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Old Jan 24, 2013, 03:49 PM
M0unt@in M0del$ minion
turbojoe's Avatar
United States, AZ, Mesa
Joined Jul 2002
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OK so I'm thinking about dragging my EXI 500 out again. I put it away after fighting an irritating vibration/harmonic even with no main blades. Balanced, balanced and rebalanced everything and it was still there. New bearings and shafts. Lots of Align and Tarot parts. Still there. I don't remember if I had received and changed the main gears at that point. I think I'll do it just for grins before going any further. If I get the vibration sorted I'll be looking forward to flying something again. It's been a while.

What I need now is a gyro. My Futaba GY-240 and GY401 are now in 450 helis that I will be selling soon and I want to sell them BNF. Early last year I picked up one of those el cheapo no name GY-401 clones and put it in a spare T-Rex 450. What a piece of crap. After about one minute I was constantly chasing tail drift worsening as time went on. It was like a Blade CX when the battery starts going dead. I see a lot of new low priced gyros available now. Any of them worthy of putting on a bird this size? I have a fused left thumb so tail/throttle control is difficult at best. Needless to say 3D performance is not a requirement or even a possibility for me. I just need a rock solid tail for slow circuits and hovering. Maybe a loop or roll now and then. Cost is also a huge concern as I'm a poor boy now.

Joe
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Old Jan 24, 2013, 05:27 PM
Need More PURPLE !!
Dejavu*Xion's Avatar
United States, NV, Las Vegas
Joined Aug 2012
3,713 Posts
Tail gyros are super cheap nowdays...Scour the classifieds and you can now find align gp780's for $40, And quarks for $50.. Not as many as there were this time last year,,But i see 1-2 up for sale in a weeks time.
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Old Jan 24, 2013, 07:24 PM
M0unt@in M0del$ minion
turbojoe's Avatar
United States, AZ, Mesa
Joined Jul 2002
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Originally Posted by Dejavu*Xion View Post
Tail gyros are super cheap nowdays...Scour the classifieds and you can now find align gp780's for $40, And quarks for $50.. Not as many as there were this time last year,,But i see 1-2 up for sale in a weeks time.
Boy you're right. Everyone seems to be going FBL and dumping gyros for a song. I went searching on most of the heli sites and stumbled on a GP750 for $35.00 shipped on RunRyder. The guy has stellar feedback there. I Googled a bunch of reviews on the unit. While a few swear at it it seemed many more swear by it. I went ahead and bought it. Hopefully not a mistake.

Now to go after that vibration.........


Joe
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Old Jan 25, 2013, 08:05 AM
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United States, CA, Highland
Joined Mar 2009
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I spun mine up for the first time and its doing a really weird wobble, it seems fine when I have the main blades off, I can run it up and there is a vibration but it doesn't seem bad and smoothed out at higher RPM. Here's the weird part, when I put the main blades on I can run it up to almost half throttle then it starts to occilate on its skids...it's kind of like the toilet bowl effect in hover except still in the ground. I've spent several evenings setting all the linkages, checking my pitch angles, making sure travel is the same, and just about everything else I can possibly do. I'm running Curtis Youngblood blades and I've made sure they're balanced, I did change the head dampers with the align firm grey ones and also installed the plastic sleeve between the dampers, my buddy thinks this could be the problem, maybe running the sleeve is causing the head to increase even the smallest vibration since now the head is basically solid? Please help!
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Old Jan 25, 2013, 12:12 PM
M0unt@in M0del$ minion
turbojoe's Avatar
United States, AZ, Mesa
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Originally Posted by JLink125 View Post
it seems fine when I have the main blades off, I can run it up and there is a vibration but it doesn't seem bad and smoothed out at higher RPM.
Hmm. I wonder if this is just the nature of this beast and maybe just harmonics but it has kept me from even mounting the main blades. If they all do it then I'll move forward when the gyro gets here.

I hope you get the main blade issue sorted. Make sure you post what you found. Knowing my luck I'll probably have problems there too.

