Twinn Rexx owners' thread

[chinookmark]

Hey guys. I just maidened my new Twinn Rexx today, and man was it a thrill! When I was waiting for the kit to be released, I had planned on taking tons of photos and making a nice thorough build thread. I even considered making build videos .... Well, I got so excited about building the helicopter, I completely forgot about photos and build threads. Now the kits are being released, and I've seen a few people either building or waiting for their kit, I figured I'd start a thread where we can share information, tips, and tricks, and help each other out building and setting up this phenomenal machine.

My setup reads like I copied the recommended parts list:
1. DX7, AR7000
2. (6) HS-65HB servos
3. (2) GY240 gyros
4. Align 35G ESC
5. Medusa 5V 3.5A BEC
6. Tandem controller - TH-2GP + mounting plate + extender board
7. Motor - JGF 500T (1900KV)
8. Thunder Power Extreme V2 2200 maH 4S
9. 12T pinion
10. Align 325 Pro wood blades
11. (2) RC-Tek Phantom 450XL plastic rotor heads.

First off, why did I stray from the recommended parts list? I used a 12T pinion instead of an 11T because that's what I had. It'll also give me a little more flexibility in finding the right headspeed while I get to know the helicopter. The JGF-500T is a powerhouse, and on 4S, won't break a sweat. Even with a 12T, the heads will barely break 2000 RPM.

Why did I use the RCT Phantom 450 heads? Easy -- check out the price. $33 each plus 10% off for the holiday sale. The cheapest I saw Align plastic heads was about $60. Then add the benefit that they are compatible with Align parts and I can get replacements at any LHS or Walmart ... I'm sold. The quality on these heads is good, although I've never worked with Align plastic heads. I'll take a closer look at my supervisor's Trex SA when I get a chance.

Why plastic heads? Honesly, I see these as a temorary stepping stone on my way to three blade heads. Why spend all the extra money on fancy aluminum that I'm going to take off and sell on eBay in a few months anyway? Although if I was planning on staying with two-blade flybar heads, I would probably go with RC-Tek Skyshark aluminum heads. There are three reasons for this: 1) the quality of my Diablo is outstanding, and I wouldn't hesitate to buy more from them, 2) the price is right: $89 vs. $149 Trex heads (if you can find gray Trex heads), and 3) the overslung flybar. Comparing the Twinn Rexx to actual CH-47 technical drawings, I think the lower blades of the overslung head would give a more scale position to the rotor disc. Of course, that may come back to bite me when someone finds out the hard way that the lower blades like to chop up the fuselage.

[chinookmark]

I just realized how late it is, I've been babbling, and I haven't even gotten to the good stuff yet. Oh yeah, and I haven't wrapped my kid's Christmas present yet!

When the box arrived, the first thing that struck me was how big this thing was going to be. Compared to a Trex, the plastic CH-47 fuselage seems massive. Going through the box, the next impression I had was how little there was. Aside from the main beam and driveshaft, the rest of the machine was packed in a tiny little Priority Mail box. I was half expecting a mechanical nightmare (I work on real CH-47's), yet discover a project that seems almost too simple.

If you've built a Trex (or any other helicopter), building the Twinn Rexx will be a familiar task. However, I offer this advice: have the right tools. A decent 1/8" flathead screwdriver and metric nutdriver are a necessity. I did most of the build with one of those little pen-sized computer screwdrivers and a 7/32" socket. Not fun. The Twinn is constructed with flathead screws insead of socket heads, so be mentally prepared. You will need a file. A few of the bolts need to be ground down for clearance after assembly. A drill also comes in handy. I drilled about 8 holes for zip ties to secure the wiring.

That's all for tonight. I hope to post some pictures in the next few days.

