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Author Topic: Sinbad Jr. 30 inch glider micro RC project  (Read 1286 times)
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bgrove
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« on: June 12, 2017, 05:57:51 PM »

Hello:

This is my first micro RC build and my first time working with electric motors, batteries and ESC etc.   I had to ditch my old Futaba Conquest since it's not even legal any longer  Smiley  It was only 25+ years old  Cheesy

So a few weeks ago I finish my Sorceress build and I started to build the Sinbad Jr.  A 30 inch span glider that I built quite a few sizes of as a kid.  I always flew them free flight off the hills in the Silicon Valley (Palo Alto, CA.).

As I was building, I don't know what happened, but the RC bug bit me.  So now I'm modifying the build for RC, adding a power pod and have invested in new RC gear - mostly micro.  I did get the transmitter with the standard receiver since I know I'll want that someday.

Here are some shots of my progress.

Brad
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OZPAF
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« Reply #1 on: June 12, 2017, 08:10:09 PM »

Hey you're not wasting time there Brian. It 's coming on well

You shouldn't lose this one with RC.

happy building.
John
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daveh
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« Reply #2 on: June 13, 2017, 02:21:23 PM »

That's a lovely looking model Brian and I'll be watching the build with interest. I have a 36" span ATO 36 glider, a kit design from about 1946, that I converted to electric R?C about eight years ago and it flies superbly. Mind you, I put the motor in the nose and it was nose heavy at first until I added a bit of church roof to the tail skid and fitted gurney flaps onto the elevators. It's beginning to look a bit battle scarred now and could do with re-covering but allsorts of other projects keep getting in the way. Hey, ho - the life of the average aeromodeller I guess.

I loved the Sorceress build by the way.

Dave
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bgrove
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« Reply #3 on: June 13, 2017, 04:42:12 PM »

Here are some shots showing the radio gear I have for the Sinbad Jr.  I have two slightly larger servos versions as well, but each is about a gram heavier.  The only thing not shown is the ESC (electronic speed control), but it's very small.

The photos also shows my progress on the power pod and the motor I got.  I'm going to build the pod directly into  the wing when I join the two halves.   I'll make a second wing if I want to fly without the power pod.

I'm also making the entire top/front of the fuselage removable for radio access.

I need to get out my soldering iron and shrink tubing and figure out how to hook all this up.  I ended up buying about 3 adaptor cables that I need to cannibalize to be able to connect the ESC and the battery (to the receiver and the charger).  I guess I missed the fine print that read "some user assembly required"!!!
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daveh
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« Reply #4 on: June 13, 2017, 05:50:56 PM »

You should have plenty of power with that motor and battery. I have the same setup in my ATO 36, except that the battery is 240 mAh, and I seldom use more than half throttle. I can easily get 12 minute flights so I reckon you will be able to get at least 8 minutes.

Dave
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bgrove
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« Reply #5 on: June 13, 2017, 06:27:05 PM »

Dave:

Do you fly with power to altitude and then power down and soar?  Or is that not an option with the added weight and you really need to be under power the whole time.

This micro RC stuff is fun  Smiley

Brad
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MKelly
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« Reply #6 on: June 13, 2017, 08:34:58 PM »

Brad,

I'll chime in - with my RetroRC Sinbad I use the motor to climb, then throttle off and go thermal hunting.  I usually do 4-5 climbs per flight (typically around 1 minute run time per climb) using a 250mAh battery and the GWS motor setup in RetroRC's pod (the setup I showed in the pics on your Stick and Tissue thread).  My flight times (measured using the transmitter's built-in timer) vary from 10-45 minutes depending on how successful I am finding lift.

In Georgia I had no trouble finding lift most days; here in Texas I haven't been as successful, but I also haven't flown it as much since I've been doing mostly free flight.  The 36-inch Sinbad will definitely thermal in spite of the weight of the power system - it's no competition sailplane but it'll go up nicely.

