(This is the first post in what will become a series on the building of the dual-yoke system for the cockpit project. You’ll find an image gallery at the end, as an experiment instead of threading the images throughout the post.)
It’s been a while since there was an update here. I haven’t been doing much on the project of late, as real life has intruded – as it tends to do. However, over the last few weeks I have been planning for and acquiring the parts to open a second front on the project, to give me an opportunity to work on something other than just the shell. Among the many items that I need to fabricate for the sim is the yoke assembly. I decided to get started on this as my second string of activity, and I’ve been building the yoke – slowly – for the last few weeks.
My basic yoke design is derived from Ken Brand’s innovative design for his Pilatus PC sim. You can see more about the design at his site here. My own version varies slightly in the elements, notably the use of gear and chain to connect the yokes rotationally instead of tensioned wire, and there are several other differences, but otherwise the designs are pretty similar. Do check out Ken’s site, by the way, as he has designed and built several other controls including a throttle quad which are all very impressive, and is now in the process of converting his sim into a Boeing 777 pit. Lots of interesting stuff there.
The part of the yoke design which is the hardest to fabricate is the handle itself. I have no facilites to mould plastic, and my wood carving ability certainly isn’t up to the standard required. Fortunately I already owned a CH yoke which I had always planned to re-use for this project, albeit not quite as drastically modded as it now will be. This gave me one yoke handle. I needed another identical handle, so a quick scour of Ebay turned up a CH yoke in great condition which I won at an acceptable price (about 1/2 what it would cost me new). The yoke turned up and, after plugging it in to make sure it worked, I set about taking it apart.
I had previously disassembled my own CH yoke some months back, so I knew what needed to be unscrewed and where. Unfortunately, because of the relatively small diameter of the screws used (2mm), and the deep recesses in which they were set, I had to use a long but very small screwdriver, and it turned out that I could not apply enough torque to get four of the eight screws out. I stripped most of the heads trying. Since the yoke casing would not be needed for this project, I broke out my trusty Dremel, fitted a router bit, and proceeded to rout out strips from the case around the screw fittings. With these exposed, I was able to cut through the fitting above the end of the screw itself, and the case popped open.
Stripping out the guts of the yoke is then a fairly simple matter. The handle and shaft pop out easily enough as a unit, and the rest comes apart into pieces with minimal effort. There are a further ten screws in the handle that must be undone to open it up. While some of these were also rather badly stuck, the recesses were shallow enough that I could apply a power driver to them and get them all out without stripping any. Phew.
Inside the handle, the shaft has a couple of flanges on it to keep it in place and a cap which keeps it seated vertically, and between the two this couples the shaft nicely and avoids any movement. I would have to find some way to replace this mechanism for my build, which was going to dispose of the plastic shaft in favour of a much longer metal one.
The new shaft material was going to be 25mm steel tubing, the sort used to make clothes rails in wardrobes, which can be bought in most DIY stores at standard diameters of 19mm or 25mm. As it happens, 25mm is the exact diameter of the CH yoke shaft, so we’re in luck. I bought a couple of metres of this tubing, and a cutter to trim it with. I then needed a mechanism to keep the tube in place while allowing it to rotate freely, and – taking my cue from Ken Brand again – I ordered a set of pillow-block bearings. These will hold the tube firmly in place while allowing free – and smooth – rotation. These are the most expensive parts of the build so far at almost £20 each, but they are worth the expense. They’re also very heavy, which will give a nice feeling of weight to the yoke action. I decided to use a gear-and-chain mechanism to connect the yokes rotationally – the gear sprockets go on the end of each tube and a chain is strung between them so that when one yoke rotates, the other follows suit. I ordered the parts for this as well as some shaft collars.
Once I had the tube, bearings and sprockets on hand, I tried a test fit, and – disaster. The tube would not fit inside the bearing or the shaft collars. It seems that while the tube is supposed to be 25mm diameter, this refers to the inner diameter; the steel is only a mm or so thick, but even so this was enough to stop the tube from going through the bearings. There was no way to force the tube into place, short of cutting a slot all the way down the tube and curling it in on itself, destroying both its integrity and that nice brushed-metal look. To resolve the problem, I would have to think laterally.
I went out and bought an old-fashioned wooden broom, removed the head, and cut the handle into appropriately-sized lengths. Prior experience told me that the standard fitting for a wooden broom takes a 1-inch diameter rod, which is about 25mm but actually just slightly less. I guessed that the wooden rod would fit nicely inside the steel tube and bearings alike. I was right. The wooden rod I obtained fits snugly inside the metal tubing, and while not so snug inside the bearings – which were designed for 25mm rod precisely – is fine once the locking nuts in the bearing have been applied. My yoke shafts would be half steel tube – the half that sticks out of the front of the panel and looks good – and half wooden rod – the half that does the job behind the scenes. I would have to find a way to join them securely and without movement, but a good two-part epoxy glue, secured with a few bolts or screws, would do the job.
