elux wrote:Devin,
Please look at the title of the graph you posted. The torque-speed curve you posted is for a PMDC motor. That is a brush DC motor that has no controller. Apply DC Voltage and the commutator will change the DC into AC and the physics of the back EMF (Faraday's Law, google it) limits the current. It is a very different type of motor from the brushless DC motors that the VESC is designed to operate. FYI this type of motor was invented by Thomas Davenport in 1835 and it was awarded the first ever patent for an electrical device.
The VESC limits the current to the motor using pulse width modulation (PWM). It inverts the DC current into 3 phase AC in precisely the right frequency and phase angle for peak efficiency operation. So the mode you desire is already programmed in by Benjamin.
It is disheartening to read some of your posts. It's clear that you enjoy learning about motor theory and you have a great imagination and a spirit of inventiveness. Unfortunately, some of your posts contain misinformation that would be easily cleared up with a quick search on wikipedia.
For example, your misconception regarding the K_v rating of a motor and the winding resistance. The back EMF of an electric machine depends only on the rate at which the flux linking the windings is changing (Faraday's Law). This law is the fundamental basis for the connection between electricity and magnetism. If you change the material of the wire (to aluminum for example) and change with resistance without changing the number of turns or magnetic field strength, the back EMF and the K_v rating of the motor won't change.
That is a brush DC motor that has no controller. Apply DC Voltage and the commutator will change the DC into AC and the physics of the back EMF (Faraday's Law, google it) limits the current.
Assuming 100% duty cycle, the motor physics are the same, & I specified 100% duty cycle. (yes the vesc isn't capable of this at stall @ 50V, but the physics ratios remain). If one substitutes 10V for 50V, the math is the same, and the physical description is also possible and safe. Yes the VESC enables safe high-voltage operation but this doesn't change the motor ratios. Also, strictly considering the formula in the first post it would be safe as well, but as mentioned it would require a different algorithm for low speed operation due to the limited watts.
For example, your misconception regarding the K_v rating of a motor and the winding resistance. The back EMF of an electric machine depends only on the rate at which the flux linking the windings is changing (Faraday's Law).
@elux... and yet the correlation remains... I think you will see the following formula agrees with what you are saying regarding the number of turns without specifying the number of turns or termination.
D=sqrt(E/(V*N))
E=N*V*D^2
V=E/(N*D^2)
N=E/(V*D^2)
D = Change Factor of KV (rpm/v)
E = Change Factor of Conductor Resistivity (ohm-meters)
V = Change Factor of Conductor Volume (meters^3)
N = Change Factor of Conductor Resistance (ohm)
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If you change the material of the wire (to aluminum for example) and change with resistance without changing the number of turns or magnetic field strength, the back EMF and the K_v rating of the motor won't change.
@elux... I agree copper vs aluminum with same geometry winding should be the same KV in theory, which agrees with your position and the aforementioned formula, however despite searching I haven't yet seen hard fully convincing proof for this, and I intend to do the copper vs aluminum experiment and post the results. I've also observed that in a copper winding wye motor, changes in no load rpm correlate linearly & proportionally with changes in electron drift velocity at stall (100% duty), and copper and aluminum have different drift velocities, so I personally want to use a VESC as an experimental tool to observe the discrepancy.
devin wrote:I've also observed that in a copper winding wye motor, changes in no load rpm correlate linearly & proportionally with changes in electron drift velocity at stall (100% duty), and copper and aluminum have different drift velocities, so I personally want to use a VESC as an experimental tool to observe the discrepancy.
Examples:
- doubling battery voltage doubles electron drift velocity at stall and doubles no load rpm.
- halving the number of turns doubles electron drift velocity at stall and doubles no load rpm.
- doubling the wire thickness doesn't change the drift velocity and doesn't change the KV.
If copper no load rpm changes are proportional to changes in electron drift velocity at stall, and copper and aluminum have different drift velocities at the same number of turns, what would then cause the copper and aluminum to have the same KV at the same number of turns?