Adding force feedback to home-build yoke

[Guest]

Below some info on how you can make your home-build yoke feel more realistic. Most force feedback joysticks use small electro motors that will try to move the stick in x and y direction via gears. The electronics of those sticks can be used for adding the same thing to your yoke. To make it feel realistic, the forces need to be much higher (esp elevator). I bought a Logitec Wingman Force 3D (USB),opened it up and measured & tracked the electronics diagram. (See below simplified diagram) This stick uses 100K potmeters for the 4 axis, so connecting your external yoke potmeters for elevator, aileron, throttle and rudder is no problem. The totally 11 switches are in row/column style, which can be copied and connected to your yoke switches as well. The two little motors for x and y axis are driven by a dual H-bridge IC that gets its x and y info from a micro processor. Via the PC software, the potmeter position and the motors form a closed loop servo system. More or less stiff spring action is for example obtained by increasing or reducing the loop gain. Moving elevator trim shifts the center voltage of the servo system. Effects are added in open loop. Works simple and reasonably well.The dual H-brige sends out normal and inverse signal to each motor lead. Motors are 82 Ohms so the driving current is limited, the IC already gets hot during normal stick operation. To drive external motors you need to add some kind of current buffer. For elevator I used a medium size motor 30V 5A or so (from the dump). It moves the yoke shaft in and out via 0.8mm steel wire. See picture. Experiments showed that I needed around 12V to get a good force feeling. Remember that you are operating the motors in stalled condition. Current will even rise when pulling the yoke against the force. I got 3Amps max.For the roll movement, I added a smaller motor (from old VCR)on the yoke shaft that rotates the yoke via 0.5mm steel wire over a 50mm disk on the yoke rod. see other picture. This motor needed 18V to get good feeling. The Logitec stick gives an external 24V adapter for the H-bridge IC. I used a 18V / 4Amp brick to supply the IC and external current buffer. The 30kHz PWM signals of the H-bridge IC are averaged to get DC voltages that drive the current buffer. The current buffer is a medium power OP driving two power transistors in class B operation. It may seem somewhat power consuming, but DC operation is much easier than 30kHz PWM. I added some attenuation in the elevator drive to get the forces more even.One side note: When you are pulling the motors against their torque, there is a slight uneven feeling as the brushes pass the different contacts. The original stick had the same problem. Using motors with more brushes and contacts will help. The PWM signals can also be used for adding other effects in for example chair shakers or motion platform. Works with all games that support force feedback. Logitec stick cost me US$ 45. The stick w/o electronics can still be used when connecting the potmeters (via shielded wires) to the game port. Of course only 4 switches are supported then.RgdsRoland

[Guest MikePowell]

Most impressive, Roland. Your productivity in this hobby is amazing. This, especially when one considers that your projects are technically challenging.Are you using the existing drivers (software) from the joystick, or are you developing new code?Mikewww.mikesflightdeck.com

[LawnDart 19]

Nice work! I have been looking for a FF design and this may be the best approach.One thing that concerns me though about this particular design is heat dissapation. In a free-spinning design, the motors provide their own cooling, however in this setup the rotors are stationary, with some substantial current on the windings, leading to heat generation. Assuming that in cruise flight, the controls will be 'tight', which means that the amount of current (Heat) will be greatest during cruise.With the motors mounted as they are, I fear they are too close to the wood supporting structure... if they overheat you may have a serious problem on your hands!Just my $.02Ray

[Guest]

Thanks Mike. I really enjoy building electro-mechanical structures, just from the stuff I have in my junk box. (actually several junk boxes) ;) I'm however no good at software, so I used the original drivers of the stick, that allow tweaking the FF settings. RgdsRoland

[Guest]

Hi Ray, You are right that motor heat needs to be carefully checked. The elvator motor dissipates around 36W, but that's only when you pull against the torque. (like pulling up from a dive)Stationary flight will give about 15W before trimming, and around 5W after trimming. Temperature for the (big) elevator motor is was no problem.The smaller aileron motor does get hot, (aound 60 degrees C on the body) even though it only dissipates around 12W max. I'll probably add some fins on the body and use a small CPU fan for cooling. It is not directly mounted to the wood, so that should be OK. The current booster dissipates around 20W at times, so a big heatsink as on the picture is required. (not the most efficient and cost effective solution, but is was all junk anyway, and hey this is hobby, not work) :-) The 18V brick has a 4amp current limit build in, so I don't expect fire hazard. RgdsRoland

