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Multiplex Twinstar II Build Blog

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I too had problems with one of my controllers, it was a Turnigy 18A and it always started way before the other one.

I ended up pulling a Castle Phoenix 25 ESC out of a model heli and I found another one in my spares cabinet. I re-flashed the latest firmware into them, but haven't had the time to install and test them.

what paint to you use to paint Multiplex foam? I can't find anything that sticks well and doesn't flake off.

I didn't have any prior experience with the Multiplex foam, so I guessed at the painting process. I started with a coat of automotive plastic bumper primer. This is a clear bonding agent that is used to help paint stick to the plastics used on cars. Then I sprayed my polyurethane colors over that. I had to be careful with the masking tape since I found it would scar the freshly cured paint. I have no idea if the paint job will last -- ask me again in a few months.

By the way, the color scheme is from a guy named Workshop over at rcgroups. He had posted photos of his Twinstar at the time I was preparing to paint mine. I had the spray colors, so the rest is history. :)

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Hi... got a Twinstar for christmas (after strongly suggesting it to my wife). It will too be more or less exclusively used for FPV and other photo and video purposes. I am thinking about making it possible to disassemble the two halves of the fuselage for some future changes. 2-4 Nylon screws and some tape should do the trick..

Since i am in Germany i need to stick to 2,4 Ghz for Video and can´t completely use your example for my setup. I´ve got zilch experience in FPV but after reading your Build Blog here i appreciate the idea of moving the video transmitter away from the rest of the RC components. Where do you think would be a nice place to situate the video-transmitter and antenna?

Hope it is ok to mess up your blog here with my own questions and maybe some future build pictures? If not, just say the word and i will open my own thread.

Merry Christmas, Jens

Edited by D4RK1

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Yep I made one that splits in half, made it very easy to get all the gear in. Mine split just behind the rear of the wing but I dont make them split anymore. it worked fine but after getting the gear in the first time I never split it again so now I dont bother.

I look forward to your build though ;)

Terry

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well maybe after i´ve had some experience with the TS II and the FPV stuff it won´t be necessary to open it up again, but since i got 3 different TXs so far and no idea which one will work best i thought it might be a good idea to have it as versatile as possible :P

Have you got any tipps about putting the TX and antenna in, Terry? I see u are in the UK so i guess if you are FPVing you are stuck with the same guidelines as i am.. (almost the same).

Jens

Edited by D4RK1

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Have you got any tips about putting the TX and antenna

Unlike what I did with my 900MHz Tx, with 2.4GHz you shouldn't remote mount the antenna (coax losses will be too high). To determine if your chosen Tx mounting location will be fine, just temporarily install/test it and see if it causes any problems.

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i was thinking about putting the tx directly behind the wing, antenna pointing up... is there any length limitation about the wires between TX and camera? On the other hand... ESCs will be somewhere under the wing too... so maybe thats not the best location...

I´ve got 2 txs i can use... the third is 200mW which makes it illegal around here

http://www.rangevideo.com/index.php?main_page=product_info&cPath=35_22&products_id=91 <-- this one is 5V and my camera is this :

http://hobbywireless.com/cart/index.php?main_page=product_info&cPath=6&products_id=12 so i think it would be better to use one Voltage for both TX and camera, that´s why i bought this :

http://www.immersionsflug.de/index.php?a=77

antenna is small and flexible so it might be possible to put it in pointing down...

Edited by D4RK1

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Hi Jens,

I always put the video TX in the nose with the aerial out throgh the side but angled down so it hangs below the fuse. On landing it just swivels back as it touches the ground, remember to fold it back down before take off though ( ask me how I know :))

Terry

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well i guess you are using a ruber duck antenna? Mine is just a small wire so i guess there´s no way for me to put the TX sideways and point the antenna down.. Since the TX is very small it might be possible to carve out a hole in the side of the nose which would allow the TX to be mounted downward as well and the antenna sticking in the foam downward too.. do you think the foam would block the signal?

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No the foam is see through to RF so would be ok but remember the other parts in the plane are not. yes I'm using a rubber duck type aerial with a swivel base. I put the TX in the nose to keep max distance from the RX which is behind the wing.

Terry

Edited by Terry

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thanks for sharing this!

i've got a TwinStar on the way with the brushless kit. couple observations and Q's...

regarding the A/V Tx heat, you could maybe look into changing antenna lengths. i just read a post somewhere where a guy went from something like a 1/4 wave to a 1/2 wave and drastically dropped the temp at which the Tx runs. i don't remember the freq., but i don't think it would matter as far as benefits to be gained from changing the wave length.

to maybe dump some antenna weight, you could look at stripping the plastic housing from the antenna, or just making your own from a piece of coax. i have learned from heli's, where there's little room to spread stuff out, that getting the A/V Tx away from the radio gear is important, but it is also important to get the antenna away from the radio gear and not mounting it on the same plane as the radio gear. in heli's i would typically let the A/V antenna hang well below the airframe (12" or so) and i'm wondering why i'm not seeing this with the planes? i'd be curious if anyone has range checked with an antenna hanging low verses mounted right to the airframe.

is there a need for having 2 ESC's? couldn't the 2 motors be run off of one? the only advantage i can think of is if you wanted to do some mixing, such as with the elevator or ailerons -- is anyone doing this?

