737ng Yoke Force Feedback Mods...

[sagrada737]

Hi Guys,

I wonder if anyone has modified their 737ng Yoke/Rudder System for "Force Feedback".

Has anyone modified a MS FF joystick for this capability with their sim project?  The spring loading/gas shock setup gives such a static/passive feel to the yoke.  Seems like force feedback on the yoke system would add greatly to the sense of immersion.

BTW - The utility "fs-force" really takes the "clunck" out of the MS FF joystick, giving it a much more realistic feel on the ground and in-flight.

Mike

[fordgt40]

Mike

Two links here. One with a mechanical solution ie actuators/springs/cams. The other using electronic motor control

http://bffsimulation.com/index.ph

http://www.737flightsim.com/737center.html

David

[sagrada737]

Hello David,    Thanks for the comments and links.  Interesting information - especially the 737ng system of artificially loading control forces.  The cam system adds an additional dynamic over the more common spring only centering approach.

Regarding Motion Platforms:  I wonder if anyone is experimenting with Inverter Drives for motor control.  These units offer low cost 3-phase dynamic digital control of start/stop, direction, acceleration and terminal velocity.  I wonder if this simple digital interface control could be applied to existing sim software compatible with FSX for controlling a 3-DOF platform system?

I use this type of inverter driver control system in my robotic observatories for dome control, which moves a 3,000 lb. steel dome structure.   I think these kind of Inverter Drives (with their reasonably fast response times) could be applied to a motion system (as perhaps they probably are) given the fairly slow axis roll movements of a 737ng "heavy" type of aircraft in normal flight modes.  I would guess that the simplicity of a inverter driven motor/gearbox reducer/lift arm would suit this kind of motion solution if it would could be interfaced with current FSX motion control software (such as what 737flightsim is providing).

Any thoughts on the above?

Mike

Mike

[Maurice]

Hi Mike,

Based on all your highly technical questions, it sounds like you'll never be happy unless you end up with a Level D simulator (like a few others around here)  . So my advice to you is to forget about building and start saving for a CAE simulator instead  .

I'm just kidding of course. I could have saved myself a lot of aggravation by more careful planning at the beginning, much like what you are doing.

Maurice

[sagrada737]

Hello Maurice,

Thanks for the heartfelt comments.  I know exactly what you mean, as I have been down that road a dozen times before with various projects.  Maybe we should go out and buy the real thing, but we always think we can build it for less, or customize it better, etc.  There is no end to the stuff that dreams are made of.  The only caution is not to share too much detail with your wife as her eyes will tend to glaze over :-)

Regarding technical stuff...  It only becomes technical if you don't know what you are doing :-)

Since I clearly don't know the ins and outs of a 737ng sim as yet, it surely is technical to me at this point in time.  However, I love solving problems, as I have been swimming against the corporate tide most of my life.  Amidst the confusion, there is always a way to procede, the biggest problem is deciding which way that is - especially when there are multiple forks in the road.  If you don't know where you are going, then it doesn't matter which way you go.  Hence the need for planing.  All this points to is the need for realistic planning and discernment.  With regard to my sim project, it make good sense to follow what others have found to work, and innovate where possible to add that personal touch we desire in anything we do ourselves.

Experienced sim-builders like you and others can see the pot holes a mile away.  Newbies like me have to be a little more careful, hence all the questions.  I see this all the time with my other passion, which is CCD Imaging of Deep Sky Object using my robotic observatories.  Guys come along all the time and want to jump in, not realizing just how big the learning curve really is - or the high cost for that matter.  In that regard, I see their aspirations and try to guide them the best I can - much like what is going on in this Forum, where most everyone is civil and very helpful.  There is a lot of joy in helping others.

My approach for this kind of project is to typically push the limits (virtually) and consider what the possibilities are or might be - then throttle back and establish a plan that seems realistic for the resources at hand, plan for the best outcome - then cut metal.  I'm guessing that the "No pain - No gain" expression applies to home cockpits as well, and I suspect that most experienced sim builders would do a lot of things differently given the chance to start over.  But that process is what makes anything worthwhile in the first place.  We tend not to appreciate that which comes easy, and we take for granted that which we did not earn.

As I think you have pointed out in previous posts...  there is a great sense of accomplishment along the way.  I have just started my project and all I have right now is a pile of monitors, a couple of computers, and demo 737ng software, but I'm as happy as a clam flying this disjointed collection of hardware and telling my wife "Look how cool this is!".  Yep... I'm looking forward to every step down the road toward building up my 737NG Home Cockpit.

Thanks again for your kindness and responses on this Forum.

