caliliving949 said:
Thanks for the reply.
But what would varying the amount of current the motor sees have to do with sensors?
'Chopper' means that the MOSFETs are switching the battery current (i.e. chopping it) rapidly on and off: if the battery is only connected to the motor half of the time, then the motor only 'sees' half the battery voltage. By varying the chopping ratio you can vary the amount of battery the motor sees, so varying the speed of the motor.
Taken from http://www.4qd.co.uk/fea/mos.html
Comments much appreciated...
I think maybe we need to take a couple steps back, just to for clarity.
1st point: The RC motors you see on this site are called BLDC (BrushLess DC) motors. In this type of motor, the windings/electromagnets that you are powering do not move, rather the permanent magnets move. The motor generally has 3 wires comming out of it. If you hooked two of those up to say a car battery, the motor would not rotate. It would rather get really hot, pull alot of current and then start to smoke. The reason is, in order to keep pushing the shaft around you need keep switching the elctromagnets on and off. In a BLDC motor there are 3 electromagnets, generally at any time 2 of them are powered, one pushing the permanent magnet away, the other pulling it forward. That is what the BLDC motor controller (or RC Electronic Speed Controller) does, they switch the coils on and off so that they are always pushing the permanent magents forward. The motor you may be used to is called a 'brushed DC motor' In that type of motor the electromagnets turn, and they have brushes (which are sort of like a rotary switch), which controls the powering of the coils so that they are always pushing the motor in the same direction.
2nd point: In order for the controller to know what coils to power, it needs to know where the permanent magnet is. An RC controller does this electronically, by measuring the voltage accross one of its' coils (the one that isn't powered). This works well, however the motor needs to be turning for it to work so these controllers don't work well when starting from a stand-still. An ebike motor has 'hall effect' sensors inside which give a signal depending on magnetic field. These sensors are always giving the controller feedback on what position the magnets are in, so the controller always knows which coils it should power, even when the motor is stopped.
So, as was stated earlier, if you want to use an ebike controller with an RC BLDC motor, you need to add hall effect sensors to the motor to give the controller the magnet position feedback it needs.
I hope that made sense.
-Matt
