Thursday, June 25, 2009

Good batteries for a Spektrum DX6i

Those of you with a Spektrum DX6i transmitter will know that the LCD display constantly gives you a battery voltage reading, and that under 4.8 volts the transmitter will warn you about low voltage. What is annoying about this system is that while it's great to show you the voltage, battery consumption differs wildly between Alkaline and rechargeable batteries.

For example, you might feel great that your Alkaline batteries are reading 6 volts, but you can be surprised by how quickly the voltage drops as the battery discharges. In comparison, if you use rechargable Nickel-metal Hydride batteries, the charged voltage can often be less but the voltage reading doesn't necessarily change as greatly as the battery discharges. The DX6i voltage meter has to basically "split the difference" because it has no idea what kind of batteries you are using. And because of this, it errs on the side of caution.

My Spektrum DX6i came with a set of Nickel Metal Hydride (NiMH) batteries rated at 1.5 amp hours (1500mAh), and they were pretty crap with regards to holding a charge. Straight off the charger after a good three cycles of charge and discharge, they only ever show about 5.5 volts, which on the DX6i voltage display looks very close to the "too low" mark. And this can make you concerned. Certainly it makes *me* concerned, even when I may not need to be.

Enter the Low Self-Discharge NiMH battery. I went out today to pick up a set of rechargables and was about to grab a set of 2500mAh AA batteries when I saw a pack of what was called "pre-charged" NiMH batteries, of only 2100mAh capacity. I was curious - a pre-charged NiMH battery? How can that be - they're supposed to self-discharge when on the shelf! I ended up buying this pack, but shortly afterwards felt bad because maybe the extra 400mAh of the standard pack would come in handy.

When I checked Wikipedia (link above) for the details on these batteries though, I was surprised to read they are indeed a new type of battery, released onto the market in 2005. And have a look at the features which I ripped from Wikipedia:
  • Voltage is more stable (less load- and capacity-dependent).
  • Reduced heat buildup when the battery is quickly charged or discharged
  • Higher efficiency
Well Hello! Voltage is more stable, eh? That's great for my DX6i, because it means I won't see the lower voltages like 5.3 volts or so for a longer time. That is reassuring And I can charge the battery at or near 1C with less concern and less heat? That also is reassuring.

I discharged this battery pack today (4 AA batteries) down to 4.2 volts, and then charged it back up between .8 and 1.1 amps on my Thunder T6 charger in Delta-peak mode. When it finished, the pack read a comfortable 6.0 volts on the DX6i, which is very nice and quite similar to a fresh pack of Alkaline batteries.

If you wear an anorak, you might tell me at this point that I'm actually less safe because these new batteries have more of a voltage "cliff" where the voltage will not drop much until the batteries come close to being flat, before dropping suddenly. Well NUTS to you, sir: the voltage warning of the DX6i is 4.8 volts, which will give me plenty of time to land my plane, thanks.

All up, I thoroughly recommend these new low-self discharge NiMH batteries for your DX6i, DX5e or DX7. They are for sale nearly everywhere, and you can pick 'em by their "pre-charged" or "ready to use" branding and maximum capacity of about 2100mAh.

As always, cycle your batteries a few times (discharge and full charge) and be aware that some cells can be duds from the factory!

Wednesday, June 24, 2009

Teaching Dad how to fly

Being the RC Muppet, it is probably a bit cocky of me to think that I can teach someone how to fly given I only have a few hours of flight time myself. But what the hell, I mean, I'm the MUPPET so it would be out of character not to!

And this is exactly what I did last weekend with my father. We had both chipped in for a new Parkzone Radian sailplane and it came with a DX5e transmitter which I made a trainer cable for. Saturday afternoon had rolled around and Dad must have been keeping an eye on the weather forecasts, because he called me on the phone and I could tell he was keen. The conversation went something like this:

"Hey there"
"Hey Dad"
"What are you doing tomorrow?"
"Not much, why?"
"The weather looks good for flying, perhaps I should come round?"
"Hellz yeah!"

OK so maybe I don't use "hellz yeah" in general conversation but you get my drift. Before long it was Sunday morning and Dad had rolled up on his Bandit 1250, replete with backpack containing his DX5e. We didn't waste much time, grabbing both the Radian and my DX6i as well as my complete Mini Super Cub kit, and spare batteries for each.

