An Interview With Justin

[flecc]

For me it was good to hear Justin being not tied to electrical power for personal transport, or even e-bikes for that matter. Though not a message suited to this forum, bikes can't alone be the answer.

Modern history shows that people almost universally make every effort to get away from bikes into what they see as improved forms of personal transport. That, combined with the vagaries of weather in many parts of the world, means we need to have a more open view of the nature of future personal transport.
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[trex]

it seems to me from watching the video that Justin's business vision is on DD motors. Justin is indeed a very clever guy but is that wise?

 

[flecc]

it seems to me from watching the video that Justin's business vision is on DD motors. Justin is indeed a very clever guy but is that wise?

Yes, I raised my eyebrows at that clear bias, I wonder how much that's related to BionX being Canadian like him? He clearly doesn't like crank drive either.

I was also surprised that he said the returns rate for DD and internally geared motors was roughly the same. In my experience DD are far less likely to fail than geared motors.
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[anotherkiwi]

I was also surprised that he said the returns rate for DD and internally geared motors was roughly the same. In my experience DD are far less likely to fail than geared motors.
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Even if you are chucking 72V at them? The North American e-bike usage seem to be much different from Europe: over volting, thrashing the bikes around at speeds beyond what a bicycle frame was designed for, burnouts!...

 

[flecc]

As someone who can't see any possible interest or benefit in computer games, there was another way in which Justin pleased me, in response to a VR question. That was his caustic reference about those wasting their lives away playing computer games!
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[danielrlee]

Ferrofluid doesn't just cool, it also brings a rise in efficiency and I'd most like to know how much that gain can be in DD hub motors.

For example, in loudspeakers, which are linear motors of course, the efficiency gain comes from the ferric element of the fluid directly coupling the magnetic field to the windings, rather than it being weakened in bridging an airspace. That's a side product gain in addition to the heat transfer cooling, something that oil cannot do.
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That's an angle that I can't remember having been discussed in the hubmotor FF cooling thread over at ES. I shall put the question to Justin and see what he has observed.

 

[danielrlee]

the air gap in a high power loudspeaker is about 1mm which favours liquid for cooling but in the case of a large e-bike motor, the core is a reasonably good heat conductor in itself. Improvement in core construction and core material should be sufficient without the need for liquid cooling. But even if it did, then they can just run pipes through the core.

The mass of the stator can only be relied on to conduct enough heat away from the windings for very short periods of time. Prolonged heating can only be dissipated by air convection from the motor casing to the ambient air as the bike moves. It is the transfer from windings/stator to the casing that FF appears to aid so well.

 

[anotherkiwi]

As someone who can't see any possible interest or benefit in computer games, there was another way in which Justin pleased me, in response to a VR question. That was his caustic reference about those wasting their lives away playing computer games!
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And those who have a healthy life mix: some computer games (racing car simulators mostly), riding my e-bike and fishing? Maybe he was just referring to those without a healthy balance between several activities?

 

[flecc]

And those who have a healthy life mix: some computer games (racing car simulators mostly), riding my e-bike and fishing? Maybe he was just referring to those without a healthy balance between several activities?

No, there was no qualification, he very obviously sees all time spent in VR as wasted time.
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[Cyclezee]

it seems to me from watching the video that Justin's business vision is on DD motors. Justin is indeed a very clever guy but is that wise?

Justin also has a close relationship with eZee and Grin sell more eZee geared motor kits than anyone else in the world.

 

[trex]

good business decision. Ezee motors don't need FF.

 

[danielrlee]

good business decision. Ezee motors don't need FF.

It's not that they don't need it, just that they don't benefit from it like DD hubs do. I certainly wouldn't want any excess heat transferred to a plastic gear set anyway.

EDIT: Actually, scrap that last bit. FF wouldn't be attracted to plastic gears.

 

[Cyclezee]

It's not that they don't need it, just that they don't benefit from it like DD hubs do. I certainly wouldn't want any excess heat transferred to a plastic gear set anyway.

EDIT: Actually, scrap that last bit. FF wouldn't be attracted to plastic gears.

The planetary gears in the current generation of eZee motors are harder wearing composite as shown below rather than nylon.

