Thread: Discussion Parkzone UM Spitfire with AS3X
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Old Feb 12, 2012, 09:24 AM
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Originally Posted by electricrc68 View Post
i dont really know much about motors, so what is the issue with using a brushed motor?
Adding to what RG posted....

Brushed motors are typically less efficient than well-designed brushless motors. A brushed motor with a given output power will be lot heavier than a brushless motor of similar output. Brushless motors usually last far longer than brushed motors, and their power output remains constant over their lifespan.

Here's the deal with these little motors. The 8.5mm brushed motors used in these UM planes are called 'pager' motors. They are not intended to be used as powerplants. Rather, they are designed for intermittent, very low duty-cycle applications - such as vibrating pagers & cellphones, operating DVD drawers, changer carousels, and the like. Their brushes are very delicate, and they used brass bushings instead of ball-bearings.

Using them as aircraft powerplants is about as close to the polar opposite of the manufacturer's intended use as one can get. Because of this, we have seen significant variability between samples. Reliability is all over the map. Some last for hundreds of flights, some die right away, while most fall somewhere in-between,. Also, we've seen ~20% variability in power output between samples. That's not a big deal when you're vibrating cellphones or operating DVD drawers. However, a 20% difference in power is a very big deal in an aircraft.

The small brushless motors are designed for use as powerplants. Since there are no brushes or commutator strips to wear out, their output power does not diminish over time. Power output between samples is also far more consistent than it is with the cheap pager motors. They also use ball-bearings instead of bushings - which contributes to their long life.

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