternate channels as reported by the Rx. If the current channel is becoming too noisy it can initiate a change to another, better channel. The switch over takes less than 1ms. This is probably the cleverest of the R/C spread spectrum system designs, at least on paper.

* Due to the high bandwidth of the channels and the low volume of data required for R/C, the Tx use a low duty-cycle transmission scheme. That is, unlike FM Tx that are on all the time, the new Tx (modules) are actually only transmitting for a few milliseconds for each frame. This has two consequences. It significantly reduces the average power require by the Tx and hence improves runtime. It also further reduces the chance multiple Tx interfering with each other since they are all only ever transmitting in short bursts.

* You cannot ever be shot down in terms of someone directly conflicting with your control of the aircraft. Yes the ISM band is open to any and all uses and users. Personally I don't think it will be a problem. There has already been lots of testing by the Mfrs and for Spektrum and starting recently XPS, by end users. All kinds of weird stuff. One guy jiggered a microwave oven to operate with the door open. Put his Spektrum Rx 3m from the open oven and had not trouble operating his DX6/AR6000 combo with a 1kW of microwave energy coming out of the oven (compared to <100mW from the DX6)! The systems have been tested operating flawlessly next to pairs of WiFi base stations, flying around cell towers, flying around pager towers etc. It really does work!

The legality of 900MHz for R/C varies country by country. That is a major reason why the 2.4Ghz ISM band was chosen, because it is globally available.


Rick

[PsychoPilot145]

THANKS!!!

You just saved a crash for me. I have been just cursory checking the main screws that I can get my fingers on up 'til now...

After reading this post, and having about 3-5 flight hours on the bird, I thought I would give her a thorough check up. I actually went over all of the screws with a screwdriver.

One of the screws holding a mixer arm on was loose.

It was not yet working its way out, but tomorrow is Helicopter day, and I am planning on running 10-12 packs on each of my Rexs. There is little doubt that this screw would have worked it's way out and brought the bird down in flames.

My flying sucks bad enough. I don't need any help crashing due to a mechanical failure.

[ShellDude]

Something that has annoyed me and many others is getting a definitive answer on what HDE and CDE stand for. Now we all know they translate between standard and CCPM but what do the actual acroynms mean? I'm assuming their origin is from a language other than english and things simply don't translate, but I'd like to know, even if it was the full meaning in the "native" tongue.

[trexfrek]

Just wanted to say Thanks for the info. AS a beginer it all helps.It's also nice to see someone from PA. What part of Easton are you from. I am from Allentown or rather Emmaus PA.Talk to you soon.

[BryMeister]

Hi. I just wanted to say how informative I found this thread / FAQ. Thanks to all hat contributed to it.

I have my TREX V2 kit, my radio and my work bench arrives tomorrow. I have downloaded all of Finless' video clips and watched them once already. I will probably watch them 5 more times before I open my first packet of parts!

One question, though is "in what order" should Bob's video steps be performed?

Sorry if I am posting this to the wrong thread, but it seemed a likely place to post this.

[Onad]

This FAQ has really great information! Hoping my questions will lead to updating the head speed calculation info.

I was reviewing the Head Speed calculation formulas and had a question. So motor KV is used in the formula. I assume this calculates the head speed at 100% throttle/power for the KV rating of motor?

Wondering if is there a power (KV) curve graph somewhere that would correlate the KV at a given power input to a motor so I could calculate head speed say at hover (75% power).

Obviously, the best way is to Tach the head….

Hopefully I made some sense here?? I’m brand new to this hobby.

Tx, Onad

Originally Posted by Cryofix

How to calculate your head speed
A simple very easy to use spreadsheet was created in order to do this exact thing so there is no need to know complicated mathamatatical equations, and here it is http://video.helifreak.com/?subpath=...calculator.xls
Here is a simple easy to use calc for headspeeds
http://www.readyheli.com/Online_Head...lator_s/81.htm

[jwilliam]

Originally Posted by rdlohr

Please add the info from that link that Bob put in answers to all the different REX types. That gets asked regularly.

