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Old Feb 13, 2009, 02:33 PM
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Joined Feb 2008
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My work on binary 900

Hi guys,

I'd like to show you my current progress on this cute DLG and the modifications I made so far to the original tail. I'd be happy If you share your experience on similar designs. Most of all I wanted to make an all moving elevator then decided to make the rudder pull-spring system also. I still doubt whether to use steel spring or tiny rubber band. The vertical and horizontal stabilizers are little airfoiled and carbon reinforced around, bacame 2 gr. lighter than those supplied with the kit.
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Old Feb 15, 2009, 04:57 PM
Foamy Season is here! MX2#1
pitviper51's Avatar
Elizabethtown, Kentucky
Joined Nov 2005
3,396 Posts
Well the project is started haha.. no pictures of this step.. i poped the manual cd in the pc today and printed out the manual.. (note this cd has the manuals for all the models they make), even BIII.. hmmm. so idecide to go ahead and glue the wing halfs together today, so i put a strip of blue masking tape onthe bottom of the wing and lined things up, and scooped in the 5 minit poxy then held it to settle.. i will use 30 min poxy when i fibergalls the wing joint later. so far i have to say this is a sharp looking lil plane.
mike
ps, the open wood looks good!
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Old Feb 17, 2009, 12:38 PM
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hummm....
mine came with the wings glued!
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Old Feb 20, 2009, 03:22 PM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
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not quite right...

So after a few outings with my B900, I've come to really dislike the elevator setup. I have definite centering issues and a double neutral. Whenever I touch the elevator it will come back to a false neutral, and I will either be diving or stalling (the B900 appears to be very sensitive to elevator).

grumph.

I suspect the Cirrus CS101 servos simply aren't very good, but I also don't like the spring return on the B900. The stock mechanism relies on a bent spring pushing on a small FRP plate. Although small, there is some stiction in this mechanism, and you don't always have a smoothly varying return force. That certainly isn't going to help an already marginal servo.

Since I broke the h-stab off today, I think I will take the opportunity to install a more conventional spring return - either a music wire torsion spring, or perhaps a spring or rubber band pulling on the control horn.

If that doesn't make it behave better, I'll rip out the servos and install something with a more solid reputation, like D47's or Pico's.

I've already been thinking about mods to implement on my 2nd B900

-matt
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Old Feb 20, 2009, 06:38 PM
Foamy Season is here! MX2#1
pitviper51's Avatar
Elizabethtown, Kentucky
Joined Nov 2005
3,396 Posts
hey good to know , i was planing on maken control rod set up anyway.. tho i almost regret getting this plan now haha sincei found a way to get the full house ship i was originally wanting when the process started haaha.. likly now gonna have both hahah, as for the issue with the elevator i wonder how hard a pull pull woul dbe to set up on the ele?
mike
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Old Feb 20, 2009, 07:06 PM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
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Quote:
Originally Posted by pivlrs
So after a few outings with my B900, I've come to really dislike the elevator setup. I have definite centering issues and a double neutral. Whenever I touch the elevator it will come back to a false neutral, and I will either be diving or stalling (the B900 appears to be very sensitive to elevator).
I forgot to mention - each launch is a semi-random adventure!!!
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Old Feb 20, 2009, 07:21 PM
Foamy Season is here! MX2#1
pitviper51's Avatar
Elizabethtown, Kentucky
Joined Nov 2005
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makes it fun what have a i done!
mike
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Old Feb 21, 2009, 10:04 PM
a.k.a. Matt Nelson
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North Tustin, CA
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Quote:
Originally Posted by pivlrs
[...] Since I broke the h-stab off today, I think I will take the opportunity to install a more conventional spring return - either a music wire torsion spring, or perhaps a spring or rubber band pulling on the control horn. [...]
Done. I pulled out the coiled spring that was supplied with the kit, and installed a simple torsion spring into the hinge. I used 0.015 music wire with a low-torque bend in it (it only required about 30 degrees of twist to install). The result is a nice smooth spring action with a very light restoring force - even the CS101 servos should be able to handle it.

As a plus, I looked at the carcass of the coiled spring I yanked out lying next to a couple test versions of the torsion spring - I think the torsion spring has about 80% less metal = lighter tail.

The whole thing looks a lot cleaner now, too. And we all know it's all about appearances...

I would heartily recommend that anybody building a B900 consider replacing the coiled spring with a torsion setup. Lighter, smoother, cleaner.

Since I have to replace some of the elevator pull line, I am also pre-stretching some spiderwire by hanging a 3lb weight on it. Should be able to bypass the stretching I saw last time ( )

-matt
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Old Feb 22, 2009, 12:01 AM
Landing is inevitable
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Singapore
Joined May 2006
198 Posts
Hi Matt,

I'm about to start on my b900 build and this is my first DLG. DO you have any references or any pictures of how your torsion spring looks?

Thanks,
Adnan
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Old Feb 22, 2009, 10:15 AM
Foamy Season is here! MX2#1
pitviper51's Avatar
Elizabethtown, Kentucky
Joined Nov 2005
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that shoudl prestretch it haha, i still dont see how this spring back concept is good.. i like positive control both ways.. i havent started my build yet, just to much other things to finish..
mike
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Old Feb 22, 2009, 10:39 AM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
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Quote:
Originally Posted by randomtask
Hi Matt,

I'm about to start on my b900 build and this is my first DLG. DO you have any references or any pictures of how your torsion spring looks?

