This heavy duty pulley is CNC-machined from a solid billet of 7075-T6 aircraft
aluminum, broached for the ISO25 spline (25T ø6mm). Installation is axially on the
6mm diameter, 25T-spline shaft (lightly greased), and secured, with M3
Allen-head machine-thread bolt. Disassembly is the reverse, begin by
removing the M3 bolt securing the leader cable to the pulley, then the
M3 bolt securing the pulley to the splined output shaft.
Why a pulley? Simple, it's because pull-pull cables won't go slack
transiting from one extreme to the other. Just make sure the control
horns align with the hinges and you'll be golden. Your benefit is unlike
with tiller arms, the leader cable on the downwind side of the control
surface when using a pulley doesn't tend to go as slack so you maintain
better control when there is buffeting in the air as the surface remains
rock solid.
Way it works is simple. Begin by using a couple of sticks of hardwood
with rubber bands at each end. Slide this down over the rudder and
vertical fin to clamp them into alignment. Next, you're going to make a
continuous loop from the left-side rudder control horn, to the pulley
where it makes a figure-8, and back out to the right-side rudder control
horn. Since you want to sneak up on the proper tension, begin with the
eye-bolts about where you want them in the plastic ball-link and then
unscrew them until maybe just 5 turns is all that holds them in.
Basically, you want to have 6-8 more turns of adjustment to tension the
leader cable without the eye bolt bottoming within the link, understand?
Next . . .
- Radio system on, wheel sub-trimmed so the pulley is at neutral, set transmitter out of the way.
- At leader midway point, make the figure of 8 at the pulley, lightly snug the M3 bolt (but not tight).
- Next, thread each leg of the leader to the right and left side rudder control horns.
- Slide the crimp onto the leader cable, loop through eye, and back through crimp, slide crimp toward eye.
- Repeat for the other side, once again, slide crimp toward the eye until they're about equal on each side.
- Eyeball and confirm servo remains at neutral, and leader hasn't slipped off the pivot point.
- Next, lightly tension cable on one side, now crimp it. Go easy on then tension, we'll snug it later.
- Repeat on the other side.
- Now adjust tension using eye bolt into ball-link until you're happy - not too much though!
- Go back and confirm the figure of 8 looks good and tighten the M3 Allen head bolt.
Finally,
release hardwood sticks holding rudder in alignment with vertical stab. Now operate rudder with the transmitter and confirm tension throughout the range.
Make slight adjustments as needed but remember, the tension is carried
on the servo output shaft bearing so don't make it like a guitar string,
leave it lightly tensioned, only. Anyway, if there's a downside of a continuous loop system it's when you need to slacken or tighten the leader cable, you must to do
both sides the same amount. Not a big deal in practice.
Note; what usually happens is
after a few flights you'll need to snug it up about 1-2 turns on each side until the system takes a set.