Hope this helps,

Mike
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ZK-AUD
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« Reply #7 on: June 13, 2017, 08:47:40 PM »

I really like that Mike and the power pod looks very in keeping.  I think a bit bigger would be good - I see it was kitted as 62" but somewhere around 100" would be nice.  Not the world's most efficient sailplane but as you say it'll get up there and what lovely old style!
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bgrove
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« Reply #8 on: June 13, 2017, 08:49:19 PM »

Thanks Mike.  Great information and beautiful plane!!  Wow.  What is the span?

What did you do for pushrods?
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MKelly
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« Reply #9 on: June 13, 2017, 11:28:26 PM »

The RetroRC Sinbad is 36" span.  I built it per the kit instructions with pull-pull rudder and elevator - basically monofilament fishing line between servos and horns, with short segments of aluminum tube crimped to secure the lines at each end.  Works well.

Mike
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Yak 52
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« Reply #10 on: June 14, 2017, 04:31:11 AM »

Nice little design  Smiley

Pull-spring control is also perfect for this size of model and even easier to set up with zero slop:
http://peterboroughmfc.org/technical-articles2016/3-PullSpringControl%20.htm

(You will find pull-pull a bit awkward with a linear servo.)

Jon
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Konrad
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« Reply #11 on: June 14, 2017, 09:33:05 AM »

Never done this myself.

How are the servos holding up with the pull string and spring set up? Is there a concern with digital amps vs analog amps fighting the spring? Is there a noticeable increase in the time weighted current  draw? Would one need to use a larger Rx battery?

All the best,
Konrad
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Konrad
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« Reply #12 on: June 14, 2017, 09:40:34 AM »

Thank you for this thread. I just learned about RetroRC.
http://retrorc.us.com/gliderkits.aspx
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Yak 52
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« Reply #13 on: June 14, 2017, 11:03:43 AM »

How are the servos holding up with the pull string and spring set up?

The set up as shown in the article is for a 30" DLG with Emax ES9251 2.5g servos which have now flown around 90 hours and well over 3000 launches without a whimper. You do need to be careful to match the spring to servo torque though. You can get some whining/buzzing from the servo being under load but I've never noticed it affect amp draw or battery life. The 30" DLG will fly 2-3 hours on a 1S 300mah Nanotech. Pull-spring on 1S is standard practice in F3K these days.

Presumably with a power set up like this you will have an ESC providing 5 volts (ish) and a BEC - it may be worth checking that the little linear servos can handle that much as many are designed for 1S operation - ie 3.7V~4.2V


Jon
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Konrad
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« Reply #14 on: June 14, 2017, 11:17:30 AM »

90 hours of servo life, that's a lot longer than the life of most of my airframes!
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daveh
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« Reply #15 on: June 14, 2017, 03:27:31 PM »

Do you fly with power to altitude and then power down and soar?  Or is that not an option with the added weight and you really need to be under power the whole time.

Brad,

Most of the time I just use full power (or I should say high-ish power as the model will climb quite happily on no more than three quarters throttle) for a very short time then throttle back and just cruise around. Sometimes the model will hook a thermal and will cruise around or even climb with the power off but I don't really go thermal hunting as such. I'm generally happy just to fly about for ten minutes or so and then bring it back so that I can fly another model but I have sometimes done the climb and glide technique described by Mike Kelly. Even then, though, I tend to get bored after twenty minutes or so and want to get another model airborne. As you wrote, micro R/C is fun. Enjoy.

Dave    
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daveh
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« Reply #16 on: June 14, 2017, 03:41:26 PM »

You will find pull-pull a bit awkward with a linear servo.

I use pull-pull, or closed loop, with linear servos as on the Spektrum 'bricks' by linking the servo to a small bellcrank. There's an illustration in my Sopwith Tabloid thread. Even with the push rod and bellcrank it's a lighter setup than using a receiver with separate rotary servos. Although I do use pushrods all the way back to the tail sometimes, I now prefer closed loop/pull-pull both for scale appearance and because it saves weight at the back end.

Dave
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bgrove
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« Reply #17 on: June 14, 2017, 05:53:31 PM »

Thanks for all the input and ideas.  I don't know exactly what I'll do yet, but I have great options.

