The Lazy Bee motor & prop saga - cont'd

[Spikey]

Bear with me chaps ...

So I thought I'd got my flying testbed Lazy Bee sorted with the 880kV motor and 9 x 6 SloFly prop. It pootled about the sky quite happily and I liked how controllable the motor + prop combination was.

Unfortunately I didn't realise at the time that as soon as there was the usual amount of blustery breeze that there is where I fly, the Bee was actually underpowered.

I've standardised on 2S LiPos, and with the 9 x 6 SF, I was getting 83W and 10.3A on the bench. I swopped to a 9 x 7.5 SF, which gave a me 90W and 11.4A. The Nice Man On The Phone said I needed to go to 10 x 4.7 SF, so I did - and got 78W and 9.8A.

Question One - am I right in assuming the obvious (to me) that in order to get more reserve of power in the air with that motor, I actually need to go up to a 10 x 7SF? (The motor's rated 305W and 20.6A max, and the reason I'm using SF props is because ... erm ... I like to fly slowly and quietly)

OK, now the water gets even more muddied (or at least that's how it looks to me right now) ...

I intended to buy another 880kV motor to go in the Bee I'm building now, but the one I'm using in the flying testbed Bee is apparently no longer available (it's an N2836/09 from Giant Shark). No problem, thinks I, I'll just get the nearest equivalent. But alas, I can't find such a thing online. So now we come to ...

Question 2 - am I right in assuming that for the kind of laid-back flying I do, I'm better off sticking to a motor below 1000kV? The reason for my assumption is that I ran Lazy Bee #1 with a 1500kV motor. It went like the proverbial, but unless I was imagining it, I couldn't control speed as finely as I can with the 880kV one.

What's the way forward, chaps?

[J Moyler]

I will give you the details of what I use in my Lazy Bee. Sorry do not have the specs of my motor to hand.

Weight - 29oz.

Current - 20 Amps (full throttle) 3 cell 1800mAh pack

Prop - 11 x 5.5 APC Electric

220 Watts, 121 watts/lb

I fly mine in strong winds without problems, the only problem is on landing - getting to the lazy bee before is is blown over.

With the motor you are using on 2 cells you will not get much more power. To have enough power to fly in windy conditions I would suggest you need double the power you have at the moment (160 -180 watts). If you want more power use three cells and APC electric props. Once you go up in power I would not advise using SF props as they can throw a blade (It happened to me).

Hope this is some use.

JM

[Engine Doctor]

Hello spikey . Why go for such a low KV motor /battery combination when you have a throttle ? Surely a reserve of power for your blustery site would be a good idea .Why not go for a slightly higher kv motor and/or a 3 cell pack that should give the reserve power needed.

[Spikey]

Cheers JM

Gosh, I'm more confused than ever now! All things being equal, wouldn't going from 2S to 3S mean more RPM, in which case I might as well stick with my 2S packs and go from 880kV to 1500kV?

Maybe I'm looking at this from completely the wrong angle, but to my way of thinking, what I'm after is torque rather than revs (to use a motor car analogy). Do I understand you to say that by trying to go down that route with a Slow Fly prop, I risk shedding a blade? I thought it was revs that was bad news with them, not power as such.

Oh boy ...

[Spikey]

Hello Doctor

It's the reserve I'm after

The reason for 2S is simply that's what I've got, and I don't want to squander any more of my pension by buying 3S if I can help it. especially when that will also give me more revs The reason for the low kV is that I fly slowly and precisely, and I like my aeroplane to be as quiet as possible. I was therefore originally advised to go for <1000kV and Slow Fly props.

As I said above, I did have another Lazy Bee which I flew with a 1500kV motor on (on 2S), and it had far more power than I was likely to need, even in 8-10mph gusting almost to 20. The only reason I'd prefer not to end up with the same or similar setup for the current build is that it was noisier than the 880kV setup and I didn't seem to have such fine control over engine speed.

To my way of thinking, if in theory I connect an 880kV motor and a 1500kV one directly to the same supply voltage via the same variable resistance , I will get better proportional speed control with the 880kV one. I assume that in practice, the overall chain from throttle stick pot on the TX to the output voltage from the ESC functions in the same way and the relationship 'twixt stick movement and motor voltage is the same.  But does it though? 

For the record, the Bee in question weighs 28oz and with the 1500kV motor on 2S, I was getting 140W/18A with a 9 x 4.7, 218W/28A with a 9 x 6, and 170W/22A with an 8 6 - all Slow Fly.

Edited By Spikey on 22/07/2014 13:54:20

[J Moyler]

I did not know that you only 2S packs, in that case I would try the same prop that I use 11x5.5 APC electric and see how you get on. Otherwise you will have to go back to your higher Kv motor. Mine is over powered but do use the floats at times and I need the extra power then. If I want to just cruise around I can fly for 30 minutes.

I have just used WEBOCALC (google it, it is a basic electronic flight calculation program) .

It suggests 11x8" Prop but I would try the 11x5.5" first.

JM

[Spikey]

Gosh JM, that's another new one on me! It looks jolly interesting, so thanks a lot for the above