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Changing 1/4 to 1/2 wave is not going to make a difference, its how well the aerial matches the TX that will make it run cooler. If the 1/2 wave aerial is a better match then yes it will run cooler.

Mounting on the same plane Im sure makes a difference, that the other reason I hange the video TX aerial and point the RC aerial up.

Go for 2 ESC's they are cheap and you will get better running plus 2 BEC's so safer too. Dont bother mixing unless you want to do some silly 3D stuff.

Terry

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These are my efforts so far to make the Twinstar easily possible to disassemble:

7n26-k5.jpg 7n26-k6.jpg 7n26-k7.jpg 7n26-kb.jpg 7n26-kc.jpg 7n26-kf.jpg 7n26-kg.jpg

for the screws i glued in some plywood pieces to keep them from being pulled through the foam under duress. For the nuts holding the tail i did more or less the same, for the nuts holding the halves of the fuse together i cut out pieces of foam, pierced the foam, put in the nut and glued it back in place.

Edited by D4RK1

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As to using one ESC for two Brushless Motors, it has been known to work ok occasionally but as far as i have heard and seen there are often problems. A fellow modeler i know tried that and he said that in 1 instance out of 20 (which is good, usually it is worse, if it even works) one motor failed to start on throttling up. In normal circumstances you just pull the throttle back and try again but with all that expensive FPV stuff on board i don´t think it is worth the risk to try. The weight savings aren´t that big.. maybe 10-20g i guess since you need to use a bigger ESC when driving two motors with one.

I am not sure about the Twinstar but i happen to know that some 2Mot-Planes react quite badly when completely loosing power to one side. Friend of mine tried that on purpose (switch) with a Do-228 and almost lost control, only switching the second motor back on saved the plane. So i guess it is not advisable to have it happen during a landing...

Edited by D4RK1

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thanks for answering my questions guys

D4RK1 - here's another type of nut that probably weighs a bit less than the "T" nuts - look at the 'Retainers for Threaded Studs'. don't know if this would work for you though.

i think i'll be doing something similar to make this thing easier to split.

Edited by eMan

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have been thinking about lighter nuts myself but haven´t found anything yet. Those nuts you proposed look light, but i think they might a) wear down the threads of the nylon screws after a while and B) will be a bitch to position in more or less exactly a 90° angle. Would be nice to have similar nuts made of Nylon or plastic though. Normal nylon hex nuts i have seen somewhere.. but i don´t think those will be of much use.

So here´s what i have been thinking about positioning the electronics :

7n26-kh.jpg

ideas, critics?

Edited by D4RK1

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i'm no expert, but i think i would be placing the A/V Tx as far away from everything else as possible, including the batt. i'm thinking of sticking mine in the tail and shielding it the best i can, maybe with aluminum foil, as well as shielding the cables. the antenna i will likely let hang below the fuse on about a 8 in. + extension that provides just enough stiffness to keep it fairly vertical. anyone aware of any consequences of having the antenna touching the ground upon landing? i'd be worried that placing the Tx near the battery might pump RF into the battery and therefore the whole system.

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hm.. reread the previous posts and it got me thinking about the "planes"... my RC Rx and Video Tx (guess it´s the antennas that matter) are on the same plane in my current Distribution. Maybe i should position the RC Rx on the upper side with the antenna going on top of the fuselage. Problem there is that this puts the Rx close to the ESCs which is usually also not too good an idea. Could go back a bit to avoid that..

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from what i have read so far "as far away as possible" is always good but in most cases some inches seem to be enough. So i hope the distance in my proposed distribution is enough. Dunno if the video tx shouldn´t be close to the battery but Terry said he puts his Tx in front which almost always means close to the battery. Putting the tx way back means really long cables or another battery back there which in either case has its own hazards. In both instances weight is of some concern and long cables sometimes add their own problems with RF glitches.

Guess after hearing what the more experienced guys have to say it´s down to Try-And-Error :P

About just dangling the antenna below the fuse, don´t think that´s an good idea since it will get bent on every landing and might break after a while, worse might break without you noticing and on the next flight you´ll find out the hard way...

Edited by D4RK1

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regarding the "plane" on which the video Tx resides, i was talking about the antenna. in other words you don't want the side of your antenna, where radiation is the strongest, to be on the same plane as any of your other gear. in earlier pics i think you chose to mount it sticking up near the vertical stabilizer which i think would be OK. as far as i'm aware, having the Tx itself on the same plane as other gear isn't going to matter, just so long as there's some distance between it and the other gear. how the optimal distance is determined i have no idea. might want to power up the whole system and move the A/V Tx around and see how it affects it. from my experience with heli's and the same type of A/V Tx's, except on 2.4 GHz, i would say yes, a few inches is probably good. for whatever reason the video Tx worries me the most however and, personally, i'd keep it as far away as is reasonably possible.

