Twinn Rexx owners' thread

[billyd]

Chinook,

I understand the importance of the sync, and certainly mechanical setups are certain to keep the rotors from crashing.

However, if you used an ESC of double capacity (In our case 70 amps) driven off of a single battery, and connected the motors to that single ESC with a Y connection, both motors would recieve the same phase information at the same frequency and should theoretically maintain sync.

Just toying around with different ideas. No doubt it's scary. Perhaps between the motors and the ESC there should be a small computer to ensure each motor gets the same information and would probably require some kind of feedback loop such as an RPM sensor or even more to the point a blade position sensor.

I know it's kind of crazy, just thought it would be interesting. And nice to get rid of that drive shaft and bevel gears. At considerable expense though, lol. But it brings up interesting possibilities of control such as altering the phase spacing between the blades in flight.

[ch53e]

I've been enjoying reading all your inputs and drooling over the website for the Twinn Rexx.

As for your last post by BillyD ...

I understand the importance of the sync, and certainly mechanical setups are certain to keep the rotors from crashing.

However, if you used an ESC of double capacity (In our case 70 amps) driven off of a single battery, and connected the motors to that single ESC with a Y connection, both motors would recieve the same phase information at the same frequency and should theoretically maintain sync.

The main gears could stay in sync ... but unless you disable the auto-rotation one way bearings ... you could still get head crash if the main shafts ever slipped in the bearings.

What Tech Model Products has made is already a great product from what you all have proven. I wish I could see one in person before I make the leap. Guess I'll have to just go for it.

Thanks again for all that you guys have shared with us.

[billyd]

Great point about the autorotation. Another bad idea bites the dust, lol. :o

[ch53e]

I ordered my Twinn Rexx today. Hope they get it boxed up and shipped out soon. After reading all of your entries, I'm very excited and cannot wait to get started.

[v22chap]

Ch 53
welcome aboard the hook group ... you are going to love it all the way from the box to the air :thumbup::hug:

[ch53e]

How is the CG on these birds? Has anyone modified or asked Thunder power to make a long thin pack ... making 2 stacks of 2 cells and putting them end to end (hence a long pack)? Just curious.

[v22chap]

There is plenty of room to adjust for CG .. I have run 3 S TP and 4 S TP and have 4 S Air Thunder ,,that are heavier than TP's and still can move them forward enough to balance it out .:thumbup:

[michaelfsB4MHX]

Is it possible to get exactly 90 deg phasing between the heads? When I align one flybar at 90 deg, the other is 15 deg off the centre line of the frame. I have tried changing the mesh of the gears but it always finishes up the same.

Regards... Michael

[tungym]

For adjustment of 90 degree phase, you should have the miter gears screw on the vertical and driveshaft.

Remove the screws of the drive shaft bearing mount and get some clearance of the rear miter gears pair.

Turn the front rotor still they are phase by 90 degree.

Align the drive shaft bearing mount and screw tightly.

Then adjust the mesh accordingly.

[joe@tech-mp]

See the Twinn Rexx assembly manual section 6 for setting the rotors timing.
This dosen't need to be exactly 90 degress. Just get it as close as you can.

http://www.tech-mp.com/Twinn_Rexx_docs/TR_Assembly_Manual.PDF




Joe

www.techmodelproducts.com

[ch53e]

I know this event is awhile away (Oct. 3-5) and so is getting my kit assembled and in the air. I hope to not be the only tandem flyer at this event. Will any of you be attending this event? I would love to see another one of these in person, especially if I'm still having trouble then.

http://www.helifreak.com/calendar.php?do=getinfo&e=50&day=2008-10-3

Would love to see more HOOKS at any event.

[chinookmark]

Nope, sorry. I'll be on an all-expenses-paid government-sponsored vacation to a very large beach, but without the water and bikinis.

[chinookmark]

Re: rotor phasing. I've been flying* mine with the blades phased about 45 degrees. The only difference I've noticed being it's quieter.


* by 'been flying' I mean flown twice :( Stupid weather!

[michaelfsB4MHX]

Sorry everyone for the slow reply, my hard drive gave up the gost. I have run it up like it is and everything is running smoothly. Hav'nt had a chance to put it in the air yet. its been very windy.
Thanks

[MadDogDan]

I need a little help here. I am at the end of my TwinRex build and at the point where I am working on the TH-2 constants. I know when you give a positive collective pitch command both swash plates move up together, when you give a right aileron command both swash tilt right, and when you give a forward elevator command both swash plates tilt forward.

When you give a right rudder command (moving the rudder stick to the right) which way do the swash plates move? Is the front swash supposed to tilt right and the rear swash supposed to tilt left? If so, mine is reversed. If I need to reverse the servo direction do I do it by changing the TH-2 constants or by the transmitter?

I am also having a problem centering my servo control arms. I centered them mechanically by plugging each servo into the same receiver chanel, one after the other and manually adjusting the control arms. When I route the servos through the TH-2 I can only center 4 of the servos. There doesn't seem to be enough travel adjustment in the constant files to center the rear pitch servo and front aileron servo. They are both off by about 25 degrees. Anyone have an idea how to fix this problem? My transmitter is set up just the way Joe specified and the constants file is set up the way Joe has specified as well. I am at a loss.

Any suggestions would be greatly appreciated,
MadDog :arggg:

[chinookmark]

MadDog

Your right about the yaw channel. Right yaw should tilt the forward swash right and aft swash left. If it's opposite, reverse the rudder channel in your TX. Check the gyro, too. When you turn the helicopter right, the forward swash should tilt left, and the aft right.