[chinookmark]

Here's a quick video from the maiden flight:

http://www.youtube.com/watch?v=urKmgAy3vcM

[chinookmark]

Flight report:

I've flown about 6 packs over the last two days, and I'm starting to get a feel for the flight characteristics. Compared to a Trex, it's both easier and more work to fly. It's super stable, and just kind of floats around in the air, but you need to stay on top of the tail. Yaw control is from opposing aileron movement of the two swashplates, which lacks the authority and reaction time of a conventional tail rotor. It's a little loose feeling in terms of yaw control. This isn't a bad thing, since yaw isn't a byproduct of collective torque like a conventional heli. The yaw control is too slow to use AVCS (heading hold) mode in the GY240, so the yaw gyro is set to AVCS off (rate mode). I'd like to try it out with a GY401 with the delay turned up, to see how that will work. Or maybe a Logictech 2100 with the rotate rate turned down. Too bad I just traded my LGT 2100 to my LHS for some other goodies ... :) But really, it's not bad ... you just need to steer the tail, that's all.

The guys at work love it. Two of them almost have themselves talked into buying one. One of my friends is going to build his own, similar to the one in the back of RC Heli magazine from a month or two ago. So far, I've only flown slow FF, and shallow "S" turns. It looks really cool taxiing around and standing up on it's hind wheels.

[v22chap]

Cool Chinook
I love mine too ,,, to cold for this old man to be outside yet ...but the garage is fun .I too love the tail stands ... I need to try the roof top landing (pail duct taped to floor and land with only the back wheels on the pail )
Here is a short bad vid taken with my digital camera on the 4 th pack but it will give the guys the sound and idea of this neat little bird .
http://www.youtube.com/watch?v=F1i1R9_bvdQ

[chinookmark]

v22, what motor are you using? I find the JGF 500 has a cool high pitch whine, and if you start and stop it slow enough, it sounds surprisingly like the APU on a real chinook.

I cheat ... I work in an aircraft hangar, and I fly in there during lunch and after work. My garage was just a little too small to be comfortable.

[v22chap]

I am using the JGF 500 T and yes it has that whine ,, on my Bergen electric (. 60 size ) I left the clutch in the system just so you could hear the Actro 32-3 whine up to RPM and the blades still were not turning ..then slowly they would start to turn ... it was cool ,,but only those close by could hear it and especially if you were at a funfly with other IC guys flying around you .

This is my setup on the Tandem :

1. Jr 9303, Berg 6 ch RX
2. (6) HS-65 MG servos
3. (2) GY240 gyros
4. CC 35G ESC
5. Medusa 5V 3.5A BEC
6. Tandem controller - TH-2GP + mounting plate + extender board
7. Motor - JGF 500T (1900KV)
8. Thunder Power 2150 maH 4S
9. 13 T pinion (was all I had )
10. Align 325 Pro wood blades
11. (2) 450XL plastic rotor heads.(already had almost two :) )

The 13 T seems to do o.k. too .. I can get the RPM I feel comfortable with and still no heat in any area other than the battery is a little warm to the touch . So 12 T would probably be perfect .The only other pinion I have is an 11 T ,,but I think that would put it the other way and the motor would become the warm one and I would rather have the pack be warm and not the motor .... already lost one motor from the magnetcs letting go and they say that was heat ,,but I don't think so as I measured (with a temp gun ) almost every flight .


Must be nice to have a big hanger ,,,my two car garage gets to be confing at times :( I have already did a tail turn and flew right into the garage door :(

But it is better than no flying during the long winter months ....

[chinookmark]

You say your motor is cool with a 13T? Mine comes down fairly hot. Do you think maybe from the increased pitch due to the lower headspeed? That's wierd because the 500T is designed to run high pitch props on racing airplanes. I wish I had a tach and whattmeter. Oh, wait -- I have a gift certificate to the LHS! It was supposed to go for an Ultrafly P-40, but I should probably spend it on something I won't destroy the first time I use it.

My current throttle curve is 0-60-70-80-90, and it takes off about 3/4 stick. Maybe a higher throttle curve would help? The ESC comes down cold, and battery barely warm. How is your throttle curve set? Looks like I have more testing to do. On a side note, it will even take off and climb very scale-like with a 0-55-55-55-55 curve, but there's no bail-out power, although the blades do give a nice humming sound at the lower RPMs.

