Tuesday, September 16, 2014

Trojan T28 Repair, Flap Servo

So, what do you do when you have a flap servo go out in your Airfield/FMS T28?  This is not a regular servo but the slow rate servo.

Well, if you're a normal person, you find a source for this special servo and order/buy another one.  But, if you're a cheap Dutchman like me, you fix it!

This video shows the failed servo.  When I first tried to move it, it was locked completely and did not move.  By the time I made this video, it freed up and appeared to be working OK, but I think you can see (even with the bad focus) that was not working smooth and was catching.

One good thing this video shows, is that the servo circuitry should still be fine.  It just needs new gears.

Here is the server just after popping it loose from the wing.

Here is  the servo with most of the glue removed and sitting next to the tiny Phillips screw driver tip that was needed for the tiny screws (better get your glasses prescription up to date).

You may be asking by now "How are you going to fix this broken servo?"  Well, it just so happens that I have the burned up servo from my front gear door repair, and this servo looks exactly the same (see the photo below).  If you read my blog post on this, you know that the a jamb caused the burned up the motor and/or circuitry.  Now this "donor" servo does not have the slow circuitry, but that's not what I need.  I just need the gears, and they should still be fine.  The broken flap servo should only need a gear or two replaced, as the circuitry is fine.

This below, photo shows the start of the tear down of both servos.

This photo shows the broken gears removed and set aside (on the right in the middle) and the gears from the donor servo (left) already removed and installed in their place.

There was one difference between the two and that was that the case screws from the original were slightly shorter that the donor screws.  The donor screws also had longer threads for a more secure bite.

Since a test fit showed that the longer screws worked just fine, I decided to use them in the repaired servo.

Below is a video of the assembled servo showing that it is now working just fine.  There's that focus problem again!

In this case, this repair saved me about $15 and shipping for a replacement servo.  Some times it pays to be a cheap Dutchman keep all of your old broken crap that most people would just through away.

Ya, another one down.  Still more to go.

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Tuesday, September 9, 2014

Trojan T28 Repair, Nose Gear Repair

From my last post you know that I have several repairs to complete on my Airfield/FMS Trojan T-28.  In this post I'll update you on how I repaired the nose gear strut.

The strut had a compound bend mostly back and to the side.  I have no idea how it bent this much without any damage to the plastic parts or the servo.

Any way, this is how it looked:

A big concern of mine was "how am I going to bend this back without breaking the thing?"  It really looks like any pressure on this thing is going to shatter any and all of that plastic.

My first thought was to use a bench vise and smash the thing straight again.  The big problem with that is that this method does not always come out completely straight and, worst of all, it most likely would leave lots of marks that would prevent free movement.

What else to do?  I thought about using a large pair of pliers or vice grips, but they tend to become unwieldy and would also most likely leave marks as well.

Needing some help, I browsed some forums for advice.  I did find one post that reported the same repair to their T-28 gear and they did use a vise, but only as a support to pry against.  They also mentioned that you could put a considerable amount of force on the plastic covered part without it breaking.  This sounded pretty good, but my vice isn't mounted down well enough to pry against (just sits on my bench).  So what next?

I was at work and thinking about where I might find something that I could insert the gear into that was sturdy and I could pry against.  This wasn't exactly what I was thinking of, but it's what I found.
I used my Excelite driver handle.  It worked great!  What I did was to hold the gear in my left hand and the Excelite screw driver handle in my right hand.  Then I used by thumbs to lever against the bent section.  Sorry but I did not get any photos or video of the process.  It did take some time as I took it slow, not wanting to over bend it or put too much force on the plastic.  I started with correcting one direction and got that straight and then worked on the other direction until it looked straight from both sides.

Soon, I had something that looked like this:

This was enough and it slipped right back into the trunnion of the gear servo without any issues.

After this I realized that I could have used any sort of pipe or tubing that was sturdy and long enough.  This sure seemed a lot better than using a couple of pliers.

So, with this resolved, I just had to take the landing gear servo apart and put it all back together with the strut back in place.

One down and how many to go?

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Trojan T28 Repair, Again

Well, the last time I took out my wonderful Airfield/FMS Trojan T-28, I was experimenting with the flaps and coming in for slow passes.  I was having a log of fun with this.  Until I came in low and hit that point where it tip stalled and did the left roll thing down into the ground.  Everything after that was pretty much a blur.  The air frame survived without much more than scratches, but a lot of little things suffered.  Needless to say I now have a bunch of repairs to do.

So now here is my list of my needed repairs:
The nose gear strut has a nasty compound bend.
  It's not real clear from this photo but the bend is mostly back and also to the side.

The nose gear door broke the horn.
I've tried gluing this part several times and with different glues and have yet to find a good solution.  I've tried super glue, epoxy, and model glue.  Nothing holds very well and eventually breaks loose.

