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Brushed motors

Motors
In what we call a ‘brushed’ motor, the coils of wire are wound around the poles of the armature which is caused to rotate inside a permanent magnet or magnets. These magnets are fixed around the inside of the motor case. The almost-universal way of conducting the electrical current to the coils of wire around the armature is via fixed carbon ‘brushes’, which rub tightly against brass contacts on the armature as it spins around. These contacts form what is called the commutator of the motor. The rubbing action creates quite a lot of friction and heat; it can also create electrical sparks which in turn put out a very messy radio signal. This unwanted radio frequency (called RF) can interfere with the signals received by the radio in your model and cause servos to twitch uncontrollably. This effect is known as Radio Frequency Interference or RFI for short. You can, and should, fit small suppressor components called capacitors to the motor as shown in the diagram, Figure 17, to eliminate the effects of RFI, Photo 17.

Motor suppression is not as necessary if you are using a microwave-frequency radio (2.4GHz), but if you are sailing with others who aren’t, then the RFI created by your motor might just be 'loud' enough to interfere with their radios. Further measures may be needed if the RF still causes twitching servos in your model. These can include earthing the case of the motor(s) to the propeller tube; twisting the two wires from the speed controller to the motor together and/or passing these wires through and around ferrite rings. A full treatise on suppressing motors can be found on the Internet at:


 
 
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