Also, add "SA" to the list of gyro mounts I make.


Thanks
Rick

So where is this?
I am a total NOOB when it comes to Heli and I would like to know about the different T-Rex heli models. I was looking for that when I found this thread.

Also on the first page:
Blade balance: One of the most important things you can do to help your tracking is to make sure you blades are balanced you can find a simple balancer ReadiHeli or RcHover
The ReadiHeli link:
http://www.readyheli.com/K10289A_Mai..._p/rh-0106.htm doesn't work.
I think it should be:
http://www.readyheli.com/K10289A_Mai..._p/k10289a.htm
Or at least that is what I end up with when I search for K10289A.

[mensaboy]

theres actually a very good description on Wiki

http://en.wikipedia.org/wiki/T-Rex_(RC_helicopter)

[Pinecone]

I'm surprised this hasn't been added before:

Trex 450 Models

450X - Original model with short boom, plastic frames (very first ones had grey plastic, soft frames), mechanical mixing. Maximum 315mm blades.

450 XL HDE - Stretched version of the X with longer boom and belt to allow blades up to 335mm. AFAIK, all were a better grade of black plastic. 420L motor and 25 amp speed controller.

450 XL CDE - Same as the HDE except it used eCCPM mixng, but still mounted the servos up front and used bellcranks to trasnfer the motion to the swash.

450 SE (V1) - Moved servos to direct servo to swash connections. Full CNC parts, carbon fiber frames. More powerful 430L (3550Kv motor) and 35 amp speed controller.

Was not called V1 by Align, but V1 is used to differentiate from the V2 when it came out. There was a LOT of confusion as Align makes running changes to kits and people were calling a mid-run changed kit as a V2, but that is now commonly called a V1.5. The late V1 kits had many upgrades from the first kits.

450 SA - Pre-assembled with a mix of CNC and plastic parts. Came with either aluminum or carbon fiber frames.

450 S - Same heli as the SA, but came in more of a kit form.

450 SE V2 - Upgraded SE kit. CNC parts are a deeper blue. Comes stock with fiberglass canopy, the rotor head uses a larger (4mm) spindle shaft, and the main grips have thrust bearings to deal with high head speeds. The tail servo mount has longer arms to more easily accomodate the mini servos most people are using. The frames are modified - different battery mounting plate angle, boom block flipped to allow under boom gyro mounting with an adapter. Dark blue gears, with a screw in hub to mount the one way bearing (was a running change late in the V1 also). MOre powerfull 430XL motor and the ESC was changed to provide 6 volts to electronics.

[markb]

I keep seeing this same issue come up on the forums, and it came up yet again. I’m not that experienced at flying helis, but I have loads of background in control systems, so I thought I’d give my 2cents on this issue. It’s a complex subject, but here goes…

What everyone says about “not adjusting the rudder travel for a HH gyro using transmitter endpoint settings”, is true. Don’t try to do it. You have to adjust the rudder servo travel range using either limits on the gyro, or mechanically. If your gyro has no limit adjust, you’re stuck using mechanical adjustments. You have to adjust the linkage to the servo so it cannot push the pitch slider up against either stop. Preferably, it can just barely reach both.

The reason is this. A HH gyro contains an “integrator”. Its what distinguishes a HH gyro from a rate gyro. What the integrator does, is each time the gyro figures out what to do with the servo, it ADDS the answer to the previous signal it sent to the servo. So, if the stick is centered, and your heli is rotating left… the gyro will sense “I need more right”, and add a little right correction to the servo. If the heli continues rotating left, it will add still more right. For as long as the heli is rotating left, the gyro will keep ADDing right rudder. More and more and more.

That’s the essence of integration… continuous adding. So what, its adding, big whup? The thing is, no matter what limit you put on your transmitter rudder channel, the integrator in the gyro can repeatedly add little corrections, which over time accumulate to a full scale travel on the servo. Even with ZERO input on the rudder channel. So, the limit on the rudder channel does NOT affect how far the gyro can move the servo at all! You can set the limits on your TX to zero, and the gyro can still move the rudder to the stops.

