Variable strength electric motor

[GreenAce92]

The title may seem dumb because increase in voltage but

I wanted to have sort of like a transmission for an electric motor which again... increase in voltage which may make this idea unnecessary but

I wanted to have a motor that was built like a cone within a cone so that you could slide the magnets in and out which would change the strength of the motor by changing the proximity of the magnets to the stators while it rotated.

Thoughts?

 

[Simon Bridge]

Yeah - you can change the torque that the motor can produce by changing the magnetic field strength - which you do by moving the magnets.
But no need for cone shape - just change how far apart the magnets are.

 

[GreenAce92]

yeah pretty lame design, not even logical

I would go off something like centrifugal force making the tolerance higher and higher consequently increasing the repulsion forces

 

[Plant_Boy]

You could go with a number of coils that you can switch on and off or pulse width modulation?

Pulse width modulation (PWM) is normally the most effective for control of the power. But if you want to change the number of poles (If the magnet is on the rotor then you're going to have a hard time changing magnet slots) I would say make a number of coils that you can switch on and off. It'll complicate things more so than PWM but it would also be an interesting concept.

 

[CWatters]

Changing magnets in a motor can have apparently strange effects...For example ...

Lets say you have a DC permanent magnet motor with no load. When you apply a DC voltage to it the motor will accelerate until the back emf is roughly equal to the applied voltage. OK so far?

If you then substitute weaker magnets the motor will have to spin faster to achieve the same back emf.
If you substitute stronger magnets the motor will spin slower to achieve the same back emf.

So making your magnets weaker can make your motor go faster.

For this reason if you replace a ferrite magnet motor with a rare Earth magnet motor you typically have to reduce the number of turns if you want the motor constant to remain the same.

 

[Plant_Boy]

If you then substitute weaker magnets the motor will have to spin faster to achieve the same back emf.
If you substitute stronger magnets the motor will spin slower to achieve the same back emf.

So this is like changing gears in a car. Weaker magnets would be like 5th gear and stronger magnets would be like 1st gear. Would you also get the appropriate torque response?

 

[zoki85]

Inefficient

 

[GreenAce92]

So it would be an AC motor then, no magnets.

Yeah I wanted to apply it to a Lamborghini Aventador, but I want to match the same specifications as a gas version which my friend argues is not really possible or likely due to weight of batteries and turbocharging of gas motors.

Still, I also want it to be stick which could be a simple voltage range limiter engaged by an artificial clutch. The sound is just horrendous in my opinion...

Thank you all for your time.

 

[CWatters]

So this is like changing gears in a car. Weaker magnets would be like 5th gear and stronger magnets would be like 1st gear. Would you also get the appropriate torque response?

To some extent but it would be inefficient. For something like an electric car you want maximum efficiency. Stronger magnets mean fewer windings which means reduced copper losses.