Do ESC's control Speed or Torque?
#1
Do ESC's control Speed or Torque?
I know the name Electronic Speed Controller implies that it controls motor speed but is it possible ESC's actually control motor torque?
I ask this because I think accelerator pedals in automobiles actually control torque. When I push the gas pedal down 15% I don't expect my engine to go 15% of it's max rpm.
If ESC's really do control motor speed I wonder what the "feel" would be like if it controlled or torque, and vice versa.
I ask this because I think accelerator pedals in automobiles actually control torque. When I push the gas pedal down 15% I don't expect my engine to go 15% of it's max rpm.
If ESC's really do control motor speed I wonder what the "feel" would be like if it controlled or torque, and vice versa.
#2
the accelerator pedal in a fullsize car doesn't control torque or speed. all it does is control airflow into the engine. An electronic speed control is just a high-frequency switch. Unless you have a current limiter, it does not directly control torque or top speed.
#3
Tech Fanatic
iTrader: (2)
Sort of. Electric motor torque is based on the amount of energy draw (amperage) is made available to them over time. Time is the key part of an ESC.
Torque simply is energy applied to a lever - "rotational force".
Torque is T = r x F
where,
r is the vector from the axis of rotation to the point on which the force is acting. (or, the radius of the lever)
F is the vector of force.
So, what the ESC applies control over is the F - the force, or electrical flow. This is done through controling a FET by pulsing it. It's like trying to fill a glass of water by flipping on and off the water faucet at a controlled rate. If you flip it on and off 10 pulses in 1 sec. - takes 10 seconds to fill. If you flip it on and off 20 pulses in 2 sec. - takes 5 seconds to fill.
The ESC flips on and off the flow of electricity to the motor at different rates based on your throttle setting. Full throttle is kind of like hard-wiring the battery to the motor. 1/2 throttle means your flipping the flow on and off at 1/2 the full rate (on/off/on/off). 1/4 throttle is (on/off/off/off/on/off/off/off). The rate of on/off is based on how fast the ESC can flip the voltage on/off into the FET.
So, an ESC is an Electrononic Electrical Flow Control type of thing. Since motors are wired with different turns - each will "draw" more amperage than another as the turn count drops. Flipping on and off the flow is the simplest way to handle any type of motor. Otherwise, you'd need some type of Amperage limiter using various resisters and capacitors to do the same thing through a physical means.
More reading for you: http://www.math.niu.edu/~behr/RC/pwm.html
Torque simply is energy applied to a lever - "rotational force".
Torque is T = r x F
where,
r is the vector from the axis of rotation to the point on which the force is acting. (or, the radius of the lever)
F is the vector of force.
So, what the ESC applies control over is the F - the force, or electrical flow. This is done through controling a FET by pulsing it. It's like trying to fill a glass of water by flipping on and off the water faucet at a controlled rate. If you flip it on and off 10 pulses in 1 sec. - takes 10 seconds to fill. If you flip it on and off 20 pulses in 2 sec. - takes 5 seconds to fill.
The ESC flips on and off the flow of electricity to the motor at different rates based on your throttle setting. Full throttle is kind of like hard-wiring the battery to the motor. 1/2 throttle means your flipping the flow on and off at 1/2 the full rate (on/off/on/off). 1/4 throttle is (on/off/off/off/on/off/off/off). The rate of on/off is based on how fast the ESC can flip the voltage on/off into the FET.
So, an ESC is an Electrononic Electrical Flow Control type of thing. Since motors are wired with different turns - each will "draw" more amperage than another as the turn count drops. Flipping on and off the flow is the simplest way to handle any type of motor. Otherwise, you'd need some type of Amperage limiter using various resisters and capacitors to do the same thing through a physical means.
More reading for you: http://www.math.niu.edu/~behr/RC/pwm.html
#4
Tech Lord
iTrader: (3)
First off you're getting way more technical than you need to be.
On a real car, you're controlling the engine speed by allowing more or less air into the intake. Well, that's the way most cars work. BMW does something different, but is essentially the same concept. By stepping on the accelerator you allow more air in, and the engine responds by increasing RPM, in other words it spins faster.
Technically, if you rev an engine with the transmission in neutral, the torque output is zero, since the engine is not doing any work.
