All right I'm not a real life pilot so any of you folks with actual logbooks feel free to correct me if I'm wrong. I trying to design a trim mechanism for my first pit build that's not just a trim wheel or hat switch the enters key presses. I'd prefer to simulate trim mechanically to to implement it correctly. As we trim in the sim the stick slowly returns to neutral rather then staying in place, obviously an incongruity between real life and the simulation. I'm trying to get a better understanding of exactly what happens in certain situations to understand exactly what I need a mechanical trim to do.

When for instance the aircraft is in a nose high attitude, and we wish to bring it level, we push forward on the stick, and then trim it to whatever pressure we feel comfortable with (heavy to hands free). Now for whatever reason we chop the throttle to idle, drop the flaps, and gear. As the plane slows, the nose is going to drop. If we use the stick to keep it level, we now have to provide stick pressure equal to that needed to deflect the control surfaces to the correct amount PLUS that needed to counteract the nose down trim we added in earlier, correct? Back to our trimmed level aircraft (nose down trim), if we decide that we need to dive then we need to provide stick pressure equal tot hat needed to deflect the control surfaces to the correct amount MINUS what is already applied to the stick by the trim correct?

So overall trim is merely resistive force applied in one direction or another to the stick, to prevent it from deflecting (or as much) against that force?

I'm thinking that some sort of cable drive similar to how the old Logitech FFB worked, but much simpler. Use cables attached to all four points (X,-X,Y,-Y), that then connect to a small electric motor capable of overcoming the centering spring force to full deflection. The motor and pulley is in turn is mounted on a sliding platform that is attached to a fixed point by a spring that is slightly heavier then the centering springs used in the joystick. The trim switch then activates two motors on that axis (ie trimming in back pressure, cause the motor at X and -X to activate) one tightening, the other releasing to keep it balanced. The spring that the motor would be mounted to would to be allow the trim force dialed in to felt when deflecting the stick in the trimmed axis.

Thoughts? Did I mess up any assumptions? If I had a big budget I'd just do it how it's probably done in real aircraft with adjustable shock absorbers. However as I also doubt the wife would approve of hydraulic fluid on the carpet I think electromechanical is the way to go. I should have time to mock it up later this week, and I'll post pics.

-Jenrick

Have you considered a FFB joystick and using the program http://www.fs-force.com/ which sort of does what you want, but only in MS Flight Sim. I think this would save you a lot of hard work and frustration. However most sim pit builders are a hard headed bunch, so if you do work out your mechanical trim system please post it. (extreme over engineering is always appreciated, especially if it uses carbon fibre and polished alloys).

See you in the air

'rep

Actually that'd be a nice easy way to do it in FSX. I'm hoping that I can get mine built without needing to break out the welder, but hey that's why I own the sucker

-Jenrick

I think if you are going to do this, it would be best to remove the springs from the joystick, so the motors would provide all the resistance. That way you would reduce required pressure, current and possible hunting. Or you could move the spring gimbal housing and keep the pot gimbals in place, its gonna be alot of fun working that out. Good luck

'rep

Jenrick

What SIM you use?

This that you propose, mechanical chance the center of stick axis already exists in CH joystick - and many old joys, is DOS era legacy - but is not very practical to use in IL-2 for example.



Or, are the same mechanical trim system used in gimbal of some R/C transmiters like old Futaba - actually I think they use some digital trim system.

Tarmac Aces Universal Base allow this type of trim, because they don't use springs, but dampers, so stick stay in any position that you leave.

See in this video:
http://www.valiant-studio.eu/tarmac/html/en/accessories_action.php

Sokol1

SytRep: Actually your comment about letting the motors provide the resistance ant Sokol1's mention of mechanically changing the zero just gave me a great idea.

Sokol1: I fondly remember the days of the old joysticks that had a mechanically adjustable center, not a bad idea actually.

I'll primarily be flying a lot of FSX (mainly military aircraft or old war birds), and whenever it's released the DCS A-10C followup to Black Shark.

Man hat Tarmac Aces universal base would be a great way to go, but it's a bit out of my budget range at the moment ($750 for the base alone). Maybe with my tax return for next year.


So my new idea....

Why mess with the stick with all it's springs and such, when you can just tilt the base? If you have to hold the nose down, you can push the stick forward or elevate the front of the base if you lock the stick at straight vertical. The pots/hall sensors/whatever, cant tell the difference so long as the arc of movement is the same amount and same direction.

Imagine bolting your joystick down on a board that a buddy is holding rock steady. You can push the stick forward just like normal, but eventually your arm might get tired. You can then tell him to tilt the board's front down until there is zero spring return pressure on the stick. Basically trimming it into place. For that matter you can use it to adjust the angle the stick sits at in the first place. An additional advantage is that you could use just about any stick you wanted, including force feedback and only need to find a way to secure it level and squared on the base.

Hmm two solid low speed motors running fine toothed gears ought to do the trick. I've got one motor from my old icemaker...

-Jenrick

If you move the whole base then the pots inside it would move as well.

You would have to build a three part mechanism.
The base with the pots is stationary.
The stick can move freely and turns the pots.
A third part holds the spings that will attempt to center the stick to this part.
That third part can be moved by the trim.

jeroen: Yeah that occurred to me last night as I was going to bed. What you described is basically what I had come up with.

-Jenrick