[Guest PeterK]

PeterKRoland..I work on electronics all day...You got me..Im impressed!pete

[Guest]

Ronald, This is a WOW! That's the most impressive, and thanks for sharing your work. I must confess, I am a little envy of you. As matter of fact I am planning on mounting a stepper or servo motor for dual yoke, using x and y axis along with H-Bridge/PIC circuits. This is in purpose for force feeback and auto yoke control when enaged autopilot. I betcha it's going to be a lot of work huh? I was told, bigger servo that handle less weight structure produce less magentic heat effective, maybe a bigger servo would be a solution, but it wouldn't be able to fit, or mount in underneath the cockpit. Plus it's $$$$.... I am still researching on those details maybe later on my ideas will just appear in my mind. Again, this is a nice pieces of work Ronald!

[Guest]

Arthur,I'm not sure stepper motors are the best solution for force feedback. You can control movement very precise, but are they controllable in closed loop as a servo motor-potmeter combination (where you'll force the motor out of the center point?) When turning a stepper motor rotor, you can clearly feel the rotor angle "jumps". This might make the feeling of the yoke less smooth. Just some thoughts, as I have not experimented with steppers yet. On the size motors: The one I have mounted for elevator is definitely strong enough to give you the right feeling: At full power 14V / 3.5A I could hardly pull the yoke. The travel/rotor rotation ratio also plays a role. Steel cable + pulleys are very convenient for controlling motion. BTW, someting similar can be done for rudder pedals. But then the FF power needs to be increased, as your legs are much stronger. RgdsRoland

[Guest]

Hi Ronald, *GASP! Did you say, Servo motor-potentiometer? rotary style?That's what I've been looking for since lately, I couldn't find any of these when I go through so many electronics manufacturer or through webpages, I only found the sliding potentiometer-servo motor. It wouldn't have a good mechanical strength to attach to yoke(s). This is why I go on with another option using stepper motor with gears attached to regular 100K ohms potentiometer. Would you be more than happy to give out the manufacture's name that creates the servo motor-potentiometer I would love to order 2 of them. 1 servo motor-potentiometer would be good for X axis Yoke (Yaw L/R?) and other one would be for Y axis (Pitch U/D) if you come up with idea, please share it out with me. I'd appreicate that = )

[Guest MikePowell]

This is such an interesting thread, I just have to add my two cents worth...There is a type of AC induction motor called a torque motor that should work well for force feedback. On a standard AC induction motor, the speed-torque curve tends to drop with increasing speed. A torque motor is designed specifically to flatten this torque to speed relationship, aiming for constant torque over a broad range of speed. Torque motors have been used for applications like reel motors on large tape recorders. The bad news is that torque motors are relatively specialized beasties, are not made in the same large quantities as standard induction motors, and therefore are rather more expensive, not to mention hard to find on the surplus market. Using a standard induction motor in service as a torque motor suffers from at least two disadvantages. The torque varies with speed, and the motor current, and hence power, rises at low rotational speed. In a home brew sim, however, neither disadvantage may be an issue.The variation in torque may not matter because the motor is generally operated stalled or very nearly stalled. The variation over that small a range of RPM probably won't be noticed.High motor current can be addressed in several ways. First, limit the current. You're not going to want full torque all the time anyway. Second, use a larger motor for better heat dissipation. For example, open frame washing machine motors which appear to be somewhere around 3/4 HP, and/or motors from moderate size fans, which I think are about 3/8 to 1/2 HP. A third way to address the effects of motor current is to use a small fan to blow air through the motor.AC torque motors offer fairly smooth action throughout their rotation without brush-induced variations, or cogging due to magnet to pole face interactions. The down side is that they must be driven with an AC power source. Options might include using an automotive audio power amplifier (if it goes on sale) or a PIC based pulse width modulated scheme.This scheme provides tha possibility of rapidly varying the loading on the controls. You could, for instance, reflect the effects of turbulence in the controls. This is pretty attractive, but occurs at the expense of an involved, expensive control loading system.If only slowly varying loading is acceptable, a rather cheaper solution is possible. Use the standard spring set up for loading, and couple the springs to a lead screw arrangement so the loading can be made tighter or more loose using computer control. The would allow the feel of the controls to be varied with airspeed, but would not be rapid enough to inject turbulence into the control loading. The lead screw could be rotated through use of a stepping motor, or by using the motor and gear train from an electric screw driver.Incidentally, threaded rod with a standard thread tends to become a bit sloppy as it wears when used in repetitive motion applications such as lead screws. A more robust thread called an "Acme" thread will last longer. An Acme thread leaves more metal between the grooves for more stength. The gives the threads a flat top appearance. Acme threaded rod and nuts are occasionally available from a good hardware store. They can also be mail ordered from outfits like Enco www.use-enco.com Well, I guess I'm way beyond just two cents worth. Once again, Roland, an excellent project and thanks for telling us about it. If I had access to your apparently fantastic junk yard (which I am greatly in envy of) I might well be considering another approach to control loading. Mikewww.mikesflightdeck.com

