Keeping within limits

[Steve Colman]

Recently acquired a second-hand VQ Model Spacewalker. The model had been flown with a 3548 1100kv motor, 13x6.5 prop, 60A ESC, 3s 4000mah lipo. The motor is rated for 42A.

Trying the above on a wattmeter produced around 550w at 53A. This seems to be stretching the limits a tad in my opinion.

I would prefer to fly the model with a 4S lipo. Ideally, the motor should be replaced for another of lower kv more suited to the model, but for the moment I'm being a cheapskate and experimenting with different props.

Today I got the following figures using a freshly charged 4S 4000mah lipo and a 10x6 prop.

75% throttle = 560w @ 36A

100% throttle = 720w @ 48A

While at normal flying/cruising speed the figures are well within acceptable limits I believe. Now, given that the motor is rated for 42A should I be over concerned about the 48A reading obtained at full throttle which may be used occasionally in flight?

I will also be testing a 10x5 prop tomorrow which should bring the figures down very slightly.

Your thoughts and advice gladly received.

Steve.

[Dave Hopkin]

I take manufacturers specs with a skip full of salt usually, if the motor has been run many times on the set up you inherited drawing 53A I dont see that its going to come to harm drawing 48A on the 10x6 to be honest

[Bill_B]

Take cheap Chinese motor specs with a pinch of salt if you like, but quality manufacturers like Mega, MVVS, Hacker, Plettenburg etc. usually provide figures that ensure the best efficiency is extracted from their motors.

[Andrew767]

Posted by Dave Hopkin on 06/04/2015 21:41:26:

I take manufacturers specs with a skip full of salt usually, if the motor has been run many times on the set up you inherited drawing 53A I dont see that its going to come to harm drawing 48A on the 10x6 to be honest

+1

If 42 amps is constant then 48 at burst should be no problem.

Andrew

[Tim Mackey]

And also remember that those static figures will reduce by at least 10% as the prop inloads as it moves through the air.

[Bill_B]

Tim, I now the following info is probably not relevant in Steve's case, but not all props unload in the air, some actually increase their loading. An example can be where the diameter and pitch are equal, or the pitch is more than the diameter. But then props such as a 13" x 6" folder can equal their static Amp reading if used for constant vertical performance such as in a Hotliner.

[Steve Colman]

Thanks very much for your responses gentlemen.

I will try a 10x5 prop today and then decide which way to proceed. Long term I think the purchase of a more suitable motor will be the way forward.

[Old Geezer]

And don't forget all the figures specified/claimed are predicated upon your ESC and motor being adequately cooled.

[Cuban8]

Posted by Steve Colman on 07/04/2015 07:17:03:

Thanks very much for your responses gentlemen.

I will try a 10x5 prop today and then decide which way to proceed. Long term I think the purchase of a more suitable motor will be the way forward.

Have a feeling the 10X5 on 4S will be down on performance in comparison with the the 13X6 on 3S. Noisier as well. Interested to hear how the test flight goes given the UUW of the model is quoted on Ripmax site as around 6lbs.

[Steve Colman]

I flew the model on Sunday.

Rather stupidly, first flight on 4s with a 11x5.5 resulted in plenty of power but way too many amps.......I landed after a short test flight and 10 seconds later I had no control of either the motor or control surfaces. A very lucky escape!

Later, after checking that all was OK, I tried a 3S with a 12x6 prop and this set-up was way underpowered and the lipo wasn't happy at the end of the flight either.

Hence, my present quest to find a balance between the two extremes. The previous owners 3s set-up did provide adequate performance but at 53A I felt that this was too much for the motor. I do agree that with the model weighing 5.5lbs a 10x5 / 10x6 prop on 4S may not perform quite as well and I may end up disappointed. That being the case, I think a small investment in a new motor will have to be the way forward.

[andyh]

try something like this with a 12x6:

**LINK**

I reckon it'd be worth the £15 investment

[Steve Colman]

andyh,

I have that one on my radar although it's currently out of stock in both the Euro and UK warehouse. The Space-walker currently uses the 1100kv version which in reality is too high.

Also looking at an Emax 2826/06 which would suit the model well I think.

Edited By Steve Colman on 07/04/2015 15:34:51

[Reno Racer]

On electric models of 40 size and over, I have alway fitted an OPTO ESC and used a standard NIMH or LiFe for the receiver, as a glow model. That way If all the Amps escape from my lipo battery driving the motor, at least I can dead stick it back onto the patch.

[PatMc]

Posted by Steve Colman on 07/04/2015 15:33:41:

andyh,

I have that one on my radar although it's currently out of stock in both the Euro and UK warehouse. The Space-walker currently uses the 1100kv version which in reality is too high.

Also looking at an Emax 2826/06 which would suit the model well I think.

Edited By Steve Colman on 07/04/2015 15:34:51

I use an Emax 2826/06 on 4s in my Ripmax Druine Akrobat. It only weighs 4.25lb so a 10x7 pulling 32A for 470W is more than ample. I have tried the motor with an 11x7 figures are 14.5v, 39.8A, 575W & 9900rpm.

[Steve Colman]

Posted by PatMc on 07/04/2015 22:33:06:

Posted by Steve Colman on 07/04/2015 15:33:41:

andyh,

I have that one on my radar although it's currently out of stock in both the Euro and UK warehouse. The Space-walker currently uses the 1100kv version which in reality is too high.

Also looking at an Emax 2826/06 which would suit the model well I think.

Edited By Steve Colman on 07/04/2015 15:34:51

I use an Emax 2826/06 on 4s in my Ripmax Druine Akrobat. It only weighs 4.25lb so a 10x7 pulling 32A for 470W is more than ample. I have tried the motor with an 11x7 figures are 14.5v, 39.8A, 575W & 9900rpm.

PatMc,

Thanks very much for that info, just the sort of real world experience I wanted to hear.