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Let Retract unit

Anything to do with gliders & gliding.
Elliot Howells
Posts: 333
Joined: 18 Mar 2015, 08:18
Location: West Wales
Contact:

Let Retract unit

Post by Elliot Howells »

After struggling for a couple of hours trying to get the geometry right, I'm giving up.

The retracted position doesn't move the lever far enough properly lock out and thus move the wheel into the wheel well.

Anyone had success with this scale type arrangement? I'd love to fit a Fema, but making it fit the glider would be a nightmare.

Cheers, Ell.
Phill Tadman
Posts: 329
Joined: 18 Aug 2015, 20:38
Location: South Cambs

Re: Let Retract unit

Post by Phill Tadman »

Hi Elliot

I had a similar problem on my Antares retract which, I think, has a similar construction.

I only achieved the proper travel after programming the servo for an extended throw.

Phill
john greenfield
Posts: 497
Joined: 18 Mar 2015, 07:52
Contact:

Re: Let Retract unit

Post by john greenfield »

Hi Elliot

If I recall correctly the LET retract requires a "retract" type servo with 180 deg of travel. Some modern digital servos can be programmed for 180 deg travel but a simple analogue "retract" servo like the Hi-tec HS75BB will do the job just as well.

AEB
AEB = Aeronautical Energiser Bunny (with thanks to CW)
Barry_Cole

Re: Let Retract unit

Post by Barry_Cole »

I did a few of these before I turned away from the Dark Side.

On all the ones that I sorted, the arm on the retract moved 90 degrees, from locked open to locked shut.

So Pythagoras rules. A squared plus B squared equals C squared. Where A and B are the length of the arm on the retract, from the shaft to the hole that you are going to use. If this is 25mm

Then A sq (25 x 25) = 625 B sq (25 x 25) = 625 So C sq = 1250 so C = Sqroot of 1250 or 35.35

If you use a retract servo (You really should), they turn through 180 degrees. So the arm on the servo needs a hole 35.35/2 or 17.67 mm from the centre of the output shaft of the servo. 17.5 mm would be fine.

It works every time.

If you cannot do the maths, or you need a servo arm drilled accurately let me know.

John is right, you need a servo that moves 180 degrees, the main reason for this is that there is no load on the servo at each end position as the arm is in line with the push rod. This gives another locking mechanism.
Attachments
Retract.pdf
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Elliot Howells
Posts: 333
Joined: 18 Mar 2015, 08:18
Location: West Wales
Contact:

Re: Let Retract unit

Post by Elliot Howells »

Thanks for the input chaps,

I'll post a couple of pics later, I am using a hitec 77 I think, retract servo anyway.

The problem lies in the geometry of the final close position, the locked down is perfect, difficult to explain from my phone, I'll take some explanatory pics later.

Ttfn, Ell.
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terry white
Posts: 508
Joined: 18 Mar 2015, 21:08
Location: wareham,dorset.england

Re: Let Retract unit

Post by terry white »

Hi Barry,

[quote]So Pythagoras rules. A squared plus B squared equals C squared. Where A and B are the length of the arm on the retract, from the shaft to the hole that you are going to use. If this is 25mm

Then A sq (25 x 25) = 625 B sq (25 x 25) = 625 So C sq = 1250 so C = Sq root of 1250 or 35.35[/quote)


We are all astounded with such a brilliant answer, now if we could all understand it------ :roll:
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chris williams
Posts: 1549
Joined: 10 Mar 2015, 10:50
Location: Blandford Dorset

Re: Let Retract unit

Post by chris williams »

We are all astounded with such a brilliant answer, now if we could all understand it------

Ah, if only he could fit a canopy, though... :lol: (Pyth-aggro-arse leaves the room at that point)
roo Hawkins
Posts: 557
Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: Let Retract unit

Post by roo Hawkins »

if we could only understand barry :lol: :lol: :lol:
Barry_Cole

Re: Let Retract unit

Post by Barry_Cole »

You are all assuming, that I understand me...

:shock: :shock: :shock: :shock:

BC
Elliot Howells
Posts: 333
Joined: 18 Mar 2015, 08:18
Location: West Wales
Contact:

Re: Let Retract unit

Post by Elliot Howells »

Here's a couple of vids showing the problem, I've managed to fudge it for now but I'm still not quite happy, I think a non retract type programmable monster servo is the solution though.

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