Messages

61

How to... / How to cut a good foam wing

« on: October 26, 2010, 13:21:29 PM »

It's a long time since I hot wired foam wings. We used to do it as a two man operation. We'd mark graduations along the templates say at 20mm intervals (closer at the LE) and call out the numbers as we went along to make sure we were in sync. I tried doing them solo a couple of times but found it very difficult to get a good cut this way. I'd agree with Bill's diagnosis. Dragging is caused by going too fast for the heat available. Getting the speed right is the hardest bit, especially for wings with lots of taper.

62

Park Flyers / Foamies / Li Po Batteries

« on: October 25, 2010, 11:42:54 AM »

Sean,

Sorry I didn't get a chance to talk to you yesterday.
I hope you found the indoor experience interesting!

Aidan

63

Park Flyers / Foamies / Li Po Batteries

« on: October 23, 2010, 15:33:58 PM »

Aidan, please allow me to correct you slightly re Li-Po voltages.

3.7V is the cells nominal voltage.
It’s fully discharged voltage is 2.7v although most people would say 2.75 to be on the safe side.
And to be even more safe most LVC’s cut the power at 3v/cell.

Yes, I know I’m a pedantic old bastard :evil: ……………….but I can’t help it! :lol:

K.

I have to disagree with your disagreement Keith!

Those voltages refer to the loaded voltage not the resting voltage which is what I was discussing. The resting voltage of a discharged cell is 3.7V. They should normally be stored at about 3.85V which equates to approx half charge. Full charge is 4.23V.
Under load the voltage will "sag". How much depends entirely on the size of the load, the capability of the cells, the charge state and the temperature. If you're at the limit of the cell's output the sag can be pretty significant.

LVC limits early on in lipo use were typically around 2.7V but that was because the cells available could only barely deliver the currents needed and sagged A LOT! A typical 6C or 8C lipo operating at it's limit might trip the LVC at 2.7V under load but would come back up to about 3.7V at rest. However newer cells don't sag nearly as much so an LVC set at 2.7V would allow the cells over-discharge enough to damage them.
An LVC of about 3V is still normal practice but for high C rate cells it's often suggested that this be raised to 3.2V or so.
As far as I know there is no "correct" LVC value. It all depends on the resting voltage you end up with and that depends on all the factors listed above... and more.

Well - I've got to get off my ass now and go finish a new plane for Middleton and charge all my lipos for some indoor fun.

By the way - in case it helps persuade you to come along tomorrow - Ralph usually brings cakes! :clap:

Aidan

64

Park Flyers / Foamies / Li Po Batteries

« on: October 23, 2010, 11:06:17 AM »

HHHMMMmm, pity there is no flying today Sean……..But there is a gathering of indoor fliers in Cork tomorrow

It is that time of year again and the Cork Model Aero Club Indoor fly-in will be held on Sunday Oct 24th 1.00pm till 6.00pm in the Hall in Middleton.
All Welcome, tea, coffee and cake will be available. A small fee if any will be charged. Helicopters, planes and freeflight welcome.
For more info contact Ralph McCarthy at 087 8322791 or rmccarthy@cit.ie
Looking forward to seeing everyone.

A lot of the indoor boys also fly gliders and, in addition all indoor models are electrically powered, so you will be able to get plenty of advise there.

See if you can make it............You'd learn a lot from them. :?:

K.

Yep, and we might manage to convince you to try indoor next!

65

Park Flyers / Foamies / Li Po Batteries

« on: October 23, 2010, 10:22:21 AM »

I would just say however, that in general I believe it's better to use LiPos in a regular way. In other words, charge until the charger shuts off, and discharge until the controller shuts off, then immediately re-charge.
Putting LiPos on charge from a 'half charge' state can upset some chargers.

Personally, I avoid discharging the battery until the controller's low voltage cut-off (this is usually abbreviated to LVC) when I can. Occasionally I misjudge and do hit LVC but it's not hte plan! The consensus is that the lifespan of the cells is much better when you don't discharge them below about 20% on a regular basis. Still, on cells costing less than €10 it's not really worth worrying about. I'd would be very worried about any charger that get's confused by part discharged lipos! I'm inclined to think the charger is one piece of equipment that you shouldn't skimp too much on!

If you don't already have one, you should get yourself either a Multimeter (you can get pretty cheap one's in places like Maplin) or a purpose designed power meter for electric power systems. A power meter (mine's an Astro Whattmeter) will typically show you the voltage, current and power simultaneously on a screen while you run your power system and will be a big help in matching up power systems and troubleshooting. You can also use it to check the voltage of your cells or you can use a multimeter for this (a multimeter isn't suitable for checking current as they usually can't handle more than 5A or 10A).