[chinookmark]

Speaking of testing ...

Now that I'm getting more comfortable flying the Twin, I was experimenting mixing elevator and yaw to try and compensate for the DCP. The TH-2 mixer board software has a setting for yaw compensation, but I didn't have my laptop handy, so I tried using the DX7's programable mixes. 50% yaw to elevator was WAY too much. I dropped it down to 30%, and it's still too much, but I think a little master-slave expo would help. I think that's what the OFFSET control is for in the DX7, but I gotta check that out in the manual. I've never used programmed mixes before (does the learning never stop? :) ).

During this testing, I set the mix to the GEAR switch to turn it on and off. Whoops. The DCP is set to channel 5, and the endpoints set to +50/-50. Channel 5 is also controlled by the GEAR switch. The helicopter was sitting on the ground at flight idle when I flipped the switch. I'm not quite sure what changing the value from +50 to -50 does to a channel that's slaved to another channel, but it sure does funny things to the helicopter. As soon as I flipped the switch, the Twin reared up on it's hind legs high enough to bat the rear blades on the ground. Post flight inspection revealed coursely sanded blade tips, still intact, and still flyable. Note to self: check the function of new mixes before you start the motor.

[v22chap]

Well ,, when I say no heat ,, I mean no finger burning type stuff . All of it is some what warm (motor and ESC ) but the battery is the one that is the warmest ... but still within limits I am sure as I can still leave my fingers on it . I will have to get the temp gun out .... been having to much fun with it to worry much about temps and Amps. or RPM's

My throttle curve is 0-20-41-61.5-76- 87-100 on my 9303 .. it is a nice up arch looking curve
and mine lifts off at just over 1/2 stick have not had it out where someone could tach it for me ,,but I am guessing it around 1900 RPM and have had it lower to start out with ,,probably in the 1700 area ... felt a little wobbly .
Yea I have not played with the mix yet . will keep your incident in mind when I do :O


.. I am noticing a drift of the rudder while hovering first one way then the other , I thought he was using the elevator / rudder mix to just control yaw differentail in forward flight ,,, but does this have anything to do with it in hovering , do you see this ??? I am sure it has to do with the DCP ,,but am not sure what to adjust or which way to go on any adjustment !!!
It is controllable ,,but not what I would like . I guess I need to poke around in the TH-2's constants a little more and see what all is in there ... I pretty much loaded his base settings and that was about all I have done with it .

[Gra55h0pper]

Very cool Chinookmark and v22chap! Nice to see another one successfully making it into the air!

After several "in between" projects, I'm now ready to resume work on mine. As part of installing the body, one thing I'm definitely going to do is to replace my Medusa motor with the JGF T. The Medusa gets *really* hot (way too hot to touch), and inside the body I'm almost certain that'll cause problems as will be much less rotor wash blowing over it.

[v22chap]

Grass
You will be happy with the JGF T motor .. it seems to love about any gearing you can throw at it . hope to get it out here in a couple hours and also heat gun and get an exact temp reading on things.But knowing Joe as I do ...the 12 T is probably the best for a full fuse bird ;)

[v22chap]

Well here are the temps.... had to go outside to a parking lot as the wife was sleeping getting ready for work ... It was about 28 degrees outside and a 10 to 18 gusting wind ...which with all trex's makes for a little bounce ...that I was not use to seeing in the garage .

My 3S 2150 TP was really strecthing it in the wind unlike the garage .The head speed was not enough and I played with the throttle curve a little ,,but I don't have the 3 S test model curve setup on gov mode yet and didn't do any fast climb outs ...just hovering
Temps for 3S TP's
Motor 54 Deg
ESC 28 Deg
Batt. 48 deg

For the 4S TP's ..(which handled the wind better ,,but I had to up the gov setting from 70 to 84 )the temps are :
Motor 78 deg
ESC 40 deg
Batt. 56 deg

I also was able to do some fast climb outs and this might account for some of the increase in temps . I did notice the motor bog some in the climb outs ... so I am thinking that I do need to order the 12 T with the fuse .

