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Old Jan 22, 2013, 02:26 PM
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Australia, ACT, Kambah
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Originally Posted by beerbrewer View Post
Thanks scirocco,

Yes, I am getting closer. I will replace the wheels before the maiden since they are woobley and turn poorly. Also I need do some patching on the monocoat covering.

I feel that a lower pitch is better on the Lt-40 since it is designed for slower flight for beginners. I have tried to find where I read it but the way I understand this is that the pitch is like gearing on a bicycle or car. In high gear it is hard to get going vs low gear and this massive wing wants to cause "ballooning" if coming in too fast for a landing. Can't forget to mention the drag the wing creates at higher speed. This baby is a floater and gentle flyer so I feel slower is better and have the power to spare. If I wanted, I could easily fit a 14 x 7 inch prop on it with the way I built the new motor mount since I have 8.5 inches from the centerline of the motor to the ground.

If and when I get my donated (free) Sig King Kobra going I fully agree with the higher pitch prop that you are recommending.

I did some playing around on the battery hatch and for people who do not know, there are some very strong magnets in hard drives. To remove them you need to bend the metal backing to remove them. The magnets are quite brittle and will break if you try to pry them off.
I don't think the gearing analogy is apt for electric systems. There are several factors here. First, electric motors develop more torque as they are loaded, so as long as the motor is big enough, and yours is, it will cope with the load. Second, think of the motor's Kv x voltage as a rev limiter - under load it can't exceed that rpm. If pitch is too low, your top speed is limited and you may not have the speed range you desire. Third, the model is well overpowered as pretty much all electrics are, so in the cruise you will be back at much reduced throttle and rpm. The prop needs to have enough pitch to match the flying speed you want at the reduced rpm. Fourth, on approach you will likely have the throttle closed, so the prop will be windmilling and generating drag not thrust - not the same as a IC engine with a minimum idle speed and thrust, so pitch makes minimal difference here.


Having said all that, the only way to know what works for your model is to try it out, and props are cheap. But do try the higher pitched props at some stage - I think you'll be surprised at how much more lively the model feels throughout the speed range.
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Old Feb 18, 2013, 12:58 PM
Microbiology at it's best.
beerbrewer's Avatar
Waverly, Nebr.
Joined Apr 2009
231 Posts
Every story has an opening line that can stick in your mind making you wish that you had thought of it first. The one I usually go with is, "There I was..."

There I was, on Saturday morning working on the Lt-40 conversion. I had replaced the old wheels that were filled with slimer goo and also centered all of the control surfaces with their respectful servos. The nose wheel was as straight as I could get it by simply rolling the plane accross the basement floor. I knew I had to give it a better rolling test and check out the actions of the servos. It was turning into a nice day outside so I decided to leave the main wing off and take the plane outside into the street. So far so good, a little throttle and it easily starts rolling. I did this a few times just watching how well the motor is pulling. When I tried to turn to the right, it went left. I knew what I had to do, just simply reverse the servo's action. No problem, the transmitter is a basic 4 channel Tower Hobbies running 72 MHz, with the servo switches on the bottom.

I gathered everything together and headed back inside. So, there I am, standing in the kitchen straddling the fuse facing forward. Servo 1 is the ailerons and they are on the unattached wing, no need to even play with the switch. Servo 2 is the elevator and I can't see the action because it is behind me. I decide to change my position to behind the plane so I can see all of the actions. Big mistake!!! I should have just turned around while keeping the plane straddled. OK, the elevator or servo 2 is working correctly but I play with the switch anyway just to see it reverse.

Now, I do know that servo 3 is the throttle and number 4 is the rudder. As a slimer, I have seen the throttle servo reversed while the motor was off so I did not give it any thought as to what will happen as an electric. I just wanted to reverse servo number 3 because I could.

So, there I was, standing behind the plane with my brain working (or not) faster than my fingers. Just as I started to flip the switch, I realize that this is a very bad idea and I attempted to abort but it was to late. The motor instantly went WOT and in the blink of an eye, the plane lept forward 5-6 feet and slammed into the wall. The impact broke the motor off and the inertia of the turning motor ripped the motor wires out of the ESC.

The pictures say it all. Yes, the prop is stuck into the door casing and it measured 1 inch deep.
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Old May 13, 2013, 05:12 PM
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Waverly, Nebr.
Joined Apr 2009
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Back at it

Well I have gotten a couple of new props and have reglued the fuse along with rebuilding the motor mount. I also replaced the wheels and the wire LG. The poor thing had too many hard landings long before I got it, so it looked like it was almost tail dragger. I also made a new battery hatch cover that is vented to keep everything cool.

I had also gotten a couple of new batteries and had checked them out by cycling them. The last one I hooked up to the system to bring it down to close to storage voltage since the charger was timing out multiple times. I ran it at about 2+ amps with the watt meter inline. My thought was to not over heat anything at all, just a slow drain. After about 45 minutes I shut it down and the ESC was quite warm. In my biased opinion, the thing should have been room temp.

Fast forward, I came across a thread titled "too long battery wires will kill ESC over time: precautions, solutions & workarounds" and I did some checking. To get everything in place my battery to ESC connection was 19 inches. There was just no room under the hood to have anything shorter. I also put in a high current arming switch that I just absolutely love. Long story short, I will be getting a few capacitors to eliminate any of the voltage spiking that could be causing the ESC to heat up. While it is a 60 amp ESC, I do not want to take a chance.