 

[danielrlee]

The planetary gears in the current generation of eZee motors are harder wearing composite as shown below rather than nylon.
View attachment 12935

I can't remember the exact details (they're all contained within the thread over at ES), but I think it's something to do with the RPM's of a geared motor being too high, surface area being much smaller and the thermal pathway being much worse than that of a DD hub.

 

[flecc]

I think it's something to do with the RPM's of a geared motor being too high,

I'd guess that the high RPMs etc in a geared motor would also introduce a drag factor with any fluid filling.
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[trex]

centrifugal forces should push the fluid against the magnet casing.

 

[danielrlee]

Ferrofluid doesn't just cool, it also brings a rise in efficiency and I'd most like to know how much that gain can be in DD hub motors.
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Flecc, I received a reply from Justin on your question regarding efficiency:

"No, it makes zero nadda no difference whatsoever in the electromechanical properties of the motor. We're talking having a fraction of a gram of nanopartical magnetite (which is pretty weakly magnetic in the first place) distributed over like 200-300cm^2 of air gap space."

 

[flecc]

Flecc, I received a reply from Justin on your question regarding efficiency:

"No, it makes zero nadda no difference whatsoever in the electromechanical properties of the motor. We're talking having a fraction of a gram of nanopartical magnetite (which is pretty weakly magnetic in the first place) distributed over like 200-300cm^2 of air gap space."

Thanks Daniel, I wondered whether the comparatively very large airspace volume made a difference and clearly it does in Justin's judgement.
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[trex]

I must say I was surprised at Justin's published results on measured thermal resistance from core to ambient in the link that John provided. The reported improvement on thermal resistance is about 30% - 50% compared to the naked motor.
We are talking about the beneficial effect of 5% x 6ml (about half a gram) of nano sized magnetite spread over the 300cm2, 6kg of ferric spinning core and magnet ring. The effect must come from lamination flow of air over the well sub-mm cones of the ferrofluid, the cones increase the contact area. I think that even if the conductivity of the FF is an order of magnitude better than air, the fluidic layer is too thin (sub mm) to make much of a difference.
It's not clear from the post how Justin derives the thermal resistance from core to ambient air. Did he have a thermal sonde attached to the core and another to the external side of the case? I imagine a precise method should be measuring how many calories are dissipated inside the enclosure within an hour while maintaining the motor at the same voltage, current and speed. More heat = better dissipation = higher temperature on the outside case. That may seem counter-intuitive to some.
Personally, if I want to cool the motor, I would simply paint the casing with black matt paint.

 

[danielrlee]

I must say I was surprised at Justin's published results on measured thermal resistance from core to ambient in the link that John provided. The reported improvement on thermal resistance is about 30% - 50% compared to the naked motor.
We are talking about the beneficial effect of 5% x 6ml (about half a gram) of nano sized magnetite spread over the 300cm2, 6kg of ferric spinning core and magnet ring. The effect must come from lamination flow of air over the well sub-mm cones of the ferrofluid, the cones increase the contact area. I think that even if the conductivity of the FF is an order of magnitude better than air, the fluidic layer is too thin (sub mm) to make much of a difference.
It's not clear from the post how Justin derives the thermal resistance from core to ambient air. Did he have a thermal sonde attached to the core and another to the external side of the case? I imagine a precise method should be measuring how many calories are dissipated inside the enclosure within an hour while maintaining the motor at the same voltage, current and speed. More heat = better dissipation = higher temperature on the outside case. That may seem counter-intuitive to some.
Personally, if I want to cool the motor, I would simply paint the casing with black matt paint.

All the details of Justin's testing methodology are openly published in the thread already linked to. It is an extremely long thread, so we can all be excused for not having read it, or not being able to recall specific parts. What I can say, is that I have no element of doubt that Justin's testing data is anything but 100% reflective of fact.

One quick quote I have been able to pull from the thread is:

"The effect of black paint is measurable but pretty small (much much less than vent holes or FF) in terms of its contribution to motor cooling".

At this moment in time, ferrofluid looks like the best single option available for the purpose of aiding heat removal from direct drive motors. I only hope the ongoing longevity tests don't throw any spanners in the works.