In an electric RC car, the speed control varies the effective voltage to the motor. The speed of an electric motor is directly proportional to the voltage. The more voltage, the faster the motor spins. The torque of an electric motor is related to the amount of current it draws. So the more current the motor draws, the more torque it's producing. Speed controls can control torque by limiting the current. Older speed controls had a small knob you could turn, newer speed controls do this through software. That's bascially what you do when you choose a particular profile. More punch means you're allowing more current, less punch means you're allowing less current.
Brushless motors work a little different. Speed is controlled by the frequency of the pulses to each phase, but you still need voltage to push the current through.
On a real car, you're controlling the engine speed by allowing more or less air into the intake. Well, that's the way most cars work. BMW does something different, but is essentially the same concept. By stepping on the accelerator you allow more air in, and the engine responds by increasing RPM, in other words it spins faster.
Technically, if you rev an engine with the transmission in neutral, the torque output is zero, since the engine is not doing any work.
In an electric RC car, the speed control varies the effective voltage to the motor. The speed of an electric motor is directly proportional to the voltage. The more voltage, the faster the motor spins. The torque of an electric motor is related to the amount of current it draws. So the more current the motor draws, the more torque it's producing. Speed controls can control torque by limiting the current. Older speed controls had a small knob you could turn, newer speed controls do this through software. That's bascially what you do when you choose a particular profile. More punch means you're allowing more current, less punch means you're allowing less current.
Brushless motors work a little different. Speed is controlled by the frequency of the pulses to each phase, but you still need voltage to push the current through.
#5
Tech Lord
iTrader: (3)
Sort of. Electric motor torque is based on the amount of energy draw (amperage) is made available to them over time. Time is the key part of an ESC.
Torque simply is energy applied to a lever - "rotational force".
Torque is T = r x F
where,
r is the vector from the axis of rotation to the point on which the force is acting. (or, the radius of the lever)
F is the vector of force.
So, what the ESC applies control over is the F - the force, or electrical flow. This is done through controling a FET by pulsing it. It's like trying to fill a glass of water by flipping on and off the water faucet at a controlled rate. If you flip it on and off 10 pulses in 1 sec. - takes 10 seconds to fill. If you flip it on and off 20 pulses in 2 sec. - takes 5 seconds to fill.
The ESC flips on and off the flow of electricity to the motor at different rates based on your throttle setting. Full throttle is kind of like hard-wiring the battery to the motor. 1/2 throttle means your flipping the flow on and off at 1/2 the full rate (on/off/on/off). 1/4 throttle is (on/off/off/off/on/off/off/off). The rate of on/off is based on how fast the ESC can flip the voltage on/off into the FET.
So, an ESC is an Electrononic Electrical Flow Control type of thing. Since motors are wired with different turns - each will "draw" more amperage than another as the turn count drops. Flipping on and off the flow is the simplest way to handle any type of motor. Otherwise, you'd need some type of Amperage limiter using various resisters and capacitors to do the same thing through a physical means.
More reading for you: http://www.math.niu.edu/~behr/RC/pwm.html
Torque simply is energy applied to a lever - "rotational force".
Torque is T = r x F
where,
r is the vector from the axis of rotation to the point on which the force is acting. (or, the radius of the lever)
F is the vector of force.
So, what the ESC applies control over is the F - the force, or electrical flow. This is done through controling a FET by pulsing it. It's like trying to fill a glass of water by flipping on and off the water faucet at a controlled rate. If you flip it on and off 10 pulses in 1 sec. - takes 10 seconds to fill. If you flip it on and off 20 pulses in 2 sec. - takes 5 seconds to fill.
The ESC flips on and off the flow of electricity to the motor at different rates based on your throttle setting. Full throttle is kind of like hard-wiring the battery to the motor. 1/2 throttle means your flipping the flow on and off at 1/2 the full rate (on/off/on/off). 1/4 throttle is (on/off/off/off/on/off/off/off). The rate of on/off is based on how fast the ESC can flip the voltage on/off into the FET.
So, an ESC is an Electrononic Electrical Flow Control type of thing. Since motors are wired with different turns - each will "draw" more amperage than another as the turn count drops. Flipping on and off the flow is the simplest way to handle any type of motor. Otherwise, you'd need some type of Amperage limiter using various resisters and capacitors to do the same thing through a physical means.
