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HomeScaleAircraftHelicopterScale Model RC Helicopters › TT MD530 (Civilian) & TRex600E build thread
03-05-2008 12:01 AM  10 years agoPost 21
Daniel Reese

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Urbana OH

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Got the swash, installed and rechecked all the mechanics then, finally, after what seems like forever, took it our for a maintenance flight in pod-n-boom configuration.

....had problems....

I dont know what the CAUSE is but the problem was sudden and dramatic pitching backwards! At spin-up there's an odd sound...maybe...kinda like when your blades are WAY out of track (these arent) and there's no vibration...i chalked it up to not having flown it pod-n-boom in over 6 months- that i'd just forgot what it sounds like. It hovered fine. I was able to ease it forward, back, left, right, center...and then it would suddenly balloon upward and lean WAY back- coming at me! I didnt have Idle Up engaged and was able to dump headspeed and ground it before it got very far; afterall, I was only about 3' AGL.

Immediately powered down, unhooked the batteries and inspected all the links and servos.

No faults found.

Powered up with just the RX battery and ran the servos through their full range of motion again, checking for stripped gears, jitters or binding.

No faults found.

So, i tried it again, and had the same result....random and dramatic pitching backwards....

Still, this may be a problem with "operator's headspace and timing"....
The RX has a revolution base-loaded antenna...but it wasnt installed. So the RX antenna was only about 4" long. The TX antenna was collapsed too. Obviously this has an effect on range but I was only flying the heli about 5'-8' in front of me. Even with both shortened antennas I shouldnt have had any glitches...but it could have been that.

Also, it was a bit gusty out so it may have been reacting to the wind but I dont think the wind was blowing AT me so much as oblique from the right...

I need to dig deeper into the mechanics to reassure myself that there's no mechanical problem and try it again with the RX antenna on and the TX antenna extended.

Got the canopy installed as well. Boy, that was a fight! Version 1 canopy went in like it was molded to it...this one took alot of pulling, pushing, stretching and adjusting to get it to fit. It eventually did and I didnt have to cut anything but it was a more than a little challenging. The imperfect fit of the canopy to the fuse is making me question my plan to have the cockpit removable through the front...we'll see.

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03-06-2008 12:06 PM  10 years agoPost 22
Daniel Reese

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Urbana OH

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Went through the mechanics with a fine tooth comb- no faults found - so I put in a fresh pack and took it back outside.

Musta been operator headspace, as I had feared.

It flew just fine. Still making that funny sound...its like a full-size helicopter "whopping" sound that I dont recall hearing it make before when it was in the fuse. The blades are tracking perfectly, the paddles likewise. Thee's no noticeable vibrations....I dunno. Other than sounding funny it seems fine.

I'll try finishing up the lights today. I should be able to get the mechanics mounted in the fuse and take it for a spin all mounted up.

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03-06-2008 04:36 PM  10 years agoPost 23
coptercptn

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Mesa AZ. USA

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I could be the increased head speed with out the weight of the fuse on them. Kinda like a Huey with the blade stall sound? Lots of air getting shoved around...

Home of the "Sea Cobra".....

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03-07-2008 12:48 PM  10 years agoPost 24
Daniel Reese

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Urbana OH

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Actually, the sound comes during spin-up, before any loading. I dunno. Everything seems to work fine tho so Im gonna suspend worrying for now....the old Head-in-the-sand routine....

Once upon a time I remember going through this before and discovering that the sound was caused by wind blowing across the disk during spinup. It only happened the one or two times back in virginia but its alot more windy here than it was there. Perhaps this is the same thing all over again.

Then again....

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03-09-2008 02:09 PM  10 years agoPost 25
Daniel Reese

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Urbana OH

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Im at another decision point with the build- I test hovered the 4-Blade cascading tail modification and it worked just fine. It was an easy mod; flipped the stock plastic gearbox, pulled the tr pully of the stock shaft and pressed it onto a TRex450 mainshaft. Installed a stock hub (backwards so that its rotating up into the downwash); Added a ball link to the top of the Pitch slider/blade grip; then cut the extensions off the blade grips of a second hub and screwed in some ball links, installed it about 60* off the first and about 1/4" further out on the drive shaft; made up a pair of links to connect the two and set the link length so that the Pitch of each blade matched; reversed the gyro and viola- proper side, 4 blade tailrotor.