[chinookmark]

.. I am noticing a drift of the rudder while hovering first one way then the other , I thought he was using the elevator / rudder mix to just control yaw differentail in forward flight ,,, but does this have anything to do with it in hovering , do you see this ??? I am sure it has to do with the DCP ,,but am not sure what to adjust or which way to go on any adjustment !!!
It is controllable ,,but not what I would like . I guess I need to poke around in the TH-2's constants a little more and see what all is in there ... I pretty much loaded his base settings and that was about all I have done with it .

It's the nature for a tandem helicopter like this to yaw left in forward flight, so some sort of mix might help that as well. But it's the DCP that makes the yaw motion at a hover. When aft elevator is applied, the forward blades take on more pitch -- and more torque, while the aft blades reduce pitch -- and reduce torque. The helicopter yaws clockwise. Aft elevator does exactly the opposite. At a steady hover with minor corrections, this is hardly noticable, except for not having a locked-in feel to the rudder. It's much more noticable if you start cranking on the elevator stick. If you shove the nose down hard, it will definatly turn left.

[v22chap]

I guess I just got to get my head out of V-22 mode and think about tandem for awhile ...duh ...
happens alot when you get old ya know ,,, can't multi task at all now .

And Joe does talk about adding a mix for the forward flight left yaw ...and I guess that was mixing me up some too!
Thanks chinookmark

[SoupZ]

hi folks! nice chinooks man, i luv all ya chinooks! but i was tinkin' iv u were 2 use the 3 bladed heads on it, will u need 2 use a more powerful motor & esc or juz stick wif the 500T & 35A?

& iv u wanna use an extra cyclic gyro, do u oni nd 2 use 1 gyro wich will b connectin' btwn the rx's aileron channel & the TH 2's aileron channel??(bcoz the elevator areadi has a GY240 DCP gyro, am i rite??:P) or do i nd more gyros?

btw iz the DCP gyro 4 the stablility of the elevator??

thks in advance:thumbup:

[SoupZ]

oh ya & hw do u connect the TH 2's elevator,rudder, pitch & ch5's input 2 the rx when its oni a single pin connector?? thks!:lol:

[v22chap]

Soup
Usually the same motor can be used for multi bladed heads as you go shorter on the blades and the 500 T has power to spare ... as will the esc .

If I was you I would learn to fly it first with the 2 bladed head before going multi as this bird has some different flying charateristics that need to be learned ..before going on to scale heads

I also would wait for Joe (factory ) to do the reasearch on heads as there are different styles out there and some are better than others ....and he is working on this right now .

I think you could use another gyro on ail ... but it is not really needed as ail axis is really stable as is now .
maybe if you go multi head it will need it ,,but I don't think so .

Yes the DCP gyro is for elevator stablity .

You also hook the Th-2's wires up to the signal pin on the RX ( the pin that usually gets the light colored wire of the normal 3 wires ,, red and black are the power supply and the Th-2 servos get that from a seperate source)
Just use a needle nose pilers to push it on or if you want buy servo leads and resolder them to the Th-2's single lead making sure to get it on the lighter colored lead of the new lead .

[SoupZ]

Thk u so much mr v22, it was really helpful 2 mi:noteworthy:lol:chinook iz 1 of mi dream helicopters & i wud really wanna gt 1 so i'll work on mi funds fers:YeaBaby:

oh ya izzit true tat iv u use the extender board, u'll juz oni hav 2 connect the ail connector(wich iz the primary power source:P)& do nt have 2 connect the spare power supply wires wich they say iz safer?? or izzit betta 2 juz connect it too??:)

& i saw ur chinook flyin' on youtube(great job!:thumbup:)izzit difficult 2 gt it setup 2 fly well lyk i mean 4 eg. iz the TH 2 complicated 2 setup & program, r thr alota mixes here & thr(especially the programmable mixes, wich i'm nt familiar wif coz i'm quite a newbie:lol:)coz i read the posts on the tandem section here & read through some of the techmp TH 2 support page & it gt mi kinda confused haha!hw was it 2 u??:roll:

[v22chap]

Soup
Yes ,, Joe likes to have backup power coming to the extender boards and also to the Th-2 itself ,, this way you don't have any surprises while flying .

