maandag 31 januari 2011

Multiplex EasyStar Building Tips

I received an Easy Star from my girlfriend! Before building I collected some building tips so if you're getting into this wonderful EZ* plane make sure to read them through. Good flight characteristics start with a proper build ;-).



  • Double check that all the parts are included in the box before modifying any part. You won't be able to return them otherwise!
  • The rods are attached to the lid of the box using tape. Make sure to remove all tape excess before putting the pushrods into each other. This would stick and result in obsolete friction otherwise.
  • Keep the box for transport. Once the tail surfaces are in place you'll need to modify the box a bit to make it still fit. Check the web for pictures on some great mods. Some people even added a holder for their tx!
  • Always test the glue you're going to use on the elopar foam on a place it wouldn't hurt the model. Use foam safe CA glue or polyurethaan glue (like gorilla glue) for glueing the fuselage and wing cf rod holders. You can add some kickstarter to speed up the process. Non the less make sure to stick to the instructions that came with the glue. For the tail surfaces use a quicker drying glue (not super glue since that will break!) like hot glue so you can level things out and don't get any wrong angles during glue dry time.
  • Put the servo's in place and use some tape on the fuse to smoothen the surface. This will reduce drag and is an extra security not to loose any servo in flight.
  • Tape the nose with strong fibertape to protect your model on hard landings. You can also add a small stroke to the tailing edge (TE) of the wings.
  • Replace the foam skid by a real skid from hard plastic (tie wrap for instance) since that foam will wear out very quickly.
  • Share your experience and let us know how the maiden went!

If you bought the kit version of the multiplex easy star you'll need to add your own brushed speed controller, servo's and tx/rx system

Make sure to wrap in your receiver before flying and securely attach it so you won't break it that easily on rough landings. I lost a micro receiver using my EZ*. No need to go for micro anyway. You could also go for a more advanced tx/rx system, but for beginners this will only make it more difficult to fly your model. 

The cheapest servo's available from HK (in fact great servo's so don't be afraid of the cheapness) do fit in the Easy Star fuselage but you'll have to glue them in tight since the openings are a bit to large to hold them securely by tape alone. 

If you're a beginner, like most of the Easy Star buyers, you'll want to start off with the stock motor. You can get a cheap brushed controller from HK in case you went for the kit version. Once you can fly it that way upgrade to a (more powerful) brushless setup. This is an example brushless configuration for your easy star:

HXT 2030 (130S) 3500kv Brushless Inrunner (providing comparable power as the 400 can motor, if you need more power get a bigger one!)
Folding Propeller w/ Alloy hub - 6x4 (folding is better to reduce drag when floating, this easystar can float)
TURNIGY Plush 18amp Speed Controller (or cheaper with less programming options: Hobbyking SS Series 18-20A ESC)

dinsdag 25 januari 2011

Low voltage lipo charge error fix

Well you shouldn't empty your lipo cells in the first place! Believe me you only damage them doing so. This fix sometimes (not all times!) works and even if it works you loose some of the lipo's capacity.

I discovered it when I damaged a lipo pack in a transmitter that I left on over night. It's an old transmitter so it didn't have any timeout build in. Too bad it happened with a brand new 2200mah pack :s. I have a simple Turnigy 2-6 cell charger and it would only show me the "low voltage" error on any lipo setting. This is how I fixed it:

  • Load it carefully using the NiMH program up to a save voltage according to the amount of cells. That is only 6v for 2S, 9v for 3S, etc. Keep an eye on your pack, it shouldn't get hot! For safety you could use a special lipo bag.
  • Set your charger back to LIPO and it should charge now. If it still doesn't work you can as well toss your lipo away. Discharge it completely using a 12v automotive light bulb, take it apart and throw it away.


Most ESC's (check yours to be sure) have a built in lipo saving feature so they don't drain your lipo battery below a certain voltage. If you don't have these or just need another way to make sure your lipo is cut off on time you can go for a battery monitor.

The cheapest solution is the battery monitor with a simple alarm (sound + led) when voltage drops. Check Hobby King Battery Monitor 2S, 3S, 4S, 5S or 6S. They all go off on a different voltage based on the amount of cells in your pack. Make sure to match or this is just no use at all.



If you don't really need the sound and can live with a bright led only you could go for the HXT 3S Lipo monitor or the HXT 4S Lipo monitor.



Another slightly more expensive solution is one of the all in one battery monitors that even come with a display and work with 2 to 6s lipo's.

And keep balancing your packs while charging. Discharging your pack to its normal level when you have an unbalanced pack will cause one cells capacity/voltage to drop too low, resulting in a faulty cell which will very quickly reduce the packs performance.

A properly balanced pack can last 600 cycles or more. However, unbalanced packs rarely make it past 100 cycles before at least 1 cell becomes faulty.