Thanks,
Adnan
If you search these forums, you could probably find other photos and discussions, and that's how I learned about this sort of torsion spring. Attached are some photos of the spring I ended up with. Descriptions follow:
  1. The basic spring. The idea is that one of the ends is inserted into the edge of the elevator flap, and the other end is inserted into the edge of the horizontal stab. Some people describe the springs as being fabricated to look like a big staple - but I found that with the 0.015 music wire I have, a full 180 degree twist gave too much restoring force on the control surface, and was difficult to install. Perhaps if a lighter wire was used, this would work better. You will need to experiment to get something that works for your combination of wire and servo.
  2. Compared to the remains of the original coiled spring, the 0.015 music wire torsion spring adds less metal to the tail of your plane - a Good Thing!
  3. Close-up of the inserted spring. It is centered on the control horn, and if you look closely, you can see where it is inserted into the edge of the balsa surfaces. I added a small drop of CA after it was installed and tested to ensure it doesn't somehow work itself loose.
  4. Edge-on picture of the elevator surface. The deflection shown is almost the natural resting position of the spring - only a little force holding it up this far. Experiment with several bends until you find one that gives the correct force. I have half a dozen discarded springs littering my workbench...
I hope this helps.

-matt
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Last edited by MattN; Feb 22, 2009 at 01:43 PM.
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Old Feb 22, 2009, 10:56 AM
a.k.a. Matt Nelson
MattN's Avatar
North Tustin, CA
Joined Oct 2008
1,753 Posts
Quote:
Originally Posted by pitviper51
that shoudl prestretch it haha, i still dont see how this spring back concept is good.. i like positive control both ways.. i havent started my build yet, just to much other things to finish..
mike
I'm still on the fence on this one. I think the pull/spring setup can be very good (lot's of folks use it!), but the biggest "problem" I have is that the servos I'm using are pretty wimpy/crappy(?). With something like a JR DS188 6g sub-micro digital servo, I'm sure it would be rock-solid. (I'm starting to think that, because centering is so crucial for elevators, digital servos should always be used there). In fact, if I still have problems, I'll probably replace my current servos with a D47 for the rudder and a DS188 for the elevator.

If/when I build my second B900, I might consider using something like ECM's micro pushrod kit.

-matt
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Old Feb 22, 2009, 11:20 AM
Landing is inevitable
randomtask's Avatar
Singapore
Joined May 2006
198 Posts
Quote:
Originally Posted by pivlrs
If you search these forums, you could probably find other photos and discussions, and that's how I learned about this sort of torsion spring. Attached are some photos of the spring I ended up with. Descriptions follow:
  1. The basic spring. The idea is that one of the ends is inserted into the edge of the elevator flap, and the other end is inserted into the edge of the horizontal stab. Some people describe the springs as being fabricated to look like a big staple - but I found that with the 0.015 music wire I have, a full 180 degree twist gave too much restoring force on the control surface, and was difficult to install. Perhaps if a lighter wire was used, this would work better. You will need to experiment to get something that works for your combination of wire and servo.
  2. Compared to the remains of the original coiled spring, the 0.015 music wire torsion spring adds less metal to the tail of your plane - a Good Thing!
  3. Close-up of the inserted spring. It is centered on the control horn, and if you look closely, you can see where it is inserted into the edge of the balsa surfaces. I added a small drop of CA after it was installed and tested to ensure it doesn't somehow work itself loose.
  4. Edge-on picture of the elevator surface. The deflection shown is almost the natural resting position of the spring - only a little force holding it up this far. Experiment with several bends until you find one that gives the correct force. I have half a dozen discarded springs littering my workbench...
I hope this helps.

-matt
Hi Matt,

Really appreciate the pictures you've uploaded and the explanation too. My bad, should've searched around a bit more for pictures/examples of the torsion spring.

Thanks,
Adnan
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Old Feb 22, 2009, 06:36 PM
Foamy Season is here! MX2#1
pitviper51's Avatar
Elizabethtown, Kentucky
Joined Nov 2005
3,396 Posts
Quote:
Originally Posted by pivlrs
I'm still on the fence on this one. I think the pull/spring setup can be very good (lot's of folks use it!), but the biggest "problem" I have is that the servos I'm using are pretty wimpy/crappy(?). With something like a JR DS188 6g sub-micro digital servo, I'm sure it would be rock-solid. (I'm starting to think that, because centering is so crucial for elevators, digital servos should always be used there). In fact, if I still have problems, I'll probably replace my current servos with a D47 for the rudder and a DS188 for the elevator.

If/when I build my second B900, I might consider using something like ECM's micro pushrod kit.

-matt

ok ill let you know how it works haha,, think i will get some
mike
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Old Feb 22, 2009, 09:07 PM
a.k.a. Matt Nelson
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North Tustin, CA
Joined Oct 2008
1,753 Posts
Quote:
Originally Posted by randomtask
Hi Matt,

Really appreciate the pictures you've uploaded and the explanation too. My bad, should've searched around a bit more for pictures/examples of the torsion spring.

Thanks,
Adnan
No problem! I didn't intend to sound like I was scolding you for not searching the forums! I was merely pointing out that you could find even more information if you need it by looking around here. It's fun sharing as I figure these things out myself

-m@
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