[Guest]

Arthur,Sorry, you got me wrong: By motor-potmeter servo system I just meant the usual electro-motor that drives a structure where the potmeter is used for position feedback. However, in a yoke force feedback system as mine, the potmeter could be very well directly coupled to the motor axis if you use multi-turn pots. My motor rotor makes less than 10 turns over the yoke movement, so a 10-turn pot would work well. Of course, no slip is allowed when using this setup, which is guaranteed when you use the steel cable drive structure.The below circuit shows a power servo control circuit suitable for medium power DC motors (up to 30V/10A or so)that makes use of a servo control IC found in radio control toys. Normally these need 1.0 - 2.0 msec pulse for position setting, but with the modifications as shown, you can use 0 - 5V voltage input for driving. I originally intended to use this circuit for my motion platform, but the system has one drawback: The IC's work at low PWM frequencies (50 - 100Hz) which makes audible noise. In my platform it souded as if I was drilling into the wall :-lol For smaller servo systems it could be quite useful though.Roland

[Guest]

Indeed a nice subject, isn't it? Mike, thanks for your in-depth explanation of various motor configurations. Did you happen to be a teacher in electronics of some sort? ;) I think I got a few of those induction type motors lying around: They are used in pen recorder systems. I couldn't resist my curiosity when I saw a 3 channel unit on the dump, so stripped the servo system and electronics to check it out at home. The two motor windings are driven with 90 degree phase lagging sine waves that go up in frequency as the torque needs to increase. The electronics are not that complex, two OP driven bridges, driven an oscillator with some feedback, that's it. The induction motor scheme indeed gives very smooth control (in pen recorder you could not allow cogging action ruin the resolution, right?)BTW, if the force feedback system isn't fast enough, turbulence effects can easily be added by placing small tactile transducers on the yoke at the right positions. You could drive these either AC coupled from the FF signals, or from audio channels. (Described in my DIY cockpit controls doc in the library) http://ftp.avsim.com/library/sendfile.php?DownloadID=13666The junkyards in Taiwan here are indeed a fastastic deal. The rather sad background is that the economic downturn is hitting Taiwan pretty hard; :-( many production lines are closing down (most companies have already moved all production to China). This ofcouse leads to lots of industrial stuff getting junked....Roland

[Guest MikePowell]

Roland,The bulk of my career has been spent as an electrical engineer working in academic and industrial R&D labs. Both are good positions for being involved in a wide variety of systems, not strictly limited to electronic. I am now in the happy position of focusing on hobby projects.Mikewww.mikesflightdeck.com

[Guest firmo]

Hi Roland,Thanks for once again providing information on how to make things for a home cockpit.I hope you will have the time to do a more detailed document on adding force feedback to home-build yoke.I do have a question though.Is it realistic to have a yoke or joystick jumping in your hands and resisting every move you try to make?I think a good feedback on the yoke would be just the following:a) on Taxi: a small vibration;:( On rotation: no more vibrations of any kind, until,c) On landing: a proportional vibration to how hard the landin was.The above appears to be (to me that is) more realistic and easier to implement. However I have no idea from where to take the appropriate events to drive (perhaps) a tactile transducer.Any comments?Best,Firmo

[Avcomware 1]

Hi. Add to that:1-Lazy 8s, if we could simulate these forces we would have it made.2-Stalls.3-Steep turns 4-Chandelles etc. etc. Making a realistic feel in a force feedback is one of the most difficult things to achieve in a Simulator. Even the Million $ sims have a problem with that. I find it frustrating in using one because they are so limited, and maybe I am a bit too critical. Keep up the good work. TV