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Multi Rotor Helicopters - Tandem Multi Rotor Helicopters - Tandem


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Old 05-18-2007, 10:53 PM   #41 (permalink)
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Quote:
One thought, the full scale 47 has one wheel and tire on each side of the rear of the aircraft. Is there anyway to recreate this detail?
Sure! I'm more into fun-scale myself (which means I don't mind so much), but you could just shorten the axis, omit the inside tire and put something like a retainer collar on or something like that.
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Old 05-24-2007, 10:26 AM   #42 (permalink)
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It's nice to see someone else building their Twinn Rexx. I'm hoping to get mine airborne this weekend.

Shawn
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Old 05-25-2007, 12:43 AM   #43 (permalink)
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Hi ShooShoo!

Nice to hear that! Mine should be airborne this weekend as well. I'm finishing the CCW head and then it's just blade balancing and go-fly!

GrassHopper.
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Old 06-01-2007, 06:34 PM   #44 (permalink)
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OK... so I have a question.

Will the IR sensor work within the fuselage (when you fit it) or do you intend to either a.) remove it at that time and fly without it, or b.)mount it outside of the fuse?

I haven't played much with them, but my spidey sense tells me that the sensor needs a clear view of the horizon.

Ashley
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Old 06-02-2007, 06:49 PM   #45 (permalink)
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Haven't posted in a while... :? Time to catch-up!

Here's pictures of the finished heads. Note that the front head is set up for counter clockwise rotation, which means the head assembly is mirrored compared to the rear head assembly (which rotates in the regular T-Rex clockwise direction).

Some more details can be found here:
http://www.thetrexforums.com/index.php?topic=1465.0.
A very nice build description of a fellow Twinn-Rexx pilot... :mrgreen:
Attached Images
File Type: jpg rear_head.jpg (851.4 KB, 353 views)
File Type: jpg front_head.jpg (813.4 KB, 339 views)
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Old 06-02-2007, 07:11 PM   #46 (permalink)
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We're airborne! :mrgreen:
Ran through about 4 batteries earlier today. After a minor mishap last week, she flies great now!

When I first spooled-up last week, she lifted up without any problem, but then started to rotate quickly around the yaw axis. I countered (of course) by applying opposite rudder and by reducing the throttle as I was only 1 feet or so up. With a heli with skids the landing while rotating would have been no problem, however I was unlucky in that one of the wheels "caught" in the grass causing the heli to tip over... Yaw axis gyro set for the wrong direction... And I thought I doublechecked...
Luckily, very minor damage: one bent front main shaft. Had to order a new one from Joe though. His service is excellent! After only a few days I had a new shaft waiting to be installed.

Today, I tried again... After reversing the gyro direction of course... :mrgreen:
No problem whatsoever this time! She took off, I hovered for a few seconds. Landed to add some subtrim. Took off again and flies great!!! Though not neccessarily more difficult or less stable then a regular heli, it definitely is somewhat different. You have to be on top of the rudder as the DCP causes torque differences to occur between the front and rear rotors causing the heli to want to yaw. Need to experiment with the "yaw compensation" function in the TH-2. If you've ever flown a cheap helicopter with a cheap rate-only gyro, then you'll have no problems "staying on top of the rudder".

After a couple of hovers, I switched the elevator gyro to AVCS-mode ("heading hold" is not a good term here). When attempting take-off, the heli wanted to tilt forward badly so I had to reduce power to prevent it from tipping over. I figured I probably needed to make sure the gyro was "reset" so I powered off and on again. On second take-off, she went straight up. Definitely more stable in the elevator axis! Though without AVCS, she was perfectly flyable, the difference is like a regular helicopter with heading-hold and without heading-hold. Flying without AVCS (rate mode only) is certainly no problem, but with AVCS on things are much nicer.

The Twinn-Rexx rocks! Time for Bob "Finless" to do a build video!!! :mrgreen:
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Old 06-02-2007, 07:17 PM   #47 (permalink)
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Sorry, no pictures of my airborne Twinn-Rexx yet...