First of all, I took the disassembled handles and removed all the electronics from them. The switch and hat caps can be removed from the electronics, which is ideal as I wanted to spray paint them the same colour I was going to spray paint the yoke handle bodies – satin black, to complement the original powder finish but replace the drab gray colour and obscure the all-too-obvious CH logos. I then painted all of these with three coats of acrylic spray paint, which required a good 48 hours to try to a proper finish.
Once I had the handles nicely painted, I needed to find a new way to attach them to my steel tubing. The flange system used in the stock yoke would not work, but the plastic cap that sits on top of the tube provided an anchor point inside the handle and the flange on it sat nicely inside the steel tubing. I then drilled two holes through the plastic collar at the rear of the handle assembly and through the steel tube underneath, each hole being at 90 degrees to the other. Into these went a small bolt, with the nut being secured inside the tube and the whole thing bolted tight. This keeps the tube firmly attached to the yoke handle and doesn’t have slippage when turning, pulling or pushing the yoke.
Now I needed to find a way to attach the gear sprockets to the wooden rod. Originally, when the whole shaft was going to be steel tubing, the sprocket was sized to fit inside the tube and be locked in place by one of the shaft collars. With the new design a new approach would be needed. The sprockets have a 10mm hole in the middle for a bolt or thin shaft, so I purchased some 10mm masonary bolts. These are designed to anchor themselves in stone or brick walls and support the weight of an object bolted to the wall. I drilled a 10mm hole in the end of each of the wooden rods, to the approximate correct depth, and put a generous quantity of Araldite two-part epoxy glue in the hole, as it was important that the bolts not be able to rotate in the hole at all. 48 hours later the glue was set rock hard and the bolts set in the end of each rod. The sprocket then goes onto the bolt and a nut goes on top and is tightened to keep the sprocket fixed to the rod. For extra protection against unwanted rotation I glued the base of the sprockets to the wood, which does mean it’ll be very hard to ever get them off again, but I can’t see why I would need to.
With the handles attached at one end and the sprockets at the other, it was time to worry about the exit point from the instrument panel, where the yoke shaft emerges. A simple hole would work, but it would allow some lateral movement of the shaft and it wouldn’t look as nice as a designed solution. I looked first at using simple rubber grommets fixed into a hole cut into the panel, but then I realised that the hole would have to be placed extremely accurately, and my capability for mm-accurate drilling and cutting is almost nil, so I decided to have some kind of plate or box assembly on the yoke shaft itself, which would be attached to the front of the panel and would allow for a much less accurate and larger hole or square to be cut.
In the end I settled for buying two switch box blanking plates – plastic plates made to fit a standard light-switch or plug box to provide a cover for boxes not in use which might be used later. This has a nice curved front and screw-holes already in place. I took these plates, sprayed them the same black as the yoke handle assembly, and then cut a 30mm hole in each. In hindsight I should have done the drilling before the painting, because stray bits of plastic managed to scratch and remove flakes of paint and I had to re-do the painting.
The reason for using a 30mm hole is because I’m being sneaky and recycling a part from the original yoke casing. Inside the casing there are a couple of plastic bearings through which the shaft slides, and these are thus exactly the right diameter for our new steel shaft too. The bearings are simple plastic tube segments, about 10mm long, with a 3mm flange ridge around the mid-point. The width of the plastic plus the flange add up to about 8mm, so I was able to insert the bearing into the hole in the blanking plate, and using Araldite again, glue the bearing to the plate by the tube exterior and the flange, which also nicely covers up the edges of the holes I drilled. The end result looks rather like a purpose-made solution, which is nice.
The final step in the first part of the build was to fasten the steel tube and wooden rod parts of the shaft together. Before doing so I threaded the rods through the pillow blocks and the exit plates, as, once joined, the only way to get anything off the tube is to remove the yoke handle which, while doable, is a pain. In case your inquiring mind says at this point ‘but how are you going to get the wiring in?’, then full marks for being on the ball; but rest assured, I have a plan for that which will be revealed in a future post.
I’m now ready to start cutting the wooden base for the yoke assembly, and to start part two of the build. More on that in a future installment.
[…] an article about the yoke build for my new project, which supercedes this one in all respects, go here.) The classic CH […]