Pre-production Twinn-Rexx build pictures

[v22chap]

Yes Joe ,,, you are the man ,,,, and I am watching the website every day from now on ... if you need some one to help with beta testing a unit give me a call ,, would love to help you out on this project .
Larry

[Gra55h0pper]

Cool Joe! I'd love to hear about your experiences once you are able to share. I'll post mine here of course, but that won't be for a while as I want to finish and fly with the fuselage first before I change more variables... Of course I'll be cheating at first as I can always turn the flight stabilization on if I need it...
Ultimately of course, getting to a 3-bladed head setup which flies close-to just as good as with the 2-blade flybar heads without using additional gyros/flight stabilization would be really cool!!! Nice to hear you're not sitting still and taking the hobby even further when it comes to tandem helicopters!

[chinookmark]

Put me second on the list for beta testers, Joe! I kind of have a head design bouncing around my brain that I'm going to try and make. It'll cost a few dollars in Trex parts, and a case of beer for one of my machinist friends. Not knowing any better, my head is going to be very similar to a real CH-47 rotor head. I'm a flight engineer at heart, but I've been working as a prop and rotor mechanic for the last few years. As a matter of fact, I just started ripping apart a pair of full scale heads today.

[rodney foster]

Iam Joe,This is Rodney in Irag. I love my twin trex I bought from you,would like foe you to send me a picture of the three blaided.Ill buy a 600E from you.
Rodney

[Gra55h0pper]

Finally, some progress... See attached pictures...

[v22chap]

Awsome grasshopper ,,,she is going to be a sweetie
definately easy to see in the air .and not your old army, navy ,,marine colors

[sokal]

To all you big windy junkys (hail hail)
i just got in to the rc heli hobby 6mos ago and my goal is to have an rc ch47.
iv been looking in to the hirobo and the twin rex. i do perfer elec.
so any in sight would be great. also figured ill give a pic off my beutyfull ladys

[tungym]

Your photos look good.

I really want to put some "parachute regiment.toy" in my electric chinnook and remote control a servo to drop a few parachute high in the sky.

[Gra55h0pper]

Sokal,

Cool pictures! Do you fly these?

If you prefer electric, then the Twinn-Rexx is the way to go! You could of-course convert the Hirobo to electric (it's been done), but that's not a straightforward mod.

Note that the Twinn-Rexx is not exactly a helicopter for beginners. Before you buy one, I suggest you are fully comfortable in forward flight and in sideways and nose-in hover with a heli like a Trex 450. Also, experience in how to set up a model heli is a must as for a tandem it's very important that it's mechanically set up right. Given that a tandem has much less yaw authority, it might also be a good idea to practice on a 450 with the gyro set in rate mode and the gain fairly low (practise "hunting the tail").

Provide you meet these "criteria", then my advice would be to go for it!!! Building and then flying the Twinn-Rexx is a super rewarding experience! My next challenge is to finish the body (some decals and clear coat) and then fly it with the body. That'll be sooooo cooooooooooool !!!!

H0pper.

[Gra55h0pper]

Mounted and tested a 401 gyro today for rudder. Unfortunately, I was only able to hover as I was flying in my back yard. Next to the swimming pool...

I tried rate mode first, setting both the delay and gain to 50%. At first I didn't really notice that much of a difference from the 240. However, when I started some experiments quickly changing heading by about 30-45 degrees, the 401 seems to perform much better! With the 240 it always seemed difficult to quickly "lock-in" to the new heading, requiring several stick inputs to "help" the gyro. It seems the 410 gives more of a feeling of having authority over yaw, i.e. the heli is much more responsive to inputs from the rudder stick.

I then started playing with different gain and delay combinations. I came out to 40% delay and 75% gain. I have the feeling that being able to set the delay really helps given the dynamics of a tandem's "cyclic-induced yaw".

Next, I decided to try heading hold mode, starting with a delay of 40% and a gain of 25%. The helicopter seemed to hover just fine, indeed applying small corrections to correct for heading changes caused by the wind. However, when I tried to "actively" change heading (by about 30% or so, slowly at first), it resulted in a big overshoot followed by an "overshooting" gyro correction the other way, etc. Although it seemed to even out after a couple of oscillations, I'd say it was on the verge of becoming an unstable system (I tried all this very close to the ground such that I could easily set her down in case the oscillations really wouldn't stop). I tried many delay-gain combinations, but was not able to get rid of this "overshoot oscillations" behavior.

My findings so far:
- The 401 performs better than the 240. There's much more of a feeling that the heli responds immediately to stick inputs and the gyro is able to stop a rotation much quicker. It really feels (even) simpler to hover the Twinn-Rexx.
- Unfortunately I couldn't get heading hold mode to work for me. At all delay-gain combinations I tried, the heli starts oscillating around the yew axis (with a swing of easily 45 degrees or so!). This oscillation only slowly dampens out over time. Observers would think there's a drunk pilot at the sticks

I'm going to stick with the 410 on yaw and the 240 on DCP. On DCP I don't see a reason to upgrade. On yaw, the 410 performs better than the 240 but not as good as I'd hoped for (heading-hold mode).

H0pper.

[v22chap]

Now I haven't flown my 401 in the wind outside ( to cold for this old man ) ,,but in the garage I found about the same as you ...other than I didn't get the oscillation when in HH .. but it is definately better than the 240 ,, even in non HH .
I am now having some kind of glitch problem that I can't find and it is getting worse ... I have tried about everything and can't seem to stop it .

[Gra55h0pper]

Just realized I hadn't posted my findings on my change to the JGF 500T motor yet. Basically, it's just like in Leapfrog's tests. The motor just gets warm, but not hot (you can actually keep your fingers on it) after a bit of excersize (didn't try any extreme pitch changes). The ESC (an Align 35) stays cold and so does the BEC (Medusa). The battery just gets luke warm. I couldn't really feel much difference in power between the Medusa and the JGF 500T. All in all, this seems like an excellent set up for the scale body which is slowly nearing completion!