Joe
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Old Jan 25, 2013, 12:29 PM
just gotta mess with it!
2Doggs's Avatar
North West Louisiana
Joined Nov 2009
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Originally Posted by JLink125 View Post
I spun mine up for the first time and its doing a really weird wobble, it seems fine when I have the main blades off, I can run it up and there is a vibration but it doesn't seem bad and smoothed out at higher RPM. Here's the weird part, when I put the main blades on I can run it up to almost half throttle then it starts to occilate on its skids...it's kind of like the toilet bowl effect in hover except still in the ground. I've spent several evenings setting all the linkages, checking my pitch angles, making sure travel is the same, and just about everything else I can possibly do. I'm running Curtis Youngblood blades and I've made sure they're balanced, I did change the head dampers with the align firm grey ones and also installed the plastic sleeve between the dampers, my buddy thinks this could be the problem, maybe running the sleeve is causing the head to increase even the smallest vibration since now the head is basically solid? Please help!
Did you lube the feathering spindle? Does it turn relatively easily if you use a hex key on the bolt? I presume the blade bolts aren't too tight - I tighten them just enough to support the weight of the blades when the mainshaft is horizontal. Do you have another set of blades you can try? If not, check for different spanwise C of G in the blades - try the Finless Bob style balance whereby you match the C of G's then do a conventional prop balance and add tape at the C of G of the lighter blade. It's a bit of a long shot but you never know....
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Old Jan 25, 2013, 01:11 PM
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Hmm I honestly can't remember if I lubed the spindle shaft, I don't have any other blades but I only balanced them like a prop so an off CG could throw it off, I'll check some things after work. Thanks for the ideas! I'll post what I find, anyone else have an idea? I can use all the help I can get at this point.
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Old Jan 25, 2013, 02:24 PM
M0unt@in M0del$ minion
turbojoe's Avatar
United States, AZ, Mesa
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When I got my first T-Rex 450X kit many years back I fought an insane wobble like you describe. Don't know why it took so long for me to notice but I had one blade upside down! It had those crappy plastic paint stirrer blades they came with and no markings. At least that's my excuse..... Probably not your case but thought I'd throw that out there.

Joe
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Old Jan 25, 2013, 03:08 PM
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Haha nope blades are on correctly.
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Old Jan 26, 2013, 01:23 PM
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Maryland
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turbo joe, If you have a way of safely securing it to the ground or a picnic table, you can totally remove the head and spin it up. You have to isolate a head vs. tail issue.
If it vibes, it's the tail, then start taking things off the tail.
Remember, a shaft can cause the problem and it won't vibe when you remove blades or head/tail mechanics.
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Old Jan 26, 2013, 01:55 PM
M0unt@in M0del$ minion
turbojoe's Avatar
United States, AZ, Mesa
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Originally Posted by Melnic View Post
turbo joe, If you have a way of safely securing it to the ground or a picnic table, you can totally remove the head and spin it up. You have to isolate a head vs. tail issue.
If it vibes, it's the tail, then start taking things off the tail.
Remember, a shaft can cause the problem and it won't vibe when you remove blades or head/tail mechanics.
For a long time I've been meaning to get over to Goodwill to see if I can find an old record player for cheap. Several years ago a buddy got one and clamped his 450 bird to it. Made it easy getting the initial gyro setup as well as chasing down vibes. I'd probably have to add a BUNCH of weight to it for testing the 500 once main blades are mounted.

Joe
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Old Jan 26, 2013, 02:46 PM
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I'm sure it's not a tail issue, the tail is holding and seems to be working well. It's definitely in the head but I'm not quite sure where yet, I'm going thru the elimination process now.
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Old Jan 26, 2013, 04:06 PM
just gotta mess with it!
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North West Louisiana
Joined Nov 2009
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Lazy Susan

Quote:
Originally Posted by turbojoe View Post
For a long time I've been meaning to get over to Goodwill to see if I can find an old record player for cheap. Several years ago a buddy got one and clamped his 450 bird to it. Made it easy getting the initial gyro setup as well as chasing down vibes. I'd probably have to add a BUNCH of weight to it for testing the 500 once main blades are mounted.

Joe
I use a mountain bike front wheel on a work stand and a piece of wood.....

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Old Jan 26, 2013, 04:30 PM
M0unt@in M0del$ minion
turbojoe's Avatar
United States, AZ, Mesa
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That's a pretty cool setup! I love making my own tools so instead of a record player I think I'll dig around at work to see what I can come up with for goodies to make a dedicated test stand. I work for a major university and you'd be surprised at what they throw away. They waste more money than the US government!

Joe
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Old Jan 27, 2013, 01:56 PM
M0unt@in M0del$ minion
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United States, AZ, Mesa
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Got to thinking a bit last night. That's usually dangerous but this time worked out well for me. I went over to Home Depot and grabbed a 6" Lazy Susan bearing plate. It was only $4.49. Using some scrap plywood and 1/8" plexiglass I cobbled this rig together. I drilled new holes in one plate that mounts the plexiglass. I tapped the plexiglass for 6-32 screws. Turns out where the screws protrude through the plate they are perfect for locating the skids on my 450 and 500. I thought about using clips to mount the bird to the plate but I have a bunch of different sized 6061 aluminum bars. The two shown in the picture weigh almost 6 pounds total. It's not going anywhere with no main blades. I already dialed in the gyro on my 450 using the rig. I may refine it to make it look better but I don't know. It works pretty good as ugly as it is.

Joe
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