The right wing gear came loose.
It was only loose, but I decided to take it out completely to make sure it gets secured in good.

The left wing flap servo is jammed.
This is a view of the servo after being removed.

This video shows how the servo is sort of functioning, but you can hear is clicking as the gears skip.  Sorry for the blurry image.  If it was clear you could see the current and voltage readings on the meters.

The motor mount/firewall is loose.
You can see from this video that something is loose and in multiple directions.

There are also several misc repairs such as a loose cowl exhaust flap.
The flap here isn't broken, but it is loose and a little floppy.

Well now you know what I'll be doing for the next few (or many) blog post.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Monday, August 25, 2014

T28 Gear Door Follow-up

If any of you have been following my blog, you know that I had issues with my Airfield/FMS 1400mm Trojan T28 electrical system.  In blog post T28 update and putting test equipment to good use the result was a smoked front landing gear door servo.  In this post, I'll review what I did to fix this as it did not turn out to be as easy as it seemed.

On the outset, it looked like all I needed to do was to replace one servo and be done with it.  Such was not the case.  Not only did I need to source a replacement servo, but I still needed to make sure that what blew the first servo would not destroy the replacement.

Sourcing a replacement servo did not initially seem like a big deal as when I removed the original, it looked to be the same size as the cheep HK servos I already had.  The only difference that I could see was the the mounting flanges were slightly off, with the original black plastic servo sitting a little lower (one, maybe two, mm).

This did not turn out to be that big of a deal and pretty soon I had the replacement in.  I had already centered the servo and so I just screwed the servo arm in place at a 90 deg. angle, facing inboard, as the original was.  Then I hooked up the linkage, in what seemed like a neutral setting.  I then plugged it into the sequencer.  Then I plugged the sequencer into into my servo tester.  And finally, a battery pack into the servo tester to power everything.

Suddenly everything is going wonky!  The doors are closing and the landing gear is cycling down!  I reverse the servo tester and then the landing gear is retracting before the doors are opening.  Dog gone it!  I pulled the power.

What the heck is going on!?!

After some research on the Internet, I find out that the sequencer and my wiring are not messed up, but the front landing gear door servo needs to be reversed!

Out it comes again.

I don't want to wait and order just one reversed servo.  Especially as I'm not even ready for another parts order.  So, online I go again for more research and find a couple of good videos on how to reverse a servo.  Since I have a background in electronics and am proficient at soldering, I decide to tackle it.

An hour or so later (I took it slow to make sure I had it right), I had a reverse servo ready to go (sorry, but I don't have any photos of this).

Back in it goes and I'm ready to test.  Servo to sequencer, sequencer to servo tester, servo tester to battery pack.....and...phew!  All is working fine and the doors and landing gear are sequencing as they should!

A little adjusting of the linkage and the doors are closing flush and appear to be opening fine.  I can hear a little servo noise with everything sequenced open, but don't think too much as it seems like that is the norm with servos today.

Now, knowing that this is not the end, I add my servo and system power meter into the mix (check out this post on how I made this meter: Can't get enough test equipment).  Low and behold, I'm pulling similar amp readings as when the original servo blew (over 1 amp!)  I notice that this is when everything is sequenced open and when the servo is making noise.  This is not just some stray noise.  This is a jammed servo.  No wonder the original blew out.

This is the original servo and arm position when closed.
I studied and studied the linkage and servo movement.  The door linkage did not need to move as far as the servo was trying to make it go and could not move that far.  I tried moving the pin in the servo arm in one hole, but then it did not have enough throw and the doors would not open far enough.  What to do?

I thought about using my programmable radio to just reduce the throw, or end limits, of that servo, but with the sequencer in the mix, that would not work.  No way was I going to try to set this up without using the sequencer.

The more I looked at it, the more frustrated I was getting.  There had to be something to do.  Then I looked again at the linkage and how the main push rod from the servo was slender and maid of spring steel, and how it had some flex to it.  Then I remembered mechanical equipment that I had worked on in the past with levers connected to push rods, and how they would lock into place by essentially going past top dead center.  Now any force on the lever (or servo arm in this case) is back toward the shaft and not back on the gears.  That is what I would do.  I set the arm position a few notches forward on the servo, adjusted the linkage so the doors would be closed in that position.  With the doors unhooked, I watched as I sequenced the door servo.  Sure enough, it went up to dead center on its rotation, compared to the link, flexing the push rod as it did.  It came to rest with a little push rod flex but no strain noise from the servo!  I tested it several more times and then connected the doors again.  All was working well.

It felt good to resolve a problem and find a solution that I was happy with.

To help out with visualizing what I did, I added some pictures and a video below.

End position
Start position
The left photo shows the starting point and the right photo shows the end point of the arm travel.  With the arm in this position, any pressure on the arm is straight back and not on the gears.

