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green_is_now

1/4/2013 11:07 PM EST

The switches need to be able to handle both high current in one scenario and ...

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green_is_now

1/4/2013 11:02 PM EST

The problem is in all the IR and reactive losses of the matrix wiring and ...

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# Electric hub motor improves EV range: Part 1—Technology basics

## 4/28/2011 3:52 PM EDT

Motor calculations
The following computations are done with a 0.6-T field, in order to be conservative or allow the use of cheaper magnets.

Printed circuit disks are made of two networks, each made of 24 radial wires (shown in red and green in the previous figures), connected as “serpentines.” The series resistance of the wires is assumed to be the resistance of the radial axes, as the circular connections can be designed sufficiently thick for essentially zero resistance. The cross section of the radial wires is 2 mm2 (4 mm large x 0.5-mm thick) in the center part of the disk, up to 8 mm2 (16 mm x 0.5 mm) in the outer part.

The twin networks are powered with 90° phase difference, as shown below, in order to maintain the motor torque during the switching time of the current on the complementary phase.

The length of the 24 wires is 24 * 15 cm = 3.6m. The rotation force on these wires is:

F = B * I * l = 0.6 * 3.6 * I = 2.16 * I

This force is applied in the middle of the wires, at a distance from the axis of 12.5 cm. The motor torque per stack is

Γ = F * r = 2.16 * 0.125 * I = 0.27 * I

The total motor torque generated by the 12 stacks is:

Γtot = 12 * 0.27 * I = 3.24 * I

A 30A current generates a mechanical torque of 97.2 Nm.

A vehicle driven by four wheels has a total driving torque of 390 Nm, when 30A is flowing through all stacks. This corresponds to the driving torque of existing high-performance cars.

A 15-cm copper wire, with a cross section varying between 2 mm2 and 8 mm2 has a resistance of 6 µΩ. Assuming that interconnections between radial wires have a negligible resistance, the total resistance of a printed circuit disk wire is 24 * 6 = 0.145 mΩ.

A 30A current flowing through this wire generates a 4.5 mV voltage drop, and 130 mW power dissipation. The total power dissipation for the 12 stacks of a wheel, when 30A are flowing in all disks is 1.6W.

All wires of all stacks are connected to the command circuitry, located close to the axle. Each wire is connected to an electronic switch, with a series resistance of 0.2 Ω (conservative number, in order to take into account unexpected parasitic resistances). This switch represents the major contribution in the estimated total resistance of the electric circuit, and generates most of the joule losses (carefull selection of these MOS transistors has a direct impact on the energetic yield of the system).

Bob Lacovara

4/29/2011 10:16 AM EDT

It's a nifty motor, and might find application in non-automotive applications. To read that some of the control circuitry now in use needs liquid cooling is rather discouraging: that's a lot of wasted energy. One other point: recovering braking energy isn't merely a matter of being able to lay hands on it at the motor. You have to do something with it, typically put it into your battery. Trouble is, batteries don't recharge in seconds, and some fraction of that energy is lost. Some type of supercap might be indicated.

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Efried

5/4/2011 3:30 AM EDT

batteries might be designed for 2C-5C charging, supercaps failed so far to define their business model in transport - too bulky, too expensive

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prabhakar_deosthali

4/29/2011 10:19 AM EDT

A very informative article on hub motors for EVs. I would have liked this article to contain some graphics - Torque speed waveforms and schematics showing how commutation is achieved. Some comparative charts showing the efficiency and range improvement over other similar motors will also add value to this article.

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agk

4/30/2011 6:40 AM EDT

By reading this article my thoughts go back to the VCR 's head drum direct drive and capstan direct drive motors. The same design in a small size and lower power it was working there. But here this motor has to meet many more things as shock proof, water proof,dust proof,heat proof and carry atleast two times more than the specified weight.

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elPresidente

5/2/2011 5:15 AM EDT

This seems awfully naive(full blame is on EET editors for accepting the piece), almost like it was written by a high school kid, and there's nothing novel or "nifty" about it for all you guys caught agasp in the comments section - do the math on the cost of a printed circuit motor with enough layers to be both mechanically and electromagnetically sound, appropriate layup Tg, and copper thickness and you very quickly have a \$8000 weak torque motor per axle.
The Maker community have been building axial flux alternators and generators (which is what this is) for well over a decade for wind power and have figured out how to bury windings ECONOMICALLY without the excessive cost of prepregs and laminating presses. Read Hugh Pigot's book if you want reality and cost-effectiveness versus fantasyland equation based nonsense.
The issue of flux saturation and reluctance in the air/epoxy gap also is not addressed in this math exercise, which will seriously limit the mag field contribution of the 1 Tesla magnets that are being assumed in force calculations.
To suggest fixing the axle to the frame of the vehicle to "simplify shock absorbers", is extremely naive as well as is the notion that much less than 10cm is a large enough axle stub to support a 1.5 tonne vehicle hitting a pothole...LOL this has the same shaft diameter as a 1/2HP furnace blower motor. Clearly, the author's never designed autmotive drivelines; apparently just a dreamer with a glass of wine and a fireplace and enough engineering knowledge to be reckless.

