Testing 12V Brushless DC Encoder Motor

Bit of context behind the project:

Project is related to surface drill rigs in the mining industry. Basically I’m design a control system that modulates the rotation speed of the drill to accomodate for the different types of ground conditions it experiences.

Hard Ground Conditions = Slower Rotation

Soft Ground Conditions = Higher Rotation

Due to time constraints I did not have enough time to explore toque applied as rotation and torque go hand in hand

Hi Steven


A0 should be connected to the centre or variable pin on the potentiometer. The idea being to provide a variable voltage to A0 to vary motor speed.

OK as far as it goes. The AVERAGE voltage will change but to get this average a bit more is involved.

Should be via a current limiting resistor. The gate of the mosfet will be a short circuit at the instant of switching so the driving device (Arduino, RPi etc) output needs to be current limited to prevent damage.


Here is where you go wrong.
The mosfet is a switch being rapidly switched on and off by the PWM pulses. These are a series of pulses which vary in width depending on potentiometer position. PWM stands for “Pulse Width Modulation”. The mosfet switches full voltage to the motor but the TIME it is ON is controlled by the PWM signal. Thus the AVERAGE voltage (which would be the voltage measured by a DC meter) varies in proportion. This method has the advantage that almost full torque is available at low speeds due to full voltage being applied to the motor at all times. It is only the relative ON and OFF time that changes. If it was just the DC voltage that changed there would be almost zero torque available at very low speeds and the motor would be lucky to start under load.
There have been volumes written about controlling motor speed using PWM and I am sure Core etc have provided tutorials. I would suggest you do some reading for yourself.

Have no idea. All pretty confusing.
Cheers Bob

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As it happens in the mid 50’s during my misspent youth I worked for a couple of years on diamond drill rigs mainly core drilling for coal. These machines were powered by quite large 6 cylinder petrol engines and one was diesel via the normal truck type clutch and gearbox eventually rotating the drill head and powering the winch. One machine was converted to electric for use inside a coal mine. This was a large intrinsically safe electric motor and control system replacing the normal power unit. I think from memory the clutch and gear box were retained. The whole thing was run from mine power.

What I am getting at here is the comparison in sheer size. I am assuming your exercise is getting a handle on how this might be done using more manageable devices. I fee sure some of the main principles would apply only on a very much larger scale. I wasn’t into electronics at the time and I haven’t dealt in control of such a large beast since so have no idea of the finer details.

I have no idea what size your drill rigs are (the ones I had dealings with were Mindrill A2000 I think they were which implied a 2000 Ft capability with A drill rods) but practically, electric power could be a problem but that is not the subject under discussion.
Cheers Bob


Hi All,

The DC motor all of a sudden stopped working? Any suggestions as to why?

After I have rigged up my project it was working well, left it how it was on the table did not touch or move it for a few days and went to test it today and its not working. Pulled everything apart and re built it and still nothing. Wired it up how I did to test the motor (as shown above) and nothing.

3 days out to my presentation and my project stops working any suggestions would be greatly appreciated



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Problem Solved:

Went back to the very start and re soldered all the wires and it works now.

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Hi Steven

Well that is not a terribly smart idea. If it was working before there is nothing wrong with your wiring (connecting points etc) and there is a fault. You are not going to find it by rebuilding the whole thing. If it repeats are you going to just keep rebuilding it?

Working now? Good. Probably a bad solder joint but you will never know now will you???
Cheers and have a think about the benefits of some logical trouble shooting.

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