Getting my head around electric motors ??

[Christopher Morris 2]

Trying to get my head around the power on electric motors for my Nova 40. The manufacturers recommend a 3520 840KV Brushless & i am having trouble finding one, so i am looking for an alternative that in preference is the same or sightly more powerful. Would be looking more at torque than speed.
Would a 2830 900KV 2-4S Brushless Motor match the above. I was looking at this one, as it got good reviews & a very good price.

[SIMON CRAGG]

Try looking at the "4 Max" website.

Loads of useful info on choosing the best motor, with lots of examples.

If nothing else, it should give you some idea of where to start.

I have recently been down this road, and it can seem really complicated!.

I have been using a programme called "e.calc" which was also useful.

Good luck!.

[kc]

If you give more info about your model and the proposed motor then someone may be able to advise you more. I assume the Nova 40 is the Morris Hobbies Nova 40 which was made for a .40 to 50. glow. This is a model that is not very common in UK but could be compared to a Wot4 52 inch with it's fat wing section. Stating the weight of your model will help.

Also a link to your proposed motor might help determine if it's suitable.

The 4Max site gives a motor for an Aero Flyte Nova but that's a very different model to the Morris hobbies Nova!

Edited By kc on 26/11/2019 12:10:48

[BackinBlack]

I recently acquired a previously cherished (ARTF?) Nova 40 from our clubs recycling centre (ie the corner of the clubhouse where members leave items they no longer want). It's in good condition, with no repairs to the airframe, the covering has faded but otherwise intact. It was previously fitted with an unknown glow motor. I propose to use it for a little relaxed flying over the winter. I was going the glow route but have now decided to convert to electric.

The airframe with servos weighs just over 2.5 kgs or 5.5lbs and at 65" wingspan is somewhere in between things like the Precedent Hi-Boy and Uno Wot or Wot trainer. Accordingly, applying the recommended 100 to 120 watts per lb a motor of 550 to 660 watts would be appropriate.

4-Max recommend a 3547-900 for the Hi-Boy or the 5055-595 for the Uno-Wot. I have opted for the larger motor as the Nova appears to need that weight up front for correct C of G. Also the larger motor will come in useful with my plans for future aircraft.

Hope that helps.

Edited By BackinBlack on 26/11/2019 12:44:47

[Piers Bowlan]

It may be the Ripmax Nova 40 (now discontinued I believe) but they are still selling the Super Flying TRI-40 which looks very similar (63in wingspan) and they recommend a 3520-840kv motor on a 4s 2600LiPo and 60A ESC.

A 2830-900 motor is physically smaller and would not be able to handle the power (Watts) of the larger motor specified (without melting). A phone call or email to 4-Max will take the guess work out of it no doubt and save you wasting your money on something that turns out to be unsuitable. Good luck.

Incidentally, I have had some good results with the Aerodrive SK3 motors from Hobbyking. This one is quite close to the recommended spec. albeit a little longer but the best way to establish the most suitable propeller for it is to run the motor with a watt meter.  

 

Edited By Piers Bowlan on 26/11/2019 13:18:26

[Martin Harris - Moderator]

The important thing to bear in mind with electric motors is the importance of the choice of propeller. If you're coming from an IC background you would be used to experimenting with propellers to achieve the best model performance and maybe noise combination. With electric power, a change of propeller can lead to overloading the motor and rapid irreversible damage to its windings or terminal damage to the ESC.

Either stick to a known combination of components or be sure you understand the calculations and measurement required to avoid overloading the various power train components. Programs such as motocalc and ecalc are a useful way to establish likely performance and suitability.

[Bob Cotsford]

the 3520 looks to be much the same as the 3536 900kv motors common in the Wot series of foam models, Riots and the like and is described as being Power 32 class. I'd have thought it a bit small for a 40 size trainer, I'd go for a 4240 650kv Propdrive on 4S for this size model, though the 4-Max 5055 595 would be ok on a 13 or 14*7 prop.

[Alan Gorham_]

I'd consider prop clearance on a 40 sized trainer before thinking about using a 13 or 14" diameter prop. You might be restricted to 10 or 11" (12" at a push) unless you fitted larger diameter wheels.

Edited By Alan Gorham_ on 26/11/2019 14:24:35

[Peter Miller]

Just Phone George at 4-max with gthe details and he will give you the perfect set up.Simples!

[Christopher Morris 2]

Thanks for the feed back. Oddly enough i picked up two old planes cheap that are in there boxes new.. One being this one we are talking about “Ripmax Nova-40” & also a Seagull Boomerang 40 & looking at the planes & taking a few measurements, they are about the same in size & weight. Now, for the Boomerang Max 4 recommended a kit they do for the conversion **LINK**
Using a 3547-800 motor with a 50amp esc & a 12x6 prop. I am thinking the same kit for both. But just so i have a little in reserve, what would the next size motor up be from the 3547-800. I already have a couple of 80amp ESC with 5amp becs spare, so its the motors & batteries to get. Thanks
Ps: both planes will be tail draggers with larger wheels, so prop size should be ok.