More reading for you: http://www.math.niu.edu/~behr/RC/pwm.html
Sorry couldn't resist.
#7
Tech Elite
iTrader: (6)
First off you're getting way more technical than you need to be.
On a real car, you're controlling the engine speed by allowing more or less air into the intake. Well, that's the way most cars work. BMW does something different, but is essentially the same concept. By stepping on the accelerator you allow more air in, and the engine responds by increasing RPM, in other words it spins faster.
Technically, if you rev an engine with the transmission in neutral, the torque output is zero, since the engine is not doing any work.
In an electric RC car, the speed control varies the effective voltage to the motor. The speed of an electric motor is directly proportional to the voltage. The more voltage, the faster the motor spins. The torque of an electric motor is related to the amount of current it draws. So the more current the motor draws, the more torque it's producing. Speed controls can control torque by limiting the current. Older speed controls had a small knob you could turn, newer speed controls do this through software. That's bascially what you do when you choose a particular profile. More punch means you're allowing more current, less punch means you're allowing less current.
Brushless motors work a little different. Speed is controlled by the frequency of the pulses to each phase, but you still need voltage to push the current through.
On a real car, you're controlling the engine speed by allowing more or less air into the intake. Well, that's the way most cars work. BMW does something different, but is essentially the same concept. By stepping on the accelerator you allow more air in, and the engine responds by increasing RPM, in other words it spins faster.
Technically, if you rev an engine with the transmission in neutral, the torque output is zero, since the engine is not doing any work.
In an electric RC car, the speed control varies the effective voltage to the motor. The speed of an electric motor is directly proportional to the voltage. The more voltage, the faster the motor spins. The torque of an electric motor is related to the amount of current it draws. So the more current the motor draws, the more torque it's producing. Speed controls can control torque by limiting the current. Older speed controls had a small knob you could turn, newer speed controls do this through software. That's bascially what you do when you choose a particular profile. More punch means you're allowing more current, less punch means you're allowing less current.
Brushless motors work a little different. Speed is controlled by the frequency of the pulses to each phase, but you still need voltage to push the current through.
The last line isn't entirely correct. A brushless esc sends a pulse width modulated voltage to the coils just as a brushed esc does. The duty factor of the PWM signal will change the RMS voltage seen by the coil. Based on this RMS voltage, an RMS current will be drawn according to ohms law. The motor coils and the ESC for a RLC circuit whose rise time is the solution of a 2nd order differential equation. By changing the RMS voltage, you change the RMS current and thus the natural response of the differential equation. This is how you change the speed of a brushless motor. When it is time to move to the next coil, the controller does so but this is determined by the electrical properties of the motor and not based on a change in frequency from the controller.
#8
Tech Lord
iTrader: (3)
The last line isn't entirely correct. A brushless esc sends a pulse width modulated voltage to the coils just as a brushed esc does. The duty factor of the PWM signal will change the RMS voltage seen by the coil. Based on this RMS voltage, an RMS current will be drawn according to ohms law. The motor coils and the ESC for a RLC circuit whose rise time is the solution of a 2nd order differential equation. By changing the RMS voltage, you change the RMS current and thus the natural response of the differential equation. This is how you change the speed of a brushless motor. When it is time to move to the next coil, the controller does so but this is determined by the electrical properties of the motor and not based on a change in frequency from the controller.
#9
#11
Geez guys, no need to bring the thunder, lol
So duty cycle of PWM is regulated to create average voltage (speed).
Thank you
So duty cycle of PWM is regulated to create average voltage (speed).
Thank you
#12
Tech Initiate
First off you're getting way more technical than you need to be.
On a real car, you're controlling the engine speed by allowing more or less air into the intake. Well, that's the way most cars work. BMW does something different, but is essentially the same concept. By stepping on the accelerator you allow more air in, and the engine responds by increasing RPM, in other words it spins faster.
Technically, if you rev an engine with the transmission in neutral, the torque output is zero, since the engine is not doing any work.
On a real car, you're controlling the engine speed by allowing more or less air into the intake. Well, that's the way most cars work. BMW does something different, but is essentially the same concept. By stepping on the accelerator you allow more air in, and the engine responds by increasing RPM, in other words it spins faster.
Technically, if you rev an engine with the transmission in neutral, the torque output is zero, since the engine is not doing any work.