Here are some shots of the power pod progress.  It's not as nice as the RetroRC pod and Mike's build, but not bad for just going for it.  I'll have to drill out a hole in the firewall for the wires to pass through.  I'm not sure how fancy I'm going to get with trying to conceal the wires going down the side of the pod and into the wing.  The pod currently weights less than 2 grams (my scale only measure in full grams  Huh) and reads 1 gram and I don't want to add too much extra weight.

Also a shot of the standard micro servo I have as an option.

Once I get the front deck built, I'll temporarily piece everything together and work on the electronics placement to achieve proper balance.

Brad
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MKelly
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« Reply #18 on: June 14, 2017, 08:12:49 PM »

Brad,

Definitely mock everything up and check the balance before committing to equipment locations.  I found that the motor, prop and power pod drove the CG forward more than I expected.  For first flight I had to add a chunk of lead to the tail to get the CG properly located.  I later moved the receiver and ESC back to the cg (under the battery compartment in the pics in your S&T thread) to let me get rid of some of the tail weight.

For what it's worth, the wings on my Sinbad join via two rods across the center and a music wire keeper spring to hold the panels together.  The power pod slides onto the wing rods between the panels - if desired you can pull out the power pod, reassemble the wings with a center rib the same thickness as the power pod and go flying as a pure sailplane.  I haven't tried this yet, but it's nice to know I could.  It should be fairly simple to do this on your Sinbad if you so desire.

Mike
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« Reply #19 on: June 14, 2017, 08:31:06 PM »

I noticed in your article, Jon, on Pull-Spring control links the reference to an equaliser spring on the servo end.

That is really elegant and is enough to make me consider this system more carefully for small models.thanks for the link.

John

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bgrove
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« Reply #20 on: June 16, 2017, 05:29:24 PM »

I have the removable canopy/nose coming together nicely.  I little bit of work on the belt sander should have it shaped up quickly.

I also have worked out a bamboo center strengthening spar.  It passes between the two spars and extends past the center to the next rib.  It also passes through the power pod base.
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bgrove
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« Reply #21 on: June 19, 2017, 02:39:44 PM »

The wings are now officially joined.  I will add additional shear webbing out to the second rib from center.  I still have to decide on how I will mount the wing:  rubber bands as per the plan or with small, light nylon screws into blind nuts (or similar) with a front peg in hole method.

I also mounted the motor/prop setup.  28 grams.  Hmm.  That seems heavy but I have no frame of reference on a 30 inch span wing.  I will be covering both sides of the power pod sides with light 1/16th balsa for added rigidity. 

The removable canopy/nose piece is looking better and I have a plan for keeping it aligned and in place.  My servo tray is 1/64th ply laminated to 1/16th light balsa.

I built the power pod before buying the motor -   Huh - and it does sit quite a bit further forward than I had anticipated.  It's not bad, but I'm sure that the battery will need to be under the wing, toward the rear to offset the weight.  I will also need to make 'removable access panels' on the fuselage sides for access to the radio system.

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Bill G
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« Reply #22 on: June 19, 2017, 03:31:40 PM »

Coming along well.  The APC prop probably weighs at least half as much as the motor.  They're supposed to out perform GWS HD series, but I can't get past the weight of them.  Obviously at this model's light weight, the difference in performance wouldn't be an issue. Not per plan, but the dowel pin/rear hold down does look a lot cleaner.  Had a wing depart once, due to less than new rubber bands also. 
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MKelly
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« Reply #23 on: June 19, 2017, 05:20:10 PM »

Looks good Brad!
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bgrove
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« Reply #24 on: June 21, 2017, 04:57:23 PM »

Bill G.  I think you are right about the prop being heavy.  I hadn't even noticed it before.  The APC props were the only ones my hobby store had that fit the motor.  I will look for an alternate.

The good news is that I loosely assembled the entire plane and roughly placed the radio components into position and the balance was just about perfectly located!!  I'm sure I'll have room to move components enough once the plane is completed to adjust for any changes.

Bad news.  Weight  Angry  I'll definitely weigh this again taking more time to make sure it's correct, but the entire plane with radio gear (less receiver) showed 72 grams.  I am pretty sure the airframe with motor is around 55 grams (plus/minus) that leaves 17 grams for the battery and radio gear, that seems a bit heavy.  It's more of a plane than a motorized glider at this point.
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