Brushed Motors compared to Brushless

[EarlyBird]

I have been given two old gliders one is a Precedent Electra Fly and the other is a Carl Goldberg Electra unbuilt kit.

 

Both have brushed motors.

 

Should I bin these and install modern brushless?

 

 

[leccyflyer]

I'm of the opinion that if the old brushed motor works, in getting the glider up there to start gliding, then, unless you are competing, it's making good use of something that works. You'll probably have a motor run of a minute or so to get up there and for most of the flight the motor is just noseweight.

 

Finding a brushless inrunner to drop right in can be a challenge and most cheap brushless inrunners will be far to hot to be a direct drop in replacement, without going to a small prop. 

 

If it were me I'd keep the Electra Fly with the original sp600 and if I had the gear in stock would consider doing the same for the Electra.

[MattyB]

It depends. If the current powertrain is operational then you should be able to  fit an alternative Li based pack of a similar voltage, re-prop to get the current right and go fly. The advantage here is that you won’t need to make any structural changes to the model and you will get more pack capacity than you had before.
 

However, if your motor or ESC is dead you’ll really struggle to replace them now with a brushed setup, so you’ll have to go brushless. That will give you a much better performance of course, but due to the reduced powertrain weight you will probably have to undertake structural changes to the fuselage to get the CG right. For the models you list that should not be an issue, but with fibreglass fuselages it can end up being quite a bit of (very fiddly) work. In your case though I would probably stick to the brushless for the Electra Fly, and convert the Electra from the get go.

Edited March 20, 2021 by MattyB

[MattyB]

PS - This thread might help you on the Electra...

[leccyflyer]

That's one of the issues with going brushless in a glider that wasn't designed for an outrunner -it might need some quite tricky modification to the front end, especially with a slender nose. One of the things to be solved is where do the motor wires go? Outrunners where the motor wires exit the rear of the motor and outrunners in a can can help with this.

 

I have boxes of retired brushed motors and ESCs on the shelf, which didn't stop working when brushless came along. For a model that flies on the motor I'd pretty well always bite the bullet and make the conversion to brushless, but with a powered glider the motor is just a means of getting the glider up there and I'd weigh up the required structural changes to the model and whether those are worth it.

[Cuban8]

Agree, almost certainly not worth the trouble to convert in this instance. The real big plus is of course not having the weight of Nicads that we had to contend with back in the day. A big performance boost in that alone.

[Simon Chaddock]

EarlyBird

One way to look at the comparison between brushed to brushless is that the total installed weight of a brushless/LiPo system will be just under half that of a brushed/NiMh set of the same power. If power to weight is a factor in the performance of the plane then the conversion makes sense even allowing for any installation difficulties. If the existing brushed/NiMh weight is part of the performance and in a glider it might be then the benefit of the conversion is less obvious.

[EarlyBird]

Here is the CG motor.

 

 

 

What surprised me was the lack of any speed control, there is only an on off switch.

In the CG instructions a servo can be linked to the switch or mount the switch onto the fuselage. In the Electra Fly the switch is a micro switch and servo actuated.

The motors can then be switched on and off using a switch on the Tx.

Did anyone just switch the motor on and let it go until the batteries were drained? ?

 

The power train is all very heavy in comparison to a brushless.

 

Looking at this arrangement I am surprised that electric ever caught on.

[leccyflyer]

As it's a powered glider there really isn't any need for anything other than a switch. You handlaunch with the motor running, let the glider climb out to a reasonable altitude, then switch off the motor and do some glidery things. You might have a second or third motor run, depending in how successful you are in finding a thermal.

 

That motor should work with a 2 cell lipo, which will be much lighter than the NiCd pack - but remember you'll still need to balance the model. The micro-switch and servo activation is a bit archaic and could be replaced with a brushed ESC. Does the battery pack also power the radio?

 

That power train isn't representative of electric flight, even at that time, it's just a cheap way of getting a glider up in the air.

[EarlyBird]

11 minutes ago, leccyflyer said:

Does the battery pack also power the radio?

Not according to the instructions.

 

 

Which is obviously good.

 

This is all very interesting to me.

I guess this kit goes back to the early days of RC using converted IC free flight models that flew until they ran out of fuel. 

 

Thanks 

[Dad_flyer]

Is that a servo driven switch?

