Stick and Rudder for flight simulator

Stick and Rudder for flight simulator

Flight simulators are great training aids for getting your private pilot's licence (PPL). However, light aircraft are flown by the seat of the pants they say. Some realism is necessary, especially when it comes to flight controls. I think the most important to master is the rudder control. The joysticks at the shop may be good, but the twist grip for the rudder will not get you far in terms of practice. With that in mind, I built this stick and pedal set in 2010. 

Stick and pedal set general view.

This was designed to be built from readily available materials at the hardware store, plus a few RC model parts. You can build the electronics, or use the internals of an unused PC joystick. Some soldering will be necessary. One note, the pedal set is hinged to the bottom frame, and is not horizontally movable as in the Saitek pro rudder pedals. However, they do work in unison and have stops.

Let me begin with the stick. which looks like this:

The stick. CD is for size comparison.

 The stick is built onto a piece of wood shelving base. At the center is the gimbal assembly. Around the gimbal assembly are the four springs for centering, and in the front are the electronics and the "throttle lever". The grip is from an ancient DK Tronics Joystick for the Sinclair Spectrum. Its push buttons are not wired due to ignorance.

The gimbal assembly, centering springs, electronics and "throttle lever".

Here is the gimbal assembly. I took the trouble to build it with coinciding pitch and roll axes to make it feel "real". However, many aircraft do not have this ideal kinematic setup, and frankly, during use, especially a few minutes into the flight, you would hardly notice the difference. Anyway, the gimbal is built onto a 3mm thick aluminium plate. It was difficult to find small mountable bearings to fit in the small space, so I used industrial ball links sized to fit 5mm threaded rod. This rod was used to build the gimbal axis shafts also. The gimbal is mounted on two short aluminium tubes to the front and back of the stick. 

The potentiometers are mounted on aluminium brackets, which is screwed to the gimbal plate.  Some plastic tubing connects the ends of the gimbal axis shafts and the potentiometers. Make sure to choose fairly hard tubing, because the potentiometers have grease in their bearings to increase the viscous friction. This and a soft tubing means the pots will not respond well to fast stick inputs.  Make sure to select the "A" type potentiometers; the linear kind. The "B" type pots have a nonlinear angle to voltage relationship and are not suitable. Do not worry about the direction of rotation at this stage, it will be adjusted from within the simulator.

The centering mechanism consists of flat springs, attached to the base using corner support angles from the hardware store. They are set at an angle to the pitch and roll axes, but this is only to make it easy to fit. The springs themselves are iron saws, again from the same store, cut in half. Normal spring steel would be quite difficult to cut and drill. However, these saws only have the edges hardened, and softer centers, so they are not too difficult to drill into. They connect to the stick using large RC model rudder horn hardware, including some ball links. I could not find good ball links of the correct size, and those that are installed have some play in them. This is not acceptable, because every time the stick passes through neutral to the other side, you can hear and feel them click.

Finally at the front is mounted the small circuit board for the electronics, a USB PC joystick emulator. It is an open source project RC Joy NG^2. The original project website is nowhere to be found recently, but the ghost of the project can still be seen on the Internet. The board is fully configurable so that you can select which analog inputs are used for which control etc. Obviously the pitch and roll axes are on board. The throttle control is also connected to this with a long cable, and is nothing but a bare potentiometer -"A" type-, a galvanized corner support angle for mounting, and a plastic lever to make it easier to turn. Finally the pedal set is connected to the stick by a connector.

Some detail shots of the gimbal assembly follow:

Close up of the gimbal assembly. You can see how the ball links that support the pitch and roll axes are arranged, the potentiometers and how the potentiometers are connected to the axes.

The "throttle lever". Nothing but a potentiometer and angle support to which a plastic lever is glued.

This shot shows the centering mechanism. The mounting brackets, iron saw "springs" and connecting rods to the stick can also be seen. All from the hardware store and RC shop.

Next let us have a look at the rudder pedal set. The pedals themselves are made of 15mm shelving wood, cut to approximately the size of my feet. They are mounted on the same material wood base using window hinges (those used in plastic window frames) . They are strong enough to take a beating. Galvanized brackets at the bottoms prevent feet from slipping off.

The pedals are connected to a see-saw bar, as seen to the right in the above picture, which is also made of wood. However it rotates on a simple bushing to reduce the friction.

The connection between the pedals and see-saw bar are made with small industrial ball links to take the loads, and hardware store galvanized brackets attach everything together.

Close up of pedal to see-saw bar. The black hex bolt goes through a bushing that is hidden from view and threads straight into the post below.

 The rudder position potentiometer is conveniently attached to the carrier post for the see-saw arm,  and connects to it through a plywood horn and pushrod. This arrangement has some benefits: It is easy to change the ratio, simple to mount the pot, and easy to keep the heavy loads away. I used ball links to avoid play in the mechanism.

 Rudder centering springs are also from the hardware store, along with the galvanized brackets for attachment. There is a subtle twist; I ran ropes through the springs to act as stops. Even if you press hard, the spring will only stretch up to a certain extent. This is especially good during calibration.

 Finally, the whole bunch together. The stick just sits on top of the pedal set with some anti-slip pads. This makes it easier to take apart for storage. Here is a video of it in use with X-Plane 9, (notice the "Attitude Visualizer", the plastic plane in front of the screen which is the subject of the previous postprevious post). The plane in the simulation is, well, a Cessna 172...

 How does it perform? Basically it is good. It fulfills my expectations well. I can now use my feet and get a feel for how they control the airplane. There are a few points worth mentioning for prospective builders though:

• The range of motion of the stick is small by definition. That means the stick potentiometers turn very little. If I would redesign, I would connect the pots higher up on the stick and connect them like the pedal pot. This will give more motion, and thus better resolution.
• The centering force is not very large. Near the center the force diminishes. This is inherent from the design of the springs. Hobby shop joysticks use a different (and simpler) mechanism for centering. The same can be said for rudder pedals. Near the center the force is very small, which can cause unintentional slips.

You may also be interested in my DIY aviation altimeter post, which describes how you can build a full functioning digital altimeter with QNH setting, from this link.

If you are interested in the small model airplane in the video that moves in sync with the simulator, you can find it explained in another blog post of mine, at this link.