quote:

ORIGINAL: olnico

Yes, the Firgelli actuators have 0,1 mm of slack. Pretty much unbeatable.
The problem is to ensure that 1 lb-torque at approx. 15 mm/s is enough on a 20 mm travel.

I think that the only way to find out is to order a PQ12 and a L12-30 and try both solutions in-situ.

The problem with the hydraulic solution is the amount of elongation the system will take before the piston actually starts moving. This is mostly due to the elastic nature of the plastic tubing used. When the hydraulic fluid transmits the pressure from the command piston, the lines expand a bit and that creates some sort of hysteresis in the piston motion. Very difficult to control, especially considering the fact that the tubing elastic point is varying with the outside temperature...

quote:

ORIGINAL: kirkj

OK..... here is the fix. from a fluid power systems engineer (me)

only use 1 cylinder on the servo end - not two.
bleed both cylinders very well. submerge the bare cylinders in a bowl of oil, reach in and stroke them till no air comes out.
before you pull them from the oil bowl... retract one cylinder completely - and extend one cylinder completely.
leave the cylinders positioned this way. take great pains to not compress or extend them.
(you can use vegtable oil if you want.)
install the master and slave cylinders on the servo and gear leg.
bleed your lines the same way in a bowl, and fish them thru the leg, and hook them up.
VERY IMPORTANT... hook 1 line from the rod side of the master to the rod side of the slave. and from the blind side of the master to the blind side of the slave.

clean up oil , and enjoy.

when you now center the master, the slave will center, and so on.
Kirk

quote:

ORIGINAL: AndyAndrews


1-2.) the system leaks, doesn't move the nose gear properly, won't center, requires too much force to move and when it does it only moves 1/2 of the time. There is no way to bleed the air.
3. ) replace with closed system with a pump, cylinder block type system or improve on the cylinders provided. I need a system that won't leak causing air bubbles.

I guess my post drew some attention. Thanks for offering to help.

Andy

quote:

ORIGINAL: olnico

The problem with the hydraulic solution is the amount of elongation the system will take before the piston actually starts moving. This is mostly due to the elastic nature of the plastic tubing used. When the hydraulic fluid transmits the pressure from the command piston, the lines expand a bit and that creates some sort of hysteresis in the piston motion. Very difficult to control, especially considering the fact that the tubing elastic point is varying with the outside temperature...

quote:

ORIGINAL: AndyAndrews

I'm going to try the bleeding methods you guys have posted (Thanks btw!). Here is a post on the A4 Skyhawk thread where I was about to buy a complete hydraulic pump and system. It's amazing what the scale truck and tractor modelers use for these systems:

-from the other thread:


I'm looking into some more sophisticated hydraulic solutions. IE, using a hydraulic pump and valve system to actuate the hydraulics instead of a servo. I have been doing research in the ''Earth mover'' RC group and found a bunch of info related to this. Here is a company that makes hydraulic retracts. I believe we can utilize this system to actuate our hydraulic stearing cylinder. I've found all kinds of different cylinders to. Here are the links:

http://morpower.net16.net/index.php?route=product/category&path=59

http://www.robbe.de/zubehoer-ersatzteile/modellzubehor/hydraulik.html?p=1

http://www.gardentrucking.com/products.tpl?action=search&cart=13489864724756251&eqCATEGORYdatarq=Hydraulics&eqMAJORCATEGORYdatarq=products&Titlesumm=t&Titlesort=1&max=10

Electric cylinders:
http://www.cti-modellbau.de/index.php/cat/c32_.html

This one under Hydraulic (lower page):
http://www.leimbach-modellbau.de/

Well, this is a start. I had no idea how incredible and technical the RC truck and Construction gang was:

http://rctruckandconstruction.com/forumdisplay.php?f=7

quote:

ORIGINAL: AndyAndrews

quote:

ORIGINAL: kirkj

OK..... here is the fix. from a fluid power systems engineer (me)

only use 1 cylinder on the servo end - not two.
bleed both cylinders very well. submerge the bare cylinders in a bowl of oil, reach in and stroke them till no air comes out.
before you pull them from the oil bowl... retract one cylinder completely - and extend one cylinder completely.
leave the cylinders positioned this way. take great pains to not compress or extend them.
(you can use vegtable oil if you want.)
install the master and slave cylinders on the servo and gear leg.
bleed your lines the same way in a bowl, and fish them thru the leg, and hook them up.
VERY IMPORTANT... hook 1 line from the rod side of the master to the rod side of the slave. and from the blind side of the master to the blind side of the slave.

clean up oil , and enjoy.

when you now center the master, the slave will center, and so on.
Kirk

Wouldn't veg. oil gum up over time? I sell rest equipment and that stuff gets real sticky when used as a lube, like on screw adjustments on slicers.

quote:

ORIGINAL: AndyAndrews

These won't work. The amount of torque needed is in excess of 10 lbs.

quote:

ORIGINAL: eaticus

Let me have a go at it...

The master cylinder and slave cylinder must match in size (bore and shaft dia); just purchase two identical cylinders. see attached illustration.

Installed the system in the model ''dry'' to size the length of the lines. remove the lines from one of the cylinders (but leave the other attached).
Soak the cylinders and lines in a tub of hydraulic fluid (a light weight oil such as 3-in-1 would work as hydraulic fluid). Assemble the lines back on the cylinder ports. avoid trapping air in the lines. (If necessary, attach the lines in thetub of fluid).

That should do it...

PS: Avoid large bore cylinders as it will need to push a lot of fluid, thus need a larger servo. Smaller bore cylinders will have a better steering response.

The steering cylinder that you have shown should work just fine!

quote:

ORIGINAL: Vampire

I support the previous post by kochj on the use of ''Hard'' (Brass or S.S.) tubing in place of the Vinyl or Urethane tubing as this tubing is susceptible to ''expansion'' under various loads (in particular in LONG LENGTHS) and may likely not deliver repeatable performance in this application. Unless noted otherwise, I believe this tubing is designed for fluid (air or gas) transfer and may not be intended for use in an ''linear control'' scheme.

The use of the tubing I see in the pics may produce ''over drive'' performance which leads to non-linear movement due to ''swelling'' under input load and when the input command stops, the tubing will try to return to its original shape (dia.) but may tend to ''overdrive'' the point your trying to achieve not to mention that when a side or ''centering load'' (due to the trailing fork design) is applied by the nose wheel, it can have the reverse affect and back pressure the tubing in effect will expand it and lose the position control your trying to maintain. It's all about pressure containment.

I wish to add you will want to INCREASE the inside diameter of the hard tubing as well as the 2nd benefit is it will yield QUICKER response time to input. (larger dia. = more pressure transfer and quicker response). A shorter, larger Dia. cylinder is a good thing as well. This will help response times too.

Of course some degree of flex tubing will be needed but should be keep to an absolute minimum length for the reasons mentioned and the same amount (lengths) to be used in BOTH lines to ensure repeatable movement in BOTH directions.

I have made several assumptions above on the type and sizing of the tubing provided for the application and these are just my htoughts on the subject issue.