But....this is a belt drive and Im already a bit uncomfortable with a belt drive in a scale heli as I cant easily monitor the health of that belt. Things arent helped by having to use the almost totally enclosed stock tail gearbox. Lastly, and probably most importantly, The drive gear on the tr drifeshaft is just pressed on with a bit of loc-tite. The stock driveshaft has rather robust splines on it- mine is just "roughed up" with a dremel cutting wheel (made some pretty deep scratches but that's about it). Im VERY concerned that under a load the gear could (will) slip on the drifeshaft and I'll instantly lose the tail rotor. Im not THAT good at autos and doin em on a pod-n-boom is a hellovalot less nerve wracking than on a scale ship.

So, im left with deciding to go ahead with the cascading tr on the proper side or regular belt drive on the proper side or, my almost preferred solution of using the torque tube on the wrong side....or....

I picked up the insturction manual for the CH47/TRex450 kit where it details how to flip the motor/ESC wires and all the guts in the head to have a reversed main. If I reverse the main, then I can use the torque tube on the correct side....

Decisions, decisions, decisions.

What I need is a machine shop that can precisely drill a cross-pin hole to pin the tr belt drive gear, or better yet, the torque tube tr drive gear to the tr driveshaft. That would make the decisions ALOT easier.

In the mean time I still have to build the outrigger for the spotlight, make some hinges for the engine compartment doors and just commit to finishing this thing. Its been draggin on way too long.

The cockpit base frame is done and all the servo locations are spotted/plotted. All that's left is to buy the 6 S75 servos and finish building the thing. Im toying with the idea of getting into the A123 market since I could build the pack into the belly of the heli and have the cockpit remain in place permenantly...but Ive got 6 nearly new 22v packs...it'd be kinda silly to quit using them...then again, im sure I could find another use for such a lovely power source

When Ive got pictures of anything worth lookin at, I'll post em. At present its just an ugly mass of marked up fiberglass, wires and tape.

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03-09-2008 04:18 PM  10 years agoPost 26
Rodan

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Prescott Valley, AZ

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On my TRex 450 with the 4 blade tail, I did exactly what you did, cut some grooves in the shaft with a dremel (where the original was splined), but I used a bit of epoxy instead of loctite. I know there's going to be more load on the 50 size, but I haven't had any problems with the pully.

Also, remember the full size rotates down, so the TT drive would actually be correct when flipped if you keep the right hand rotation. I don't think you will have any trouble with tail authority, especially with four blades.

Finally, I've had no problems with the belt in my R50/MD500,and it's been flying for nearly a year, probably 5-6 gallons. I just check it whenever the mechs are out of the fuse (every couple of months).

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03-10-2008 10:24 PM  10 years agoPost 27
Daniel Reese

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Urbana OH

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Rodan- thanks for the advice...got alot of thinking to about that. I love the cascading tail but I think I like the torque tube more. The only problems with using the torque tube are rebuilding the head for reverse rotation and having to find a way to get the bevel drive gear stuck on the extended tr drive shaft. Rebuilding the head isnt so bad more on that later- and I can wait on the 4 blade tail til I find a way to make the driveshaft more secure. Heck, most 5 blade MDs have 2 blade tails anyway.

Got the servos built into the cockpit framework today and tested them out. Initially I was stoked- they worked just like I hoped.

...but then I noticed a problem...the TRex600 uses ECCPM mixing- the elvator is tied to pitch is tied to aileron...moving the left stick forward (increasing pitch) makes the "cyclic" move too.

Damn.

Ok, so, there's pretty much no way the cockpit controls can be operated by the flight controls - It would need a separate radio with no cyclic/collective mixing. Or is there something I can do to separate them after "arriving" at the rx?

About reversing the main- not a big problem. Just swap two of the wires from the ESC, and relocate some parts on the head. I do have a favor to ask of the esteemed members of the board here; Please verify this for sanity: When swapping the direction of rotation, the blade grips are reversed and so the upper mixing arms must also be "flipped". However, just turning them around will cause them to bind on the flybar holder. In fact, you cant even put them on the flybar holder because of the shape of things. Anyway, Im pretty sure that if I just flip the flybar holder (see-saw?) with the upper mixing arms in place, that would accomplish the same thing. The only other bit to change would be flipping the washout base...that verifying servo direction and switching back to straight gears from the helicals that are on it now. Is that about right or am I on crack?

