Force Stick Mark III

By Paul van Dinther

The Force Stick is clearly a subject that interests a lot of people. I decided to write this third article and explore the possibilities of the Force Stick a little further thanks to the excellent feedback I received.

The most significant change is suggested by Fredrik Thörnell. He suggested to allow the PC to control the electrical trim. Now an autopilot function in the software can create a real loop involving the actual control (like in real light aircraft).

Following that thought I decided to implement electrical Roll Trim as well. Electrical Roll Trim would serve two purposes. It offers a way to properly mechanically center the yoke as the springs can cause a slight error from the center. And secondly it can also be driven by the software.

A second good idea from Fredrik Thörnell involves the repositioning of the springs in such a way that the roll centering force would be somewhat increased and thus ensuring proper centering.

The Force Stick Yoke concept now exists in three flavors and the fun thing is that each step does not have to exclude expansion to the next.

The Basic Force Stick is based on a single bracket with the springs acting on the central shaft. The pilot can apply control inputs but can not mechanically trim.

The Trim Force Stick is based on a double bracket concept (article two) and adds electrical trimming to the functionality.

This latest design will add a third bracket that will allow for Roll Centering. Since both pitch and roll trim are electrical it is possible for the PC to command those trim functions and thus fly the aircraft on autopilot with the actual yoke in the control loop.

The above picture show a Mark III Force Stick with neutral trim and no forces applied. We have the Frame Bracket on the outside. This bracket is stationary and mounted to a fixed platform. The next bracket is the pitch bracket and can travel forward and backward using a thread driven by an electrical motor. The yellow bracket is the Roll Bracket. The springs are attached to the Roll Bracket. The long yellow rod is driven by an electrical motor and drives the yellow roll bracket to tilt left or right. The yoke will follow because the centering springs are attached to the Roll Bracket thus moving the natural roll center. Roll trim can be used to center the yoke or can be commanded by the simulator software just like a real autopilot circuit.

I am not quite sure about the positioning of the roll motor. It can also be mounted on the Pitch Bracket thus reducing complexity. On the other hand it is nice to have both motors together at the back.

Currently I am examining ways of using the gameport's Midi capabilities to get the autopilot trim commands to the Force Stick. Advantage of using Midi is that there will only be one interface cable. An additional power supply will be required to drive the electrical motors.

Now I need someone with a good idea in how to pickup the central rods displacement and rotation because that is what this is all about.

Paul van Dinther
dinther@geocities.com
FreeTrainer Forum
Read Article 1
Read Article 2

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