Trim Device With Proportional Controls

By Ed Bult
23 March 2010

If you like to fly airplane simulations you are probably using a joystick to keep your plane in the air. A good stick with trim options will cost you a lot of money but eventually it gets worn out and it will probably end up at the scrap yard. So why not buy a cheaper one without the trim options and build your own (USB) trim panel. Total costs about €45.

The components I've used are top quality and will last for years to come. As you can see on the picture I have built it in an air filter box. It was not a real air filter box but an accessory for on your dashboard to put your junk in. Of course you can use all kind of boxes or make one yourself, just keep in mind that it must be strong enough. The yellow knobs are the trim pots and as an extra, the orange are push buttons.

What You Need

4 potentiometers linear 100k and knobs preferably with a marking
4 push buttons (make contact when pushed)
Wire (I've used telephone wire, it is stiff, it is colored and you can slide it in the USB converter)
Game port to USB converter (not a plug)
A box to put it all in
USB extension cable

Tools I've Used

Soldering iron 15 watt will do
Soldering wire
Drilling machine and drills
Round file
Pliers
A pair of compasses
A multi-tester I've used it for centering the pots and knobs, but it is not essential.

Some Tips

To make this device you don't need to be an expert in electronics but if you read this and you have any doubt in making it yourself... don't hesitate to ask a friend, neighbor, uncle or whatsoever to help you or even make it for you. If you don't have the tools, borrow them. Be patient and take your time for it, haste leads to faults and in the end it will cost you more time and frustration.

The Connections

A game port connector uses the following connections (wiring):

1. +5v
2. Button 1
3. X-Axis
4. Ground
5. Ground
6. Y-Axis
7. Button 2
8. +5v
9. +5v
10. Button 3
11. R Axis
12. Midi transmit
13. Z Axis
14. Button 4
15. Midi receive

Wiring The Pots

Before you start soldering it is better to have your casing ready with the holes drilled of course. The dots you see on the diagram I've made are connections. The black wire on 4 is the gnd and is soldered at the metal casing of the pots. The red wire on 1 is +5v and must be connected on either the left or right pin of the pot. The blue wires are connected to the middle contact of the pot and going straight into the connector.

The Switches

Connect one side from each to the gnd (5) and the other sides to the connector (2,7,10,14).

Detailed Build Instructions

When you buy a game port converter it must have a switch with a wheel option; switched in this position you can use all pots and buttons. You don't have to worry about installing, it just plug it in and Windows recognises it as an USB device. Calibrate it, start up your game and add the new functions like rudder trim, aileron trim, elevator trim and in IL2 Sturmovic I even use a pot for the flaps.

When you start putting things together start with the box. Assuming it is large enough to put all the parts in, take the knobs and buttons (you can use some coins to for this) and divide them on top of the box. Now you can see how it looks when it is finished. Measure the center of the coins (measuring the distance between, for example, left sides of the coins) gives the same result. Take a piece of paper and draw the outlines of the box on it. Divide the measured centers inside the outlines of the box. Keep the distance between the centers even. Check it by putting the knobs (coins) on the paper. When you are satisfied cut out the box shape and put it on the box. Take a small sharp object like a nail and carefully make small dents on the center points. Depending what material you are using (for plastics I use a speed drill; if you use an iron drill run it in reversed direction) drill holes for the pots. Start with a small drill like 3 or 4 millimeters (not necessary when using a speed drill) then, depending of the diameter of the pots drill the final hole.

For the switches (the one I've used needed a hole of 18 millimeters) I've drawn the holes with a pair of compasses on the box, drilled them and used the file to widen up the hole.

   

You may be thinking that the instructions above are a bit exaggerated but, if you ever drilled holes in plastics you have undoubtedly noticed that it isn't the easiest thing to do and before you know it your drill runs out of center or even breaks chunks of material away. Be careful with this or your box will end up as scrap. Believe me it looks better when all is in the right place.

Once you have drilled the holes you can start wiring the pots and switches. Don't put them in the box yet, saw the axes of the pots to the right length. It is better to put a pot in its hole and hold the knob next to it, make a marking about 8 millimeters above the tiny screw from the knob (was perfect for my knobs but not all knobs are the same). First solder the middle wires on the pots. Be sure they are long enough, the same goes for the switches, each switch one wire. If you can reach the contacts of pots and switches with your soldering bolt when everything is in the box, you can put them in place now. If not, wait until all wires are connected before putting it all together.

Now take one piece of wire for the +5v and solder it to one of the pots. Lead it to the contact of another pot and on the place where it must be soldered remove a piece of insulation and solder it together; in this way you need just one wire for four pots. Do the same for the gnd of the pots and the gnd of the switches.

If you like you can center the pots and knobs. Take your multi tester and switch it to 100K ohms. Put a pin of the tester on the middle contact of the pot and the other on one of the outside contacts. Twist the pot axle until you reach a value of about 50 K ohms. Then put the knob on the axle with its marking in the middle and tighten the screw, or wait until the device is ready and connected and use the USB driver for centering. You can even do this from within the game.

Once you have all wires attached, you can put them in the converter. Remove a long enough piece of insulation, bend it a little to be sure it makes contact within the converter. Alternatively you can break (open) the converter apart and solder the wires to it. I've used some tie-wraps to bind the converter to the pots but you can glue it or use double sided tape for it. Don't forget to put the switch on steering wheel.

Ed Bult
thefootclan@chello.nl