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03-11-2008 01:32 AM  10 years agoPost 28
Rodan

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Prescott Valley, AZ

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I've no idea about the mixing arms and flybar cage, but don't forget to reverse the one-way bearing!

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03-11-2008 06:18 PM  10 years agoPost 29
Daniel Reese

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Urbana OH

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Now I dunnit...
I successfully "flipped" the main rotor and had an uneventful though VERY brief shakedown flight on it!!!

First I pulled the entire rotor head/mainshaft group,
Then pulled out the flybar,
Then flipped the see-saw/flybar holder to get the upper mixing arm attachment points in the right place,
Then flipped the upper mixing arms,
Then rolled the blade grips over (now the blade root bolts are upside down so I'll have to swap left/right to get them back right side up,
Then took the washout base, pressed out the brass bushing, cut the "boss" off the bottom side of the washout base and pressed the bushing back in (upside down) then flipped the washout base and put it back on. (needed to remove the boss on the washout base as it prevented it from going up high enough on the mainshaft)
Then pulled the helical main gear set to be replaced by a straight-tooth gearset,
Then pressed out the one-way and put it back in upside down,
Then swapped the black and red wires from the ESC to the motor,
Then flipped the belt at the TR gearbox so that the tail blades rotated up into the propwash.

Presto Chango, the mains go the correct direction and the TR is on the correct side!

When I first started to spin it up (terrified!) I tried cyclic inputs at low rpm to verify proper phasing and rotor disk reaction 'n all that but it was all over the place! It wobbled in wierd and unpredictable ways and I was sure I'd buggered it all up good..but then I remembered some other fellas talking about multiblade heads that need to get up to speed before the disk acts as it should...sooo...I took it outside and gave it a go at full speed.

No problems!

There might be a bit of drift in the tail but I suspect that has more to do with the change from a fixed rigid TR pitch pushrod to the flexible pushrod that I used to route from the bottom mounted servo to the top mounted pitch slider. I'll need to set the exact pushrod length- its VERY close but it might be off by a turn or two. Then again, it's kinda windy today and that is as likely to be the problem as anything else. Might need some aileron trim too but then again, could be the wind.

A successful flip! But I still fear the belt drive and my half-baked solution to fixing the belt drive gear to the tr driveshaft. Im plagued by nighmares of the pully letting go mid-flight for a spectacular, no-tail-rotor-landing...For now, I'll go back to the torque tube tail drive with 2 blades until I make the torque tube driven cascading tail. A 2 blade tail is fine for now as most fullsize 530s have that configuration.

Back to the cockpit "unmixing" problem...
If I switch to a 9 ch RX, (Currently using an 8ch)I could concievably link ch 8 and 9 to aileron and elevator thereby effectively un-mixing the aileron/elevator/pitch but that ties up two more channels on my rx that I'd rather use for something else...I dunno what I would use them for, but Im sure I can come up with something. That and a 9ch rx is about $160 and thats $160 more than I have in my build budget. The cockpit might be on hold for while. At least until I finish the rest of the build. At least I know I got the geometry right!

I want to make the engine compartment doors open-able. Vario has wonderful hinges and if I were doing a model that's twice as big as this one, Id get those sweet vario hinges...but sadly, they'd look more than a bit odd on this little heli. So I picked up some brass square-walled tubing and will try making my own hinges from that. If I can make serviceable hinges, I'll proceed with the engine doors. If not...

Then there's the operable cargo hook. I plan on using ch7 for that- it's a bit odd but the searchlight and landing lights will come on when I open the hook since they share the same ch but Im ok with that for now... ties into what I said about finding things to do with spare channels. Im going to try to build the cargo hook similar to vario's version since its pretty simple. But their hook doesnt look like anything Ive seen dangling from the belly of any real helicopter. Their hook is just sticking out of the skin of the fuse and Im pretty sure that aint right. The few real cargo hooks Ive seen in pictures are usually part of some assembly of some sort but I havent found any good reference photos of real cargo hooks. Any of y'all know where I could find some detailed, fairly high resolution images of the hooks used on MD/HUGHES 500/530s? (So far, airliners.net hasnt proven too useful)

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03-13-2008 01:11 PM  10 years agoPost 30
Daniel Reese

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Urbana OH

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"I had a dream..."
Yeah, another of those inpirational half-awake, half-asleep epiphanies!

