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# Tag Info

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The relationship between a motor's electrical characteristics and mechanical performance can be calculated as such (note: this is the analysis for an ideal brushed DC motor, but some of it should still apply to a non-ideal brushless DC motor). A DC motor can be approximated as a circuit with a resistor, and voltage back-emf source. The resistor models the ...

34

The two are largely the same, fundamentally. However, they differer in intended application. A stepper motor is intended to be operated in, well, steps. A BLDC motor is intended to be operated to provide smooth motion. Since stepper motors are used for motion control, repeatability of the steps is desirable. That is, if you start at one step, then to ...

29

The reason to use multiple MOSFETs is to lower power dissipation resulting in a cheaper design. Yes one MOSFET can handle the current but it will dissipate some power as it does have some resistance, typically 9 mohm for the IRFB3607. At 25 A that means 25 A * 9 m ohm = 225 mV drop At 25 A that means 25 A * 225 mV = 5.625 W of power dissipation A ...

25

The torque output of an electric motor is directly proportional to the motor current (not voltage!), and the current (I) is roughly equal to $$I=\dfrac{V-\varepsilon}{R}$$ Where V is the motor supply voltage, R is the winding resistance and ε is the back-electromotive force (back EMF). KV and back EMF The back EMF is the voltage that would be present ...

19

First let's consider just a ordinary brushed DC motor. The hardware mechanically ensures that the windings are switched (commutated) such that the magnetic field is always trying to pull the motor along. The magnetic field strength is directly proportional to current, so the torque is proportional to current. So at a very basic level, the speed is ...

16

From All About Circuits: Brushless DC motors are similar to AC synchronous motors. The major difference is that synchronous motors develop a sinusoidal back EMF, as compared to a rectangular, or trapezoidal, back EMF for brushless DC motors. Both have stator created rotating magnetic fields producing torque in a magnetic rotor. Construction wise, ...

13

I'm a little late in answering this question and I can't yet reply directly to embedded.kyle above, but I wanted to correct a little misinformation given above. My expertise is motors, not controls, BTW. 1) "Universal motors" are entirely different than BLDC or induction motors. Universal motors have wound stators and armatures and have brushes. Just ...

12

It's right there on page 1 of the data sheet. The graph below shows the power output curve being 1.5 watts: - What you have calculated is the electrical input power and this does not equal the mechanical output power ($2\pi n T$). Take the example at 10,000 rpm. That's 167 revs per second (n above). Multiply it by torque (approximately 1.4 mNm) and you ...

11

Does the back EMF limit the voltage the motor can accept and hence it's speed? Hmm. I think you're a little confused. Back-emf limits the motor speed because it dictates how much voltage you need to achieve a given speed. Would an ideal motor have a very high Kt and very low Kemf? No. (The symbol $K_e$ is usually used for the back-emf constant, by the ...

11

After 4 years using and studying electrical vehicles I figured out that "gradeability" (ability to raise a slope of specific grade) depends on motor torque, and torque depends on current. Voltage instead "regulates" how fast a motor can run: the maximum speed a motor can reach is the speed at which the motor generates a voltage (named "Counter-...

11

Driving a motor blind is a bad idea for several reasons: It is inefficient. The most efficient way to run the motor is for the magentic field to be 90° ahead of the rotor. Put another way, the torque on the rotor is the cross product of the driving magnetic field and the rotor's magnetic orientation. With position feedback, the magnetic field can be ...

10

Advancing timing is a practice common to electric motors and internal combustion engines. The purpose is to increase efficiency. In other words to maximize the power out for a given power in. In electric motors, the amount of torque produced in relation to the rotor field vector with respect to the stator field vector is given by: \\$\tau = \tau_{max}~sin~\...

10

The number of poles is the number of magnetic cycles in one revolution of the shaft. When setting up for driving a BLDC, it's useful to step thru the drive phases one by one manually. I usually mark a point of the shaft, then add a sticker or something on the stator to record where the shaft is. I like to use a 12 phase drive. In that case, I go thru ...

10

L/R determines the minimum PWM frequency. To avoid excessive power loss the L/R time constant should be much longer than the PWM period, so that most of the voltage is dropped across the inductance rather than the resistance. It also smooths out the current flow, which lowers peak current and reduces losses in other parts of the circuit. Taking your motor ...

