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$1,000.00 bounty offered to fix COMP ARF A4 steering

Old 10-01-2012, 06:05 AM
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AndyAndrews
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


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...
These won't work. The amount of torque needed is in excess of 10 lbs.
Old 10-01-2012, 06:07 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

fix the leak/replace the cylinders.
Submerge everything into a bucket of oil, and make sure EVERY tiny bubble (size of dust specs ) is out of the cylinders, and lines, even let it sit a few hours to make sure air is out.
Then assmeble it while submerged.

Use 2 servos, one for each cylinder if the single servo is not strong enough.
Old 10-01-2012, 06:07 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


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.
Old 10-01-2012, 06:14 AM
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AndyAndrews
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

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?...tegory&path=59

http://www.robbe.de/zubehoer-ersatzt...aulik.html?p=1

http://www.gardentrucking.com/produc...esort=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
Old 10-01-2012, 06:32 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

Is it just te picture, or is the ball link not completly inline with the piston ?

if it is not 100% alinged, then it could be putting a slight side load on the piston rod , and that could cause a leak in the front o-ring.
Also, the cylinder on the leg has to rotate/pivot freely around as the wheel turns, agan so it gets as minimal sideload to the fron o-ring as possible.

I recenlty replaced those cylinder bearings and leaking actuators on a 737-300, so the system is quite similar to what you have.....sort of



Where are you getting leaks ?
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Old 10-01-2012, 06:40 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


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
Looking at the pictures I can see where you would encounter difficulties. The travel on the cylinder that runs the gray line has to be less than the one that runs the black line since the ram displaces a significant amount of fluid. Unless the travels are pretty much just right, when you turn one way the system will cavitate and the wheel will be free to move some amount. Turning the other way would cause the system to bind. You might could attach one cylinder with a clevis and then use a stiff compression spring between the ram and servo arm to drive the other side, which would at least get rid of any cavitation or binding. The better answer would be to use the same cylinder on both ends.
Steven
Old 10-01-2012, 07:56 AM
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rhklenke
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


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...
Bingo - another problem that this system has. I think that is one reason that you need larger cylinders on the drive (servo) side than on the actuator side - you need more volume change on the drive side to get the same pressure on the actuator side in spite of the expansion of the plastic tubing...

I also think that no matter how you do it, without a bleed fitting, you're never going to get 100% of the air out of the system, so you also need the larger drive cylinders to compensate for the compression of the (small) amount of air that remains in the system...

Bob
Old 10-01-2012, 08:11 AM
  #33  
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

From my vague recollection of hydraulics during A&P school, you also have to take into count the reduced force on the side of the piston with the piston rod. So as long as the piston rods are the same diameter, you need to cross the lines going from the master to the slave.

Maybe it would be worthwhile in running a pair of small stainless lines down the nose strut and have the flexible lines are short as possible, and have the same thing up by the retract pivot point to the master cylinders. This will eliminate some of the tube swelling
Old 10-01-2012, 08:43 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


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?...tegory&path=59

http://www.robbe.de/zubehoer-ersatzt...aulik.html?p=1

http://www.gardentrucking.com/produc...esort=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

How about adding a check valve to bleed the air out? Just like your brakes. Submerge one of the fittings with tubing into a jar of the fluid. Pump back and forth, "T" in a check valve and stopcock? Lt the air bubbles come out the "T" the check valve will not let air back in the system. You just need to find a needle valve with a nipple that can allow the fluid out. Maybe one of the Machinists can make such an item?
Old 10-01-2012, 08:56 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


ORIGINAL: AndyAndrews


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.

I used sewing machine oil (mineral oil I think) in my hydraulic setup on my SU-27 gear and it works great.

Old 10-01-2012, 09:29 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


ORIGINAL: AndyAndrews

These won't work. The amount of torque needed is in excess of 10 lbs.
Well I think you meant force, if so, you are going to have a hard time getting that much force from that cylinder.