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The earlier pictures show another Twinstar. He uses 900 Mhz for video so he can put the antenna everywhere he chooses (or thinks best). Me, i am using 2,4 Ghz so need to have the Tx where the Antenna is. Only the posts after #27 show my Twinstar (so far ^^).

Dunno if that is important to know but i will be using 40 Mhz for RC...

Edited by D4RK1

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It's time to bring this discussion back on topic. Sorry for the late update ...

I resolved the ESC issue by installing a pair of Castle CC25's. That cured the ESC low voltage cutoff mess I ran into. The motor performance was much better with the Castles, so I am happy to have dumped the Chinese made ESC's I had in there before.

I was concerned that the A123 pack would be too heavy and I was prepared to add weight to the tail to achieve a proper CG balance. But, with the two servos relocated to the rear, the model came out a bit tail heavy. As luck would have it, the 3S A123 pack achieved a perfect CG without any effort. Things are looking good!

BTW, without FPV gear the AUW is 44 ounces.

During my initial bench tests I noticed the gyros acted oddly when I remotely turned them off. They were designed for R/C heli's, so they are not expected to be disabled. So, I pulled them out and replaced them with a pair of ESKY EK2-0794B's. As before, one went on Pitch and the other on Yaw. Their remote gain cables are controlled by the Rx's Gear channel (Y-cabled their gain servo connectors together). Using the R/C Tx's T-ADJ (ATV) mix, they were setup for switchable on/off rate mode (their heading hold feature is NOT used). An educated guess was chosen for the remote gain settings (figured I would tweak them later).

The maiden flight was absolutely fantastic. A nervous first launch was with 3/4 throttle and a hearty hand toss. To my amazement it was totally dialed in from the start. I flew a few circuits without the gyros, then turned them on. The model became as tame as a kitten and flew beyond my expectations. With the gyros enabled, the model feels just like my Electro-Telemaster (ETM) which is a much larger model.

With moderate throttle management, the model averages about 75 mAH per minute from the A123 pack. Not bad. With full throttle, it moves fast without any bad tendencies. Next on the list is to get the FPV gear installed. I'll do that when time permits. In the meantime, I'm going to fly the little fellow old school.

Many thanks to Terry for recommending the model. It is a great choice for those that want something easy to fly, but bigger than a EasyStar.

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sounds very encouraging! it's not often things exceed ones expectations when experimenting with things that fly :)

i did some reading on Li-Ion/Poly technology and am far less impressed than i had been. i too will be looking harder at the LiFi.

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It's time to bring this discussion back on topic. Sorry for the late update ...

I resolved the ESC issue by installing a pair of Castle CC25's. That cured the ESC low voltage cutoff mess I ran into. The motor performance was much better with the Castles, so I am happy to have dumped the Chinese made ESC's I had in there before.

I was concerned that the A123 pack would be too heavy and I was prepared to add weight to the tail to achieve a proper CG balance. But, with the two servos relocated to the rear, the model came out a bit tail heavy. As luck would have it, the 3S A123 pack achieved a perfect CG without any effort. Things are looking good!

BTW, without FPV gear the AUW is 44 ounces.

During my initial bench tests I noticed the gyros acted oddly when I remotely turned them off. They were designed for R/C heli's, so they are not expected to be disabled. So, I pulled them out and replaced them with a pair of ESKY EK2-0794B's. As before, one went on Pitch and the other on Yaw. Their remote gain cables are controlled by the Rx's Gear channel (Y-cabled their gain servo connectors together). Using the R/C Tx's T-ADJ (ATV) mix, they were setup for switchable on/off rate mode (their heading hold feature is NOT used). An educated guess was chosen for the remote gain settings (figured I would tweak them later).

The maiden flight was absolutely fantastic. A nervous first launch was with 3/4 throttle and a hearty hand toss. To my amazement it was totally dialed in from the start. I flew a few circuits without the gyros, then turned them on. The model became as tame as a kitten and flew beyond my expectations. With the gyros enabled, the model feels just like my Electro-Telemaster (ETM) which is a much larger model.

With moderate throttle management, the model averages about 75 mAH per minute from the A123 pack. Not bad. With full throttle, it moves fast without any bad tendencies. Next on the list is to get the FPV gear installed. I'll do that when time permits. In the meantime, I'm going to fly the little fellow old school.

Many thanks to Terry for recommending the model. It is a great choice for those that want something easy to fly, but bigger than a EasyStar.

Nice report, have you considered installing the CPD4 Copilot instead of those gyros? Works really good and can be combined with a RTH GPS device

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