The Alchemy stabs were first introduced on the Allure V2 last year. They are smaller in area and thinner in section than their predecessor.
Previously, the stab servo cut-out was marked on the underside of the stab. This is no longer done. Some may ask why the servo cut-outs haven't been done? Well, it means the stabs could be setup as pull-pull if the builder wanted to go this way. It also allows smaller servos to be used or even laying the servos on their sides.
For this build I decided to go with the MKS HV6130H servos. These are a bit smaller than say the Futaba BLS173SV or the like and are actually lighter at 23 grams. Torque at 6V is 6 Kg and goes up a Kg for every volt increased. Awesome power from such a little package! Zero gear slop and excellent centering.
The first task was to determine the servo location in each stab. Masking tape is used to mark out where the servo will go, linkage position at neutral and also the control horn location. You also want to mark the Servo screw mounting hole locations.
The factory supplies a light ply servo plate which suits a BLS173 sized servo. Because I used the MKS HV6130H, a new plate had to be made. I drew the plate up on Fusion 360 and then cut out the plates on my CNC Router. Perfect fit. These plates are then glued into each stab with the Servo mounting screws used to hold things in place whilst the epoxy cures. Oh, you’ll need to drill the Servo holes in the stab skins first. I find making a dent in the skin with a centre punch helps stop the drill wandering off. These holes can normally be made by hand with the drill bit in a pin vice or tap wrench. See pictures above.
It’s now time to fit the control horns. The control horns are made from 1.5mm carbon fibre. The elevator control horns have three (3) 2mm linkage pickup holes. You’ll need to mark out on the elevators the slot for the horn. I mounted the horn so the tab to be glued in is on the edge of the elevator spar. If you fold open the elevator it’s easy to measure the distance back from the edge and transfer this to your Masking tape. Remember to allow for the ball joints on you linkages when marking the slot in the root to tip direction. Once you’re happy that both elevators are marked out correctly, use a sharp scalpel to cut the slots. Take your time here and you’ll end up with a neat slot. The control horn should sit flat on the elevator skin. If it doesn’t, you need to make the slot deeper until it does.
Remove the masking tape from the elevators. Next take each horn and rough up the tab to be glued into the elevators. Some 220 grit sand paper does the trick here. This just give the epoxy more bite on the control horn. I use 30 minute epoxy mixed with some glass fibre rovings for this job. You could just use epoxy but I like the extra body that the glass rovings give the epoxy. Push some epoxy into the slots cut in each elevator and also add some epoxy to the horn itself. Ensure the slots in each horn tab are filled with epoxy. This helps to anchor the horn into the control surface. Insert the horns into the elevators and wipe off the excess epoxy that squeezes out. Cotton buds with methylated spirits works a treat for cleaning up epoxy. Then tape the horns into position to hold them flat against the surface and at the right angle. See pictures above.
When the epoxy has cured, remove the masking tape. Make a mark on the stab edge to allow for the elevator horn clearance slot to be cut. The slot only needs to be a couple of millimeters deep to clear the horn and get the required elevator throw. A round file or dremel is the tool of choice for this task. See pictures above.
Linkages - I use lightweight 2.5mm titanium rod and dual axis ball ends on the elevators and Ailerons. This gives a light rigid and slop free connection between the Servo and control surface. With the servo and control horn in place, it’s easy to determine the length of titanium rod needed. Then it’s just a matter of putting a thread on each end. I used to run a die over the rod by hand but now do it in a lathe. The results are much better with the lathe. If you want linkages made just contact us with the dimensions. We also sell the dual axis ball ends here. The linkages are attached to the Servo horn and control horn with M2 x 8mm Titanium Screws and M2 Aluminium Nyloc Nuts.
The Stabs are now done.