What are the benefits of bushless motor

[yclui]

Hello everybody,

I am thinking of getting an electric plane for those windless days on the slope and after going through a number of web sites on electric planes, I still can't tell the major differences between bushless motors and those with bushes - except for the price of course.

Can anyone shed some light on this ?

Thanks,

Y C Lui

[SteveLewin]

I guess you mean BRUSHLESS ?

There aren't any really simple answers. Generally brushless motors are more efficient than brushed motors so you get more power and/or duration out of your batteries. The ones we use are also purpose made for us unlike the cheaper (Speed type) brushed motors which are made by the million for all sorts of other things. So brushless are generally higher quality.

However you can also get high quality brushed motors like those made by Astroflight and several European manufacturers.

Only you can decide if brushless are worth the extra money bearing in mind that they also need special (expensive) controllers. Because of the way they work you can't use the same ESC for brushed and brushless.

Steve

[yclui]

Thanks ! Steve, now I am getting a better picture. I came from the glow engine community so electric powered flight is totally new to me. I have a couple of other questions in mind :

1) It seems that there is an established measure of the "class" of motors. E.g. speed 400 is the term that appears most often in web sites that I have visited. May I know what it means ? do we have (something else)400 ? What does the figure 400 stand for ? Is class 380 motor less powerful or more powerful than class 400 motor ? Does this measure apply to motors of all makes ?

2) Can I use propellers for glow engines in electric powered models ? From photos in web sites that I have visited, most electric powered planes are equipped with propellers having wider blades and they look oversized when gauged with the scale of glow engine models. Is there any reason for that ?

Y C Lui

[SteveLewin]

I tried to post a pointer to a useful electric flight FAQ that would answer your questions but this place obviously blocks all mention of other web sites. Sorry about that, I'm sure someone else will help, I will not be visiting here again.

Steve

[Dave Robelen]

Hello Y C Lui,
I will try and touch on those questions regarding the sp400 motor vs. others, and the prop issue. The speed 400 is a category that basically designates the physical size of an inexpensive brush type electric motor. Within the 400 category, there are a variety of different armature windings that provide a variety of power outputs. And yes, the 400 group is a bit more powerful than a 380. The Hobby Lobby website www.hobby-lobby.com has some very useful information about the motors and props.
Assuming the case where the motor is coupled through a gearbox, I find that the power is about the same as a .09 glow engine. When run direct drive with a small prop fitted to the motor shaft, the thrust seems comperable to a hot .049.
There are a whole different family of props designed to get the most out of an electric motor. Some manufactures include APC, GWS. These props have wider, thinner blades, usually with some undercamber. They are wisely marked with the warning not to mount them on a glow engine. There is no special problem using a "gas" prop, but it will be heavier and make less thrust.
Regards, Dave

[yclui]

Thanks Dave, Regarding the prop issue, I think I will need to try it out before I can fully get it but your note does provide a good ground for me to start from.

Y C Lui

[2NG]

I still can't tell the major differences between bushless motors and those with bushes

Let me see, if I can try to answer, this already answered question.

Brushes is to conduct electricity to the commutator, which then conducts the current to the armature, which consists o plates wrapped with wire. The commutator and armature spin the middle of the motor because of the magnetic fields generated by the current provided by the battery. Magnets bonded to the side of the motor cas interact with these fields, and that makes the comm/armature turn.

Brushless motor have the armature wound on the inside of the bell, and a shaft mounted magnets rotates in the middle. A special ESC sequentially sends current through the armature to spin the shaft that holds the magnets, There are no brush and no commutator, so this is a benefit -- no electrical arcing between the brush and the commutator. Brush motors run cooler, of course that is why it's darn expensive.:) and it is slightly more efficient, but they also required special ESC, well more expensive, as well.

Planetary GB works best with these motors, and the power, is great. Again the only thing is the Pr$ce for each, but the fun is breath taking....:cool: