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Servo Covers - why not make your own  ???????

     

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 years I 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 sufficient I 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.

Having looked 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.

The initial 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.

Being a 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 sheets).

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 the box.

The replica servo cover 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 to size.

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.

Colin W

 
 

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