I have to say I was initially nervous about getting Dad into the air but really excited too, because - aside from motorbikes - we haven't many chances to spend time together with a common purpose. Dad's a great guy, but he's not really into "just hanging around and shooting shit"; he needs to be actively engaged in something, preferrably complex and mechanical (or just riding his bike). RC planes turned out to be the perfect thing for us, because once I had gotten into it myself I remembered dad used to have an old glow plug motor in the shed he was going to fit into a scratch built plane one day (which he never got around to, but I still think he has the engine!). He saw my USB TX and simulator software and was so excited about it I bought him a set for his birthday. I actually don't think I've seen the raw excited side of Dad for a long time, so I knew he was going to be interested from that point on.

Well anyway, we hooked the DX5e up to my DX6i, turned on the plane and my radio (not the DX5e because it was the slave radio), and did some controls testing using my radio and then his radio while I held the trainer switch. Sure enough, all looked good. So we hit the skies and once I had some decent altitude I let dad go for it. This is where praise for the Radian comes in - it has really nice gentle handling and hangs in the air, giving you plenty of time to think. Unless you whack the throttle open, it won't get so fast that the plane is ahead of your brain - and I had planned ahead for that, getting Dad to keep only low throttle inputs.

Sure, he had the usual problems at first:
  • flying too close in and over his head
  • flying close to the sun and risking blinding himself
  • flying too fast for his level of skill and reaction time
  • flying too low and maneuvering too aggressively
But these were only small events quickly rectified by me releasing the trainer switch and taking control of the plane before we got into trouble. I think we kept this up for about 90 minutes and only two batteries (hey, it *is* a Sailplane you know!) before mental exhaustion got the better of Dad. At this point I whipped out the Mini Super Cub and had a short fly to give Dad a rest. I figured he was ready though, so I offered him complete control of the 'cub by himself, no buddy box.

Now, Dad's first attempt at flying were some weeks ago and with the super cub. They were less than stellar! Since I had mentioned the plane only has rudders he was trying to steer left-stick (we're mode 2), and I didn't realise it. He also was too low, and too aggressive on the controls and - even though the super cub has "Anti Crash Technology" he crashed nose down at full speed and snapped the nose off (which I repaired with hot glue and toothpicks).

But that was weeks ago. This day, dad picked up the radio and with throttle held, I hand launched the super cub for him into the wind and he flew really well. He was a little aggressicve on the controls at first, but only because the Radian has very soft handling and could even be called "laggy" on the rudder. The Super cub on the other hand has very fast handling responses and is best flown with a deft touch. It's not hard - it's actually a REALLY easy plane to fly - it's just quick handling.

Dad was flying so well, the only mistake he made was that he got cocky and decided to dogfight with a crow (they HATE my planes and they think where I fly is their airspace!). The crow bugged out, but not before Dad was low, fast, over a road, and into a spiral dive. He pulled out not in time to avoid crashing, but enough to avoid damage! Not that I really mind, the Super cub has taken a fair beating and keeps on tickin'. Heck, I snapped the wing in two and glued it back together with hot glue fer feck's sake!

All up it was a really great day and Dad earned his wings from me. Before he left to go home, he was already talking about a Spitfire ARF kit he had seen online.

Bug. Bitten. And don't I love it.

Friday, June 12, 2009

Using a DX5e and DX6i as a Buddy Box system

WARNING: Do not connect an older "DX6" to a DX6i, DX5e or DX7! It has twice the voltage and will do nasty things to your newer transmitters, like blow fuses!

The ParkZone Radian that me and my father just chipped in for together was an RTF kit, which included a Spektrum DX5e transmitter. I already have a DX6i, so the two of them together created a very powerful capability: the Trainer function.

All the new Spektrum 2.4Ghz gear (DX6i, DX5e and DX7) can be hooked up together to create a buddy box setup which allows one of you to be the master (active) transmitter, and the other to be the slave. Whichever plane the master transmitter is bound to can be controlled by the slave transmitter as long as the operator of the master transmitter is holding the "Trainer" spring-loaded switch.

It's very easy, and all you need is a trainer cable (and of course the two transmitters). "But wait!", I hear you say, "where do I get a trainer cable?". Well, you can buy an official one from JR or Spektrum, but nobody seems to advertise these and you can bet they will be overpriced. Save yourself the money and buy a simple mono "headphone" cable which is male at both ends, like so:

If you happen to only have a stereo cable, that will also work just as well. Alternatively, if you're a junk hoarder like me you only need to dig through all your cables until you find two cables which both have these small headphone jack ends on them, and then solder them together. The cable is "straight through", meaning that at both ends of the cable the wires connect to the same part of the headphone plug.

Spektrum recommends you don't use a cable longer than 15 feet. Personally I think the message should have been "don't use cables shorter than six feet!". If your cables are too short, one of the operators will spin around or do something else ham-fisted and end up yanking the other person's transmitter out of their hands. THIS WOULD BE BAD, especially if that was the master transmitter which was just tossed to the ground.

