Low power output on 4-max (purple power) 595KV

[Jason Hyland]

Hi all,

I'm building an AcroWot with this setup from 4 max

It's essentially a 595KV motor running on a 4s with a 14x7 APC e-prop. My last test was to see the power output via the watt meter. With a fresh charge I was getting just over 600W, roughly 50-60% of what I was expecting.

I'm not sure if I've done something stupid, but I'm confused. I can't seem to calibrate the throttle range on the ESC as it doesn't seem to need it - first time I've come across that, but I wondered if that was the problem?

Any suggestions please!?

Regards, Jason

[FlyinBrian]

The motor specs say 5s to 8s batteries, perhaps a 4 cell pack just isn't enough.

[Jason Hyland]

Posted by FlyinBrian on 13/08/2016 14:46:27:

The motor specs say 5s to 8s batteries, perhaps a 4 cell pack just isn't enough.

Hi, thanks for replying.

It's a bit weird, the specs do indeed say that, but they also say this for the motor

Prop	14x7 - 4S LiPo 13x6.5 - 5S LiPo

Also, the "kit" was supplied with a 3300 4S

Part Number Description Price Qty Acro Wot EP/GP (Balsa) (airframe only) Acro Wot EP/GP (Balsa) (airframe only) (RRP £139.99) £125.99 Acro Wot EP/GP (Balsa) (electric conversion kit A-CF007/ELP) Acro Wot EP/GP (Balsa) (electric conversion kit) (RRP £19.99) £18.99 Acro Wot EP/GP (Balsa) Power Set Motor PO-5055-595 ESC PP-TESC60AU Prop APCE 14x7 (RRP £111.30) £99.99 LiPo Battery 4 cell (14.8V) 40C rated, 3.300mAh LiPo Battery £43.99 Servos 4x Servo XL-38HMB £41.96

I have emailed George at 4-max, so hopefully he can put me right.

Edited By Jason Hyland on 13/08/2016 14:55:01

[Jason Hyland]

Perhaps I am OK ? I just weighed the AcroWot all up she weighs in at 6.2 llbs, so with about 620W of power this gives me exacty 100watts/llb which I think is about "right" for a sport plane intending to do mild aerobatics

[iqon]

!00w per lb is not that much for a sport plane, you want closer to 200w but maybe thats just me

[Steve Colman]

I'm with iqon here.

100w per lb would be very anemic for an Acrowaot. I fly a Spacewalker which weighs in at just under 5.76 lbs. On 4S it gives 700W at 45A which = 121W per lb. This is just about adequate for general flying but not sufficient for aerobatics.

I would consider 150W per lb a minimum to do justice to, and to make the most of, a model such as the Acrowot.

Steve.

[PatMc]

Battery capacity is seems also low for decent flight duration.

[Chris Bott - Moderator]

Good grief how times have changed. It wasn't long ago we only dreamed of 100w/lb. Then it became a really good rule of thumb. That was using brushed motors and really heavy batteries where the drive train was at best 60℅ efficient.
Today we have lighter systems and much higher efficiency. 100w/lb is plenty. 200w/lb is unlimited vertical and 3d territory.
I think you'll be fine on that setup, although I think I'd be looking for more battery capacity for longer flights.

[Denis Watkins]

We cannot rewrite the "needs" chart to suit what we have. 100 watts per pound has worked fine up until now, so beware newbies reading that 200 watts per lb is the target.

Also, 6.2 lb seems quite heavy for such a small model/missile

I think a good target for the model would be 4 - 4.5 lb

And in that case, Georges/4 max set up would work fine

[kc]

I agree with Denis - 100 watt per pound is OK and 6.2. pounds is heavy for an Acro Wot.

[Frank Skilbeck]

Just run through a similar kv motor and that prop on a 4s battery on ECalc and it says 600 watts, so with that combo there's nothing wrong with your system, also says around 3 kg (6.6lbs) static thrust, so you've got 1:1 static thrust, probably not good for pulling out of a prop hang but it won't be lacking for normal flying.

[Jason Hyland]

Thanks for the replies, all useful. A couple of things spring to mind.

First 6.2 llbs is the weight of the assembled ARTF, plus battery, esc, motor, rx and servos. There is nothing special about these, so I can't see how a comparable mk2 kit would come in much less ? I'm not sure exactly what I could do to lighten ? Any suggestions where to look - perhaps the motor is quite heavy (303g) ?

I guess until I fly her, I can't really tell if 100w/llbs is enough. Doesn't feel it from what I've read, but I will defer to those with the experience I'm worried what I'll have in the "tank" towards the end of the flight - at about 3.8v/cell I got about 450watts !

I will weigh her again - I did have one set of scales tell me it weighed almost 20llbs - needless to sat those aren't being used any more!

