Building The Yoke

I developed the toggle to momentary circuit for use with a yoke I was building. I got a lot of inspiration for the yoke and electronics from this from this how to. I really want to thank Roland van Roy for giving me so many great ideas.

I had several problems with commercially available yokes. The cheaper ones don't have the travel real yokes got, only about half. This applies to the pitch as well as the roll axis. 18 cm from full down to full up elevator. Aileron axis travel is 180 degrees from full left to full right, as measured in a Piper Archer. The expensive ones aren't much better. Exceptions are possible as I may have overlooked one or two. Usually the yoke is just that, and I wanted more features, more like some products which are becoming available nowadays. I wanted switches for battery, alternator, engine start, all the lights, gear, flaps trim, etc.

I needed some donor hardware. I chose a game pad Yes indeed...Not the first thing you expect to be a donor game control especially for a yoke. But the Logitech rumble pad has 5 axes, on 2 joysticks and one throttle. Plus a lot of buttons, which I could use for a lot of functions. And I had already used other Logitech devices. I want to stick to one manufacturer to prevent problems with drivers, etc. The rumble pad gave me one other very interesting possible feature, a stick shaker! The game pad has 2 motors in it with off center weights on it. If I would be able to incorporate this in the yoke I would have several nice gear or stall effects. I first tested the rumble effects with the device intact. After disabling the control forces I had a very acceptable effect. A little rumble on takeoff roll or after landing, a nice gear up thump and subtle gear down click and the stick shaker worked well in the jets. But that would be the icing on the cake!

Desk Layout

I've got an IKEA desk named Jerker. Fortunately it's not as annoying as its name would make you think. It is very adaptable. Height of all the level surfaces can be chosen or changed. I did not stick to one of the standard IKEA set-ups but figured out my own. The desktop is rather large and deep as well. I've got 2 monitors on it, one 19" and a 17" as well as my speakers. And plenty of space in front of the monitors to put my hardware or do my taxes

Figuring Out The Dimensions

The idea is to build a box to house the yoke rod and the switches. The box has to be easily installable and removable as well. Typing your mail etc. around a yoke tends to increase the chance of RSI. So size does matter. With a forward travel of 18 cm the yoke needs a lot of depth. The total length of the yoke shaft is more than twice this value because you need to attach things to it and it has to be supported. Real yokes in planes are just supported where they enter the instrument panel and where they are held by the links to the controls. This would take up too much space. The bottom of my monitor was about 15 cm above my desk top. I did not want to build higher than that. The yoke needs springs to be centered and simulate control forces. In 2 directions. This was the hardest part. To figure out a way to have all this travel and still build a compact housing. 25 cm deep, 45 cm wide and 15 cm high. Those were the dimensions I chose. The width was chosen to accommodate all the planned switches and still have access to them around the yoke.

The painted box with holes to mount the switches, etc. The wood used is 9 mm plywood.

Pitch And Roll Centering Springs

Roland van Roy had provided some nice solutions to connect the springs and potentiometers to a tube. A threaded rod is the heart of the yoke's rod. It provides a means to attach things like springs and the yoke off course by using nuts. On parts that need to be smooth a tube around the rod provides the answer. Pretty simple but you have to come up with it. Roland van Roy also had a pretty good spring solution but I did not have as much space so I needed to change the set-up somewhat. See his yoke here.

To save height I wanted to position the roll spring horizontally instead of vertically. Which was not a problem after all. Depth on the other hand was. A spring takes up a lot of space when not stretched. Mine had to be about 10 cm long unstressed to be able to extend to up to 30 cm total. This is needed to accommodate the 18 cm travel and still be under a little tension in full up or down position. I attempted to position the springs from left to right inside the box and use a cable to connect them via rollers to the yoke rod. It did not work well, the rollers caused so much friction that this was not a viable option. I tried a different approach, to place the springs diagonally. That way when the spring is not under tension it is parallel to the front or rear of the housing. When fully extended it runs diagonally across the box.

This diagonal spring set-up saved me a lot of space and I could get a travel of 18 cm in a box with outside depth of 25 cm (the wood is 9 mm thick). Also the spring was able to be extended in full up or down deflection without being over stretched while still being under a little tension in the other position. It did cause a bit more friction in the rod guidance, but I came up with a solution for that. More on that later.

Roland used a threaded rod to attach everything to; this seemed like the way to go. Nuts can be modified and turned into mounts for all kinds of things. The pitch springs will be attached to a bolt in the middle of the yoke rod. This bolt serves more functions. It will also be used for the roll spring and the link for the pitch potentiometer. All this on one bolt? By soldering a plate to it you can enlarge its surface and provide a space for all kinds of things, and you can solder threaded rods to it as well.

What's The Big Idea?

The whole things comes down to this:

The yoke rod consists of the threaded rod on the inside and an aluminum tube on the outside. (I am now thinking of replacing it with chromed steel for a smoother feel and less wear.) Nut 1 holds the tube in place as well as nut 2. Nut 2 also has a piece of threaded rod attached to it which in turn is connected to the roll spring. Nut 3 has been smoothed on the inside so the threaded rod can move freely in it. There are two pieces of rod attached to nut 3. One to connect the pitch springs and the other which runs along the guidance bar. The roll spring is attached to this bar as well. The guidance bar prevents the rod with the roll spring to turn but lets it move back and forth. The blue lines are nylon spacers to let nut 2 and 4 turn smoothly against nut 3. To let the yoke rod move smoothly I used nylon rings where the rod enters the box. These are mounted on the outside of the box.

This is nut 2 with the roll spring.