Anyway, once you have your cable, you just need to connect it to each transmitter (it's on the side of the DX5e, and the back of the DX6i). We're going to use the DX6i as the master here, as it has greater range of functions for servo mixing and the like.

You will notice as soon as you plug the trainer cable into either of the transmitters, they will switch themselves on. This is normal - your power switches on the front of the transmitters now define which one is the master and which is the slave, like so:

Note that the DX6i on the left has its power switch ON and the DX5e is OFF. This has set the DX6i as the master transmitter. From here on, the DX6i will operate as normal until the "trainer" switch is held. When held on, the sticks on the DX6i will not respond and all control inputs are taken from the Slave transmitter.

What's nice about this solution is that the "instructor" can hold that trainer switch until the trainee makes a dog's breakfast of flying. The instructor then can release the switch and have immediate control of the aircraft.

Now let us cover the critical things to do BEFORE YOU GO FLYING:

First, make sure all servo reversal switches on the slave match the settings on the master. If you don't do this, when the trainee takes over they will instantly turn the wrong way, dive rather than climb, and possibly go to full throttle when their stick is at idle. THIS WOULD BE BAD.

Next, TEST THE CONTROLS ON THE GROUND. Use the trainer switch to let the trainee take over and make sure their stick inputs make the control surfaces go the right way and that the throttle functions as expected.

Lastly, define that each person must set their control sticks in the failsafe position when not in control. THIS MEANS LEAVING THE THROTTLE AT IDLE! If you are the instructor and give control to the slave while leaving your throttle at 100%, then when the trainee gets ham fisted and you release the trainer switch you will accelerate into the ground at warp factor 10. THIS WOULD ALSO BE BAD. I recommend setting up some pre-agreed language for when instructing, like "instructor has control" and "slave has control", and to mentally associated those statements with the action of setting your throttle to zero when control is taken by the other person.

Thursday, June 11, 2009

Converting a Spektrum DX5e from Mode 1 to Mode 2

Hi folks,

I should probably first post that the reason I have a DX5e is that it came with my ParkZone Radian RTF kit. This thing is a beauty and if you check out the YouTube videos you might also fall in love. I'll post later about the Radian.

Anyway, since I live in Australia the DX5e 2.4Ghz transmitter came as Mode-1. I hate Mode 1, so I decided to convert it to Mode 2. It's so easy, even the muppet managed it!

First up, note that there are five switches on the front of your DX5e. Actually there are six switches, but the sixth one is covered up.

Once you remove the screws from the back of the case and pop the front off, you will notice the sixth switch on the right. It's labelled "JR_SW", and this sets the Mode between 1 and 2.

You have to flick that switch down to make your TX Mode-2, which tells the onboard computer which sticks are the throttle and elevators. Having set that, you lastly need to move the springs and throttle "clicker" from one stick to the other. It requires a small phillips head screwdriver, good lighting, and some patience. So, rather than bore you with the details you can watch my YouTube videos below which show how to do this to a similar device. Fundamentally the procedure is identical but some of the screws are in slightly different places. Don't worry, you'll get it!

Friday, June 5, 2009

First roll!


Now that I have that off my chest I should explain what it all means, Stimpy. Well, I achieved my first rolls today with my Mini Super Cub! Not bad for a plane with no ailerons, and I seemed to be able to consistently do it. I also was performing stall turns and a fair amount of loops, with a wee bit of flying inverted to boot. I do have to say though that I can't fly inverted for long as my eyes start telling me strange things and my fingers get all scared when I start thinking about turning while inverted. This is usually followed by immediately getting anxious about the whole thing and yanking back on the elevators.

Oddly enough, there was little or no wind today, unlike yesterday when I managed to snap a wing off during my lunchtime flying break. I've been bitten by this damned bug so bad I want to fly - and usually do - even when it would be really stupid to do so.

Thursday, June 4, 2009

Mmmm...shiny DX6i

My latest addition to my kit arrived on Monday - a new transmitter! It's a beautiful Spektrum DX6i, 6-channel 2.4ghz unit. And the total cost when delivered to my door was $294 from ModelFlight in South Australia. I love these guys, and will only buy somewhere else if they are out of stock.

People tell me I needed to have purchased a more expensive transmitter with like 7 channels or more. Bollocks to them! All I want to do is fly planes with ailerons and maybe have flaps and retractable landing gear. 6-channels does that just fine thankyouverymuch.

Anway, Spektrum make excellent kit and I just love the feel of it. However I can't use the darn thing yet because only my Aerobird can really be upgraded to stock electrics and I didn't have either an Electronic Speed Controller (read that as "a throttle for an electric motor"), nor any servos. The transmitter came with a very tidy little Spektrum AR6200 receiver.