When a lipo cell is fully charged it should not exceed 4.23V per cell and when it's fully discharged it shouldn't be below 3.7V per cell.
The "3s" in the spec of the battery pack you ordered means there are 3 cells in series in the pack. So the total discharged voltage for the pack is 3.7V x 3 = 11.1V. The max safe voltage for the pack is 12.69V. Most chargers will stop the charge around 4.15V or 4.2V per cell to be on the safe side.
The voltage will drop below 11.1V while it's in use and just after you finish using it but it should soon come back up to at least 11.1V. If not, the cell was over-discharged.
The things to be aware of with lipos are:

1. only charge with a lipo charger and make sure it's set for the correct number of cells and the correct current. If you're unsure about this don't take any chances, anyone on here will be able to point you in the right direction.
2. make sure not to short them out
3. don't over-discharge them
4. Don't use them if they've puffed up - just discharge them to zero and dispose of them per manufacturers instructions.

I mentioned the risk of fire just to give you the full picture. It's not common but it's well worth being cautious with your lipos just in case.

Aidan

66

Park Flyers / Foamies / Li Po Batteries

« on: October 22, 2010, 23:06:25 PM »

Hi again,

If #3 is going to be used as a glider as well as general sport flying you'd be best to fit a folding prop and fully enclose the motor but I expect that'll be tricky with the style of motor you've got. A normal prop is very draggy when it's not in use so it'll really hurt gliding performance.

There are 2 potential problems with the battery from an installation point of view. One as Keith said, is the size. The other is the weight. I don't know much about the plane so I don't know if you've much flexibility on the size or location of the battery. If the new power system you're installing is a lot lighter or heavier than the one it's originally designed for you might have problems getting the plane to balance correctly. The new system is probably lighter meaning the plane will tend to end up tail heavy. If that's the case, and if there's space in front of the CG for a larger battery than I'd go for more capacity (more than 1100mAh) instead of just putting lots of dead weight (lead or similar) in the nose to get the balance correct.

I've used a couple of types of HobbyKing lipo cells and have been very happy with them so far. Flightmax and Rhino seem to get better press than Turnigy but to be honest they could all be coming from the same manufacturers, you just don't know. In general the Flightmax cells tend to have better energy density than the Rhino and Turnigy cells (if the advertised specs are accurate). I'd probably go for something like these if you want almost identical size:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6308
or something like these if you can fit a longer pack and want more duration or need the weight for balance:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6307
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6293

There's no point getting cells with a high C rating if you don't need them as they're normally a lot heavier and more expensive. You'll be fine with 20C or 25C cells.

If you want to shop more locally than Hong Kong (hard to beat them on price but shipping sometimes takes a while) you could try Giantcod.co.uk, expressfly.org.uk or Robotbirds.com.
I just had a very quick look at Giantcod and they have at least 2 packs that  are a match for size but I don't know anything about the brands:
http://www.giantcod.co.uk/rcmodelpart-1350-lipo-pack-p-405371.html
http://www.giantcod.co.uk/loong-tipple-1300-3s1p-2535c-lipo-battery-p-404432.html

You'll need a lipo charger of course.
There are lots around now. I've used Schulze, Hyperion and now have an icharger. Happy with all of them. The iCharger 106b+ is available from Hobbyking and a few other places. It's $80 but should meet all of your requirements for a while unless you make a quick move up fairly big stuff. There are much cheaper chargers available too. I haven't tried any of them so I can't really give you any guidance on them. I haven't used  I would suggest you find out what you can about using and storing Lipos before you start using them. They are less tolerant of abuse than Nickel based cylindrical cells. Shorting, overcharging, etc can have serious consequences (potentially fire) and overdischarging will harm performance and can ruin the cells. The standard advice is to charge lipos in a shed, garage, etc away from anything flammable if possible and/or supervise the charge process.

Aidan

67

Park Flyers / Foamies / Li Po Batteries

« on: October 22, 2010, 14:19:32 PM »

Sean,

There's any number of power systems you could put in a plane like that. To choose a suitable one there's a few more pieces of info needed.

What's your flying experience and how do you want to fly the plane?
As a powered glider (power up and spend most of your time with the motor off), as a basic trainer (flying around at moderate speed with occasional mild aerobatics), sport plane (a little of everything including some speed and aerobatics) or something else.

How much do you want to spend?
There is very cheap equipment around now which typically perform pretty well but if you're able to spend a bit more it does open up more options.

The critical thing with electric flight is that the batteries, motor and prop are all interlinked. If any of these 3 components aren't suited to the others for that application the performance will be disappointing.

Aidan

68

Events / !!!!!CMAC Indoor flyin Sunday Oct 24th CHANGE OF DATE!!!!!!!

« on: October 19, 2010, 15:05:57 PM »

Any one interested in the event, or maybe an excuse?
Hope to see someone, I would hate to have to eat the cakes by myself :oops:

Ralph

Ralph,

Myself and Eanna will almost certainly be there.
I think Stu is going too.
So no skimping on the cakes  :wink:

Aidan

P.S. Indoor combat?