Furthermore, the stick position is NOT telling the gyro where to put the rudder servo! This is a common misunderstanding, because on all the other channels that’s exactly how it works. Instead, the rudder stick is telling the gyro how much rotation rate you want. This is why, if you put a little stick motion in with the heli on the ground, the rudder will creep all the way to the stop. On the ground the heli is not rotating, but the off center stick says “I want 10 degrees per second of right rotation”. So again, the gyro says “I need more right”, and adds a little right to the servo. Still no motion. It adds more. And more, and more… Until the servo is all the way right, and hits the stop. Or, in a gyro with limit adjustments, it hits the point where it’s not electronically permitted to go further.

This interpretation of the stick position is also why the rudder endpoints are used to control pirouette rate! Repeating what I said above: The stick position is telling the gyro how much rotation rate you want! In servo systems, this is called a command signal. You’re commanding the gyro to do whatever it takes with the rudder servo, to achieve the stick position rotation rate. The endpoints on your transmitter adjust how much rotation rate you can command, or “tell” the gyro to aim for. With higher limits on the rudder stick travel, you can get higher commanded rotation rates… and faster piro’s.

[markb]

follow up copied from another thread... hope that's ok.

... if the gyro is in normal mode, it doesn't send any signal to the servo then? If so, then the endpoints would have to be set accordingly in normal rate so as not to overdrive the servo?

First, dont use normal mode. Far as I know, there's no flight 'regime' where its better.
But, in normal mode, the gyro is still continuously sending signals to the servo. It only lacks the integrator piece of the picture I talked about in the FAQ. In fact, in both rate mode, and HH mode, the gyro has two other factors that enter into the compound signal it sends the servo. Proportional, and derivative. Proportional means a correction that is a multiple of the error. Derivative is a multiple of the rate of change in the error. If the stick is centered, but the heli is turning, that rate of turn is error. The proportional factor multiplies the rate of turn by a gain number, and adds the result to the output to the servo. The derivative looks at how fast the rate of turn is changing, multiplies that by a gain, and adds to the output.

[3Dman1655]

Very good info markb. It helps a lot to know the inner workings of the electronics on board these sophisticated machines.

[jasdall]

Hi all i am Jason from Malta in Europe.I am facing problem with my Trex450S. I tried all the possibilitys. The problem is that i have followed all the instructions regarding link rods. This problem happened after i changed the seesaw & lower arms after a small crash.
I bought seesaw and lower arms from another supplier. Not original Align , but everything match & even the measurments of parts are exactly the same.The parts are Sonix parts and all these parts match with Trex.

Hope this is to your understandings. Any one can help please!!!


Jason Dalli

[Skarn]

Originally Posted by jasdall

Hi all i am Jason from Malta in Europe.I am facing problem with my Trex450S. I tried all the possibilitys. The problem is that i have followed all the instructions regarding link rods. This problem happened after i changed the seesaw & lower arms after a small crash.
I bought seesaw and lower arms from another supplier. Not original Align , but everything match & even the measurments of parts are exactly the same.The parts are Sonix parts and all these parts match with Trex.

Hope this is to your understandings. Any one can help please!!!

Jason Dalli

What is the problem? I don't see where you mention a problem at all....

Skarn

[Cryofix]

I cant edit this thread anymore

[VIRUSS11]

Pinecone, I pick up a new T-rex 450SE GF/Superior Edition Helicopter, Is this the newest T-rex model? Sorry but I don't know the defrents between the SE and what I got.

[Skarn]

Originally Posted by VIRUSS11

Pinecone, I pick up a new T-rex 450SE GF/Superior Edition Helicopter, Is this the newest T-rex model? Sorry but I don't know the defrents between the SE and what I got.

The latest and greatest is the TREX 450SE v2

Skarn