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# Tag Info

110

You're asking about the technical tradeoffs surrounding the selection of a traction motor for an electric vehicle application. Describing the full design tradespace is far beyond what can reasonably be summarized here, but I'll outline the prominent design tradeoffs for such an application. Because the amount of energy that can be stored chemically (i.e. in ...

83

Fans of that type have induction motors with two windings with a capacitor in series with one of the windings. For every individual motor design there is a certain capacitor value that allows the motor to develop maximum torque and operate at the maximum corresponding speed. Smaller capacitor values are used to reduce the torque so that the load overcomes ...

67

Probably you already have it, and just didn't know it. If you are driving a motor with a half-bridge or H-bridge and PWM or similar, you have regenerative braking. Let's consider a half-bridge, since for this analysis we will run the motor in only one direction: First, let's consider non-regenerative braking. If the bridge output is high (S1 closed, S2 open)...

49

The diode is to provide a safe path for the inductive kickback of the motor. If you try to switch off the current in a inductor suddenly, it will make whatever voltage is necessary to keep the current flowing in the short term. Put another way, the current thru a inductor can never change instantaneously. There will always be some finite slope. The motor ...

41

...and now why Tesla uses induction motors The other answers are excellent and get at the technical reasons. Having followed Tesla and the EV market in general for many years, I'd like to actually answer your question as why Tesla uses induction motors. Background Elon Musk (cofounder of Tesla) comes from Silicon Valley (SV) thinking, where "move fast and ...

39

I have to start with some terminology -- sorry if it's esoteric, but this will bring things into line with how folks talk about this subject. When you turn a permanent-magnet DC machine*, the armature generates a voltage internally. This is called the "EMF"** of the armature, or the "back EMF" if the machine is running as a motor. This EMF is always ...

36

The details of how a cassette drive works are well covered by this Wikipedia article. The tape is pulled by a capstan next to the playback head, and this capstan pulls the tape at a steady rate. (picture from the Wikipedia article) You probably need to click on the picture to see it full size. I have indicated the capstan by a red arrow. The take-up spool ...

35

Century old motors were well built! And probably conservatively designed because electricity was new; they didn't know which corners you could safely cut. In those days, everything mechanical was designed for easy maintenance; nuts, bolts, taper pins; simple tools to take the whole lot apart, adjust to take up wear, reassemble and use for another 10000 ...

34

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

A motor driven by an H-bridge is also a boost converter. Here's an H-bridge: Replace the motor with an inductor, resistance, and voltage source (back-EMF): Let's just consider that we are driving the motor in one direction, and S3 is always open, and S4 is always closed: Rotate V1, S1, and D1 (same circuit): flip the whole thing left-for-right (still 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 ...

32

It's hard to know exactly how your specific unit works, but in general there is a timing sensor that is used to read back the mirror's position, as in the diagram below. It doesn't continuously read every position but only once per face change. The measured error is used to compensate the firing of the laser circuit. There are more detailed patents on the ...

31

It is true that it's only the volume and the power fed to the winding that matters for magnetic field, in electromagnets and motors. Therefore, you could have a single turn winding. Unfortunately, a single turn would (generally) require a very high current and a very low voltage. This is true on the scales we tend to work at, and the values that physical ...

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 ...

27

The compressor compresses coolant on one side of a closed loop. If you shut off the compressor, you still have the load side of the closed loop full of pressurized coolant. That pressurized coolant makes it much more difficult to start the motor. A motor starting at 0 RPMs will want to draw large amounts of current. With an added load to the motor (...

27

I would be surprised if a cheap DC toy motor contained a rectifier diode since it's designed to be a DC motor, not a DC generator A cheap DC motor of the type that has a permanent magnet stator uses brushes and a rotor commutator to continually reverse the current into the rotor coil thus the effect is like feeding AC into the coil: - If you didn't do ...

25

One way to do this is to briefly stop driving the motor, long enough to let any residual current from the driving voltage die down, and then simply measure the voltage. The time it takes the current to settle will depend on the inductance of the windings. This is simple to understand, and the undriven interval can be made quite short, but this has obvious ...

24

It's hard to say what the engineers' exact reasons were without being on the design team, but here are a few thoughts: Both motors require similar drives. Brushed DC motors can run directly off a battery but the type of motor you are looking at in an electric vehicle is a brushless DC motor. The drives for an induction motor and a brushless DC motor are ...

24

The main point of a stepper motor is that you get discrete steps. However, the cost is larger size and lower efficiency than a continuous motor of the same torque. Stepper motors also have a low upper speed. The advantage of discrete steps can outweigh the various disadvantages when the system can be controlled open loop. If you're going to provide ...

23

A motor with 1 kg.cm torque is capable of holding a 1 kg weight at a radial distance of 1 cm. Here is a diagram to explain. Torque is the cross-product of force and distance: $\tau = F \times d$. So the same weight, at twice the radial distance, will require double the torque. Note that the measurement 'kgcm' is 'kilograms-force × centimetres' and ...

23

The purpose of the brushes is to make electrical contact with a rotating conductor (the commutator). Originally, these were bundles of wire that would be dragged across the commutator. At any time, at least a few strands of the wire would be making contact. These bundles, of course, look like "brushes". Things have improved though, and now we use solid, ...

21

Power efficiency The induction of the motor will cause the current to average. At the same time the transistors in PWM mode have very low impedance and therefore a low voltage drop and low power dissipation. In case of a series resistor a lot of power is dissipated in the series resistor. Speed control behavior With PWM the motor will 'see' a very low power ...

20

Use a better power supply than a 9V battery- one that does not change output voltage significantly regardless of the number of motors. You could also add a regulator. For example, a 12-volt SLA (Sealed lead-acid) battery with a suitable regulator for the currents involved would be almost perfect. Even without the regulator it would be pretty good (provided ...

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 ...

18

Torque is a measure of "twisting force". Power is a measure of twisting force x speed. Torque is usually expressed as a Force x a distance So for the same Torque if you double the distance you halve the force to get the same answer. So kg.cm is kg force x centimetre distance. In fact kg are a mass and not a force BUT kg are sloppily used as a force in ...

18

this motor has a reduction gear that slows it down, to 5 rpm at 50Hz or 6rpm at 60 Hz. Actually the rotation speed of a synchronous motor in rpm is given by: $$\frac{2 \times 60 \times f} n$$ where f = frequency (Hz) n = number of poles. The motor in your photo cannot have 1200 poles, so it surely has a stepdown gear.

18

Motor capacitors are not plain electrolytics, because the voltage across them reverses at the mains frequency. The larger value ones are start capacitors - usually bipolar electrolytic, and rated to the peak mains voltage - but not for continuous operation. They are usually disconnected by a centrifugal switch in the motor, which operates when the motor is ...

17

TLDR: No, you cannot use those batteries to power that motor. Nothing bad will happen if you try, but the safety cutoffs will engage the first time you try to turn it on and it just won't work. If your requirement demands more energy density and energy per kilogram than lead-acid can provide, your only option is to use high discharge rate LiPo cells. By ...

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, ...

16

Because AC motors are generally much more efficient than DC motors, and since they don't require electrical contacts to the rotor, are more reliable as well. Remember, a BLDC motor is really an AC motor with the drive circuitry built-in. At higher power levels, it makes sense to separate the control and drive circuitry from the motor itself. Also, motors ...

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