Designing control force loading

[WJH308]

I`m not sure we are talking about same thing. Belove is a sketch. A DC motor free wheeling on the column mechanism gives a light load, but when the rotor of the motor (talking about a permanent magnet motor) is short circuitted by a switch, it will represent a much higher load. If we replace the switch by a current regulator modulated by the sim...

Robert
Attachment 1487

That can also work, in fact it is how many exercise equipment vary tension for different levels. You will need to gear it though so the motor turns many revolutions to the yokes one.

[rsandor]

Exactly! How many times to rev motor, while yoke revs half? What is the minimal/maximal tension? How can be coupled hw and sw... A lot of questions.

[Mike.Powell]

Hi everybody!

Just now joined Your forum, and already have to say something:
Load cells, are expensive by nature (those which are already conditioned and outputting voltage in range 0-5V). Unconditioned load cells are outputting extremely low voltage. A whole study required to eliminate problems related to temperature, and so on.
What if we mount a DC motor (with constant magnet as stator) as a constant mechanical load to pitch/roll mechanisms, and short circuit the rotor via a variable current regulator? It is relatively low mechanical load to existing mechanism if the circuit is open (current low), and a much greater load if the motor (a generator this way) is loaded by current. For now don`t know the the values of required motors, as it depends on a lot of factors, but this is an idea only.

Robert

PS: The motor may be a one with short circuited rotor, and a wound stator, but than the load can be regulated by voltage applied to stator.

Hi Robert,

This scheme generates a force that is proportional to the speed of movement of the control. The faster you try to move the yoke, for example, the larger the resisting force would be. Unfortunately, this is not the behavior we look for in control loading.

In a real plane the resisting force varies with the position of the control. For example, pull back on the yoke and the control surfaces on the horizontal stabilizer deflect upward. There is an aerodynamic force on those surfaces pushing them down. This force will be translated through the rigging back to the yoke. As long as you hold the yoke back, you will feel this force.

Simulator control loading is designed to mimic the forces encounted during real flight. We need a scheme that can produce a force that varies with the position of the controls. This is why springs are used so frequently. Of course springs have shortcomings. They mimic forces over only a restricted set of flight conditions. Ideally, we would like to have stiff control feel at cruise, and increasingly mushy control feel as airspeed decreases. Then there's the whole world of turbulence, wing stall, etc.

[hercules]

iam not sure about the importance, but i found a cheap plug&play loadcell interface.

http://www.leobodnar.com/products/BU0836-LC/

It seems you can connect any load cell to it.

THomas

[nax228]

What about a hydraulic circuit system like the ones used to stear boats?
I think that way it would be easy to adjust torque and hook it up to a dual yoke setup.

[hercules]

i have a questions regarding Linear actuators. As i know they can move in 2 directions with a given max. force. So we can build a easy working trim system. But what is with the movements against the actuators with a force more than the max. force of the actuators? Is there a break trough possible, so we couls move the columns manuell?

In other words....does a linear actuator act as a variable spring with variable forces???

Thomas

[Mike.Powell]

There are many different kinds of linear actuators. They have different charateristics. Some could be applied as control loaders more easily than others.

What you describe, a spring with a variable spring rate, can be built. The general technique is to measure both the force and the displacement and use feedback to adjust the force as needed by varying the power to the actuator.

[hercules]

Mike,

ok..thx for the explanation.. But what i want to know is, does an actuator allow manuell movement? When i take a servo as an example....
As long the servo is supplied with voltage, you cant move it manuell. It also has a holding force and movement force! When you move it against the holding pressure, you will destroy the gear, but if you turn off the voltage, the servo will be easy moveable via hand without risk.

Is this the same with a linear actuator,or has it only fixed positions?

Thomas

[Mike.Powell]

Some do. Some don't. Some models of commercial control loaders are built very much like an RC servo, though much heavier. They have an electric motor followed by a gear train.

The term "linear actuator" is very broad. You really have to look at specifics to get specific answers. A servo designed for control loading can be over-ridden by the pilot because that's a design goal. A linear actuator designed to position a satellite antenna for receiving television is specifically designed to not be over-ridden by wind loading forces. Both may be called "linear actuator" but will behave in different fashions.

[hercules]

yes...thats answered my question. There are many types of Linear Actuators available with many different designs.

So it seems that the idea with control loading is not so far from reality, when we use linear actuators. I explored some on the website of trossenrobotics. They also offers force-sensor-controllers for a small money. But these sensors are not voltage based. They gives a variable resistance as output and the controller convert this resistance into a voltage (0-5V).

Thomas