Ive been working on getting the cockpit controls to behave and have pretty much concluded that I'll need that 9ch rx to do it. If I go with a 9ch rx, then I'll only need the one rx in the ship, one power sourse for cockpit servos and no need for splitters to the flight servos...the only problem with leaving it in there all the time then is weight (really doesnt weigh much yet) and that its in the way of the main battery.

Oh, but then again...!

How about stowing the battery in an "Underbelly Cargo Box"? I dont know what that box thing really is but it would work perfectly to hide the 22v lipo.

If I build a platform (plywood) attached to the mechanic's platform by 4 stand-offs; lay a strip of velcro along the underside of the platform and a matching strip on the top of my lipos, then strap the battery to that platform... The skin of the box, since it wouldnt be holding any weight could be held in place by a few rare-earth magnets. Changing the battery this way would be even easier than the current method of slipping it in through the front windows.

The ONLY hurdle to this extra layer of cool-ness is that I dont have a vacuforming rig and I know nothing about laying up fiberglass from scratch. Either way would produce a nice light thin cover for the belly-hung battery.

So, for now I'll continue to drive forward with the removeable cockpit while I sort out making the belly box. Afterall, this can be made to be removeable and leave no obvious traces on the belly of the fuse.

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03-13-2008 02:58 PM  10 years agoPost 31
Rodan

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Prescott Valley, AZ

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There was a guy over on ScaleRCHelis that scratch built (laid up his own fuse) a D model with a belly mounted luggage box (that's what it's for on the real one ). I'll see if I can find the thread and post a link...

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03-13-2008 03:07 PM  10 years agoPost 32
Rodan

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Prescott Valley, AZ

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03-14-2008 02:48 AM  10 years agoPost 33
Daniel Reese

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Urbana OH

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Rodan, you came through again! I had seen one picture of his build and it was the first time Id seen an RC model with that luggage box. That thread gives GREAT instructions on laying up fiberglass.
Thanks!

I dove in with both feet on the engine compartment thing- I made some 15mm hinges from some brass angle and some small bolts.

Having had a bit of success with the hinges I picked up the dremel and attacked the fuse.

After the shock wore off of having hacked up a perfectly good fuselage, I set about to making the plywood former.

Amazingly, nothing went wrong (yet) and its ready for the next step; laying in door jambs, grinding off the fake hinges and installing the real ones. I'll use a pair of magnets on the inside of that padernal thing on the bottom of the doors to hold them together. Also, to keep things nice and secure, I'll glue in some thin strips of metal on the inside of the door edges and some magnets inside the door jambs. That aught to keep them nice and tight in flight. I'll also make up a fake engine to snap into the opening when showing it off but mostly the opening doors are to provide access to the back of the mechanics and to aid in installation/removal of the mechanics from the frame.

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03-15-2008 01:47 PM  10 years agoPost 34
Daniel Reese

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Urbana OH

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Should be able to get some serious progress today- we'll see.

Last night I got the doors mounted up on the new hinges and started laying in formers and door jambs.

I shoulda put the formers in before cutting out the doors

The fiberglass was aparently under some tension and has a bit of memory too- now that the doors are independant of the body, they've taken on a bit of their own shape and are not easily cooperating with my efforts to realign them.

So, doing one door at a time, I'l use a screw on the top edge of the door to hold in closed and properly aligned and then using a pair of braces and screws, to force the lower edge of the door into alignment and then fit formers to the inside of the door. Once the formers are cured in place the screws can come out and the holes be filled.

This thing looks SWEET with those doors open and the cavernous space and ready access to the rear of the mechanics is well, WELL, worth the effort of making these doors functional.

On the body there's really not that much left to do!
* The T tail needs assembled with the beacon lights on it (one red strobe on the vertical stab and one solid white on the top center of the T).
* The spotlight outrigger needs completed and the spotlight itself needs redone with the tilt servo in the center...not the end....
* Rivets....
* Antennas, wire strikes, and miscelanious other small details to invite "hangar rash".