Happy Charging!

maandag 24 januari 2011

learn to fly first rc airplane

Okay I know. I should advice anyone to start flying with an instructor... But what if you can't find an instructor? This is how I started... on my own.

First of all get familiar with the basic flight manoeuvres: pitch, yaw and roll. How does a plane stay up in the air? How does it turn, land, ... and so on. You should know how the control surfaces of your plane should move to make it go where you want to. This will require you to study. Do this on those bad weather days.



Then make yourself a cheap an easy to build trainer. Go for an over powered high wing, RET (rudder, elevator, throttle) trainer model that will basically fly itself. The high wing and dihedral make it fly stable and recover to level flight as soon as you let go of the sticks. It will require your input only for the turns (yaw using rudder) and take off/landing (pitch+throttle). A good model to start with is the blu baby primary trainer.  Also something to do on bad weathers days.

Once you know how an airplane flies and you made yourself a nice, cheap, easy repairable foamie and weather cleared up you can go off to your safe flying field. Start with taxiing your plane around on the ground. If it takes off slow down (back on throttle) so it touches the ground again. Get a feel of the rudder. At low speeds it won't react that good but at least you'll get familiar with it. You'll need it to correct from the motor pulling your plane into one direction. Don't start throwing your plane into the air. You'll need time to get to the right controls and when the model isn't launched properly you just won't be in time to save it from crashing into the ground.

Once you can control it over te ground hopping around and you feel comfortable prepare for take off. Always check your batteries, range, control surfaces... everything that needs your attention before taking off. Check the web for preflight checklists. To take off you must always run it into the wind, go full power and it should take off. If not you have a design failure, it's probably to heavy, or the wings don't generate enough lift. You need to go into the wind because then the wind creates airflow over the wings generating lift. This way you already have lift at lower ground speeds.

Now go towards a safe hight first. On take off that should always be your first concern. Get some altitude so you can make errors and still have time to recover. A 3 mistake hight is perfect. Remember that you gain altitude using your motor. The elevator alone won't make your plane go up. It only changes the angle of attack. It's the propeller that pushes the airplane forward generating airflow over the wings resulting in lift. And that is what makes your airplane gain altitude.

At some point you'll have to make your first turn. That is if you want to see your model back. On turning your plane you'll notice that it will loose altitude just to make a turn. This is due to the enlarged drag of the deflecting control surfaces and the change in direction of the airplane itself. To compensate for this you can put in some up elevator (and throttle when not already at full speed). Practice your turns an keep up your height.

Now what we really want is to reduce the power and get to a comfortable level flight. For this the model will require some trimming. In fact every model (and every modification to your model) will require trim. Even the weather is involved but for the beginning I would advice to only fly at low winds, bright skies. Practice to slow down your model without losing altitude. You might have to put in some up elevator. Just be careful not to stall it yet. That is the next step!

Stalling your plane, or better to avoid it, is an important step to master your plane. Especially on landings you'll need to fly it at a high angle of attack and low speed, just above your planes stall speed. To do this you need to know at which speed it stalls. Practice stalling your model at a proper height. Once you master it's speed you can try landing and focus on keeping your wings level and the right landing spot.

And if you can land your plane properly you can take off again and again. Have lots of fun doing so!

Micro motor broken wire

A problem with micro brushless outrunner motors is that they don't have much to hold their wires on to. In the beginning I lost several very good performing small motors this way. A hard landing on the nose, a loose motor mount, ...



I found that the best solution to this problem is to avoid breaking those wires in the first place. I now add some silicone caulk (kit) where the wires exit the motor base. You could also use 5 min epoxy, goop, hot glue, ... Use a toothpick or any small tool to apply it. Make sure not to touch the belly so it can spin freely. The only goal is to fix to wires in place.

If you ran out of luck on one of these small wonders and you have enough time you could try rewinding your broken micro motor. But believe me it's a terrible job requiring a magnifying glass. Sometimes you can even just reattach the broken wire! For that you need to understand how these things are supposed to be wired in the first place. Check this page with a lot of information on brushless motors. On rcgroups you can often find rewiring threads. Like this thread on rewinding the 1811 2000kv micro brushless motor.

Oh and you'll need a small hex driver also. The smallest one available in most kits is 1,3mm. Good luck finding this 1mm one ;-). These 1811 micro motors only cost around 8 USD at hobbyking so you could as well buy a new one. Just don't forget to secure the wires this time!

dinsdag 18 januari 2011

The perfect beginner RC Plane

I flew some different RC planes before but it has to be said that this one is the best trainer I ever touched. You can easily built it from cheap foam, add some basic electronics and off you go. It basically flies itself. You just need to point it back form time to time in order not to loose it going out of sight.