 

Child_flyer was given a glider with brushed 400 motor. We put in a 2s 1300 lipo and it worked fine. The rear motor bearing gave way pretty soon, it was an old model. A friend gave me a used 400, and it flew on that until I have treated it to a new one (which is really quiet compared to either of the worn ones). I have not made a brushless conversion as it has enough power to climb, and there is limited space as others have mentioned. A lighter brushless would need weight to get the CG correct. Also the Jeti ESC in mine has a motor disable switch, which is really nice.

 

Replacement brushed motors and ESC are available, from Sussex Model Centre and others. They are very cheap.

[Andy Stephenson]

1 hour ago, EarlyBird said:

Here is the CG motor.

 

 

 

What surprised me was the lack of any speed control, there is only an on off switch.

In the CG instructions a servo can be linked to the switch or mount the switch onto the fuselage. In the Electra Fly the switch is a micro switch and servo actuated.

The motors can then be switched on and off using a switch on the Tx.

Did anyone just switch the motor on and let it go until the batteries were drained? ?

 

The power train is all very heavy in comparison to a brushless.

 

Looking at this arrangement I am surprised that electric ever caught on.

EB,

That switch is totally inadequate for the current that motor can take it is very likely to get welded on if it takes all the switch-on surge.

Letting Li-Po batteries get drained till the motor stops is a one shot deal as they will be useless after the first discharge.

[EarlyBird]

I am leaning towards brushless, I have motors, esc and batteries.

 

My plan is to convert the Electra Fly first as a test. It's old and beaten up and I can't make it look any worse.?

Experimenting is part of the fun.

 

The Electra kit will stay in it's box for now.

 

That's the plan so first I have to decide on a suitable sized motor. The Electra OUW is 48 oz in brushed version. This will reduce for a brushless set up. Working on 40 oz I guess the motor needs to be 250 watts?

[EarlyBird]

I was wondering how old the Electra is, in the instructions the Tx is Futaba Conquest.

[PatMc]

Don't even consider the brushed motor.

Even brushless with nickel cells would be better. When I have the time I'll post later to explain my reasons.

 

[EarlyBird]

2 minutes ago, PatMc said:

Don't even consider the brushed motor.

Even brushless with nickel cells would be better. When I have the time I'll post later to explain my reasons.

 

Thanks.

 

One of my reasons not to use the brushed motor is that I don't have any nickel cells. I do have a range of Lipo and brushless esc and probably a suitable brushless motor.

 

More fun on the way I think.?

 

The Futaba Tx looks to be produced 30 years ago.

Interesting. 

[Geoff S]

My first ever model was an ElectraFly.  I used my existing 2 channel 27Mhz transmitter/ receiver (I'd bought it for my 1 metre racing yacht).  As the motor was switched by using the elevator by a difficult to set up mechanism you never really knew if the motor was on or off (plus I had little idea how to fly).  It had a brushed 600 motor and a 7 cell NiCad for the motor (it must have had a separate battery for the receiver/servos because there was no esc).  It didn't last long!

 

I'd fly the ElectrFly as is with the brushed motor and esc, using a 2 cell LiPo (you could use a 3S LiPo with careful throttle control but the motor might get warm) just to see how it flies before spending time on a conversion.   I also have a Sonata E (quite similar to the ElectraFly) and when it had a 7 cell NiCad, I had to remove the wing to change batteries.  With brushless and LiPos I could position the battery further forward so removing the wing wasn't necessary.  That's really the only advantage for a non-competition glider.

[leccyflyer]

59 minutes ago, EarlyBird said:

I am leaning towards brushless, I have motors, esc and batteries.

 

My plan is to convert the Electra Fly first as a test. It's old and beaten up and I can't make it look any worse.?

Experimenting is part of the fun.

 

The Electra kit will stay in it's box for now.

 

That's the plan so first I have to decide on a suitable sized motor. The Electra OUW is 48 oz in brushed version. This will reduce for a brushless set up. Working on 40 oz I guess the motor needs to be 250 watts?

That's 100w/lb and you won;t need anything like that for a powered glider. It will fly perfectly fine on 70w/lb.

[EarlyBird]

1 hour ago, leccyflyer said:

It will fly perfectly fine on 70w/lb.

That's a little motor a 2826 on 3S ? amazing compared to the big heavy brushed motor.

 

This gets even more interesting.

