Designing control force loading

[hercules]

HI all,

i found an interesting kind of spring! Is is a gasspring, that is varibable by a dc voltage from 0-4 Volts. In this range you can change the force from 0-300N! The responstime is within milliseconds and the dimensions are about 400mm. All parameters varies from type to type.

I requested a prototype for some tests and still waiting for an answer. The cost for one spring is about 300€.

I will inform you if i get them and toke some first tries.

Regards

Thomas

[ivar hestnes]

That was very interesting. Let us know when you have tested

Expensive parts but probably worth it if it is suitable for us.

[hercules]

I have more details of the spring now.

http://www.bansbach.de/easyerf/easyERF_engl.pdf

The sping has a complete parameter table, so it seems that you can adjust the force depending on the speed of movement.

Since i use opencokpit cards, i tend to buy the output card that can handle 0-50V per output, adjustable via SIOC in 127 steps. The input of the spring is from 0-4V. Thats not so nice, because i would have only 10 steps for change the force. (50V / 127 = 0.4V) (4V / 0.4 = 10).

What so you think about this plan? I could also use a stepper motor, that moves a pot of an adjustable power supply.

I think i will get the springs next week.

Regards

Thomas

[IanH1960]

Hi,

These look like interesting devices. It might be worth just getting a little clarification from the manufacturer of their function first, especially if it is a spring with an adjustable spring rate (or stiffness) that you are looking for.

They are described as adjustable "dampers" and the brochure suggests that it is the damping force (ie the element of force that is proportional to speed of movement) that is adjustable. The basic extension force is described separately and there is an implication there that the adjustable element is only part of the total force.

My reading would probably be that each size has a fixed spring rate but with an adjustable damping force component to allow more or less resistance to be added depending on speed of movement.

Perhaps worth checking - given the cost.

Ian

[hercules]

I think only one site (push) is adjustable i relation to the speed. The other site has a fixed extension force. But i will ask for further information.

Since the dempers has only one adjustable directions, you will need 2 of them for each flightcontrol (elevator, ailerons)..one for push and one for pull.
But when iam wrong and the dampers has 2 adjustable directions, one dampers could be enough for each fc.

Maybe my informations about real flightcontrols are not correct.
Is there a difference in force in relation to the speed of move? If not, these dampers might be useless.

THomas

[hercules]

Is the force of an linear actuator not always the same? When the actuator moves to increase force to the columns, it will move the columns. But when the pilot fight against this force, the mechanics will destroy, cause the actuator can´t be move against its motor direction. May i be wrong.

Or is it the torque of the actuator-motor that can be override?

Thomas

[IanH1960]

Maybe my informations about real flightcontrols are not correct.
Is there a difference in force in relation to the speed of move? If not, these dampers might be useless.

Have a look a Mike's post here -

http://www.mycockpit.org/forums/show...0&postcount=23

Is the force of an linear actuator not always the same?

No - the force an actuator generates will depend on how it is powered - for example if it is an actuator driven by an electric motor the force characteristics will generally mirror the torque characteristics of the electric motor. If it is a hydraulic actuator the force will mirror the pressure characteristics of the hydraulic system supplying the pressurised fluid. This is a general principal only - the mechanical design of the actuator may also affect the force characteristics - eg a lead screw actuator may provide very large resistive forces if you try and back-drive it from the load end, whereas a ball screw actuator may not ....

As Mike said in an earlier post there are lots of different types of linear actuators with a wide range of force characteristics. There can be quite a lot to get your head around!

Ian

[hercules]

Hi all
i reactivate this thread, because i spend much time to the control load idea. I wrote Leo Bodnar. He made great interfaces for inputs like buttons and switches, pots but also load-cells.

He offer some load-cell amps, that could be connect direct to a analog-input off a joystick-interface. The value of this input could be read out by SIOC and could be (recalculated) send to a linear-actuator controller. If we stay on SIOC, you could use the DC-outputcard, that can handle max 50Volts in 127 steps.

In this way you can realize control-loading in an easy way.


Are this ideas the wrong way, or what do you think about it?

Regards Thomas

[cscotthendry]

I've been tossing around an idea in my head about force feedback.

From what I've read, the problem with most of the force feedback systems is that what you feel is related to what is providing the feedback force. One of the main issues I've seen discussed is the cogging of DC motors and how it makes the feedback feel unrealistic.

A solution I thought of (kick me if this has been suggested before) is a leadscrew type of control positioning device, but coupled to the controls with springs. I haven't tried this and I don't know whether the spring action would mask the motor cogging or not.

One of the problems with spring returns that I found is centering. If you have two springs opposing each other you have several choices:
a) Both springs have a bit more tension on them than what you want to feel. They should have enough tension such that when you move the control fully one way, the spring in that direction doesn't become completely slack. Unfortunately, I found that when you have springs working against each other this way, you don't get reliable return to center due to friction in the control mechanisms.
b)Instead of having the springs in line with the control movement, you have one mounted at a right angle to the control travel and mounted at the center of the control's travel. I've found that this arrangement also doesn't reliably re-center the controls.


Here's a possible solution. It has crossed springs with a center stop. (Top view)

The advantage of the design is that when you pull or push the slide, you will be working against one spring only and the springs never work against each other. Each spring only brings the slide back to the center stop. That way, both springs can have enough force to return the control to the center, but they don't need to have enough force to overcome the other spring as well. Also, you get a definite center position which you don't seem to get with opposing springs. The idea I had for the force feedback is to mount the rods and the center stop on a leadscrew mechanism. Hopefully the springs would give an even force and mask the motor cogging. The leadscrew would effectively move the center position so that for those aircraft where the controls droop when the plane is standing still this could be simulated as well as shakes and bumps.