Given the small
size of servos nowadays, most model aircraft wings now have the
control surface servos (Ailerons, Flap) embedded in the wings. If you buy a kit or a ready-made model then these will
probably come with a set of covers to go over the servos thereby
providing reduced drag and a better appearance to the wing. Moreover,
it also protects the servo arms and linkages from damage.
But not all servo
fit a specific wing especially if itís a glider wing, so what if the
servo cover needs to be modified to allow your choice of servo to be
fitted, or if you have to enlarge the servo recess to cater for your
chosen servo you may want a different servo
cover, but there isnít much choice of servo covers on the market. If you build from
plans or design and build you own aircraft like I do, then you have
quite a limited choice so Iím always at a loss to which covers to use. I
have in the past used just a flat piece of plastic, epoxy glass
board or even tape to cover the servo with a hole cut into it to
allow the servo horn and pushrod to be connected to the flying
control but this is far from ideal.
over the past few
have obtain a number of different covers from my good friend Neil,
but when Iíve made wings and kits for other people then I have
felt that it wasn't right to ask Neil for some covers to pass on to
others with my wings. To get round this and in an attempt to be self
made a few fibreglass moulds and started to make covers from epoxy
glass to provide with any wings that I made for others. But whilst
some came out really well, I
couldnít get consistent results, and it took a lot of time and
effort just for one set; there had to be a better way!
I find the
internet and especially youtube, a fantastic source of information
and on a search relating to moulding wings one particular video provider
ďwindburner1Ē from whom I have gleaned some really good information
over the past 6 months
I came across a short video of him making a vacuum formed servo
cover from some clear sheet plastic.
Well, yet again,
the video got my mind working overtime and it wasnít long before I put a
hole in a piece of MDF as per the video, got out my hot air paint stripper and the
vacuum cleaner and tried it for myself. A fettling a piece of balsa into the shape of a
servo cover, and a discarded plastic tray that
cooked meats come packed in and I was surprised with ease of making a
plastic servo cover. Not perfect, but a promising 1st
result that had to be progressed further.
into other vac forming machines on youtube, both hobby and
commercial products I decided that I could make a vac forming
machine that would be quick and cheap to make at minimum cost using
wood that I already had in my workshop.
I created a box
manufactured out of 9mm MDF, I couldnít find any perforated display
peg board in my local DIY stores, so I fabricated the vacuum surface by
drilling a matrix of holes in some 6mm MDF sheet. I also fixed some
18mm MDF to the side of the box with a hole drilled through it the
same size of the vacuum cleaner nozzle. The frame that the plastic
needs to be fixed to was made from some timber that I had hanging
around from a previous
DIY project held together with wood glue and metal brackets.
results from this vacuum box wasnít so good and I figured that the
vacuum holes were being blocked too quickly before all the plastic
had been sucked into place round the mould. One modification that I
picked up on in some other videos was to put a bead of silicon
around the mating surface of the box. but still had a inconsistent
results with some of the plastic not quite shrinking fully around
the mould. I then remembered the
unusual pattern on the
base of the commercial covers I used to get
from Neil. Checking what few original covers that I had left in my
spares box the pattern on the base of the mouldings suggested a
wire mesh had been used under the mould to allow the vacuum to
become more even across the vacuum plate. A quick phone call to Neil
to confirm, saw me going to B&Q once again to buy a sheet of small gauge wire
mesh. After a further modification by adding a layer of mesh to the
vacuum plate, I got better results, but I was still using too much
plastic per set of covers.
All this time I
had been using tray packing plastic, previously used sandwich cartons
and whatever I could get hold of. Please note, that old plastic pop
bottles do not work as they just shrink when heat is applied to
them. Given a search on ebay I found some very reasonably priced ABS
plastic sheets in various thicknesses.
I figured that I
could make 2 servo covers with an A5 size piece of plastic, keeping
the the size of plastic and frame to a manageable size whilst also
keeping the waste plastic to a minimum too.
Yorkshire man and thrifty by nature, Iíve now put my hand in my pocket
and spent some money (that
hurts!!!). I purchased a number plastic sheets of A4 size ABS plastic.
Considering I can actually make 4 covers out of 1 sheet of A4 size
plastic I figured I needed a slightly smaller vacuum box (cutting
the A4 sheets to create an A5 size meant that I only had to make two
covers at a time, it would be more easily handled and A4 sheets work out cheaper than buying the smaller A5
The new Mk3
machine is essentially an A5 size
frame so that the plastic can be held in place by bull dog clips and
fit over a slightly smaller vacuum box. whilst the vacuum
box is now smaller and a more manageable size, it still allows for a good range of servo covers to be
replicated with the minimum amount of plastic.
The final vacuum
box has kept the same construction; 9mm MDF for the sides and
bottom. This is lined with 6mm MDF leaving an 8mm gap between the
top of the lining and the top of the box. This allows for a 6mm
vacuum plate to sit inside the box with a slight recess for the wire
mesh to sit on.
An 18mm MDF
flange was glued to the side of the box with a hole cut into it the
same size of the vacuum cleaner nozzle / hose. The hole through the
side wall of the box is slightly smaller which serves to provide a
better seal around the nozzle and for a degree of the vacuum to hold
the nozzle in place.
As I said, the
vacuum plate is positioned slightly lower in the box to allow for
the wire mesh to sit flush with the top of the box. A bead of
silicon around its perimeter finished this off. The frame that holds
the plastic is now
also made from 6mm MDF with the outside dimensions equal to A5 Size
piece of plastic. The inner dimensions is made the same as the
inner parameter of the box. This allows for clips to be positions
around the frame to hold the plastic with enough room for the frame
and box to be brought together to make a good seal around the top of
moulds are made from balsa, mdf, ply or resin and are placed in
the desired position on the vacuum plate.
The plastic is
subsequently heated uniformly within the frame by using the heat
gun, it could be heated using an oven, but that brings other issues
with having to wear gloves and having to do this in the kitchen. I
donít think my good lady wife would approve as it might give the
cakes a bit of a weird tasteÖ sheís always baking!
Once the heated
plastic is very soft and pliable, the vacuum cleaner is switched on
which actually hold the moulds in place, the warm plastic
within the frame is then placed over the box and moulds. If the plastic is
heated correctly the vacuum quickly pulls the plastic into place
around the moulds. Given a few seconds without the heat the plastic
hardens enough to allow the vacuum to be turned off. A few more
seconds and the frame and plastic can be removed and if the moulds
have not already fallen out of your new covers, they can be easily
removed. All that is left is for the covers to be cut and trimmed
There you have
it, for minimum cost you can have some great looking and
functional servo covers of whatever shape or size you want.
So, if you are in the market for some
bespoke servo covers, why not give it a go.