This is nut 4 with the plate and rods. The hole in the plate is where the roll potentiometer goes. The roll stops are also visible. These stop the rod on nut 3 from going too far. On the bottom you can see the connection and part of the pitch potentiometer strip. If you look close you might see that the inside of the nut is smooth.

A Bit On Soldering

I did not use copper or silver to solder these parts even though they will take some punishment during their lifetime. Don't work hard, work smart is the key here. I drilled holes in the nuts to fit the 8 mm rods. These are copper alloy ("Messing" in Dutch) which makes them relatively easy to work on and soldering it is pretty easy as well. I used a small blowtorch to heat the parts and regular soldering alloy. The biggest challenge was to solder the plate to nut 4 wile the rods were already soldered. Using just enough heat to solder the plate but not melt the soldering on the rods. But it worked. Before inserting the rods in the nut you have to make the end match the inside of the nut.

The Result

Here's a picture of the assembly.

The gears are some kind of nylon-like plastic. I had to enlarge the holes in the gears, which is hard to do if you have to drill a 12 mm hole. The hole has to be in the middle otherwise the gears will wobble. I failed. So I had to fix it. I modified a washer to hold the gear on the yoke rod centered. The hole for the potentiometer axis was made just a little too small so it does not need additional fastening.

This shows the gear wheel and the tapered washer to keep the gear wheel centered.

This is the guidance bar. The notches are where the roll spring is attached. To let it run smoothly I used 3 small ball bearings (not visible). Two to prevent it from moving along with the roll of the yoke. These are adjusted so there is no play but no extra friction either. The guidance bar does not need lubrication but needs to be clean. The third ball bearing is used to counteract the pull of the pitch springs. That one is just visible on the far side. It can be adjusted by turning the bolts on either side of the aluminium plate. The guidance bar needs to be exactly parallel to the yoke rod for it to work.

The completed yoke box. Rumble pad and toggle to momentary circuit board on the left. Game pad and a second toggle to momentary circuit board on the bottom on the right. The pitch spring set-up can be clearly seen. The pitch potentiometer sliding strip can also be seen.

The Yoke

The yoke has a nice story to it. I asked a guy with an aircraft parts shop if he had any yokes. Well he did but they were all Cessna. I wanted Beech or Piper because I am not a Cessna fan. I got my PPL and CPL and IR on Cessnas but I prefer Piper singles and I flew a lot on the PA31 Navajo. I do like the Cessna twins by the way. A few days later he came by at the flight school where I worked and held a Piper yoke in his hand. He told me it came from a Piper Navajo, one that had been damaged in a storm. I knew the plane because I had flown it. I had a model of it and a picture on my windows desktop, now I had the yoke!

So to make a long story short I used a real Piper yoke for my project. It was the most expensive part but well worth it. It had a tube fixed to it which had to go. I made a round wooden block to fill the hole and made sure it was a perfect fit. Attaching the threaded rod was a bit harder. I needed heavy duty washers to keep the wood from being crushed. The whole thing needs to be firmly tightened so it does not give way when under stress from the roll spring.

Shown here is the yoke with horn extension on the left horn. Also the telephone type cables which provide the connections for the buttons on the yoke are visible. An external solution may not seem very tidy but it can be found on most real GA aircraft with buttons in the yoke.

Shown here is the other side of the yoke. The washer is clearly visible. The connector is still on the telephone wire; I use it for easy disassembly or maintenance. The female type is installed in the box.

A/P And Trim

I also wanted to have a pitch trim function, A/P disconnect, and f/d pitch sync on the yoke and I had to do something with the rumble feature...The buttons did not fit in the left horn of the yoke where they should be so I made an extension to the yoke's left horn.

This was made from copper alloy sheet. I was kind of proud after finishing this. The hole in the front side is for the original push to talk button which I installed but it is not functional. On the top are holes for the a/p and f/d functions. The big hole is for the pitch trim.

Rumble Feedback

The hole in the yoke which is visible 2 pictures back seemed like the right place to put 1 of the 2 the rumble feedback motor from the rumble pad. This hole will be covered by the Piper logo. The motor had to be removable to have easy access to the nut inside the yoke for adjustment or tightening. I made a wooden block to hold the motor. The total assembly has a tight fit in the yoke and the Piper logo is taped on the yoke using thick double sided adhesive tape. It used to be glued. The wiring runs through one of the 2 telephone cables. The rumble pad had 2 motors, one with a heavy weight and one with a light weight. Because I only use the motor with the heavy weight I connected it to both of the motor outputs of the rumble pad.

How To Keep It On Your Desk

I never gave it much thought how I would mount it on my desktop and keep it from moving. Then I thought that clamps used to keep glued wood etc. together would be a good idea. I bought two of these. I flattened the top part of them so they could be bolted to the side of the yoke box. I shortened the clamps and the handles after the project was finished. They can handle very thick desks. Even the ones with those annoying steel beams under them. I added a wooden strip under the front side of the box to tilt it back a little. It's only fixed with double adhesive tape and can be removed when necessary. After I had painted it black it added a nice touch to the overall appearance.

Monitor Mounts

To allow for the long yoke rod I had to get rid of my original monitor mount. I built a very simple U shaped wooden one to replace it. This one leaves room for the yoke rod to move under the monitor. I glued felt to the bottom of the mount so it slides easily on my desk without scratching. I move my monitor forward against the back of the yoke box for a nice cockpit like feel. I made one of these mounts for my second monitor as well to be able to slide it with the same ease and keep the lower sides of the screens at the same height.

Ready At Last

The yoke after the completion, I would add the extra switches at a later stage.

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