Air cylinders and flow control valve for simulated hydraulic feel, anyone tried this?

[Shawn]

I have been looking for a dual action hydraulic cylinder for use on a set of pedals and a dual flight stick but haven't found anything in my price range. The other day I was in Princess Auto and found some dual action air cylinders and a flow control valve, total price with connectors and hose would be under $40.00. I was wondering if anyone has tried this before and how did it work? If I don't get a reply either way I'll give it a shot and let you know what the results are.

Cheers
Shawn

[castle]

Here are three pics of my setup using electro-pneumatic control valves and a linear and rotary actuator. This setup is most likely outside your cost budget but some thoughts on the matter.

The pressure is controlled with custom designed boards and drivers that use DAC chips to control the vavles via a USB interface. The control loading handles changes in Q, downwash, G-loading, and trim conditions. After about one year of development and testing, the best I can say is that the results are adequate to good in pitch and good to excellent in roll, but then roll is always easier. The air supply lines from the valves to the cylinder need to be a minimum ( in our case the valves were mounted directly to the actuator ) and this presented a noise problem when air was released. Even with mufflers it was still noticeable. Moving the valves a distance away increased the distance between the valves and actuators creating delays and hysterisis problems complicating the PID controller design. ASE in Florida sells a nice 3-axis control loading unit for around $65K --- :-O don't think you're looking for an FAA certifiable unit. so .....

You can get all the control loading and force you need at a modest pressure ( say 15-20 psi ) and lot also depends on what your end goal is and the type of aircraft you are simulating. You will need a decent control algorithm and response time and a method to modulate your pressure control valve(s). Question is can the system provide a reasonable control loading and feel that mimics what is happening based on the flight dynamics of the modeled aircraft?

You might be better off with an electro-mechanical system using a self-centering cam and follower arm to set the neutral point, possibly with a spring attached to an actuator to vary the force on the follower arm and perhaps a second actuator between the stick and cam unit to set the trim position.

Just my $0.02...

Good luck

[Shawn]

Thanks for the reply Castle, very interesting setup you have. I was hoping to setup the air cylinder to act like a dampener. I thought that adjustiing the air flow would slow the action down enough to provide some resistance to a set of pedals. I've messed with it for a few hours and I don't think it's going to work? even with the airflow restricted as much as I can I don't seem to get much resistance? If anyone knows of a cheap dual action dampener I would love to hear about it. The only one's I could find online were very expensive 2-3 hundred dollars. I was hoping to avoid using two screen door dampeners but that might be the cheapest solution. Thanks again for the indepth reply and the photo's Castle.

[castle]

Thanks for the reply Castle, very interesting setup you have. I was hoping to setup the air cylinder to act like a dampener. I thought that adjustiing the air flow would slow the action down enough to provide some resistance to a set of pedals. I've messed with it for a few hours and I don't think it's going to work? even with the airflow restricted as much as I can I don't seem to get much resistance? If anyone knows of a cheap dual action dampener I would love to hear about it. The only one's I could find online were very expensive 2-3 hundred dollars. I was hoping to avoid using two screen door dampeners but that might be the cheapest solution. Thanks again for the indepth reply and the photo's Castle.

Just to finish the thought...

Remember the resistance you feel on the controls of a light aircraft is the air flowing over the control surface trying to RETURN it to a neutral positon; for a symmetric control surface that is an alpha equal to zero. Just applying a damper will not mimic that restoring force.

Did you try completing closing the valves? In that way it would be the equivalent of a spring action system, although a "perfect" seal would not be possible and there would be some leakage and the piston would not return to the same initial position, but perhaps it might be close enough for your setup. If the cylinder is leaking at the valves or across the face of the piston, you would feel some resistance that would diminish with time as the pressure in the two chambers equalized and, of course, there would be no restoring force.

Cheers
castle

[Shawn]

I have been trying to control both sides of the cylinder with one valve and I didn't have a proper seal. I think if I get another flow controller it might work. I'm only trying to get some resistance in the pedals when you push on them, I'm not to worried about having them return to centre on their own. I"ll get another flow controller today and have a go. Thanks for the replies Castle, much appreciated.

Shawn

[Crescent]

Shawn, did you try another flow controller? If so, how did it work?

[Shawn]

Hi Chris, I never did get around to trying the second flow controller but I still have the cylinder so when I get back from YWL on Thursday I'll give it a try and let you know how it works. I'm also planning to try and build a larger version from PVC pipe to see if I can get a higher resistance and less "push back" from the cylinder. I ended up buying a steering dampener designed for pocket bikes, they don't provide much resistance but the feel is quite good. I've order a few more of them and will need to add a second one to my pedals to increase the resistance so it's not a really cheap solution. One thing I did build was a tactile transducer and it works great, for a Lanc pit you would almost have to have one . I flew the DC3 and a B24 with the transducer attached to my office chair and the change in vibration associated with the throttle setting was very convincing. I'll let you know this weekend how the second flow control valve works.

These are the pedals I built using the steering dampener, still waiting on the other one to arrive in the mail.

[Crescent]

Shawn I had some excellent results with the foam I was telling you about. Since my pedistal sits in a box that is underneath the floor of the sim, I put 8 inches of "firm" foam on either side of the pedistal and you wouldn't believe how awesome it works. It gives me the perfect resistance (more resistance as you push forward or pull back) and when you let go the yoke centers itself. Cost me ten bucks.

In about three days when the paint dries I'll put up a video and start a thread.

[Shawn]

Excellent news Chris. I'm looking forward to seeing the video. I'm not sure that foam will work for my cyclic because of the 360 degree movement, I think it would eventually wear away at the foam. Worth ten bucks to try it out though I guess, where did you get it and is there a certain density rating? I'm heading to Princess auto this morning to pick up another flow control valve so I should be able to report on how that works soon.

[Crescent]

I went to a foam shop...looked it up in the yellow pages. Apparently there are different densities in the world of foam. I used the "firm" stuff which is the second hardest stuff there is.