When centering servos, you should center them through the TH-2, since they aren't getting the same information they would through the RX.

Zero out the centering constants in the TH-2.
Set the TX for 0 deg pitch, no trim, no subtrim.
Power up the helicopter, and mechanically adjust the servo arms as close to level as possible.
Then adjust the centering constants for perfectly level servo arms.

[MadDogDan]

Chinookmark,

I have it now. All servo control arms are centered and working properly. The gyros are working properly and I have set up my blades with 0 pitch at half stick, +8* at high stick and -4* at low stick. Now I just have to figure out what is wrong with my new aligh ESC. It didn't work at first until I reversed ch3 in my transmitter. Now it spools up but when I get to 1/4 stick there is a glitch that cuts the motor and all servos twitch. If you give it a little more throttle everything is fine. The radio I am using is a Futaba 7C FASST 2.4 gig radio. When I power up the ESC it goes through it's series or arming tones and then it puts out some sort of error signal and then works. I couldn't figure out how to program it so I am using the factory settings. The ESC is an Align RCE-BL35G. Anyone familiar with this ESC? Maybe I don't have it set up properly.

MadDog

[chinookmark]

To program the ESC, you have to plug in the battery with the throttle stick all the way up. But before you do that, you need to set the throttle curve to 0-50-100. If you use a normal curve (0-80-85-85-85 or similar), it won't program, because it won't "see" 100%, and you will have a hard time programming "option 2". Leave the motor plugged in so you can hear the tones, but disengage or remove the pinion for safety.

Once you plug in the battery (stick at 100%), you will hear a little melody. Bring the stick back to 0%, then you will hear another melody confirming you are in programming mode. You will then hear a series of repetetive tones indicating the current programming option. For example, single beeps indicate the first question. During these beeps, put the throttle stick in the position corresponding to the option you want. Low stick= option 1, mid stick= option 2, high stick = option 3. You need the chart on the ESC directions to know which options you are setting. I advise to circle in pencil the options you want, so you don't have to think about it while programming.

[MadDogDan]

Chinook, my curve is now set up at 0, 25, 50, 75, 100. Can I eliminate the 25 & 75 setings without disturbing the others? After I have programed my ESC do I set the throttle curve back to Normal? I also just noticed that when I give the heli forward and back elevator commands the collective response may be reversed. If I give it forward stick the front and rear swash plates tilts forward like they should, but the front swash goes up about 5mm (dcp movement) and the rear swash goes down about 5mm (dcp movement). Isn't that reversed? Wouldn't forward flight be nose up this way? Can the dcp movement be changed in my transmitter or the TH-2?

Thanks in advance for your help,
MadDog :arggg:

[chinookmark]

You should be able to get rid of the 25 and 75, as long as the throttle curve is a straight line from 0-100. After you program the ESC, go back to a normal curve. I leave my STUNT 2 mode linear for setup purposes, and fly in NORM (but only on the Twinn :) ).

You are right about the swashplates. When you push forward cyclic, both swashes should tilt forward, the aft swash should lift, and the forward should drop. I don't know if reversing channel 5 in the TX will work because it's slaved. Try it, and if it doesn't work, then reverse the direction of the master slave. I think mine is set to 70/70. Try setting it to -70/-70.

Double check the direction of this gyro, too. When you lower the nose, the forward swash should lift, the aft drop, and vice versa.

[sokal]

Chinookmark: i may have the same vacation package
might run in ya ya ill buy the first round (of water)

[chinookmark]

ill buy the first round (of water)

LOL you just gotta make friends with the right people! :)

[chinookmark]

Now that it's a little warmer, I got a chance to take the Twinn outside and let it rip. I've got it flying really well right now. As much as I want 3 blade heads, I don't really want to mess with it anymore!

I'm currently running a Scorpion motor HK 2221-12 on a Air Thunder 2200 3S battery. The JGF is in the shop right now. I talked to Vinnie yesterday and I should have the motor back this week. But in the meantime the Scorpion runs great! It's marketed as a Trex motor for 4S, but it's perfect for the Twinn on 3S. In terms of RPM, the Scorpion on 3S is very similar to the JGF 500 on 4S. Right now it's got a 12T pinion, but a 11T would work just fine.

But anyway, I was flying figure 8's, and FFF, and with the heading hold gyro, it's pretty easy to fly. I have the yaw gyro set to 100% delay, 80% limit, 35% gain, no expo, and rudder channel endpoints set to 80. This seems to be a good flying balance.

I found the hover throttle ajustment on the DX7 is handy if your flying in the wind. Crank it up if it's breezy, or lower it to make the helicopter nice and "lazy". I know it's not ideal, but it's sure more convenient than changing pinions or messing with throttle curves.

I was flying with the blades phased about 45.degrees. I didn't notice any difference in flight characteristics, except that the heli was quieter. I can only assume quieter means more efficient, but only a datalogger can say for sure. I went back to 90 degree phasing, for no other reason than it sounds a lot cooler, especially at really low headspeeds.

[joe@tech-mp]

You are using the RC-TEK RCT-G730 Digital Gyro correct ?

In an earlier post you mentioned overshoot (I think). Have these latest settings solved that issue ?


Joe

www.techmodelproducts.com

[chinookmark]

That's correct, it's the RC Tek gyro. Piro rate and expo are, of course, user preference. But lowering the limit reduces the gyro's ability to over correct. It still doesn't yaw like a Trex, but it's a lot more predictable now.

I'm out of RX channels, but I'd like to try a similar gryo on the DCP, just to see the results.