Hub Motor and Wheel Size/Diameter

[Andy-Mat]

Hi Andy. The problem with most ebike motors is that they use permanent magnets to create the magnetic field, so very little can be done to control the field strength as used with Ward Leonard above. There is a timing method (field weakening) that can be used but its not very efficient. Its possible to switch from star to delta wind but this is beyond most users.

Don't mix up your thinking with regard to Ward Leonard and modern day 3 phase DC motors, as in e-bikes, as I was only trying to demonstrate the antiquated thinking of some people here.
There are even today AC replacements for the DC Ward Leonard system on cranes, but not on any e-bike that I have heard of!
It was only hugely significant advances in transistor manufacturing, that today allows our e-bikes to change speeds so well.
regards
Andy

 

[Andy-Mat]

It is very simple Andy after all that has been said if you really knew your stuff, the geared hubs we use can only have the RPM changed via voltage despite your so called electronic expertise.

You state you are controlling motor rpm by throttle , this is not so. All you are doing is controlling the bike wheel speed this is very much different to being able to regulate or change the internal motor winding speed.

Actually, you still misunderstand how speed is changed on modern e-bikes. Let me tell you just one more time:-
The Battery voltage is NOT affected/changed IN ANY WAY AS YOU SEEM TO IMAGINE, IN A MODERN THREE PHASE DC MOTOR SYSTEM, WITH ESC (ELECTRONIC SPEED CONTROLLER)
The voltage used to drive the motor is the battery voltage, whether fully charged or not, at the time the pulse is sent. For a 36 volt battery that will generally be between 42 and just over 30 volts.
A clever controller will NOTICE IF THE VOLTAGE DROPS AND SIMPLY increase the length of the pulses, as the voltage drops during usage, giving the motor the SAME amount of energy, BUT over a longer period!!
IT IS THE LENGTH OF THE DC PULSE THAT IS SENT TO EACH OF THE 3 FIELDS, IN SEQUENCE THAT CONTROLS THE SPEED/RPM OF THE MOTOR.
GENERALLY (BUT NOT ALWAYS, SOME USE BACK EMF INSTEAD OF HALL SENSORS TO SWITCH THE ESC!) HALL EFFECT SENSORS ARE USED TO INFORM THE CONTROLLER OF THE CURRENT RPM OF THE MOTOR AND TO ASSIST IN THE TIMING OF THE PULSES, AND TO WHICH OF THE 3 FIELDS POWER MUST BE SENT TO.
AT LOW SPEEDS, SOME PULSES MAY NOT EVEN BE MADE/SENT, IF THE MOTOR IS ALREADY DOING THE REQUIRED RPM!
FOR SLOW SPEEDS THE PULSE IS SHORT = LESS ENERGY. FOR HIGH SPEEDS THE PULSE IS LONGER, BUT ALWAYS THE ACTUAL VOLTAGE OF THE BATTERY AT THE TIME.
NO CHANGES ARE MADE IN VOLTAGE TO THE MOTOR OTHER THAN THE CHANGES THAT HAPPEN NATURALLY AS THE BATTERY GOES FROM FULLY CHARGED TO EMPTY!
THE BLDC MOTORS HAVE MULTIPLES OF 3 POLES - 3, 6,OR 12 GENERALLY.
YOUR UNDERSTANDING OF JUST HOW THESE MOTORS WORK IS COMPLETELY FLAWED.

If you wish to have a second opinion, please look here which has some great coloured diagrams to assist in understanding the text:-

How Brushless DC Motor Works? BLDC and ESC Explained

In this tutorial we will learn how brushless motor and ESC work. A BLDC motor consist of two main parts, a stator and a rotor. The rotor is...

howtomechatronics.com

I read it rapidly through and I could not find a single sentence saying that speed control is affected by voltage control.
regards (for the last time!)
Andy

 

[sjpt]

Instructive reference, thanks.
It doesn't change the fact that the max speed of the motor at a given voltage is determined by the windings etc of the motor.
And though, as you say the controller does not change the voltage of the battery, it does change the (average/effective) voltage applied to the of the motor by pulse width modulation (like a class D amp).

Question: Does a sine wave controller do the same with much higher switching frequencies to generate a PWM sine wave?