How a (PMDC) Controller Works (so you can see)

Controllers work by feeding pulses to the motor- full voltage,  on/off, really fast.  What the geeks call it is “Pulse Width Modulation”.  Now, if you want to see that, you have to set up an oscilliscope, which I don’t know how to spell.  Wait.  Oscilloscope.  There. In this video we can see both the silly scope, and the controller monitor on this video:

So, watch the numbers on the Alltrax readout, especially the throttle setting.  Now, watch the silly scope lines- the lower line is zero voltage, the upper line is 100% voltage, and the length of the lines shows the width of the pulses.  With no throttle, you get a solid line a 0 voltage, right?  The more the throttle feeds the controller, the longer the line at 100% gets, until it’s solid…  You can’t really see the “curve”, or, by that I mean the vertical lines connecting the 0 value to the 100%- don’t let that throw you.

Here are some screen shots of some key events.

First, starting out at dead stop.  The line you see is the “0” voltage, indicating no pulse.

This is at 12% throttle, and you start to see the little “100%” pulse line.

This is at 67% throttle, the “100%” line gets longer, indicating the pulse’s duration at 100% voltage is increasing.

At 93% throttle the pulse is solid- you’re essentially getting full voltage, all the time.

This is interesting.  The motor is now at maximum RPM (unloaded) and the throttle is wide-open.  However, the controller has backed off on the pulse duration.  Makes sense…  it’s not working as hard since the motor is not accelerating.

This curve stayed like this for quite a while, as the motor was spinning down.  It’s interesting, too, to take a look at the various performance numbers- voltage, temperature, draw…



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