Electronics needed

hexTronik 24gram Brushless Outrunner 1300kv (great value for money and very light)
H-KING 10A Fixed Wing Brushless Speed Controller (cheapest and lightest)
Turnigy 1000mAh 3S 25C Lipo Pack (or 2s, depending on how much power you want)
2x Turnigy TG9e 9g / 1.5kg / 0.10sec Eco Micro Servo (rudder and elevator)

Pictures of the final result







update 1: Pictures after abuse

These pictures are all before flight... You should see it after the massive repairs I did so far. The cool think of these foamies is that you can just crash em knowing you can simply glue them all back together again. This is a picture of my first blu baby after I redid the wing:


update 2: Better wings 

And much later on I finally had a great set of wings. It's much better to use some solid (at least 5mm) depron sheet. I still use the carving technique where I have around 4 carves on top of the wing to bend it. Then I added some strips on the inner side for strength and taped the edges and the carves for strength. In the center I also have a carbon rond for strength.

I still fly this plane. Although I now have more experience and harder planes to fly. If it wasn't for my girlfriend who gave me a Multiplex easystar this one would be used to help people getting into this hobby. The Easy start is just a little easier to fly. This one is cheaper though.

I've been experimenting with some other motors. You can go for a much heavier motor since the model has such a short nose and the tail really needs some counter weight. 

It now has a balsa covered fuselage with the servo's in the inside. It's still basic, a box construction with some formers. But it handles rough landings much better now. Maybe I'll once make a decent full balsa wing also. Too bad it takes so much time to complete. I also did some testing with an aileron wing but for that an UC wing is just no good. Really needs a proper balsa wing.

Blue Baby inspired Pusher Setup

One of the disadvantages of the most common trainer setup is the vulnerability of the front mounted motor. On crashes the nose of the plane often gets all the impact. And in that moment you really don't want the motor to break. The motors are often strong enough, as long as it's not a micro model with tiny wiring. But the prop you've lost for sure.

Foam can take quite a bit and even if damaged you can easily repair that. Multiplex has a very successful model, the Multiplex EasyStar. It has a motor mounted just after the wing. Therefore the foam nose gets all the impact and the prop and motor is well protected in the back.

This is my latest implementation. I started creating the 24" version of the Blue Baby (over)powered with a 24gram bluewonder 1300kv. A lot of rainy/windy days so it didn't even fly to get it's next transformation. A 10g, 2000kv motor pushing with longer nose for counterweight. The 2s rhino battery has to be placed as far on top as possible to counterweigh the 10g motor and 3,5g servo's so far aft the CG. The final touch of a small keychain like camera makes this a great FPV/AP aircraft.

As you can see on the images the motor has quite some down thrust. This is to neutralize the nose down effect on full throttle. In a perfect setup the shaft of the motor should point towards CG. And a good starting point for the CG location on a custom design is at 25% of the wing chord.



Getting into foamies

Like I mentioned the Multiplex Fox RC conversion got to heavy losing its gliding characteristics (double the original weight). So I wanted to create a longer wing. Looking into moulding with foam did get me some inspiring results. Extensions of the existing wings are found over the net done with balsa, more foam etc. But I want to keep my wings in one piece so I ended up looking for other methods.

I found several cheap foam designs like this racer (I do like it's semi rounded box fuselage) and even easier to build constructions. But these have no (or almost no) airfoil and rely mostly on speed to get lifted. That's not what I need. Some more advanced designs have airfoils, like this boat hull jet.

Still I need something easier to build and fly. More like this trainer one foam design or this blu-beagle design. And that last one is how I discovered the Kline-Fogelman airfoils. Amazingly easy to build using foam sheets! Exactly what I need. So I'll get into construction of a massive wing using one of these airfoils (KFM3 I think).


In case my original MPX Fox fuselage would get to short for my wings I can always get some simple to build box fuselage. First priority is to get better, longer wings. I found some cool looking airplane designs on my search as well. Some sketches:

(check the previous mentioned link for credits and way more inspiring designs)

My Fox rc powered glider conversion

The latest pictures of my rc converted multiplex fox glider. As you can see I have the electric power setup installed and created a much bigger wing. These are the electronics I used:


 Total weight ready for flight with a 2s 360mAh lipo is 152 gram. This is with the  bigger wing of course.

For the original wing with all electronics I got 125 gram. The original Multiplex Fox glider weight without any electronics is around 50 gram.

 The canopy is made from a small water bottle. Receiver, esc and a 5g servo for rudder is in cockpit. The 9g servo for elevator is in the tail. This is for a better weight distribution. Without lipo it's well balanced this way. So I can put almost any size of lipo directly underneath the CG. The motor is a Turnigy C1818 3500kv 9g . A bit too much speed. The prop is also too big. It's now a 5x3 gws propeller. I would prefer a smaller propeller with more pitch for this motor. 4x4 would be perfect I guess. Even better would be a motor with lower rpm and folding propeller. I just don't have one in stock.