[Geoff S]

I think (from memory) that my Sonata E drew about 20 amps max from a nominal 8.4v battery (lets say 9v) (30 amp esc)  that's 180 watts, for (say) 2.5 lbs?  So the 70 watts/lb that leccy suggests isn't far out.  But bear in mind that those 600 brushed motors are not very efficient compared to even a cheap brushless so I guess you could get away with  50 watts/lb.  After all you're only using the power to get high enough to soar and you only need it in 30 second bursts.

 

I've still got a load of brushed motors somewhere a local electrical parts shop in Derby (Potts) were selling for £2 some years ago.  I think they may still be used for scale type boats where weight is needed anyway to get the displacement right.

[Frank Skilbeck]

One thing to remember is that the old Nicd and Nimh cells dropped voltage pretty quickly under load and at 20 amps I would be surprised if it was giving more than 7v, my Sonata E used to fly on a 600 with a 6 cell battery, but climb out was fairly leisurely ? but it was a lovely flying glider.

 

If you haven't got a brushless motor that fits then a using the existing brushed motor with an ESC and 2s Lipo would work fine, but brushless would be the way to go.

 

BTW the old style Sanyo SCR Nicds didn't mind being completely flattened, so just having an on off switch would be OK, but it probably was operated by a servo, my first electric models had the sophistication of a receiver operated relay with LVC and BEC, luxury ?

[MattyB]

I agree, for sport flying models like this 50-70W/lb on a fine-ish pitch prop will be absolutely fine. I have an old WLM/ Nan models Highlight that I am going to convert to 2S lipo power and prop down a tad, should fly very nicely  if I can achieve the CG without too many mods.

[Simon Chaddock]

EarlyBird

Just to give an actual brushed/brushless comparison these are actual motors I used in the same airframe to turn the same prop on a 3s LiPo.

The brushed motor weighs 3.83 oz (109g). The brushless 1.8 oz (51 g). The brushless is also electrically more efficient so even at the same thrust level it needs a bit less amps.

Just beware it is all too easy to install too much power in an old plane, particularly a glider. Be just a bit heavy handed on the elevator and the wings 'clap'!

I lost a 50 year set of wings that way. ?  

 

[PatMc]

You really need to think how you want the model to perform. If you want the model to climb at a moderate rate for quite a long power run before gliding then anything from 30w/lb to around 70w/lb would do but would limit success in  thermal catching virtually to luck. 

IMO the model performance would be pretty mediocre.

 
OTOH if you want to actively spot then fly to areas of thermal activity the model needs to be able to climb quickly to altitude whilst making progress upwind if possible. Typical climb would be 150 - 200m altitude from a 25 - 30sec burst of power.

For this kind of performance you'd need about 110 - 130w/lb using a motor of about 800 -900kv on 3s driving an 10" or 11" Graupner or Aeronaut prop. Typical suitable motor would be from 3542 & weigh from 130g, bigger & heavier would be no disadvantage if it helped with the cg. The cg position will be less of a problem than has been suggested as both models were designed to have the battery under the wing seat.

A model like this would be using the power purely as a self launch facility allowing the pilot to develop thermal gliding skills.

 

 

 

[MattyB]

2 hours ago, PatMc said:

You really need to think how you want the model to perform. If you want the model to climb at a moderate rate for quite a long power run before gliding then anything from 30w/lb to around 70w/lb would do but would limit success in  thermal catching virtually to luck. 

IMO the model performance would be pretty mediocre.

 
OTOH if you want to actively spot then fly to areas of thermal activity the model needs to be able to climb quickly to altitude whilst making progress upwind if possible. Typical climb would be 150 - 200m altitude from a 25 - 30sec burst of power.

For this kind of performance you'd need about 110 - 130w/lb using a motor of about 800 -900kv on 3s driving an 10" or 11" Graupner or Aeronaut prop. Typical suitable motor would be from 3542 & weigh from 130g, bigger & heavier would be no disadvantage if it helped with the cg. The cg position will be less of a problem than has been suggested as both models were designed to have the battery under the wing seat.

A model like this would be using the power purely as a self launch facility allowing the pilot to develop thermal gliding skills.

All true for a more modern higher performance e-glider, but I am not so sure it holds as true for these models. They do not have the right sections for the kind of “fly to the target spot under power” stuff that you can do with a modern composite model.