New hubs with magnet orientations like Tesla Raven powertrain?

General Discussion about electric bicycles.
Post Reply
User avatar
zzoing   10 kW

10 kW
Posts: 732
Joined: Feb 01 2008 12:26am
Location: Fr SE

New hubs with magnet orientations like Tesla Raven powertrain?

Post by zzoing » Nov 08 2019 12:32pm

The new motor from Tesla's Model 3, called the raven, uses complex magnet orientation to raise motor efficiency from 92 to 96-97%, allegedly.

Do you know if an motorbike and ebike motor companies will copy the idea, to have ebike motors that are twice as efficient as previous versions?

sleepy_tired   100 W

100 W
Posts: 102
Joined: Jul 02 2019 11:46am

Re: New hubs with magnet orientations like Tesla Raven powertrain?

Post by sleepy_tired » Nov 08 2019 2:28pm

This is my limited understanding:

Telsa model 3, from what I can tell, is a IPM motor. The magnets it's using are a series of smaller magnets glued together to create a halbach array.

The way these motors can be thought of is a combination of permanent magnet 'PMAC' or 'BLDC' at slower speeds and a reluctance motor at higher speeds. At slow speeds the strength of the permanent magnets create a lot of low-end torque and works the same way that our DD hub motors do. As the motor speeds up the permanent magnets help setup lines of magnetic force through the metal core in which they are embedded. Magnetic fields have a property called 'reluctance' which is the magnetic equivalent to inductance... meaning that once the magnetic field is setup it doesn't want to change. This effectively turns the entire rotor into a temporary 'permanent magnet'. Reluctance motors, like traditional AC motors, use this property to turn the rotor.

Reluctance motors are able to produce a lot of high speed power, but tend to be unstable and difficult to control at lower speeds. Permanent magnet motors provide a lot of very nice low-speed torque and control, but have a limited RPM range. So this design combines the positive behavior of both.

So I don't think that the Telsa model 3 is about creating a super efficient motor at all. It's more about providing very good low speed torque for it's size/weight while still having very good high speed performance. High torque is a bit counter productive to high efficiency.


DD hub motors are SPM, surface mount permanent magnet motors. So they can't take advantage of the reluctance in the same way that a IPM motor can. They might benefit from a halbach array.. I donno. Maybe to reduce the need for a thick iron backing hoop for the magnets. But it would make the motor more expensive.

But mid-drives and geared hub motors could copy the design. Nicer mid-drives like the QS 3000w motors are nice IPM motors already. If somebody creates a geared motor that uses this design and somehow magically solves the cooling limitations of geared hub motors then it would probably obsolete every other type of motor used with bicycles.

User avatar
MadRhino   100 GW

100 GW
Posts: 6465
Joined: Sep 03 2010 5:28pm
Location: Montreal QC Canada

Re: New hubs with magnet orientations like Tesla Raven powertrain?

Post by MadRhino » Nov 08 2019 9:49pm

zzoing wrote:
Nov 08 2019 12:32pm
...Do you know if an motorbike and ebike motor companies will copy the idea, to have ebike motors that are twice as efficient as previous versions?
Nope. Our hub motors can’t be made twice as efficient as they are. Their efficiency is pretty good already, even cheap ones. Twice their actual efficiency would make them far above 100% efficient and that, by actual law of physics, is impossible. Improving the average DD hub efficiency by 5% would be a huge step already, and would likely double their production cost.

If you seek better efficiency, it is in the design of the bike that are your best possibilities of improvement. If you seek better performance, the actual limiting factor is in battery density.
Make it fool-proof, and I will make a better fool.
Current bikes
Street:
Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

User avatar
zzoing   10 kW

10 kW
Posts: 732
Joined: Feb 01 2008 12:26am
Location: Fr SE

Re: New hubs with magnet orientations like Tesla Raven powertrain?

Post by zzoing » Nov 08 2019 11:44pm

Ah that's very interesting. The model 3 technology does also bring in a major efficiency advantage, i've heard figures of 96-97%. The raven edition of the model S using the hallbach technology has 10% higher range. Especially on highways at speeds higher than 80-100mph, the previous motor was struggling.



Okay, a halving of inefficiency from 92 to 96% is not the same as a doubling of efficiency.

Post Reply