Boomerang1

Checked the Novak website, mostly car stuff but a few useful goodies for aircraft.

http://v2.teamnovak.com/products/ind...index&cPath=13

They sell a couple of the 1s booster gadgets too.

Orangeville? There's an Orangeville about 1/2 hour from me, pop - 682.

John.

MJD

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The 5460 is what I bought. 8.5g I see.

Boomerang1

Made a start building the Roaring 20, more things to think about.

How 'authentic' to make it?

Obviously materials & techniques have advanced over the years so how far can
you modify a model & not have it loose it's vintage character? For starters the
radio gear is modern so things will change because of that. Or just suit myself,
it's my model afterall!

Even the plan, original kits & reproduction kits are different.

Should I do a build thread or are forum contributors sick of that sort of stuff?


John.

Max_Power

I've made and used some regulators exactly like boomerand has shown and been very happy with them. I'm not sure the polarity of the diagram is correct though? It shows battery positive going straight to RX negative? I also used equal value 10 pico capacitors on mine. I snagged a broken aluminum auto heater core out of the scrap bin at work and have been whittling pieces off of it to make heatsinks for the to-220. I'd like to get some 5 amps chips, but honestly the 1 amp ones radio-shack had have been fine running 4 hs-81's plus a micro on throttle. Admittedly its hard to justify making now that Hobby-King has some nice regs with a torrid included for like $3.50 Todd

Boomerang1

Oh crap! yep, that's an issue! Could result in some unwanted smoke!

I scratched out the drawing quickly on my wife's laptop using some awkward OE program.

I'll fix it now.

I made exactly the same comment at the field this morning. The Hobby King unit lacks one important thing that most of their products
lack though, the joy & satisfaction of making something yourself. When you think about it if everything in the hobby came down to
what's the most cost effective, efficient or rational way to achieve something the 1/2 A forum would be one of the first forums to
disappear! - John.

Andrew

It's almost impossible today to beat the cost of pre-fabbed Chinese products in a DIY scenario. I agree with Fizzwater2 that the switching regulators are more efficient, but the differences are relatively small at the voltage differentials and current levels the small planes use.

The downside of switching regs is that most are 5-pin packages, they require two caps, a zener diode and a coil to set up. In situations where I would need the maximum efficiency possible, these regulators offer a good solution. OTOH, I'm willing to give up some efficiency where weight and component count come into play.

For a small plane regulator, I consider four things: Current capacity; dropout voltage; component count and cost.

The KA378R05TU is linear, but has a 3A capacity; it is a LDO regulator with a .5 DOV and it can be set up with a single cap on the output side. The input cap can be eliminated since DCin is a battery and not from a power supply and if the regulator is located close to the battery. It is a 4-pin TO-220, but the 4th pin is output-enable and can simply be jumpered to Vin. It is a Fairchild product.

The upside is that it can be fabbed for about $0.65 with heatshrink included.

Max_Power

So the 4th pin "output enable" on the 4 pin setup can be used as a on/off switch for the regulator ?, or will it still drain the lipo over the course of the next few days or weeks?

MJD

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The nice thing about a build thread is that forum "hanger-outers" can choose to read it or not to. If you want to do a build thread then go for it and bet a number of us would be interested. It is what this forum is all about.

As far as authentic - these days we get to use the radio gear we only dreamed about 40 years ago, and with this gear vintage models enjoy better performance than they ever did. There is no blasphemy in that!

It might be "nice" if you used tissue and dope etc., but now that we also have light weight heat shrink films available, do whatever turns your crank. I think the key thing is, like you said, that it is your model and you should do whatever turns your crank.

I was recently re-reading the construction article on the "Pipsqueak", a little .049 racer from way the heck back (the mag is lying somewhere, forget the date but mid-late '60's) that used a then high-tech 6 ounce flight pack. The designer noted it was little hot, but he was stuck with the status quo. That model would gain a new lease on life with modern 2 channel lightweight gear. Point being, I think there is some form of tribute in the act of recreating these models and letting them reach a level of performance that the designer could only have dreamed about at the time.

fizzwater2

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that KA378R05TU looks like a nice part - but be careful, while it's rated at 3 amps, it's only rated at 1.5 watts of dissipation without a heatsink.

that means that if you are using 3A, the battery voltage can only be 0.5 volts above the output voltage without a heatsink - and that's the drop out voltage, too - where the regulator looses the ability to actually regulate.

If you are running small plane servos, I doubt you'll be using 3A. With a 2S Lipo at it's nominal voltage of 7.4 volts, and a 5V output, the max current rating would be 625mA without a heatsink.

Andrew

Fairchild lists quiescent current for this device at 10ma max. Quiescent current is the current a device will consume when not biased - essentially, when the device is "turned off" or not producing regulated output. Consequently, it would eventually drain your battery over time and should be disconnected when not in use.

fizzwater2

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Digikey has the Micrel MIC29303 regulator which has an adjustable output. With two extra resistors, you can set the output voltage at 6V instead of using a 5V output.

Most modern receivers and servos handle 6V, but I do have to say I haven't experimented a lot with small servos.