10

Say the record was mean to play sin(wt), a pure sine wave, at 33rpm, then, because of a loosen belt or any other reason, it rotates at a different RPM, how to calculate the changes in such sine wave? The pitch and tempo will change in proportion to the speed change. At 33 RPM it would already be musically flat as the correct speed is 331/3 RPM. A 1 kHz test ...

9

ESCs are controlled using what is commonly referred to as servo signals, this is basically just a 50Hz (20mS) square wave with an on time varying between 0.5mS and 2.5mS and being off the rest of the time, the timing of this pulse can vary somewhat and depends on the manufacturer of the unit. 0.5mS and 2.5mS is a good starting point for any project though. ...

8

The simplest method for sensorless commutation of a motor is to measure the Back-EMF to determine speed and use trapezoidal six-step commutation method to drive the motor. A circuit similar to this one is a good place to start: The section marked 22 is just a voltage divider to scale the phase voltages down into the range of the microcontroller's ADC. In ...

8

The base waveform can be divided into 6 points, each point with the same delay between them. The length of that delay defines the speed of the motor. The 6 points, or phases are: Phase A HIGH Phase C LOW Phase B HIGH Phase A LOW Phase C HIGH Phase B LOW You notice the sequence of phases is repeated, but the signals inverted. Basically it's 3 square ...

8

A drill manufacturer claiming higher torque and efficiency from their brushless motor is probably telling the truth - however that doesn't mean being brushless is the only reason for the improvement. They could put a really bad brushless motor in there that's no better than a high quality brushed motor, but why would they? All else being equal, a brushless ...

8

Don't backdrive it any faster than its nominal run speed on 24V. This means that the back voltage won't be any more than 24V and the commutator won't fly apart. Now you can be confident that your isolation MOSFETs won't blow up.

8

If you can put enough capacitance on the DC bus to absorb the energy without going overvoltage that would be the simplest solution without wasting energy. If not, a common approach is to use a bank of resistors and a comparator on the DC bus. When the voltage approaches the maximum allowable the comparator will turn on, which turns on a MOSFET and puts the ...

8

In a standard sensorless ESC, changing the throttle command to it changes its output PWM duty cycle, and so the mean voltage, delivered to the motor. Typically, 1mS corresponds to 0% or zero voltage, and 2mS corresponds to 100% or full voltage. The ESC continues to automatically commutate the motor as it turns, using zero voltage sensing on the un-energised ...

7

In any motor, the basic principle is very simple: rotational speed is proportional to voltage applied torque is proportional to current pulled A 100 volt motor is a motor that can take a maximum of 100 volts, and a 50 volt motor a maximum of 50 volts. Since the 100 volt motor can take more volts, if all else is equal, it can give you a higher maximum ...

7

A stepper motor is a form of brushless DC motor, but with a specific physical arrangement of coils and stator so as to achieve a fixed number of stops or detents subdividing the full circle of rotation. The number of poles of a stepper motor determine the step size or number of subdivisions, or "full steps", if you like. However, with some fancy footwork ...

7

Looks like a pretty simplistic shaded-pole induction motor. Here's a schematic that's almost identical to your photo: (second one from a Google search) As shown in that diagram, you'll want to reverse the connections on you winding coils.

7

The Zener diodes are simply Gate protection devices. They limit the positive voltage peak to 17 V and the negative to approximately 700 mV. They are typically placed in application builds to provide static protection. For example if the schematic you showed was part of a small plug in driver board and the signals GX_X were connected off board; this would ...

7

Disclaimers This post assumes the reader is roughly familiar with how the electromagnet and phase energization inside BLDC motors generates motion. I use the term "phase" rather interchangeably. The actual control algorithm for sensorless control is beyond the scope of this post. I don't have a firm understanding of that yet. Note regarding "AC" vs "DC" ...

7

The motor controller acts as a buck type switching regulator with the motor windings acting as the inductor. Since the voltage across the windings when stalled is only the resistive drop from the current passing through them, there's no back EMF to overcome from mechanical work being done, the controller will be switching at a (fairly low) duty cycle that ...

6

If only two were used and it moved then it must be a brushed motor. Brushed motors only use two terminals for the operation of the motor, brushless use four terminals I believe (three windings plus ground?). The third could be for some sort of feedback or maybe special grounding. Edit: One caveat - there are some BLDC (Brushless DC) motors that have ...

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