Brushless Motor Minimum RPM

Using Arduino Motors, Mechanics, Power and CNC
1

Hi there,

I will be using brushless DC motors for a project that requires both high and low RPM usage. I heard from someone that high Kv motors struggle to reach lower RPMs, so I need ways of increasing the range of usable RPM. Since I haven't built my project yet, I would struggle to give exact numbers, but another person is using a 1100Kv motor at 9V and finds that he gets the low speed we need, but not the high speed.

I was doing to use an 1800Kv motor at 12V but now I don't know if this will go slow enough. However, I also have a 5V step down in my build plan so I thought could use that and a relay to switch the motor from 12V to 5V for lower speeds.

My questions are these:
1: Will changing voltage work at all to slow the motor's minimum RPM? Is the minimum speed of a brushless motor affected by the voltage it receives?
2: Will switching the power supply require me to recalibrate anything at a hardware level? I don't mind if I have to deal with this in software.

Quick note: these motors will experience next to no load and I know that smoothness of the motor's movement is harmed when you lower RPM to very low levels, but this won't be a problem.

This is my first time writing a post here so if I have not made anything clear enough I will clear it up as soon as possible.

Thanks!

2

BLDC motors are kind of stepper motors. This means high voltage allows for higher RPM but can cause excess current at low RPM. A current limiter can help out.

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So could I do something like 100 RPM or under with this config?

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  1. yes
  2. depends on your "config"
5

If I have a basic ESC from Aliexpress and an A2212 1100-1800Kv motor then I can use a current limiter to achieve low RPM like 100 RPM?

6

Does my 5V idea hold any merit?

7

Then consult the data sheet of that ESC.

Same advice.

1 Like
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One thing, having done more research it seems my motors use the back EMF form the unpowered coil to detect position. This would mean that at low RPMs the back EMF is small and hard to measure by the ESC, so can't control at low speed. How would adding some current restriction help?

I have been contemplating a brushed motor or a sensored brushless too. The only issue is that brushed are noisy and inefficient and sensored brushless motors are expensive in comparison.

Does anyone know of a way of adding these sensors onto sensorless brushless motor?

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Either you need an advanved ESC like VESC, and maybe finetune with results, for low rpm operations. Or, use brushless motor with hall effect sensors. This is the common way to run brushless motors at low rpm. I

10

Yeah, I am going to buy brushed to see if I can get away with it for my project and then if it doesn't work then I'll probably end up having to add sensors to a brushless motor.

Thanks for the help!

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