Mike

[fordgt40]

Regarding Motion Platforms:  I wonder if anyone is experimenting with Inverter Drives for motor control.  These units offer low cost 3-phase dynamic digital control of start/stop, direction, acceleration and terminal velocity.  I wonder if this simple digital interface control could be applied to existing sim software compatible with FSX for controlling a 3-DOF platform system?

Mike

Indeed they do My motion base (recently sold, but that is another story  ), used Emmerson inverters to control some big AC motors with even bigger gearboxes. You do not need a fast physical response in pitch or bank, however, "heave" or yaw/sway will require a fast reaction, if you need these freedoms. As ever, the issue is software control, as you cannot buy separate motors/controllers and off the shelf software. FSX through FSUIPC provides the acceleration vectors and Gforces that are needed. A further factor to consider is that the dynamics of a cockpit responding to a motion base is considerable. Imagine the moments of force arising from an overhead panel weighing probably 40/50lb or the TV`s/projection screens which would be outboard of the cockpit. Some hefty steel framing is desirable 

Just some thoughts

David

[sagrada737]

Hello DAvid,

Thanks for the constructive comments on the motion platform/Inverter Drives.  I'm sorry you had to depart with your motion base.  From the photos, it seemed like a nice piece of gear, although quite massive.   I'm not sure that the typical 737ng home cockpit would require anything that robust as the total mass is probably less than 700 Kg.

Thanks for confirming the roll response requirement.  I agree the the movements applied to the various moments within the flight deck could provide some interesting force vectors.  As you pointed out, the Overhead systems would need to be secure enough to withstand a vertical shock, not to mention an attached display screen system extended off the flight deck.  Also, I concur that a steel framework would be preferred to support the flight deck.

In any case, a motion base is a considerable project in and of itself.  Not something I plan on tackling in the near future.  However, I will most likely construct my Base such that it could accommodate such a system in the future.

I wonder if the motion software developed by the folks at BFF Simulator Force & Motion could be adapted/interfaced to the Inverter Driver scheme?   Is anyone using their software/hardware?

http://bffsimulation.com/software.php

Have a great 2013!

Mike

[fordgt40]

Mike

If you want "heave" then the forces required to accelerate the whole cockpit at a speed where you sense the movement are quite considerable.
With regard to bffsimulation site, I did actually ask them if they could do anything to link my base with their software/hardware controller. I got a polite and considered reply saying sorry it would not be cost effective.

David

[sluyt050]

Besides the spring/gas damper loading, Rev. Sim. makes a yoke that simulates elevator trim loading. Probably I will go for that in the future. (ref. http://www.revolution-jetstream.com/Gold_Line_Yoke.html).

[MLeavy737]

Elevator trim loading???  I have to say i dont understand the logic or use for that..

Mike L

[Garys]

Me either. I think what they are trying to do is get the yokes to move with the autopilot?

Gary

[fordgt40]

I thought that when flying in manual mode, if the trim is not regularly adjusted to suit the changing configuration, then the yoke becomes heavier to maintain the desired attitude. This perhaps what is meant by "elevator trim loading", ie it mimics the "heavier" controls arising from being out of trim, until it is corrected

There again perhaps I know nothing

David

[sluyt050]

I thought that when flying in manual mode, if the trim is not regularly adjusted to suit the changing configuration, then the yoke becomes heavier to maintain the desired attitude. This perhaps what is meant by "elevator trim loading", ie it mimics the "heavier" controls arising from being out of trim, until it is corrected

There again perhaps I know nothing

David

That's what I understood from Rev. Sim too. Anyway, it is additional to the AP movement simulation. Mike/Gary, does this make sense or does elevator trim loading not contribute to realism?

[iwik]

David,
Yes thats how my FFB yoke(GA plane) operates. Its a BFFsimulation one.
Les

[Garys]

The NG has speed trim and mach trim which automatically adjusts the position of the horizontal stabilizer in relation to the set speeds in the fmc and MCP when the autopilot is not engaged. Any changes to the position of the H Stab also make changes to the neutral shift actuator which sets a new neutral meaning that the elevator control feel should remain relatively constant. During a normal flight, I don't believe that their should be a situation where the input required should be more than a simple flick of the switch or turn of the handle.

Gary

[fordgt40]

Hi Gary

Thanks for the response, apologies for being dim but I still do not understand. 

According to the Boeing 737 Manual the horizontal trim switches reposition the elevator feel and centering unit which in turn adjusts the control column neutral position.

So if the plane is out of trim and the trim switches are not used to correct this, then the current column neutral position is also incorrect. Surely this means that the effort required to hold attitude will differ, according to the degree of departure from the "neutral position". I am basing this on the premise that the force required to hold the column in a given position  increases in proportion to it`s distance from the "neutral position".