On the cockpit I built a functional rudder prototype but they're too big and hit against the chin window. After doing some more detailed research, I have a new idea about how to accomplish their movment. I hope to be able to make more progress on that area as well.

Update pictures coming.

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03-15-2008 10:42 PM  10 years agoPost 35
Daniel Reese

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Urbana OH

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The doors are coming along nicely with magnets along the upper edge to help keep them from flapping. Now that things are moving, they're moving faster- getting the formers in is easier now that one is done.

Finialized the cockpit rudder design today too. The first attempt was far to bulky, crude and, well, it just didnt fit in the cabin anyway.

This version is much more refined and based very closely on the rudder pedals on an AH6

The linkcages on the full size look remarkably like servo arms on a servo's hub...

It Works!

http://video.google.com/videoplay?d...200042874593752

Now that Function is solved...Form is next - time to make it pretty!

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03-15-2008 11:34 PM  10 years agoPost 36
coptercptn

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Mesa AZ. USA

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looking good Dan!!! Sweet.

Home of the "Sea Cobra".....

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03-16-2008 06:10 AM  10 years agoPost 37
Daniel Reese

rrApprentice

Urbana OH

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(Gritting my teeth) I just ordered the rc expert (lightning Heli) 5 blade head for TRex 600...

At $240 complete, i couldn't pass it up.

I'll post full details when it arrives

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03-17-2008 04:49 AM  10 years agoPost 38
flipped2left

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indianapolis,in.

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looking good dan! the 5 blade head will sweeten things up even better., your old fuse is in the best of care by the way,i have stored it away and have plans for it! thanks again for it! ken

Smile! people will wonder what you're up to!!

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03-17-2008 12:11 PM  10 years agoPost 39
Daniel Reese

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Urbana OH

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Ken, Im glad it will be of some use to you

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03-18-2008 10:11 PM  10 years agoPost 40
Daniel Reese

rrApprentice

Urbana OH

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slow on progress- not much time between other jobs of late.

Got the cockpit control mixing problem sorted out- Mix ch7 to ch1; that gets uncorrupted aileron action. Mix ch8 to ch2; that gets uncorrupted elevator action. Ch4 for rudder peddals and ch6 for collective (had I linked it to ch3, immediately after takeoff it would come all the way up and just stay there - Idle Up)

I have been less than satisfied with the placement of the cockpit- it sat too high and the floor was nearly level with the bottom of the window. I was able to adjust the rest of the interior to match so when looking through the window it would have been hard to tell...but I knew it was off and that was bugging me.

So, since I was making changes to it to make it prettier anyway, I scrapped the whole thing and rebuild it in the proper place. Still working out how to replicate "padded seats"....This is gonna look sweet!

Even with the battery mounted in the front, I'll still have room for the pilot (left seat) and controll-less observer in the right seat wtih the battery between them, should I decide to fly it that way. THe instrument console would have to be removed to make room for the battery but the rest could stay. Im still going to try the luggage box/battery compartment idea but I need to get this thing flying first.

I had intended to make the cockpit removeable for flying since its pretty heavy...relatively pretty heavy...but with the added weight of the engine compartment doors and the cascading tail rotor design, that puts quite a bit of weight out back that would have to be balanced by something up front. I DETEST the practice of lead weight ballast, especially when the needed weight could be accomplished with that animated cockpit!

Still, Im a long way from testing/setting the center of gravity and a long way from even weighing the bird yet.

I got the last former in the engine compartment door- those are a fight! When I cut the fuse, the cutout sections warped/distorted themselves and no longer fit properly. I had to screw down two of the three edges so I could clamp the third in place on the former...trying to figure out what shape that former should be in was no cakewalk either!

Lesson learned: Cut, shape, fit and secure ALL formers around proposed doors/hatches BEFORE cutting them out!!!!

On the same topic...how do you clean up the edges between doors and fuse? I did a pretty good job with the dremel but it still left a fairly large gap that Im not too happy with. Im working out a door jamb solution but there's still a fairly large, unsightly gap between the door and the body that Id like to close up some. I was thinking of light weight spackle over the jamb with a smaller gap left for the door...or maybe even an epoxy filler...still, those feel like awfully heavy solutions...there aught to be something lighter.???

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HomeScaleAircraftHelicopterScale Model RC Helicopters › TT MD530 (Civilian) & TRex600E build thread
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