[Gra55h0pper]

v22chap,

Have your tried to actively and fairly quickly change heading by about 45-90 degrees or so? That's when I get the oscillations. When just tail-in hovering, everything seems fine for me.

Would be great to further exchange experiences with the 401. Let me know if you'd like me to try certain experiments/settings.

H0pper.

[v22chap]

Yes I did do some quick changes almost 90 jerks like to see if it would start oscillation ( quick left and then quick right ) ... but I was only about 38 percent on the TX and full delay at the time ...when I started going down on delay is when I started noticing the pitching motion that has been there all along start getting worse .... and I started to see the front servos going nuts ...
I have completely unhooked both gyros and it is still there ... I have rerouted and resoldered all wires . I unhooked the TH-2 and run other servos on the RX to see if they would jitter while running the ESC/ BEC and motor .
I am out of ideas and still have this bad front end bounce while hovering and it will get worse if you stay in the air ,,,or it will bounce the front up and down if you leave it set on the ground with enough RPM to get the front light . It is still controllable in the roll and collective axis , so maybe it is a head problem ,,but I can't see anything wrong with it . It acts like the front collective is loose and bouncing around ...and if I leave it in the air longer it starts to do a small circle bob type of motion.

I just don't know what else to do . I guess I will jerk everything off ,,, clear out my TX settings and start all over again .

Grasshopper
Try setting the throw (limit pot ) on the 401 down to 100 as that is where I have mine . ( maybe you are getting to much swash plate movement ) I also had to readjust my linkage to manually get the non heading hold augmentation to stay put ,,,without using a TX trim offset and having your trim at neutral .... then put it in HH when you can hover good with this non heading hold centered setting ,, much like you would do for a normal tailed bird .I also am using -18 expo on the rudder channel in the TX .

[Gra55h0pper]

V22chap,

Interesting "pitching motion glitching" behavior you're seeing. It's tough to say what's going on just reading about it... As (I think) you're saying only the front 3 servos are affected, only suggestion I would have is to keep the servo wire going from the TH-2 to the front extender board as far away as you can from the ESC, motor and BEC. It could be this wire is picking up interference and as it carries the signals for all three front servos in one single line that might explain things (?).
Also, make sure to install ferrite rings on the BEC power output and the ESC input. You could even try installing a ferrite ring on the wire feeding the extender board (close to it) to see if that reduces the glitching.

On the 401 experiments, I have the limit set to 90. This setting safely (with margin) prevents the swash plates from binding when applying full roll and rudder input in rate mode. You raise a good point in that the limit setting influences the behavior of the total system. Perhaps if I go to a higher or lower limit the oscillation I'm seeing will go away. Need to try that next time I take her up...
Note that my mechanical setup is already such that with the gyro in rate mode no Tx trim is required. I agree with you this is very important.
I'm running 5% exponential in the Tx on rudder, but expo settings are very personal (depending how sensitive you want the controls to be and whether or not you use a "thumb and index finger" way of holding the sticks)). This shouldn't make a difference in gyro behavior as I've tried both making fast and slow heading changes and in either case the oscillations occur.

One thing I haven't tried yet is to turn the elevator->rudder mixing completely off. Even though no (or very small) elevator inputs are applied as we're in a hover, it might make a difference (I don't really believe it will but I'll try anyway). Anyway, for testing yaw gyros, it's best to (initially) have this turned off.

H0pper.

[chinookmark]

Gra55h0pper

I've been using a RCT-G730 gyro for yaw on my Twinn. It's very similar to the GY401 in funtion. I've even heard it's got the same guts. I found the oscillation reduced when I used a high delay setting. With full delay, I don't notice any reduced responsiveness from using lower settings, but the oscillation in noticably less. Don't forget that the travel limits (endpoints, ATV, etc) on the rudder channel control piroette speed on the 401. I turned mine down to 75, and that seemed to help as well. I might turn them down more, since I don't see myself trying a piro flip or chaos on the Twinn Rexx.

[Gra55h0pper]

Chinookmark,

That's good data! Good point on the rudder ATV settings! I haven't played with those yet and you're right in that lowering the pirouette speed might reduce the oscillations caused by gyro overshoots. That's definitely worth a try as you don't need (or even: want) very fast pirouette speeds on a scale tandem like the Twinn-Rexx. I'm not into piro flips and chaos anyway... (if I can void it... ). Also, I'll focus my experiments on higher delay settings.

H0pper.

[sokal]

yes i do crew them and is the reason i want an rc version. but i do realize i need to get thier slowly. so i feel in like a yr or so i may be ready. just wondering know were i can find the hirobo electric mod info.

for the v22 guy hope u enjoy that pic its us at the v22 training facility

well enjoy the beuties

[Gra55h0pper]

v22chap - Although this is likely not you problem, it could possibly explain things. Check that the blades on the front-rotor are installed correctly (i.e. with the correct side up). I've caught myself once having installed the front blades the wrong way around... It's actually easy to do (or so I keep telling myself) as the front rotor runs CCW and the Align logo on the CF blades normally faces up, but needs to face down in this case. Did you know the Twinn-Rexx will actually hover (sort of at least) with the front rotor blades upside down? Please don't ask me how I know... :o

[Gra55h0pper]

Sokal - Thanks for the pics. Very cool! D'ya know that for my work I actually sit on my @$$ all day...
Just practise on the simulator, build and fly a Trex 450 (with the gyro in rate mode) and you'll be ready for the Twinn-Rexx in no-time! Have you watched Finless videos on the 450 build and setup?