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roldan

5/7/2011 8:37 AM EDT

I would very much like to be a naive high school kid. Unfortunately, I am a retired electronics engineer, with 40 years of background in the industry, acting now as an independent consultant. Almost twenty patents filed. Six presentations at international conferences. One invited paper at ISSCC. My career is behind me.
To be fully honnest, when I tried to patent this concept, I found that this was already done almost twenty years ago. There are at least two naive high school kids dreaming in the world. But, apparently, the other one failed in promoting the concept.
I think, but you can disagree, that it can be very beneficial for the whole industry, and not only the automotive one. For an independent consultant, the automotive industry is too big. I'm more interested in other applications, looking for attractive small niches. But, if I can convince the automotive industry to go in this direction, this should help for developing smaller businesses.
I would enjoy replying to technical questions. In your comment, I can't see any requesting an answer. Please, consider the concept, and not the implementation details.

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davealle007

5/11/2011 10:42 AM EDT

Thats kinda scarey, just anyone that knows enough to be dangerous can post all this with the editor of EE times to go ahead and let it happen. I guess thats the downside of this kind of forum. The good side is that someone like roldan speaks up to reprove it, but is he right?

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WarlockofOz

6/5/2011 11:27 PM EDT

I think you are getting confused between cm and mm. A 10cm(100mm) axil will, depending on what it is made from will easily hand up to 5 x 1.5 tons. I've lifted components up to 30 tons on pins that thick.

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elPresidente

5/2/2011 5:16 AM EDT

And, as any HIGH SCHOOL kid can tell you, it's 1/2 m*v*v for energy, which is VERY significant energy as anyone who's hit a wall at 50km/h can tell you....you don't dump it into a resistor, especially for a vehicle carrying limited stored energy on board to start with...streetcars used to do that one 75 years ago to heat the cabin. We are supposed to be cooling the planet, not heating it with printed circuit motor braking systems or failing to recycle it for later use in moving the vehicle.
Has anyone done the math for the commutation "switches" in this wundermotor? For a 20A "starting torque" you are dissipating 400*5.6 or 2.25kW PER MOTOR, or 10kW of power in the switches for 4WD. Now add in your winding resistance. It gets a lot worse when you are using the 'sports car' 30A example that was calculated in a prior page - almost DOUBLE. The Chevy Volt only carries 16kW of batteries....
Thanks for the laughs - can't wait to see part deux. A new low, EET; a new low.

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Efried

5/4/2011 3:36 AM EDT

Please add some outlook to your criticism:
What about SRM?
Why is the mass per weight so bad with current electric motors?
Please allow for some innovation - even in early stage- My guess is that electric mobility will fail with current low RPM motor designs.

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Efried

5/4/2011 3:36 AM EDT

mass per power of course kg/kW

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astrayelmgod

5/3/2011 9:33 PM EDT

0.5mm looks like about 14 oz copper. My VERY limited experience with making coils out of PC boards was with 4 oz copper, and even that was a lot more expensive than making it the usual way. So, what is the attracttion for using PC stock?

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BOY Dela Pena

5/5/2011 9:23 AM EDT

The design looks very good and will have some other usage, The main thing is how much it will cost and how you can have more detailed information.

Thank you,

Godofredo Dela Pena

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DrQuine

5/9/2011 6:37 PM EDT

Two years ago "EE Times" reported that "Daimler bus combines hub motors, fuel cells" (http://www.eetimes.com/electronics-news/4197774/Daimler-bus-combines-hub-motors-fuel-cells) so it would appear that the deployment problems for hub motors are not insurmountable. It sounds like one challenge will relate to car handling characteristics having additional mass that will be moving with the wheels (rather than the vehicle body). This is probably less of an issue for a bus. Another design issue will be to ensure that the hub mounted motors are designed to tolerate exposure to the elements near the wheels rather than being protected in the engine compartment.

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graduatesoftware

6/25/2011 9:13 PM EDT

Readers are directed to two sites:

http://www.technologyreview.com/energy/21666/

http://www.launchpnt.com/portfolio/aerospace/uav-electric-propulsion/

It doesn't look like Exro weathered the recession very well since I haven't seen anything from them lately, but my original analysis of their approach/patent (switched coils to change torque characteristics) led me to believe that the engineering was sound. Likewise for LaunchPoint.

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HoosierDaddy0

7/5/2011 1:33 PM EDT

Has anyone heard of BionX, www.bionx.ca? They make hub motors used in boost systems for bicycles and velomobiles. Their systems go up to 500 watts and are priced around \$2,000 with a control system using regenerative braking, http://www.youtube.com/watch?v=eSFE151tRdM. Is the system described here better or cheaper than the BionX system?
I want to mass produce velomobiles with boost systems controlled by I-pads, and could use the help of some smart guys like you.

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green_is_now

1/4/2013 11:02 PM EST

The problem is in all the IR and reactive losses of the matrix wiring and switches, and there cost

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green_is_now

1/4/2013 11:07 PM EST

The switches need to be able to handle both high current in one scenario and high voltage in the other extreem.
So the semiconductors size and cost go throught the roof, add the IR loss gain for needed worst case voltage needed, making this not feasible quickly.

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