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T-REX 600 › Need help: TREX 600CF FBL conversion with BeastX
11-18-2015 04:24 PM  22 months agoPost 1
getsuyoubi

rrApprentice

Queens, NY - USA

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I'm trying to get that elusive blue light on the BeastX for my TREX 600CF flybarless conversion. I'm using the Align non-DFC head. With the bell cranks the linkages on the servo wheels have to be at the outer holes (same distance from rotation axis) as on the bell cranks, so the linkages are parallel, to avoid binding/strain. But since the bell crank arm to the swash is about twice as long as the ones that connect to the servo this results ina lot of throw (the servo throw is doubled), which is too much to get a blue LED light.
I'm sure this exact type of conversion has been done a zillion times, so I hope someone out there can point me in the right direction.
Thanks!!!

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11-19-2015 02:20 PM  22 months agoPost 2
Richardmid1

rrProfessor

Leeds, England

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With the bell cranks the linkages on the servo wheels have to be at the outer holes (same distance from rotation axis) as on the bell cranks, so the linkages are parallel, to avoid binding/strain.
Incorrect im afraid, they don't need to be parallel.

You can also use shorter balls on the inner swash or longer balls on the outer swash to get the same affect.

60% of the time, it works every time!

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11-19-2015 05:12 PM  22 months agoPost 3
getsuyoubi

rrApprentice

Queens, NY - USA

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Well, I wish you were right about the bell crank geometry, but I'm afraid you're likely not. It took me quite a while to convince myself that they actually don't need to be parallel, and after trying to calculate it during one of my lunch breaks I finally just made a scaled drawing of the elevator situation on my CF:

The sets of green and red solid lines are the two pushrods for two different rotation angles of the servo wheel (left). The dashed lines show that the balls on the bell crank would not end up on exact opposites of the bell crank if they were allowed to slide freely at constant radii. I understand that the servo rotation angle is quite extreme in this drawing, so in reality this is probably not a problem.

Anyway, I have been looking for different length balls for the swash, but so far without success. Where can I find them?

Thanks!!!

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11-20-2015 11:56 AM  22 months agoPost 4
Richardmid1

rrProfessor

Leeds, England

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Your wish has come true!

Remember, you do not want the large radius arm/wheel to move the same amount of degrees as the small radius arm/wheel, the larger radius arm/wheel will only move as far as the small radius arm/wheel lets it.

If it were a single con rod and the smaller wheel was allowed to rotate fully, the larger wheel would simply not complete a full rotation and would just oscillate back and forth.

60% of the time, it works every time!

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11-20-2015 01:15 PM  22 months agoPost 5
getsuyoubi

rrApprentice

Queens, NY - USA

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Looks like we're having the very same debate I was having with myself until I made that drawing...
In the case of the red pushrods I'm willing to accept that the drawing is not accurate enough to convincingly show that there is a problem, but the extreme case (green) clearly shows that the line that connects the two "balls" on the bell crank does not go through the center of the bell crank. I'm probably overthinking this, as this extreme case will never occur in real life...

Where can I get different length balls for my swash?

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11-20-2015 02:59 PM  22 months agoPost 6
Richardmid1

rrProfessor

Leeds, England

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We are not talking about trying to get a full rotation of the bell crank so it works just fine with zero strain. No need for the different length swash balls.

Quick UK do or did do various length M3 swash balls. Or you could try Align's DFC swash which has 2 positions for the inner swash balls, just use the inner holes.

http://www.fast-lad.co.uk/store/pro...roducts_id=7329 You could use these on the inner swash if the ones you have in are longer? They are 3mm from mounting face to the center of the ball.

60% of the time, it works every time!

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11-20-2015 03:43 PM  22 months agoPost 7
rcflyerheli

rrKey Veteran

Granbury, TX USA

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I did that same conversion on my 600ESP, with a Vbar, and had the same issues as you did. The thing(s) I had to do were as follows:

1. The FBL head is a must, otherwise you can't get the servo outputs close enough to center to make it work. Also, the shortest standoff balls on the swash where the links to the head connect had to be used.

2. I had to go to JR servos, with their white offset servo arms in order to get the pushrods to clear the center output shaft of the servo. I used 8917 servos and the ball center to center spacing is 16mm.

3. Doing this on the elevator servo also required cutting the servo mount in half, and actually moving about half of the servo outside the frame, so the angle from the servo to the "A" arm bellcrank didn't bind up.

Doing these three things gave me the Vbar equivalent of your blue lite on the setup, and I have been flying this bird for over 4 years now. In all honesty, with my style of flying, it flies as good as any other heli I own, and maybe even better than some of the more expensive 12s 700s I own.

I do still fly it, not every day, but semi-regularly. BTW, I didn't go DFC with it, just FBL head. I don't have a close up photo of the mechanics, but this one shows the head.

Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

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11-20-2015 06:19 PM  22 months agoPost 8
Richardmid1

rrProfessor

Leeds, England

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I think I had my ball links mounted on the outside of the servo wheels so the rods didn't hit the output shaft of the servo.

60% of the time, it works every time!

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11-20-2015 10:01 PM  22 months agoPost 9
rcflyerheli

rrKey Veteran

Granbury, TX USA

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Same here, but the clearance problem was getting the nuts to screw onto the ball post and clear the outer edge where the splined part goes onto the servo output shaft. Everything with "Futaba" type splines would not let you put the ball posts in close enough to center. Well, the post would fit, but I couldn't screw the backup nut onto the post from the other side.

Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

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T-REX 600 › Need help: TREX 600CF FBL conversion with BeastX
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