[Piers Bowlan]

According to the spec. sheet on the 4-Max website for the 3547-800 motor, it is only rated for 36A for 10 sec and 29A continuous. This means that using the nominal voltage for a 4s LiPo of 14.8V at 29A will only yield about 430W, which is probably enough for a trainer but with an all up model weight of 6lbs that is only about 72W per lb. I tend to agree with Bob regarding choice of motor. Perhaps the '29A continuous' is a little conservative? Fitting a larger prop will provide more power but for how long if you exceed the spec?

Larger wheels may help with ground clearance but regarding it being a tail dragger, it shouldn't make any difference during take off as the model should be in a pretty much level attitude before unsticking. Dragging a model off the ground in a nose up attitude often does not end happily.

If prop size/ground clearance is an issue and you don't wish to fit a taller landing gear, then fit a motor with a slightly higher kv and reduce the prop size accordingly. At times like these a Watt meter is your friend.

 

Edited By Piers Bowlan on 27/11/2019 11:11:03

[Shaun Walsh]

You probably need something like this, 755 watts 1250Kv

**LINK**

[Caveman]

Hi Christopher, I have a Nova 40 - it was my first RC model.

A couple of photos to show what it looked like brand new, and its current appearance after a refurb following an argument with a field of maize!!

In the original it was powered by an Irvine 46 and now by an ASP 46, both two strokes offering about 750 Watts of power.

Alan Gorman is quite right when he warns against a motor that needs too large a prop as ground clearance is definitely an issue, especially if your grass is a little long.

Mine is currently flying on a 10x6 three bladed prop which gives good performance and adequate ground clearance.

Hope that helps.

GDB

[Christopher Morris 2]

Thanks for all the input everyone. I was trying a spread sheet to help. Do the calculations look right?? or should i add a percentage . There is an example at the bottom. Or am i wrong??

Link to larger image.

 

Edited By Christopher Morris 2 on 27/11/2019 13:47:50

[Nigel R]

I can confirm that 3548 (in my case a 900kV variant) is broadly equivalent to a 40 size glow, on either 12x6 or 11x8 prop, when using a 4 cell lipo.

My setup measures approx 800W freshly charged, and 700W at end-of-flight, using a 4S 5000mAh 20C lipo, and APC 11x8.

I use a higher pitch; mine is not in a trainer. In the Nova I would probably plump for a 12x6.

[Nigel R]

The motor in question (or identical spec one) on Hobbyking:

3548 900kv propdrive v2

[Peter Beeney]

Chris,

Just to get a general comparison with an i/c engine in the Seagull Boomerang I used one for quite a while with an Irvine 53 up front. I can say, though, this really does amount to plenty of power, there is definitely a little in reserve, …and then a little more after that, too!

The Irvine power figures are 1.82PS, that about 1.8 hoss, at 17,000rpm. I reckon that a bit fanciful, there can’t be much of a prop on it at that speed so I’d say a rather more practical performance, from experience, would, on a good day anyway, be around 11,000rpm on a 11 x 7 APC. I’d best guess the output to now be down to around perhaps a conservative 1.3HP. That’s 970 watts on the hoof and if the ’rang weighs in at 6lb that equates to 160W/lb. …which by coincidence also gives it a fag-packet S&L speed of 70mph!

So finding a motor that can turn an APC 11 x 7 i/c prop at 11,000rpm might give similar results. I can say, though, that the Irvine will run flat out for 20 minutes on nine ounces of fuel. I did measure and time it. And just dropping in some more useless information, as I related in a thread long ago just to prove a point, this engine ran normally on one occasion on standard fuel with 10% of wet water added. Most of time I was flying the Boomerang I was expecting the wings to fold but they never did. In fact the model handled it all very well indeed for a long time but at this power level I would definitely use a minimum 8 count proper wide 9” lacky band wing fixing.

Of course I’m sure it will fly much more sedately, but still perfectly adequately, on much less power if you want.

As I remember about flying the occasional Nova back in the day it’s a small lighter model so I’d imagine it wouldn’t need quite such pokey motor.

Good luck.

PB

[Caveman]

Just for general interest my Nova, it's 66" wingspan incidentally, weighs 5lb 13oz without fuel, so around 6lb ready to fly.

GDB

[Peter Beeney]

Well there yer go, Caveman, I stand humbly corrected, just shows you how your memory can play tricks - especially when you get old… It was the original colour scheme that reminded me…

So slightly larger than the Boomerang then; thus will be similar power requirement methinks. Your choice of a 46 size looks good, at least for proper and sensible flying at any rate; and your conversion of 750W is standing very close indeed to 125/lb; but I’m sure you already know this anyway. For an electric power plant I think I’d may be looking at a nominal 850 - 900W labelled jobby and I also like to spend time finding exactly the right sized prop to suit the installation.

One other way that sometimes works of overcoming the ‘prop too long’ problem is to fit a slightly larger nose wheel.

Well done on keeping the model flying so long. It must be knocking on a bit by now…

Happy landings…

PB

[Christopher Morris 2]

Must say a big thanks to you all, its like being back at school from what i can remember from that far back. I will try * make up a simple spreadsheet to help with calculation from petrol to electric & motor & batteries size that is needed.

Thanks