The programing is not to hard as Joe has the constants on his site to download and then all you do is load them into the Th-2 ..the hardest part of the bird is running the wiring to everything and trying to keep ESC , TH-2 seperated from power lines .

The youtube vid was the 4 th flight and not much but trim levers on the TX were touched by then .

[billyd]

I am up and flying! It is definitely a different feel flying a tandem heli.

My rudder (Yaw) is very slow to respond. Perhaps I should reduce the gain in the Yaw gyro from the stock 50%? What other settings (in the TH2) effect yaw rate? Any help would be greatly appreciated.

Anyway by setting up the heli per Joe's instructions, it is a very stable platform. Like he said, you can put it in a hover and almost ignore it while it gently moves around. Very cool model. Excellent work Joe! :thumbup:

By the way I am using the 500t motor and 35 amp castle creations speed controller and the 4s 2200 mah battery and I am pulling about 8.35 amps at hover. I put the power monitor on it tonight just to see. Figured I'd post it here for anyone interested. The power monitor adds a little weight so maybe without it that number drops a little, but then again I'm flying without the canopy so it's probably about a wash there.

Now time to build the body. I want to go with a camo paint scheme. Anyone have any links on how to do camo paint jobs???? I've never done one before, is this something that is very hard to do?

[v22chap]

You could put a little more neg expo on the tail rotor ...that would give you a little quicker control

Camo paint usually needs an airbrush ... but you can do a cheap version with spray cans . Cut female patterns (throw away the piece you cut out and use the hole to spray through ) of the darker shape you want out of file folder or shoe box material and bend it to the contour of the fuse . Then stick it to the fuse with loops of masking tape back away about 1 " from the opening so it sets about 1/4" off the fuse. Then mask the area around that to the rest of the fuse and spray into the hole ... this limits the amount of overspray by the big can nozzle and you get a sort of airbrush effect . It takes a lot of time ..but does work .
attached is a picture of a friends CX 2 that he did this to. Not bad for a spray can .

[SoupZ]

Soup
Yes ,, Joe likes to have backup power coming to the extender boards and also to the Th-2 itself ,, this way you don't have any surprises while flying .

The programing is not to hard as Joe has the constants on his site to download and then all you do is load them into the Th-2 ..the hardest part of the bird is running the wiring to everything and trying to keep ESC , TH-2 seperated from power lines .

The youtube vid was the 4 th flight and not much but trim levers on the TX were touched by then .
thk u so much 4 all the tips & advices, i really appreciate it:thumbup:but the fers ting i'll do nw iz 2 save $$:YeaBaby: 2 b able 2 gt the kit(i mite hav more qtns by den:P). once agn thk u so much:noteworthy

[chinookmark]

SoupZ

On the TH-2 you might get by with just power from the aileron channel, but I'm not going to try, and I wouldn't recommend you to either. The TH-2 has been out for a while, and Joe has been testing the Twin Rex for over a year, so I imagine he has good reason for recommending the extra power wires.

As for the extender board, it needs it's own power lead. The wires that connect the TH-2 to the extender board are signal wires only.

[chinookmark]

billyd

A tandem heli has no "real" yaw control. That is, it has no control surface acting directly on that axis. Because yaw is controlled somewhat indirectly by applying opposite roll to the two heads, control isn't going to be as precise or responsive as a conventional heli. Like V22 said, you can reduce expo or add reverse expo. You can also increase the travel limits on the rudder channel of your TX. I haven't used the TH-2 software since initial setup, so I don't know what setting to alter. I haven't started messing with yaw gain yet, so I can't speak from experience there.