Again, perhaps I am being dim or misunderstand, so apologies in advance 

Regards

David

[Maurice]

I am basing this on the premise that the force required to hold the column in a given position  increases in proportion to it`s distance from the "neutral position".

Regards

David

I would think that the force required is mostly dependent on the airspeed & it makes a lot of sense that the more you deflect the elevator, the higher the force required to hold the yoke since the air is pushing against a wider elevator surface. But the slower you are going, the mushier the controls feel and that is a prime indication that a stall may be imminent.

Maurice

[fordgt40]

Maurice

Thanks, I fully agree and believe that the 737 has an elevator feel and centering unit which reflects airspeed and elevator position. There appears, however, to be a difference of view in respect of the trim function and its effect on column pressure. I will shortly be designing the yoke hardware/connections/interface and would hate to get it wrong

Regards

David

[N737AG]

I am using the real force/feel/centering units from a -300. The parts for the NG's are roughly the same, at least in their function. As far as I have it, this is how it works :

The elevator column and stab trim are two completely different and independent controls. On the 737 there is no such thing as an elevator trim.

The Stab Trim changes the angle of attack of the entire stabilizer, that is, the complete rear wing. This is accomplished manually by turning the stab trim wheel (the black wheel with a white stripe on the throttle quadrant, otherwise known as the knee-breaker), or electrically by pushing the two buttons on the control yoke up or down. The Stab Trim is also controlled electrically by the autopilot.

The elevator, that is the movable surfaces on the stabilizer, are moved by pushing the yoke forward or back. The yoke's columns are connected via pulley cables to a mechanical device called the feel and centering unit, which is located at the rear of the airplane. And then the centering unit is connected via pushrods to the elevator. The centering of the column is achieved mechanically by a cam inside this unit. The "feel" function is achieved mechanically by the pressure of the follower on this cam. If you look closely, the vertical fin of the 737 has an additional pitot tube. This pitot tube feeds the plane's speed to the "feel computer", which in turn controls the hydraulic valves that generate this pressure of the follower on the cam. So, if the airplane is flying slow, the force on the yoke's column to get the nose up or down is low (remember you are flying with one hand on the yoke and one on the throttles). If the airplane is flying fast, the force is quite high in order to avoid accidental large movements of the column which might compromise the plane's structure.

There is an additional function which changes the center of the columns (rotate the cam) according the the speed (mach number). At speeds higher than Mach 0.615 the center position of the elevator (and columns) will be changed in order to give the airplane more stability. This is called Mach trim. This Mach Trim is done automatically by the computers without intervention from the pilots (as far as I know). I have not been able to find out how much the centering cam rotates (or how much the angle of the column changes) with the Mach Trim.

Axel

[Garys]

Sorry Dave, I will try and explain it a bit better. Anytime the horizontal stab moves, it  backdrives the control cables and control column back into a neutral position. So although you may be out of trim based on your centre of gravity, the columns will still remain neutral. The columns have a cam and spring setup. Its the  tension of the springs that will give you your column pressure dependant on airspeed.

Gary

[sluyt050]

Very clear explanations on stab trim, elevator column and mach trim controls. Thanks! Still, I am more or less stuck with the question if the advertised "elevator trim function" (maybe one should read 'stab trim function'?) of the Jetstream Goldstar yoke does contribute to more realism. Does anyone has experience with the real thing? (It's quite a new product).

[Garys]

I think its a gimmick. As English is not there first language Im thinking they mean elevator control Loading. As Ive tried to explain being out trim will not increase or decrease the loading on the column any differently than if you were putting the aircraft into a climb or descent.

Gary

[fordgt40]

Gary and Axel

Many thanks indeed for the comprehensive replies. So, in summary, irrespective of the trim state, the column remains in a  neutral position and the force required to move it will be solely dependent on airspeed and the extent of movement required.

Clearly, there are misconceptions "out there" and I was party to them
So thanks again for clearing this up. The other good news is that it makes my control mechanisms and loading much much easier.

Regards

David

[N737AG]

In my earlier post I mentioned that the centering unit is connected via pushrods to the elevator. This needs a clarification : the pushrods are actually the PCU's (Power Control Units) with pushrods. As long as there is hydraulic pressure, the pilot will never feel anything from the control surfaces (for example the air pressure against them). The force of the follower on the cam in the centering units is all they feel.

Axel

[Garys]

That was a good post. I know how the system works but have a hard time explaining it as well as you did. Thanks for that.

Gary