 Here you can see how I have the wing mounted like the original mpx fox wing is. I did cut out in front so I don't have to put it through from the side. I can now just lift up the front and slide in the wing. The piece of foam on top keeps it in place. Here I still have the lipo temporary fixed on that stick. I enlarged the slot underneath the wing for this lipo (check original position of nokia accu). This stick was ment to hold the motor on top. This was for propeller protection since I'm not an experienced flyer at all. I got rid of this idea, mounting the motor in front (now with a balsa firewall btw). It just had way to much pitch down on full throttle. I might try again later with the motor mounted with a lot of up thrust (since I keep crashing propellers).

This last picture gives you an idea of the size of the new wing. The flat horizontal piece is 1000mm. The tips are for dihedral angle since most of the wing is just straight, made from depron with a simple 50% on top KFm2 airfoil. Tips are about 200mm each. So total wing span now is around a (for the fox) massive 1400mm.

RC broken propeller recycled into control horn

Or how to keep this hobby affordable :-)

Multiplex Fox RC conversion for gliding

The Multiplex Fox is a small (500 mm wingspan) and cheap (10 EUR) foam free flight glider. By default it has no control surfaces or electronics but it is very well suited for conversion to a remote controlled sailplane or hotliner. Many did this conversion before. You can find a lot of references on the web of great MPX Fox RC conversions and designs. This is a good tutorial on minimal RC conversion for use as a glider.

The key is to keep the weight as low as possible. This is even more important if you don't want to add a motor. It comes at around 50 gram as is with a ballast marble in front of 9 (some reported 7) grams.

Required Electronics

-> 1x < 10 gram micro receiver. I used a Pichler MASTER 4 channel micro synthesized receiver @ 5-6 gram. This is in fact a rebranded corona RP4S1 receiver. A lot of problems reported with version 1. This version 2 works just fine for me. Some glitches so don't use it on expensive models!

-> 2x 3-9g servo's. The cheapest solution are these Turnigy 9g servo's. Still affordable and a bit lighter are the HobbyKing S0361 servo's at 3,6g.

-> 1x Nokia li poly battery providing 3,7v (which is too low according to specs but it works), 860mAh @ 19-20 gram. You could get a low mah 1s cell to power everything like this Turnigy 138mah 1s 10C lipo.

Organizing electronics for balance

One of the most importance steps to get your plane up is balance. You need to have the center of gravity (CG) at the right spot or your airplane will be very hard to control or even uncontrollable. A good starting point is having the CG at 27% of mean aerodynamic chord (% of MAC).

I have the servo's and receiver up front and the battery at CG location. This way the biggest weight is almost neutralized. The weight of receiver and servo's counterbalance the tail weight. All together it comes to 84 gram in total.

Van Drop Box

More pictures and details

As control surfaces I just adde balsa crafted parts to the existing tail surfaces. 

About 25% of the original surface is fine for most planes.

Here you can see the lipo I recovered from an old nokia cellphone.

It's placed in a larger slot so I can move it around to find the correct balance point.

This is the content of the canopy. You'll have to carve it out to fit everything in.

The servo's up front.

Conclusion

I don't have any suitable motor yet so I began with a glider. I used elevator/rudder configuration with these 2 servo's but it seems to be hard to control (=keep level) with this high wing loading at low speed without ailerons. So I'm considering an aileron/elevator to fly it more as a combat slope glider.

Next step is to add some micro motor on top. You can cut the nose and add some wood on the front to mount the motor on (=firewall). You'll need a larger, 2s lipo for decent flight time. These are the parts I would go for (from HobbyKing):

ZIPPY Flightmax 350mAh 2S 20C
18-11 2000kv Micro Brushless Outrunner (10g) (Make sure to read about a common micro motor failure problem I described in this post: Micro motor broken wire.)


In the end I never got a goot motorless flight out of it. You need to launch it up high or find a slope in order to have a good start. And once up it's hard to control since it's so fast.

I got better results once I powered this airplane. It's still a fast and agile thing but at least you can keep it up without the need of high altitude launch techniques or a slope.

I would not at all recommend this as a plane for beginners. A far better option if you're just starting with this hobby is the BluBaby made from foam sheets.

vrijdag 14 januari 2011

exit screen command mac OS X

The screen command on mac OS X is great for working with serial devices. An example looks like this:

screen /dev/tty.usb123

It did take me quite some time to find out how to exit these screens though. Just hit control + a to get into command mode and then k for killing the screen instance.

Information about other commands available here: http://ss64.com/osx/screen.html