69

Radios / Moving to 2.4Ghz....

« on: October 19, 2010, 15:04:00 PM »

Telemetry definitely has it's uses.

I just started using the Jeti system a short while ago. The standard functions on all the JETI 2.4GHz receivers are RX voltage and signal strength for each antenna. It's great to know the voltage of your RX battery and know you'll get a warning well before you ever fully discharge it. Don't know about the rest of you but I probably never drained an RX pack below 50% just in case (so all my packs were heavier than necessary or I got less flying time than I could have). I can see the signal strength function being useful too although I haven't made much use of it yet. For example it'll give you some warning if you're flying in a very "noisy" area where you wouldn't otherwise know there was a risk. It should be possible to use this as a lost model finder as well! :wink:

Probably the biggest advantage of telemetry for me will be measuring battery usage for electric planes. This needs a separate sensor so I won't be using it on my indoor planes for example but for larger stuff it's very useful to be able to monitor pack voltage, current draw and capacity used while in the air. Instead of timing the flight and guessing if you've used more or less throttle than usual you have a fuel gauge and you can put an alarm on it if you like.

So for example I put a current/voltage/capacity sensor in my electric glider. It's got an 800mAh pack in it powering the motor and radio. After flying a few climbs to altitude and some thermalling I wouldn't have much idea what was left in the cells so if I was to catch a thermal I'd be wondering if I had the power left to spend an hour circling in it. But now, with telemetry set to alarm after I've used 600mAh, I have absolutely nothing to worry about until the alarm goes off telling me I need to start thinking about coming down.

The telemetry doesn't get in the way of normal flying. The information is there if you need it but there's no need to even think about it the rest of the time.

Aidan

70

Events / !!!!!CMAC Indoor flyin Sunday Oct 24th CHANGE OF DATE!!!!!!!

« on: October 05, 2010, 13:10:59 PM »

Excellent.
I'll have to try and find time to put a couple of new planes together.

71

Scale / Flair K 8

« on: September 21, 2010, 16:57:52 PM »

....thoughts???

Ralph

It'll be terrible for combat  :?:

72

Radios / Just Converted to 2.4GHz

« on: September 18, 2010, 17:49:07 PM »

I've done something similar but different.
I got a second hand Royal EVO 12 and converted it to switchable 35Mhz/2.4GHz with an internal Jeti Duplex module. Gave it's first proper test with 2.4GHz last week at Mt. Leinster. No problems!

Aidan

73

Events / Sept 2010 Glide in

« on: September 13, 2010, 09:31:41 AM »

I only made it for the last couple of hours on Sunday but it was well worth the trip! Great fun.

Aidan

74

Wanted / Easy Glider & Futaba

« on: September 09, 2010, 07:40:32 AM »

I tend to agree! Cockpit, cheap, and will do pretty much everything you want.
Available in 2.4Ghz with M link.

Or maybe you already have a Futaba radio ?  :?:

No, I don't have any radio. I wanted get something what works
every time. I won't buy something cheap and later looking for
better one..

Multiplex is high quality stuff. I've owned a Profi 3010 and now have an EVO 12 converted to Jeti 2.4GHz. I've never owned a Cockipit which is their entry level transmitter but I've never seen a bad review for it. I have handled one and the've a good solid feel to them, comfortable in the hands too although that's a subjective thing. When I say entry level - it's the bottom of the Multiplex range but Multiplex don't do any really basic radios. I'd say the Cockipit would easily match the Futaba 6ex on quality and probably easily beats it for flexibility. It's very capable with 7 channels and I reckon about the best capabilities for mixing, etc that you'll get without going to the high end side of the market. I'm not sure how the 2.4GHz Futaba 6EX and Cockpit SX M-link compare on price - I suspect the Cockpit and MX-12 cost a little more.

In my opinion the best 2.4GHz systems available at the moment are Multiplex M-Link and Jeti Duplex. Both have proven telemetry and no reliability problems that I've heard of. I like Multiplex transmitters (especially the programming). I added Jeti Duplex to mine because I preferred their range of receivers (the Multiplex telemetry receivers are a bit more expensive whereas all the Jeti receivers have telemetry and are a little cheaper).

The big difference between Multiplex transmitters and other brands is the programming. I find the Multiplex programming far more flexible, logical and intuitive than others I've tried or looked at. Once you understand the basics you're unlikely to ever need to look at the manual again but the learning curve at the start may be a bit steeper. Of course there are others who really don't like Multiplex programming but I think they're crazy.
 :wink:

As Fred mentioned the Graupner MX-12 is another nice option. In case you're interested that transmitter and the MX-16 are both available pre-fitted with the Jeti Duplex system:
http://www.puffinmodels.com/category.php?dept=202


Aidan

75

Wanted / Easy Glider & Futaba

« on: September 08, 2010, 19:27:23 PM »

You don't really want Futaba anyway. Get a multiplex cockpit!