ic vs electric

[Alistair Taylor]

Toni

re: whether you need batteries that can deliver high discharge currents - not necessarily.

e.g. if you have a model needing 150W to fly (typical parkflyer - 30" wingspan to 60" wingspan glider)

As Watts is Volts x Amps, you could power such a plane (in theory) with:

8 Nicad/NiMh cells (9.6v) running at about 16 amps.

or

10 Nicad/NiMh cells (12v) running at 12 amps

So as you add more cells you need fewer amps to deliver the same watts (keep in mind that weight goes up as you add cells....).

Generally NiMh batteries are not as good at delivering high amps, although Puffin models now sell high-flow NiMh batteries that can do this.

So you might be able to use your NiMH batteries by adding an extra cell or two and dropping the prop size, depending on what cells they are.

re: brushless motors/gearboxes

Brushless motors come in all shapes and sizes but are generally more efficient than brushed ones (they convert more electrical energy into movement, and less into heat).

Brushless motors also come in all sorts of KVs (RPM per volt) and whether you need a gearbox or not (even for a brushless motor) depends on the KV and what you want to do with the motor.

Knowing the KV will tell you whether a motor is happy spinning a large prop without using a gearbox (which is what you had to do with brushed speed 400/600 motors in the past) [NB Large props are usually more efficient than small ones] or whether it's happier spinning a small prop/EDF unit at very high rpm.

To spin a big prop slowly you simply choose a brushless motor with a LOW KV (e.g. 950 - 1100), and you will find that it is quite happy swinging what looks like an outrageously big prop, at quite reasonable amps (e.g. Axi 2820/10, KV 1100, will happily spin a 12 x 8 prop on 8 cells despite being smaller, and lighter, than a speed 600 motor).

To spin a small prop quickly, or for EDF - go for 2500 - 4500 KV motors (a 4500 KV motor will want to spin a prop at 45,000 rpm on ten cells!).

HTH

AlistairT

[Toni Ertl]

Alistair - that's fantastic, thanks for the explanation.

I was a little unsure of the relationship between voltage and prop speed, rather assuming that the speed controller would be overriding battery voltage. I'd rather wondered if it might supply constant voltage and vary current, but it's obviously the other way round. It's also easy to forget the slightly crazy levels of current being pushed through such a small piece of kit.

I appreciate the explanation of KV, having been looking at various motors and wondering if what I was seeing was really what it appeared to be. The idea of a small motor swing a big prop slowly is more appealing (at this stage) as I like the 'stealth' ability of electrics. Speed is also not too desirable - yet.

I'm quite torn between buying an ARTF 'toy' which will limit both expenditure and time involvement before flying, and doing it properly with decent controls, cells etc. I have enough expensive hobbies already. ;)

BTW if people are interested in low-cost packs, www.component-shop.co.uk have just started doing LiPo packs. I've used them in the past for NiMH packs to drive mountainbike light sets, and their prices are seriously competitive.

[Alistair Taylor]

Toni

It's quite easy to do electric on the cheap, without requiring expensive chargers/batteries/controllers etc.

A cheapy "bell" brushless setup (motor and controller) will cost less than £20. Then just buy or make a couple of eight-cell packs - you can charge these (slowly) using your TX charger.

This will power either a 30" wingspan spit/schmitt/stang/hurri/cano with 1/4" sheet-wings very well using 7x5 prop, or a 60" span glider using 8 x 4.

If you want to get airborne really quickly, two of these motors will power a Mutiplax Twinstar very well indeedy. Then you can use the bargain-priced Sub-C packs sold by the component shop :) (I'm liking these prices!)

AlistairT

[Toni Ertl]

Must resist..... the lure..... of the darkside.

;)

Thanks again.

[Toni Ertl]

BTW regarding motor & ESC was this the kind of thing you had in mind for £20ish?

I spent (way too much) time on the 'bay last night and found some direct suppliers from China/Hong Kong/Singapore. They might well come in a bit below that, although there are always potential 'issues' buyin that way. I need to interpret what I'm seeing into IC equivalents now.

[Alistair Taylor]

Resistance is futile

Ceci n'est pas un oil-covered plane in the back of a car...

:)

[Alistair Taylor]

Yep - that's one.

So's this;

http://robotbirds.com/catalog/product_info.php?cPath=38&products_id=417

try also;

BRC Hobbies

AllElectricRC

These motors are available all over the place.

I suspect that you couldn't get a similar brushed combo for the same price.

Not that I'm complaining :)

AlistairT

[Toni Ertl]

Darn, I'm going to get myself in trouble at this rate.

I've been wandering through the 'flyingwings' site. They've got a 1M DF driven glider kit there that looks promising, and they also do a 'U cut' plan for a pattern ship profiler. Both a bit lumpy but I could easily re-design the profile model into a cub/citabria type.

NUTS!

Too much imagination and wanting beer on lemonade money.

[Toni Ertl]

Thanks again (posted without refreshing while you were still posting).

I love the scent of used glow fuel, and even more spent diesel (I have an Irvine 40 diesel in my cupboard, and a lovely little PAW 15). But I also remember the mess and the constant oil film removal needed. Nice Tucano though.