The advantage of 6V - the voltage difference between a 2S lipo and the output voltage of 6V is only 1.4V, instead of 2.4V. This reduces the power lost in the linear regulator, and would still be pretty small and light.

Andrew

Certainly, with every device, there are tradeoffs.

I did initially look at switching regulators specifically because of the improved efficiency, but most were a bit more expensive and the component count was higher - frankly, I didn't want to have to add the zener and inductor since I was searching for light package that would be a quick and dirty DIY. DOv for most of the older design 78xx series runs around 2v, so should you happen to pull your 2s down to 7v, it might be problematic.

I did not expect the current demands on the smaller planes to come close to 3A, but what I did want was a little headroom if a servo stalled or locked up (probably a moot point since it likely would lawn dart anyway).

Current consumption on the smaller servos can be higher than the standards, but 1/2A flight times are usually short and I was willing to accept some heating.

That being said, the KA378R05 may not be ideal, but it is the best I've found given the performance parameters I had set up. I probably would look for another solution if I were running a 3s battery, but I settled on 2s from both a weight and size perspective.

andrew

Andrew

Most of the micro servos being shipped today will run on 6v. There are still a few of the older designs that show 4.8v only, but they are becoming the minoriy now.

In my search, I also considered several of the adjustable regulators, but I really wanted the KISS approach, so I settled on fixed output selections.

fizzwater2

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Good point, there is a lot to be said for keeping ths simple.. Less to break!

MJD

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Here's a question - seems most of us seem comfortable that we can run 6v without the likelihood of problems. But stretching it further, does the extra 0.6v of a LiFe pack at 6.6V nominal invite problems? I've seen about an equal number of comments in both directions during my searches on this question. I am sure it is fine with the current crop of 2.4gHz receivers, but back to the servos.. HS65HB, HS55, etc etc. Bad idea, good idea? I bought a couple of smaller LiFe packs thinking I had found nirvana for 1/2A models, a high energy density battery that doesn't need peripherals.. or does it?

[link=http://www.lifesourcebatteries.com/hcam6402.html]LiFe 200mAh Rx pack[/link]

The 1c rating concerns me.. too low for typical 1/2A flight packs? Servo load is certainly dynamic, not a steady current draw, so perhaps this is not a big deal.

fizzwater2

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I have used life batteries for the last couple of years in my pylon planes with a mix of old analog and new digital servos with no problems. I currently have a couple 1/2a projects going (in slow motion) - a qt and a hornet. Botb are swap meet finds, and had full sized s148 servos in them. The qt is getting hs65s, not sure on the hornet yet but it might also get 65s. I have been thinking about those 200 mah life from tower also, but that 1c rating bothers me too. Ill likely use 2s lipo with a little switcher regulator, since I really dont like nimh batteries.

Andrew

One of the problems is getting good current draw data on servos. I've seen numbers ranging from 220ma@6v up to 500ma@6v no-load operating current for the HS-65HB. It lists a whopping stall current of 1200ma@6v. Even if the lower 220ma operating current is correct, two servos running at the same time might cause your RX to drop out using that 1c LiFe battery. Lastly, since the current draw for all servos is higher at 6v vs 4.8v, expected flight time before re-charging will be lower. This would be even less at 6.6v.

I've taken the same approach as fizzwater2 - run a 2s lipo with a regulator of your choice. You'll get all the current your regulator will support; you can tailor your voltage needs and very likely have extended flight times.

vicman

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I have just started the 2s LiFe thing myself for all new batteries. The first round will be with 2.4 radio and when my 72 stuff gets back from radio S. I'll try it in that stuff too.

MJD

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The larger LiFe batteries have a much better discharge rating, but the small guy is very low at 200mA. Might be good for sub-micro stuff and small engines. Sounds like I should avoid them for 1/2A sport.

I have a couple of 430mAh LiPos and Novak 3A regulators.. much better idea.

I had a brief foray with NiMH Rx packs, using 220 and 300mAh Electrifly cells. But never did trust them completely. On a lekkie with BEC it's another story, you know if you have battery or not.

fiery

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My 'old technology' electron supply solution for micro-flyer on board avionics and servos.

A quick charge with field charger after every flight ensures there are no issues.

vicman

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Fiery,
I have a few of those but in 5s...just to be safe

fizzwater2

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Vic - how much does one of your 5 cell, 150 mah NiMh packs weigh?

I've used some of these in race planes with good luck so far:

http://www.amainhobbies.com/product_...ack-66V-500mAh

Just barely over 1 oz (30g) and rated at 500 mah. I've cycled mine conservatively, stopping the discharge at 6.0V, and get 400 mah at that point - plenty good for me.

fizzwater2

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In order to assuage my guilty feelings for hijacking this thread...

boomerang, are you going to do a build thread for your Roaring 20? Looks like a fun project.

vicman

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Fizz, I only use them for 1/2a stuff not in my pylon racers. The lowest I have gone there are 350mah 5s and I charge them after the third round.

MJD

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Ooh, I like those packs. Nice size for all kinds of stuff. I should broaden my search horizons.