Regards, Jason

[Martin Harris - Moderator]

I wonder whether this sudden reduction in the effectiveness of Watts is due to the size/weight of what is perceived as a normal electric model? I too remember when 100 W/lb was regarded as rather spirited and "expert" territory - and it wasn't all that long ago! However, models were typically in the 40 inch range and constructed with great regard for lightness. As we probably all know, as size goes up, so does acceptable wing loading and power required increases consequentially.

[Jason Hyland]

Posted by Frank Skilbeck on 13/08/2016 20:18:58:

Just run through a similar kv motor and that prop on a 4s battery on ECalc and it says 600 watts, so with that combo there's nothing wrong with your system, also says around 3 kg (6.6lbs) static thrust, so you've got 1:1 static thrust, probably not good for pulling out of a prop hang but it won't be lacking for normal flying.

Thanks Frank, I did find a chart which showed a 4s on a 550 kv giving almost 3kg thrust so I figured it would be enough. Didn't know about ecalc, one to investigate!

[Frank Skilbeck]

A 14 x 8 shows 44A and 3.2kg a 15 x 8, 54A and 3.7kg and as your motor is rated for 59A and you have a 60A ESC you've got some room for maneuver. I've just built a 3.2m ASK11 motor glider and I'm running it on a 13 x 6, 800kv motor on a 4s and it takes off on 60% power and climbs quite rapidly pulling just over 30 amps.

[Geoff S]

Posted by Jason Hyland on 13/08/2016 20:27:06:

Thanks for the replies, all useful. A couple of things spring to mind.

First 6.2 llbs is the weight of the assembled ARTF, plus battery, esc, motor, rx and servos. There is nothing special about these, so I can't see how a comparable mk2 kit would come in much less ? I'm not sure exactly what I could do to lighten ? Any suggestions where to look - perhaps the motor is quite heavy (303g) ?

I guess until I fly her, I can't really tell if 100w/llbs is enough. Doesn't feel it from what I've read, but I will defer to those with the experience I'm worried what I'll have in the "tank" towards the end of the flight - at about 3.8v/cell I got about 450watts !

I will weigh her again - I did have one set of scales tell me it weighed almost 20llbs - needless to sat those aren't being used any more!

Regards, Jason

I've bought a set of hand-held digital scales sold to weigh luggage - presumably for flying (in a full-size aeroplane of course, not the luggage on its own ). I find it invaluable for weighing medium sized models with sling round the wing. You can even off-set the weight of the sling and it can be set for either metric or imperial units. They were pretty cheap and remove the problem of trying to balance the model on the scales in such a way as to allow the read-out to be visible.

100 watts/lb is perfectly acceptable for reasonable aerobatic performance. If you want to prop hang then you will need more. It'll certainly fly well enough for you to assess the performance and take appropriate steps. My one reservation is the battery capacity. As Pat says, duration will be limited.

I anticipate my Ballerina to weigh about 4.5/5 lbs (just over 2kg) and the current set up on 4S draws 30 amps on a 12x6 prop ie roughly 450 watts. As the motor is rated at 50 amps and the esc 60 amps I have plenty of headroom to get more power with a bigger prop but I'll probably test fly it with the 12x6. It's approaching test flight time so I'll soon know.

Geoff

[gangster]

.Jason the 600 watts you are getting sounds reasonable time me for. 4s although I have not closely looked at the spec of the motor. You cannot get a quart out of a pint pot. you suggest you are expecting 1000 to 1200 watts. If you were to prop it to achieve that you would be looking to draw Iro of 80 Amps The esc would not like that nor would the duration of the flight be that long. All of the parameters of the motor must be within limits not just max power. The answer lies in speaking to the motor supplier and taking their recommendation re battery prop etc. You may even need to go to 5s I am sure the acrowot would fly on the set up you have try it and decide later if you need more power

there will always be those that tell you that you need 1200 watts to fly an aw they are probably the electric version of those who insist they need a 90 or 120 glow

[Jason Hyland]

Hi all, I thought I'd report back after a few weeks flying the AcroWot.

This setup works like a charm. I regulalry get 7-8 minutes of flight that includes it's fair share of full throttle.

It required a little lead on the tail to get the balance right but other than that I feel I have pleny of power, certainly for my standard of flight ! I can happily receommend the 4-max suggested setup and I'd also like to thank George over a 4-max.co.uk for all the help and patience he showed during my build.

Thanks everyone for your help !

Jason

[Frank Skilbeck]

Top stuff Jason, just another note to add to the flight duration, I run telemetry on a lot of my electric models and it's interesting to note

1) Just how much the motor unloads and the current drops in level flight

2) At half throttle you'll find you are pulling less than half the static full throttle amps.