Modern digital servos are giving us incredible accuracy, speed, torque and the latest statistic that keep us agonising over servo choice; ‘deadband’. But, to see these benefits you have to install them in your planes well, really well! These bearing kits are without doubt the best way we have found in improving the performance of any glider wing servos using conventional linkages. Unlike all other external bearing system available, the Fu-Fix external bearing (and servo for that matter) is designed to be bonded to both the top and bottom skins. This dramatically reduces skin flex, which you will always suffer from if mounted to one skin. The development and independent testing can be found here (BARCS.co.uk) and here (RCMF.co.uk). Use as intended and they will transform the way you install wing servos. And best of all it’s simple to do with just 2 main components.
What does the Fu-Fix External Bearing Kit do?
In any conventional linkage system virtually all servos on the market are driven from a side arm and as a result pushrod forces add unwanted side load to the head and bearings. This is compounded as our wing servos are getting smaller, typically 10mm thick but our planes are getting faster. In racing competition planes especially, there is a trend for smaller and smaller horns to produce a clean, low drag wing. These results in a higher load on our shrinking gear trains- just imagine opening a door near the hinge verses the handle. You need a lot more effort and that’s exactly what is happening to our servos! Using a Fu-Fix external bearing kit means your servo has less slop caused by head rock and those tiny gears, bearings and cases experience less wear; making them last longer as well as perform better!
Wear in the head, particularly in the shaft bearings is every bit as important as gear wear and probably a more significant factor in why we end up with a sloppy servo. The Fu-Fix external bearing kit reduces head wear. These bearing kits are perfect if not essential in all high load applications like in DS planes but it may be that you just want to protect your wing servos from wearing so that they stay tighter longer. Good enough reason alone when you consider the cost of the latest aluminium cased wing servos, which of course don’t have the same wear rate as cheaper servos but nonetheless experience the same side loads.
A lot of development went into making the installation simple and as well as, of course, extremely strong. One of the biggest considerations was what if you break an arm! The Fu-Fix external bearing kit has a bearing shaft which is made removable using a 4mm spanner or even long nose pliers, if you must! As the shaft doubles up as the arm retention screw, just unscrew and take the arm off, it’s a simple as that! Everything stays in situ, the servo and the bearing housing. So field repairs are entirely feasible. This was an important factor in the design.
Design and Manufacture
The weight gain added to each servo is less than 2g. The components are deceptively simple but are high quality and precision CNC made. The bearing itself is a high quality metal sealed ‘race’ which is better for our wing environment where ‘bits’ inside the wing can foul a open bearing. The bearing housing comes with the bearing pre-seated with bearing mating compound already done for you. It’s sized at 10mm height for 9.5mm-11mm thick servos and flip it on the other sized and its 12mm high, perfect for 12-13mm servos. Any thicker will work too, just add a suitable spacer to the skin first. The housings are made in CNC aluminium moulds and injection moulded using epoxy composite.
What Servos fit?
They are really easy to fit and full fitting instructions come with each kit. You get 4 bearing shafts and 4 ball raced housings to do a complete wing. The sizes of the shafts can be mixed and matched for different servos for example, M3 for flaps and M2.5 for ailerons depending on your servo choice for both.
Here’s a table for some of the most popular wing servos and sizes required:
(Also Hyperion DS09SCD using M1.7 shaft to re-cut thread).
|M2.3||Hitec 65, 81, 85,125 (and all Digi versions),
|M2.5||All MKS 6125 variants Incl DS6100 and DS6188,
Hyperion DS13 range.
Sanwa 762 (Airtronics 94761Z),
JR/Graupner wing servos,
Turnigy aluminium A55H,
Hyperion DS16 range.
There’s more, the list is growing as we install more brands of wing servo. You may know of others, let us know and we’ll keep the list updated. We have literally installed 100’s of servos with the Fu-Fix bearing kits, not only in wings but rudders and elevators too! It is by far the best way we have found to give strong and slop free linkages. Here’s some we have done for customers. We’ve used tiny servos, cheap servos as well as the expensive ones and they all benefit!
The cost of each Kit is £24.95. This includes 1st class post in UK. Overseas purchases will be cost of airmail letter on top.