AndyAndrews

Ok you engineering geniuses. I will pay $1,000.00 cash to the first person who can find a way to make the COMP ARF A4 nose gear steer reliably and maintain it's scale appearance. This offer is reliant on being able to do this quickly. Like in the next two months. Moreover, the solution cannot be exceedingly heavy. See this thread for more info: http://www.rcuniverse.com/forum/m_10225819/tm.htm

Any takers call email me: [email protected]

BaldEagel

Put a gyro on it.

Mike

GSR

My Feedback: (145)

I think they already did that about 7 times. S

Dr Honda

My Feedback: (4)

OK... I don't feel like reading a build thread... so...

1) what's wrong with it?

2) What is it doing?

3) What's your thoughts on a fix?

I own a machine shop, and I make RC parts for a few shops, and, a few under my own label. I would be glad to give it a look over. My main focus are motorcycles... so I will be entering my slow time of the year very soon.

Since the gear comes with the model... I would rather make a retro-fix, rather than to make an entirely new nose gear. So... If you want to send me a nose gear... I'll see what I can do.

Boomerang1

Andy's offering 2 grand on his other thread, I'd fix it over there!

Seriously, contact Peter Agnew from Intairco. Like David Gladwin says I know him
to be a guy who has to have things just right & if he's familiar with the retract
anyway he'd be my go-to guy. My opinion? A new leg with the pivot at the top at
the trunion & a dummy steering cylinder on the bottom. - John.

jetpilot

My Feedback: (48)

Ive got two sets that need fixing!! Im in!!
Scott

George

My Feedback: (57)

Scott,

If you want to send me one, I'll work on a solution. Are you going to BITW? I have to stop in Dallas, so I'll be driving through Texas on my way to Cali.

Canukk

Make the arm on the gear longer so it doesn't have to work so hard and can be more precise.

It looks very short.

bcovish

My Feedback: (8)

George, I'll be driving Scott's stuff and will be leaving from Dallas. Sent you a pm

bcovish

My Feedback: (8)

Now back to the regular scheduled thread. Sorry Andy

AndyAndrews

No worries Bob, Scott and I are in the same boat looking for a solution. I've got someone working on it right now. Lets see what comes out of it. Thanks for all of the PM's. If I can't get this thing sorted out I'm sure I'll be knocking.

AndyAndrews

That won't work. The wheel is offset from the strut. Also, the strut has to be able to extend.

shepp

Andy,
have you considered replacing the pneumatic system with Hydraulic, Use a servo to drive an air cylinder, that has been converted to hydraulic, then run lines to cylinder on steering arm. Closed system void of all air. Still need the lines to the steering cylinder, but would give positive response. Just a thought.

Glenn (Scotty's friend)

jonty

Hi guys

There is a guy in NZ with a 1:5 scale A4 with a fully hydralic nose gear set up. Not sure if it has flown yet but pics are attached. I can get you an email address if interested

AndyAndrews

Hey Glenn,

The system is Hydraulic not pneumatic.

Andy

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

kiwijet

Hi Andy,

I'm the guy in NZ that "jonty" is refering to above with the 1/5th A4 (Skymaster) AUW approx 35lbs.

It uses the Likai retracts and steering system and works smooth as silk. It is a "closed loop" hydraulic system with equal capacity rams, one mounted down at the steering point and another single ram (not twin like your ones) being driven by a JR 8511 servo. I believe both cyl need to be of equal size to get accurate, smooth easy steering.

There is no bleed point on these rams the secret is to submerge both chylinders and their respective fluid line nipples in a bath of hyd fluid (we use air tool lube oil) the rams are first purged of air independantly by exercising them back and forth, then each line is filled with fluid and purged all the while keeping the entire system submerged in the oil bath especially when connecting the purged oil lines back onto their respective nipples.

It's also important to ensure both rams are centred in relationship to each other when connecting the system to ensure equal and full steering in both directions.
Bit of a messy process but secret is keeping all inlet/outlet points submerged whilst carrying this out.

Do this.....and it works! hope it helps!

just because

HI I am a new member to rcu. could you install a bleeder in the cylinders . maybe a presure tap from a two stroke muffler. to bleed all youwould need would be a small syringe
tosuck the fluid.

mr_matt

My Feedback: (10)

From my comp arf hydraulic experience you have to devise a way to bleed them 100%. And I think a larger diameter master cylinder would help but I am not sure. Also I don't know why you need 2 cylinders, seems like you could connect it up to one master cylinder with the whole shooting match sealed. Who knows it is late!

EDIT: what I mean is connect one side of the steering ram to one side of the servo driven ram, and then the other side likewise. Not sure what a different diameter on the driven side would do but it is worth a try and that way you can't get air in if it leaks across the piston(s).

olnico

Looking at the pictures ( bear in mind that I do not have the dimensions of the system ) it could be that a Firgelli L12-30 linear actuator would work in that application.
http://www.firgelli.com/Uploads/L12_datasheet.pdf
Essentially this actuator provides 30 mm of stroke at a speed of 23 mm/sec max, a max actuation force of around 10 N in practice or 2,2 lb-force in the 1:50 gearing option. The overall length of the actuator is 90 mm between the attachment points when retracted and 120 mm extended.
L12-30R series have an integrated controller and servo plug input. Compatible with standard Futaba 1-2 ms 5V command signal.

The 10 mm stroke actuator might be available for this application in the -P version. This actuator has a dimension of 70 mm retracted and 80 mm extended. The -P version means that it has to be controlled by the external LAC controller ( see below ). This would have to be confirmed by the factory.
Price 80 USD


If the L12 series is too big, you have the PQ12.
http://www.firgelli.com/Uploads/PQ12_datasheet.pdf
It has a length of 45 mm retracted and 65 mm extended. Stroke 20 mm but the max force at 23 mm/sec gearing is lower: about 5N or 1,1 Lb-force.
Also it is more "plastic-like" and might not sustain the working conditions for a long time.
Price 65 USD

These actuators are easy to drive with their LAC control board that has a 1-2 ms 5V standard Futaba RC input.
http://www.firgelli.com/Uploads/LAC_Datasheet.pdf
Price 40 USD


http://store.firgelli.com/category_s/1826.htm

Note that these products are also fairly nice for gear door actuation...

kirkj

My Feedback: (61)

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

Lance Campbell

I'm liking Oli's train of thought. You need such fidelity of control on a nose gear to be very precice with it. I'm thinking about how little we move the nose gear steering on the high speed element of the take off / landing routine, and can't see the cylinder doing that.

Lance

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...

invertmast

My Feedback: (23)

Oli,
The firgelli actuator was what i was thinking of late night last night as well. I think the problem with those will be the size, after seeing a photo of the slave cylinder mounted on the nose gear, it appears to have very little space between it and the strut.

For the price though, they are still worth a shot

olnico

Yep Thomas.
I think it's worth spending a few bucks to give it a try.
These are also worth considering for your F-14 in specific applications like speedbrakes, some doors etc...