Still practicing holding my transmitter in my left hand and my camera in my right...
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Old 06-02-2007, 08:16 PM   #48 (permalink)
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Quote:
Will the IR sensor work within the fuselage (when you fit it) or do you intend to either a.) remove it at that time and fly without it, or b.)mount it outside of the fuse?
The IR sensor will not work within the fuselage as it needs to be able to "see" the horizon.
Not sure yet what I'll do. Either I'll mount it under the bottom of the fuse (needs to be level with the horizon though) or I'll take it off and put it on one of my other helicopters...

My first flights have defenitely shown that this heli is more stable and flies easier (or at least: "hovers easier", as I haven't attempted forward flight yet) than I had expected. In that sense, the sabilizer (which I haven't turned on yet as it won't do any good in my backyard), is certainly not a neccessity.

Only thing that worries me a bit is that it may be hard to distinguish the front from the rear when it's at a distance from you. If you lose orientation, then having an "emergency levelling switch" is always nice...
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Old 06-02-2007, 09:04 PM   #49 (permalink)
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Hi everyone, i'm fresh new in r/c field but was my dream since childhood, and am searching for a web page containing videos teaching how to assemble a helicopter and program it, to be encouraged to buy my first heli. Thanks for your help in advance and best regards to all. Andrew.
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Old 06-02-2007, 11:21 PM   #50 (permalink)
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andrew03957118,

You should check out the finless heli tech room. His room can be found on the home page, I think it's like the third one from the top. He has numerous build vids as well as basic setup and programming vids. They are extremely helpful to the hobby newcomer.
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Old 06-03-2007, 05:10 AM   #51 (permalink)
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You should run the gyros in normal mode (not Heading-Hold) when the AP-2000i is in charge.

-Angelos
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Old 06-03-2007, 03:12 PM   #52 (permalink)
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Hi Angelos,

Nice of you to pitch-in on this thread! Let me start by saying that your products ar world-class! I now have three helicopters, all of which are equipped with AP2000i stabilization and it works great. I normally fly with stabilization off, but in case of emergency, I flip a switch and the heli is level again. Many people say that's "cheating", but I guess those are the ones who enjoy crashing their helis and feel simulators are for woosies also... :mrgreen:

Let me try to understand your comment though. Just to make sure we're clear on this, my current setup for cyclic control is as follows:

- Rudder: receiver -> rudder gyro -> TH-2 (i.e. the tandem mixer) -> servos
- Elevator: receiver -> TH-2 -> servos
- Aileron: receiver -> AP2000i -> TH-2 -> servos
- Pitch (CP): receiver -> AP2000i -> TH-2 -> servos
- Differential (DCP): receiver -> AP2000i -> DCP gyro -> TH-2 -> servos

Here:
- The DCP channel is mixed in the TX to "slave" the elevator channel by 70%
- The rudder gyro is in normal mode (i.e. not heading hold/AVCS)
- The DCP gyro is in heading hold (AVCS on)
- Yaw compensation is enabled at 20% in the TH-2 to counter DCP-induced torque with rudder (I feel this is better than doing it in the transmitter as the TH-2 sees both the inputs from the gyro as well as from the AP2000i)

So when the AP2000i is in charge, it controls DCP, aileron and pitch but not elevator and (of course) rudder.

For the rudder gyro, I'd say whether to run heading hold or not is irrespective of whether the AP2000i is in charge or not (would you agree?).

For the DCP gyro, my reasoning was that as the gyro is "behind" the AP2000i, it "sees" whatever inputs the AP2000i is giving ("as if" it's the pilot giving the inputs from the transmitter) and can therefore be put in heading-hold or not-heading-hold mode without any "fighting" to occur (would you agree?).

Note that a disadvantage of this setup is that the AP2000i can only level the heli in the elevator plane by applying DCP as it doesn't control the elevator function. My ideal setup (just dreaming here ), would be to have the AP2000i control both elevator and DCP (at 70% of elevator) next to aileron and pitch, thus letting the servo4 output be DCP in a new swashplate mode for tandems... That would be so :glasses2:

The other setup (my original idea) I've considered is to let the AP2000i control elevator, with the gyro in the DCP channel. Thinking more about this, I guess for that setup I would have to run the DCP gyro in non-heading-hold to prevent the AP2000i and the gyro from fighting eachother. Possibly your comment referred to that setup?

