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29

It doesn't, the motor itself does. Once the rotor starts spinning, the motor produces a voltage that opposes the flow of current; this is commonly called "back EMF (electromotive force)". The motor's speed increases until the back EMF reduces the current flow to the level needed to account for the actual physical load on the motor (plus losses). The heavy ...


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 ...


15

No. You don't match rotations per second to PWM frequency. It needs to be much higher. You want it high enough so the motor runs smoothly (motor inertia smooths out motion and motor inductance helps smooth out current), but not so high the switching losses in your electronics is excessive. Often at least 8-10kHz, but you might want >20kHz if audible noise is ...


14

You want the motor inductance to result in reasonably low ripple in current during the PWM cycle. Here is one drive maker's rule of thumb: \$ f_{PWM} \ge \frac {0.6V_{SUPPLY} }{L_{MOTOR}\cdot I_{NOMINAL}} \$ This formula results in quite a bit of ripple, around 40% peak at the limit and D=50%, so a bit higher frequency might be desirable, especially if the ...


13

Too wide a question set, and some don't matter. How fast?: 30 kph is getting fast for something small and unstable. Energy at 30 kph is \$(\dfrac{30}{20})^2\$ which is over double of that at 20 kph. Probability of pedestrian death in vehicle impact is \$\sim\sim\sim\sim\dfrac{V^2}{5000}\$ (V in kph). At 30 kph, the chance is \$\dfrac{30^2}{5000} = \sim 20%\...


12

I was recently (today) helping someone with their home renovations, including replacement of the three-speed fan controllers. The old one, which we ripped out and replaced, is shown below. Note the crude circuit diagram on the black box object (the fan speed controller.) I infer that the fan controller works by inserting a capacitance into the fan's power ...


10

Using a voltage divider as a power source for almost anything is a Very Bad Idea. The actual voltage supplied to the load will vary with the load current. I expect that the current drawn by an Arduino will be Much, Much Greater than is drawn by your 10 meg resistor, so the voltage will be much less than you expect. You should use a DC-DC converter (AKA ...


10

Neither. You should use a potential divider: simulate this circuit – Schematic created using CircuitLab edit: Just to add, this will give a 0-4V wave at 24Vin, and a 0-2V wave at 12Vin. This is still fine, because the Atmega32 (supplied at 5V) will see anything above 2V as a "1".


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. ...


9

A control system is only as good as it's sensor, run the sensor open loop and remove the control input. Create your own input to the sensor and slide it slowly (or find a way to slide it slowly reliably) while taking position data to make sure it's not the sensor. If the sensor is noisy, then improve the performance of the sensor by getting a new sensor or ...


8

The way I would approach this is not to modify the ESCs at all. That way leads to frustration. You'll have much more luck by making an I2C -> PWM module. This is easier than is sounds. Firstly, a little about RC servo PWM An RC servo expects to see a pulse about every 20 milliseconds (50 times per second). The length of this pulse tells it what angle to ...


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

They are both acceptable solutions. Notice in a 555 timer, the discharge pin is simply an open collector version of the output signal. In circuit diagram 1 the 555 timer is configured as a square wave generator. The charge/discharge path for the timing capacitor is from the 555s output which will be near top rail or bottom rail. Since, with the pot at 50%, ...


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 ...


8

One advantage i can think of is that the low inductance of axial-flux motors means that they have low electrical time constants, allowing current to flow very quickly into the armature for virtually instant torque production , which should translate to fast acceleration and deceleration which maybe desirable for high performance servo control.. BUT: ...


7

Don't forget about the inductance and back EMF. If you were to put 11.1V DC across the winding you would wind up with 92.5A of current in that phase, but the impedance to an AC signal is higher. Once the motor starts turning it generates an internal voltage, the back EMF that fights the drive voltage. In many drives the current is controlled via current ...


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

I don't understand why only one of the MOSFETS is being driven with 15V, and the other 12V. That DC-DC converter wasn't included because the high side MOSFET needs 15 V (it does not). The NME1215SC DC-DC converter module was selected because it is an isolated design, meaning that (like the optically isolated gate drivers) the power input is not ...


6

The blue wire is a PWM control signal which can be used to adjust the fan's speed. The yellow wire is a PWM speed sense that can be used to read the speed out of the CPU. To control the fan's speed, you need to give it PWM: a square wave adjusted to the speed you desire. This is doable with a microcontroller's PWM peripheral. I'll direct your attention to ...


6

Voice of experience: Use a jackshaft and additional belts/pulleys, &/or change to a different motor (DC with DC speed controller or 3-phase + VFD (variable frequency drive) variable speed.) The DC motor and speed control can often be salvaged from a treadmill that someone gave up on using, for free. The fundamental limitation of running induction motors ...


6

It's a dimmer circuit, electronics-tutorials has a really great article on it: http://www.electronics-tutorials.ws/power/diac.html "If we wish to control the mean value of the lamp current, rather than just switch it “ON” or “OFF”, we could apply a short pulse of gate current at a pre-set trigger point to allow conduction of the SCR to occur over part of ...


6

One thing I have done in BLDC motor driver development is to put a suitable incandescent lamp in series with the bridge power supply. If the light comes on bright it just saved you a set of transistors. Of course you are going to follow proper code development techniques to make the BLDC drive logic as independent as possible of the rest of your program, ...


6

You've misread the part number. This is an ST GP7NC60HD IGBT. Steps I took to identify this: Recognize the ST logo (lower left). Go to st.com. Type the recognizable letters "GP7N" into the search bar; the rest of the part number is suggested as a search result.


6

Some things you are going to have to resolve. The motor you linked runs on 12 to 24V. Not the 3V you show in your proposed circuit. The 2N3904 NPN transistor is unsuitable for this application. They are typically good for up to ~200mA whilst the motor specs a load current of 300mA and that will grow as more load is placed on the motor. A resistor in series ...


6

One reason a gate resistor is used is to slow down the turn-on and turn-off of the MOSFET. (This is more relevant to power circuits that switch a fair amount of current.) While it may seem that very fast switching is desirable, because of lower switching losses, it can result in ringing due to parasitic inductances, leading to electrical noise problems. ...


6

voltage is proportional with torque and current is proportional with speed No. Torque is proportional to current. The back EMF is proportional to speed. A workable first-pass model of a motor is a voltage source in series with a resistance. The resistance is the physical resistance of the windings. The voltage of the voltage source models the back EMF, ...


6

It is old, old standard that predates cheap microcontrollers, and in fact predates consumer integrated circuits! The very early proportional radio remote controls used timing based on unijunction transistors in ring oscillator style arrangements, and the standard has not turned out to be poor enough to make agreeing a replacement worth the trouble. ...


6

You are correct that the problem is from friction, or possibly a combination of friction and backlash. Your plot of average speed vs. duty cycle for various pulse widths is characteristic of a system with friction. This paper explains what you're seeing, and has a compendium of solutions that have been used since forever to deal with the problems. You ...


6

Yes and no. If the motor will be going continually in one direction, you can sweep it under the rug by calling it a constant disturbance torque. If the motor will be constantly running one way or another, particularly if you have an inner velocity loop, you can measure your system response (I prefer swept-sine measurements), model the system based on those ...


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