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paulj

RCRCM Sunbird Build

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paulj

I have a new RCRCM Sunbird which I am building for some slopeside winter fun. I have some DS6100 servos for the wing, and before I get too excited with the glue, I want to confirm a couple of points:

  • The servo will be mounted with the servo arm near to the main spar on the bottom surface and with the flap / aileron horn on the top skin side. This means the linkage will cross the top of the servo. This servo type has a protrusion above the top surface, which means if I use a clevis and pushrod, it will interfere with the servo. I intend to use a 90 degree bend (or Z bend) at the servo end with the pushrod coming out above the servo arm. I guess this is OK?
  • Is there any rule of thumb for the length of the servo arm? Since the horn length looks like it will be around 7-8mm, I guess there is no need for a very long servo arm.

Many thanks!

I'll post pictures as I go along, in case anyone else is interested!

servo.JPG

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oipigface

Hi Paul,

          A Z-bend accurately made is OK. The difficulty is always making the middle part of the Z short enough to avoid it slopping around. Special pliers are available that enable a neat job to be done. I don’t know if you’ve got access to a pair or not, but if not (and even if you have) another common solution to your problem is to remove enough of the clevises to enable them to move freely. It is possible to remove close to half of the width of the clevis without compromising its strength too much. This is the installation in my Pitbull:

          7FEA4C48-A227-475B-B16C-3F5EF0570669.thumb.jpeg.ab572939e43caaffe66b950916a38fd0.jpeg

          Push rods should be as short as possible. 

           Kevin Newton’s website has much good advice on installing wing servos:

                       http://kevin-newton.blogspot.com/2001/01/mounting-wing-servos.html

          Why not mount the servos the other way round, so that the pushrods don’t run past them?

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isoaritfirst

Z bends can be made with pliers. Bend first 90, if you have a vice stick it in and hammer gently to ensure tight and square bend. 

Then bend the second (keeper) bend by holding the first one either in the vice or pliers, holding the rod and the first bend in the jaws then bend the keeper at 90 such that once bent it’s at 90 to the rod. Then twist it to straighten with the tod

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paulj
18 minutes ago, oipigface said:

          Push rods should be as short as possible. 

           Kevin Newton’s website has much good advice on installing wing servos:

                       http://kevin-newton.blogspot.com/2001/01/mounting-wing-servos.html

          Why not mount the servos the other way round, so that the pushrods don’t run past them?

Thanks - I'll have a look at Kev's site - his models are always very neatly installed and set up! If I mount the servos the other way round, the distance to the flap/aileron will be very short - possibly too short to fit a clevis in. Also, the wing is very thin. For the ailerons, I could push the servo under the skin when gluing it in, but if I ever need to get it out again...

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paulj
8 minutes ago, Stormeflyer said:

Hi Paul

You will find a helpful build thread here

http://www.rcmf.co.uk/4um/slope-soaring/rcrcm-sunbird-build/

 

4C91959D-4934-47EC-8123-6E41DB5129D6.jpeg

B680C566-CAB2-494D-B974-C61963255A2B.jpeg

This is exactly what I was thinking to do. I guess they won't come off because of the length of the tail, and interference with the skin around the edge of the enclosure. The other pictures in the thread look like they will be useful as well. Many thanks!

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isoaritfirst

Best to avoid putting cranks in pushrods. 

On small model like this I often use simple L bends. At the servo end use the smallest arm possible or drill a hole in an arm. Try got around 5-6mm radius. 

Once all is installed glue a soft balsa   Rib into the wing, as a keeper to hold the pushrod in place. If you ever need to remove, simply break the keeper rib out. 

Be very accurate in creating good square L bend. Anything less than perfect will weR the hole, and also may work its way out of position. Having a crank as in the picture makes it much harder to achieve a good accurate install( and shouldn’t be needed)

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isoaritfirst

Fuselage push rods also end with a L bend. 

Take the servo arms off and push L end up from below before fitting as back in place. 

Make a flat surface by the side of the servo to hold the rod up into place. 

To achieve correct rod lengths, make the L bend in 2mm rod and slide it into the inside of the push rod. 

When everytning is installed and lined up zap it. 

If the metal rod is too small to fit inside the pushrod, wind a few lengths of carbon tow around the rod then zap and kick. Then sand back to a fit before zapping into position

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