Please excuse the condition of the plane in these pictures and video as they were not taken after the repair, but after a subsequent crash that bent the front landing gear (that repair might be in a future blog entry).

While it was apart, I used this opportunity to take the pictures and video that I had not done before.

Some lessons learned:
If servos are making noise, check it out and make sure its not because they are jammed or stressed.
If you are replacing a blown servo, find out why.
If you run into a problem, relax and keep at it, and make use of the wisdom out there on the Internet.
And most of all, remember that this is supposed to be fun, enjoyable, and relaxing.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Thursday, May 29, 2014

Richie's Birthday Party Fly-in

Have you ever wondered what to do for a birthday party for an RC enthusiast?  Have you ever wondered what to give an RC enthusiast?  It can be tough to figure out.  Especially when they are over 16.  Everybody likes to have fun with their friends and family, so what better to do than have a birthday party fly-in with your family and RC enthusiast friends.

This is what Richie's wonderful wife did for him.  She secretly notified all of his flying friends at Sacramento Area Parkflyers and organised a BBQ surprise at the Bilby flying area.  This is a little bit of the RC Flying Fun that we had thanks to Richie and his wife.

Shaky Dave really puts Richie's birthday wing through its paces, and how!

Not just aircraft, but cars too!  Squishy let's a couple of the guys try out his sic fast RC Ferrari before he smokes it's electronics.

A bunch (6?) of planes really put on a show with no collisions!  These guys know their stuff when it comes to piloting these wings.  I think that Dr. Bob as become one of the best and as far as I know he has only been at it with the wings since last summer.

Time to leave and everyone wants to get a last flight in.  Stu gets the walk of shame twice! Ouch.  I had to point this out since he called me on a failed take off and had to walk out to fix it.  There's no film of my fail cause, well, too difficult to film myself.   Richie is rightly proud of one of his new wings and touts its durability.  Supposed to be one last quick flight, yeah right!  Things wind down with Dr. Bob and Shaky Dave comparing motors.

As you can see, if you have the need to throw a birthday party or any sort of event for an RC enthusiast, then get a bunch of their RC flying buddies together at a good flying field with good food (preferably BBQ) and let the fun begin.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Saturday, May 24, 2014

Fun With My SAP Buds at Bilby

Now, before you get a little upset that I may be being rude about my friends, let me make it clear that I mean my Sacrament Area Parkflyer buds.  You can check us out and get some more information about where we commune and fly at this site

I went out to my favorite flying area to have some RC flying fun (I like the Bilby site because it's the closest to me) and hit a snag.  I was in such a hurry to get out there that I forgot the wing spar for the one airplane I brought!  Since I could not fly, I decided to video those that were out there and record the fun and commerrodery.  The video isn't great because all I had with me was my cell phone, but I think you will enjoy them anyway.

In this video a nice 4 stroke 3D plane has problems with stalling before take off as a nice foam jet comes in for a landing.  While waiting for the 3D plane to take off, Dr Bob gets ready and tosses up an insanely speedy little wing of his and puts it through its paces.

In this video the 3D 4 stroke comes in for a nice landing while Richie is getting ready to take off his big wing with landing gear.  It's a big heavy wing so he gives himself a lot of run way.  Those of us parked at then end are grateful for the courtesy.  Surprisingly it takes off quickly. It wobbles around quite a bit but Richie soon takes control and flies it quite nicely.  Then someone gets ready to maiden their Apprentice but is troubled with steering issues.

In this video, a really cool foam jet takes of.  This is the same foam jet that landed in a previous video.  No, this video is not out of order, this is another flight.  It took some distance to take off and from my angle, it almost looked like it was going to end up in the back of my Jeep.

This next video starts with a really nice flyby from the foam jet that took off in the last video.  Just after if flew by, Richie landed his big wing with landing gear.  Unfortunately he came down a little heavy and collapsed the nose wheel.  We take a closer look while the foam jet makes some sweet flybys.  After a few more low and casual passes he comes in for a nice landing.

Dr Bob takes out another screamer.  Too bad about 3/4 of the way through while going vertical, the motor screws come loose and the prop catches the right side of the prop slot.  You can hear this in the video.  The result is that the torque causes the motor to spin and rip all of the motor wires out!  Despite this, Dr Bob deftly brings in this wing with a nice glide and drops it right at his feet.

Quite often we have someone maiddening their new plane.  That is the case with this beautiful new WW2 biplane.  Unlike the Apprentice earlier, this one actually gets a chance and flight.  Let's see what happens.
Yeah, OK, I don't know what happened, but needles to say, it didn't last too long.  He'll get a lot of help and make another attempt soon.

We have a lot of fun out here and also at the other sites around the Sacramento area.  Come out and join us, the more the merrier.  There are no fees or dues, we just ask that everyone fly and behave respectfully and also take care of the areas we fly at.

Hope to see you out there!

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.