Torque causes acceleration, acceleration increases speed. Real world vehicles have non-ideal properties such as inertia, wind drag, friction from tyres, bearings etc. All of this provides resistance which the torque must overcome to generate useful output torque. Without any losses an infinitesimally small torque would produce infinite speed. This is impossible (much more to it but this is sufficiently accurate for this post).
A car manufacturer may opt to have "regulation" systems in place which prevent specific things happening, such as revving past the redline or operating in speed control mode (cruise control). These are essentially a closed or open loop controller which output torque as a control signal to the motor while measuring speed as feedback of which it can make further decisions about how much torque is required to maintain required speed.
A simple test to check this is when you are driving on the freeway, you are doing 100km/h, you may only be slightly depressing the throttle, yet going up a steep hill you have your foot firmly planted and are only going a fraction of the speed.
In an electric RC car, the speed control varies the effective voltage to the motor. The speed of an electric motor is directly proportional to the voltage. The more voltage, the faster the motor spins. The torque of an electric motor is related to the amount of current it draws. So the more current the motor draws, the more torque it's producing. Speed controls can control torque by limiting the current. Older speed controls had a small knob you could turn, newer speed controls do this through software. That's bascially what you do when you choose a particular profile. More punch means you're allowing more current, less punch means you're allowing less current.
Brushless motors work a little different. Speed is controlled by the frequency of the pulses to each phase, but you still need voltage to push the current through.
Brushless motors work a little different. Speed is controlled by the frequency of the pulses to each phase, but you still need voltage to push the current through.
Search Wikipedia for "Motor Constants".
The way a motor behaves at its most basic level is a simple circuit which obeys Ohm's law:
Formula 1 -> V = R * I
Where:
V = voltage
R = resistance (constant, but in reality is temperature dependent)
I = current
You can rearrange that formula in terms of current as:
Formula 2 -> I = V / R
Your ESC generates a voltage and the motor generates a voltage in relation to its speed. The resistance of the motor and leads and ESC etc is between these two voltage sources.
The current that flows into the motor is then the difference between he two voltages, divided by the resistance as in formula 2.
This is only an semi-ideal circumstance. In reality there are non-linearities in the motor, the ESC, temperature effects etc. Another thing to keep in mind is that with multiphase (three in RC case) brushless motors, you can also adjust the frequency and phase of the alternating signals to get other effects, which is what timing does, both on the back of the motor (static, across all rev ranges) and in your ESC (typically dynamic and varying across the rev range).
All boost is as far as I am aware is running your motor at higher currents in lower RPM ranges which is still within the motors specifications, if not by current alone, by power rating, so give more off the line acceleration.
#13
Tech Champion
The load the motor is under is a large part of what's going on. The motor characteristics including impedance/back EMF (effective resistance in a simplified sense) change with load, load changes what is frequently called the slip angle.
The ESC doesn't control torque or current, at least not very well. Imagine the same throttle setting while holding the wheels off the ground, and while say doing a slipper test or stuck against a pipe. The current, and torque, will be dramatically different. Influences it sure, but not direct control.
Does control voltage as mentioned, but that doesn't directly relate to speed either, still load dependent. Same throttle setting is faster downhill than uphill.
I'd say it's closer to speed than torque in most practical situations, but not fully controlled.
The ESC doesn't control torque or current, at least not very well. Imagine the same throttle setting while holding the wheels off the ground, and while say doing a slipper test or stuck against a pipe. The current, and torque, will be dramatically different. Influences it sure, but not direct control.
Does control voltage as mentioned, but that doesn't directly relate to speed either, still load dependent. Same throttle setting is faster downhill than uphill.
I'd say it's closer to speed than torque in most practical situations, but not fully controlled.
Last edited by Dave H; 04-04-2014 at 03:58 AM.
#14
I always thought of the ESC as more of a limiter if you want simple terms. With out it the motor is on or off essentially (as mentioned a little more complicated w/ brushless but not). The esc can limit torque if it can NOT handle the load the motor is asking for at certain times (just as batteries can), but as long as the ESC is suitable to the system it doesn't inhibit torque unless you tweak provided settings that can impact effective torque to some extent (as mentioned above current limiters, punch controls etc). Top speed isn't really determined by the esc, but it can limit voltage through to change speed within the available range.
Last edited by 8ight-e; 04-04-2014 at 05:14 AM.