Your inputs are much appreciated! You're definitely the guru in this world when it comes to flight stabilization! :mrgreen:

Hopper.
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Old 06-15-2007, 02:13 AM   #53 (permalink)
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WOW!!!! A truly amazing thread, I've been following Joe's build info- on his site for the last two and bit years and I didn't realize there was a build thread here until he posted it on his site back the 8th of June, good luck to you hopper, a great build thread, and I love the flight stabilization equipment, many people are quick to knock these systems, but the time and money tied up in this sought of machinery can be exceptional, so if you can avert a disaster I say more power to you, great heli- I've bookmarked this thread and I will revisit to see how you are travelling :glasses2:
Cheers great stuff
Ralph
BTW-What type of radio are you using 72MHz or the new 2.4 GHz technology :?:
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Old 06-15-2007, 02:19 AM   #54 (permalink)
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I would love to see a video of this thing flying!!!
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Old 06-15-2007, 08:02 AM   #55 (permalink)
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Hey Lith,

Here's a link from Joe's website.

http://www.tech-mp2.com/Twinn_Rexx/TW-1_LQ.wmv
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Old 06-15-2007, 09:13 AM   #56 (permalink)
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Thanks!!!
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Old 06-15-2007, 04:18 PM   #57 (permalink)
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man that thing is sweet. the whole time i was watching i was waiting for a blade strike..kinds makes me want one.. this might be a stupid question but can that thing do inverted hovering. in the video it does look pretty responsive... what are its limitations..
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Old 06-18-2007, 04:30 PM   #58 (permalink)
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Gra55h0pper,

Haven't heard from you in while. Curious as to how the machine is doing.

Jason
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Old 06-19-2007, 02:56 AM   #59 (permalink)
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Good2win22,

The machine is doing great! Sorry I haven't posted in while, but I must have ~30 flights on it now. Just this past weekend, I flew it in pretty strong winds. Pretty amazing to see the 2 gyros and stabilizer work the cyclic on the two heads!

I'm sorry for those who would like to see a video, but I have no access to a camera. Besides, I'm not that good of a pilot... Also, please don't ask whether it'll do 3D, as I don't plan to find out if I can avoid it... I'll probably flip the stabilization switch well before that! :mrgreen:

Note that I decided to keep the setup as I described earlier (with respect to the gyro, ap2000i). When looking at some threads describing how to use the ap2000i as a virtual flybar on a "regular" heli, I realized that in that setup you don't have a choice but to put the gyro "in front of" the ap2000i as the ap2000i does the CCPM mixing. In that setup, I understand that it's better to have the gyro in non-AVCS mode. After the CCPM mixing is done, of course the opportunity to use a gyro to stabilize a single cyclic function (elevator, aileron) is gone...
On my Twinn-Rexx however, the CCPM mixing is done by the TH-2. This gives the opportunity to put the gyro "behind" the ap2000i. I think Angelos didn't realize this fact when replying to my earlier post. The way I look at it, is that the ap2000i is essentially a 2nd pilot which keeps an eye on the horizon. After this 2nd pilot adds its inputs, the DCP gyro (in AVCS mode) takes care of the rest.

I learned from Joe that the fuselages are getting ready (see the www.tech-mp.com site). I'll post more experiences when I have one! :glasses2: I understand one mod which is necessary is to move the rear elevator servo down in order to get it to fit in the fuse. Should not be a big problem though. I've decide to stick with the stabilizer. I'm not sure how exactly yet, but I really like having the option to stabilize the heli when the wind comes up. Also, having an "emergency leveling switch" is great when you loose orientation.

Hopper.
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Old 06-27-2007, 02:23 PM   #60 (permalink)
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Hi Hopper,
Great thread - i have been following the Tech Model Products website for a while now eagerly anticipating the day i can get one shipped to the UK.
I am shortly going to fit a three blade head to my spare T-Rex 450XL and see how i get on with it. If it works out ok i will think about using two of these on a Twinn-Rex. I hope to paint my fuselage in the British Airways colours that some of the long range passenger versions were painted in when flying to oil platforms in the North Sea.
Best Regards,
chipbury.
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