If I was building this thing from scratch, it would not be a problem. Some of these conversions can only be "ya got what ya got". There is so much epoxy in there from the previous rebuilds I do not dare to change anything else.
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Last edited by beerbrewer; May 13, 2013 at 11:38 PM.
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Old May 14, 2013, 03:38 AM
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Australia, ACT, Kambah
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Regardless of the length of the wires, extended part throttle running will heat up the ESC, arguably more than full throttle. So I would not be surprised to see a warm ESC under the conditions you describe.
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Old May 14, 2013, 08:16 AM
Microbiology at it's best.
beerbrewer's Avatar
Waverly, Nebr.
Joined Apr 2009
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The length of the bat/ESC wires makes a very big difference. Even Castle Creations recommends that extra capacitance be installed if the bat/ESC wires are longer than 12 inches due to the high voltage spikes induced by the PWM into the wires. The thread showed some very good o-scope pics of the spikes at different throttle settings. They were really bad at 20% (more spikes than pulses) while basically non-existant at WOT.

With this bird being a Sig Trainer, it is not going to be run at 100% very often since it is designed for slow and stable flight so 40 - 60% is going to be the norn. The motor to ESC wires are the ones to be lengthened in a best case senerio of which mine is not.

It is always a good day when I learn something new.
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Last edited by beerbrewer; May 14, 2013 at 12:59 PM. Reason: typo
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Old May 14, 2013, 10:31 AM
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If I may... Move your ESC out by the Engine.. Mount it someplace where it can get direct airflow...

I had to add a lot of weight to the nose of mine to get balanced.. It'll cut your wiring down. and move your weight forward.. and cool your ESC all in one swoop.

I see you made a stand-off for the motor.. see if you can mount the ESC on top of the stand-off.. cross-wise if need be.. It'll simplify a lot of things.
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Old May 14, 2013, 01:12 PM
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Waverly, Nebr.
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Thanks for your thoughts vmsguy,

I had considered that when building the motor mount. The problem is the wires on the motor are unbelievably stiff. It is like they were soldered back 2 inches from the connector, they just don't bend. Also, the motor does a very good job of placing the CG pretty much spot on with the way the mount is designed.

I do agree that placing the ESC on the outside would simplify things, but there is really no place to put it unless I totally redo the front of the fuse.

Thanks again.
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Old Jul 04, 2013, 08:33 PM
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Waverly, Nebr.
Joined Apr 2009
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Happy I. D. Americia!!!

Yesterday I received an early Christmas or birthday present. The cost for all new batteries for the old 72 MHz receivers and transmitters coupled with the savings of 15% for just taking a survey, it was almost (not really) a wash. The upgradability is superb.

Everyone in the USA, I hope you have a happy and safe Fourth.

BB
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Old Jul 07, 2013, 01:46 PM
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Aurora, Ontario, Canada
Joined Mar 2002
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I've just got a DX6i and the programming is a bit touchy, especially getting the Tx to flip between change the model and change the model settings, plus setting elevon mode (getting the right servo plugged into the right Rx plug).. Almost everyone else in EMFSO at the summer indoor sessions have the '6 or the '8 model.....

If I can find a field for next summer, I'm going to do either the LT40 conversion or shift it to a LT20 as a prkflier.....
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Last edited by byrocat; Jul 07, 2013 at 01:51 PM.
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Old Aug 15, 2013, 03:39 PM
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Waverly, Nebr.
Joined Apr 2009
231 Posts
Dx8

Had to get the battery warrantied since it would not hold a charge, after full charge it would drop to 4.3 VDC in a few days.

Thank you Horizon Hobby.

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Old Dec 10, 2013, 10:38 AM
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Bump for CNY-Dave,

Dave, I see you have looked at No Step's modifications of his build.

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Old Dec 10, 2013, 01:43 PM
My Hangar is full
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Everett, Washington
Joined May 2003
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And I'm watching this one. I've had to put mine aside for a couple months,…. home remodeling got in the way,.. I had little access to my shop so I could only go so far in the build,… frame up only. I actually started another model (Golden Oldie) because all I could do was frame up. Now I'm back to normal but will finish the Golden Oldie, then get back to the LT40 about Mid to end of January.

Fred
https://home.comcast.net/~guilfoyle72/
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Old Dec 10, 2013, 05:12 PM
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beerbrewer's Avatar
Waverly, Nebr.
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Hey NS, I am watching yours!!!

I know how life can get in the way of hobbies. My budget got freakishly maxed out just after I bought the DX8 due to things beyond my control. My new 8 channel receiver with telemetry that came with the DX8 tx is reserved for the future. (I wish I could have afforded 2-SPM8800's) I need to get this http://www.horizonhobby.com/products...eiver-SPMAR400 since I do not want to use any of my foamie rx's with limited range and it is cheaper than a HK Orange 6 channel.

I really think I should put the telemetry in the LT-40 just for monitoring the batteries to get more data regarding flight time. Yeah AMA and club dues are due 31Dec13 so somebody else will have to fly it come spring.

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Old Dec 12, 2013, 03:35 PM
DX5e fatal flaw- PM me!!!!
United States, NY, Cortland
Joined Sep 2010
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Originally Posted by beerbrewer View Post
Bump for CNY-Dave,

Dave, I see you have looked at No Step's modifications of his build.

BB


zzzZZZzzz....zzzZZZzzz....zzz*-*SKNnXch(snort)... Huh?
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Old Dec 12, 2013, 10:41 PM
Microbiology at it's best.
beerbrewer's Avatar
Waverly, Nebr.
Joined Apr 2009
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Quote:
Originally Posted by CNY_Dave View Post
zzzZZZzzz....zzzZZZzzz....zzz*-*SKNnXch(snort)... Huh?
W T ???K

What did I do to deserve this kind of response for bumping MY OWN THREAD???
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Last edited by beerbrewer; Dec 12, 2013 at 10:47 PM.
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