In my experience you can only get about 140 psi in these systems without leaking (maybe someone can get more I don't know) and Assuming the drive cylinder ram is 3/8 " diameter you getting about 5 pounds force at 140 PSI.
Old 10-01-2012, 11:01 AM
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JohnVH
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

individual brakes on the mains that go with the rudder, then a small spring to hold the nose wheel straight.
Old 10-01-2012, 01:19 PM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

Hi,

No experiance with a Carf A-4 however some how some way you will need to construct a bleed valve and possibly pressurized injection of the fluid (5-7psi) all while moving the cylinders. No way will submerging under oil get the air out...or at least not all of it. Get the correct size cylinders and ALL the air out and it should work. Good luck to you and I hope you get it resolved.

Take care
Old 10-01-2012, 01:34 PM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

Where's B-1 Bob's dad when You need him...
Old 10-01-2012, 07:41 PM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

Duplicate
Old 10-01-2012, 08:03 PM
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2walla
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

The twin cylinders on the servo are the main problem. Trying to match the two cylinders is a monkey humping a football operation. If there is ANY difference in the geometry you will have a differential between the fluid on each side of the steering cylinder. This will cause leaks, sucking air into the system, etc. Ditch the two cylinders on the servo and use one larger cylinder. This is the only way to make sure fluid in equals fluid out on both ends of the system. It's will solve most of your problems. Put a T with a valve on one lline to fill and bleed both sides of the system. Put them at the high point and the air will tend to migrate there. Also use a decent hydraulic fluid that is comparable with the plastics and orings in your system.
Old 10-01-2012, 10:26 PM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

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!
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Old 10-01-2012, 11:38 PM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

Andy,
Model car damper oil, is good quality silicon oil of different viscosity, I would go with a single ram at same size as steering ram single servo and just bleed everything submerged as in the thread above, why silicon oil, because it does not swell o,rings and is a perfect lubrication also does not hold air well and is used for this reason in model car dampers because of it low drag.
Good luck , I have seen Andreas taxi his and all seems ok with his A4.
Regards Mark Hinton. .
Old 10-02-2012, 01:22 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

They say use sewing machine oil (like Ian) Very light weight oil with the line size and drag is the important thing

Dw





Old 10-02-2012, 03:38 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

Despite some of the other issues....
Wouldn't it benefit from Stainless steel line, or replace with bent tubing..??
This would eliminate the flex in the thin tubing...
Old 10-02-2012, 05:14 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

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!
exactly.
the only thing left out was to 'time' the cylinders. have them both in the mid stroke, or one extended, one retracted to set the time.
THIS IS THE BEST AND ONLY WAY IT WILL WORK GIVEN THE ITEMS IN THE KIT.
Old 10-02-2012, 06:10 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

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.



Old 10-02-2012, 06:16 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

One other point I failed to put forth in my previous post is AMBIENT TEMPERATURE of the vinyl tubing. This factor will aggravate the problem of control as well.

Just more food for thought.
Old 10-02-2012, 06:35 AM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering


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.



All good points. The tubing used is stronger (thicker walled) than the tubing provided by CARF. We were told to use stronger tubing but nothing was said about the ID. That makes sense. I am looking at going hard pipe everywhere the system doesn't move. (ie the chase)
Old 10-02-2012, 06:29 PM
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Default RE: $1,000.00 bounty offered to fix COMP ARF A4 steering

The tubing expansion is minimal and not the main problem. All this system is doing is transfering the servos force through the fluid to the arm on the wheel. If you size the cylinders the same bore diameter a 1/4" displacement on one will move the other the same amount. The tubing size (as long as it isnt restrictive) will have nothing to do with the rate things happen. With no load on the gear does your steering servo bog down? if no the tubing is big enough. It looks like your master cylinders bore is a bit larger than the slave cylinder on the nose gear so your rates will not match. a larger diameter master cylinder gives you some mechanical advantage -which you probably need due to the short lever arm on the nose gear. so you probably want to hook the master cylinder to the servo as far in on the servo arm as possible. Assuming you get everything centered and the air bled out servo slop could be a factor too. Slop from the servo on the master cylinder will be magnified on the other cylinder. 8711 aren't the most slop free so you may want to look at a servo with a tighter gearset.

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