This little receiver has two antennas, which you mount at 90 degrees to each other to increase the reliability of your signal. And they work up to three miles. MILES! Good Lord, about the most I fly away from myself is a hundred FEET!

Well to ensure I don't have a DX6i sitting on my desk for ages gathering dust, I picked up a 30-amp brushed ESC for $25 (the Aerobird has a 540 motor with a prop that only causes it to pull about 20 amps), and a a pack of six servos, also for $25. Sure they're cheap chinese servos with nylon gears, but I'm still starting out and my whole ethos at the moment is don't waste lots of money when you are just going to crash and need to spend it again.

Some of you will say I'm stupid and that maybe I wouldn't crash if I used expensive gear but I disagree with that. Most stuff that goes wrong at this level of experience is caused by the muppet at the transmitter, not dud gear. Give me about a year and then you'll see me bitching about stripping the gears out of my servos, but not before!

Mini Super Cub, and wind

Did you know that if you fly your Mini Super Cub in 15 mile an hour winds, you can snap the wing off?

Neither did I. But I do now!!! At first I was like "whoa check out how much the wings are bending!", and then when I landed (practically without moving forwards, the wind was so strong) and taxied up to my feet, the right-hand side of the wing just fell to the ground! It was a bit like that scene in The Blues Brothers, where after beating the shit out of their car for the entire movie, it gets them where they need to go and then completely falls apart.

But no matter. First, parts for Hobbyzone planes are very cheap (wings are like $14 AUD), but since she's made from that non-polystyrene Z-Foam I just held the wing in place and squeezed some hot glue into the gap where the wing snapped. A few minutes of holding position while the glue dried, and she was ready to go again. Since a lot of the wing strength comes from the thin skin that goes over the foam though - and obviously this was ripped - I added a couple of layers of clear packing tape over the break point, and also the left-hand side of the wing just in case.

I went back out to test it and sure enough she flys, but the wind was so much worse that I actually had a couple of cartwheel crashes from crosswind-induced flipovers. Ah well, there was no extra breakage so I'm still happy.

Monday, June 1, 2009

Don't fly into the sun!

I've just bought a new battery charger for my planes, and like the muppet that I am I managed to overcharge my NiMh 6-cell battery pack for my Aerobird Xtreme, causing it to vent. I had been inspecting the charging process every few minutes and it just so happened that I was standing there when I heard the telltale sounds of hydrogen venting. Not good, but after checking the voltage of one of the cells, I was happy that I hadn't destroyed any of the others thanks to that cell's voltage being exactly 1/6th of the total battery pack. But I thought I should go for a flight to check what run time I was able to get out of the battery, just as an test exercise (and possibly an excuse just to go flying!).

It was late in the afternoon before I managed to get out to my "field" (an unfinished new estate development with roads but no houses), and the sun was very low in the sky. I hand launched the Aerobird into the wind - not facing the sun at this point - and went to perform a circuit around me. Unfortunately, I then made the fatal mistake of getting my Aerobird between me and the full glare of the sun. And right at this point, the wind gusted and cause a bank to the left. By the time the plane was out of the sun glare, it was downwind from me, heading into a dive, and I couldn't tell what direction it was heading!

Now before I go on, I need to explain one of the biggest problems with the Aerobird Xtreme - it's shape! The tailboom, the V-tail, and the wing shape all combine to create a plane whose direction in relation to you is very difficult to determine. You can literally take your eye of this plane for a second and look back only to find your brain thinking "hang on it wasn't facing that way a second ago!".

So now that my Aerobird was banking and I couldn't tell what direction it was facing, I fed the wrong input to the rudder and only made the bank worse to the point where there was no more lift and a crash began. I reacted with up elevator and managed to initiate a recovery, but I still did not know which direction she was heading. And when the wings dipped again, I again reacted the wrong way. This time I was so low that she just nosed over into a dive and my up elevator only served to shallow out the angle with which she smacked into the ground.

There was only minor damage which was repairable - as is usually the case with the Aerobird - but it served as a reminder that all of my reaction skills are still concious efforts rather than unconscious muscle memory. And that means I still have a lot of learning to do.

Seeing as I was out there to test the battery capacity, I repaired the 'bird and went out again yesterday afternoon. This time, I avoided going anywhere near the sun and instead spent the time doing simple circuits and landing practice. Even during this, there were a few times where I just lost the mental image of the direction the plane was heading and had to override what my eyes were telling me with what my brain "knew" the plane was doing last. To say these moments are an intense mental battle is an understatement, and I am sure experienced RC pilots will attest to mastery of this battle as a critical skill needed for consistently safe flying.