# 4 electric motors



## chenying (Jul 25, 2011)

Hi I'm really new to this stuff but I'm trying to research information about duplicating the differential effect but with four motors at each wheel. Can it be accomplished using a microprocessor and a sensor or is there a certain configuration of controllers/motors to imitate the differential effect?


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## bruceme (Dec 10, 2008)

Cost... you need 4 controllers and 4 motors, but it can be done.


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## Anaerin (Feb 4, 2009)

chenying said:


> Hi I'm really new to this stuff but I'm trying to research information about duplicating the differential effect but with four motors at each wheel. Can it be accomplished using a microprocessor and a sensor or is there a certain configuration of controllers/motors to imitate the differential effect?


Motors connected in series produces an open differential effect. Motors in parallel produces a "Limited slip" differential effect.

If you have a single *very* high voltage controller (600v+) you could connect all four motors in parallel (Each motor then receiving 150v+, full amperage). This would be equivalent to a 4x4 with "locked" differentials (or limited slip).

If you have a single *very* high amperage controller (4000A+) you could connect all in series (Each motor receiving 1000A+, full voltage). This would be equivalent to a 4x4 with "open" differentials.

If you have a high voltage and high amperage controller (600v+, 2000A+), you could have the wheels in series/parallel, with each left-right pair connected in parallel, then those pairs connected together in series, or vice-versa (Each motor would then receive 300v, 1000A). This would be equivalent to a 4x4 with "locked" front and rear differentials and an "open" centre differential, or if reversed, "open" front and rear differentials and a "locked" centre differential.

Or you could use 2 controllers, one for the front pair, one for the back pair. (High voltage mid amperage if in parallel, mid voltage high amperage if in series).

Or you could use 4 independent controllers. Though using more than 1 controller will mean ensuring that all the controllers are running at the same level and balanced.

This is assuming you're using DC here. ACIM or BLDC will _*require*_ one controller per motor, because each controller is explicitly connected to the exact rotational position of each motor.


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## bruceme (Dec 10, 2008)

Sure you didn't swap parallel/series? Parallel would be high voltage, low amperage. Serial would be low voltage high amperage.


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## Anaerin (Feb 4, 2009)

bruceme said:


> Sure you didn't swap parallel/series? Parallel would be high voltage, low amperage. Serial would be low voltage high amperage.


...Double checks...Yes, that's what I said. High voltage for Parallel, High Amperage for Series.


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## palmer_md (Jul 22, 2011)

Anaerin said:


> If you have a single *very* high voltage controller (600v+) you could connect all four motors in parallel (Each motor then receiving 150v+, full amperage).
> 
> If you have a single *very* high amperage controller (4000A+) you could connect all in series (Each motor receiving 1000A+, full voltage).


If you have 600volt with motors in parallel wont each get 600v?
If you have 4000Amp with motors in series wont each get 4000amp?


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## Anaerin (Feb 4, 2009)

palmer_md said:


> If you have 600volt with motors in parallel wont each get 600v?
> If you have 4000Amp with motors in series wont each get 4000amp?


No. 2 Items the same, when connected in parallel, split the available voltage, but maintain the available current (amperage). When connected in series, the voltage is maintained, and the current is split. So with 4 of the same motor in parallel, each motor would see 1/4 of the voltage and all of the amperage, whereas in series each motor would see 1/4 the amperage and all of the voltage.


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## major (Apr 4, 2008)

Anaerin said:


> No. 2 Items the same, when connected in parallel, split the available voltage, but maintain the available current (amperage). When connected in series, the voltage is maintained, and the current is split. So with 4 of the same motor in parallel, each motor would see 1/4 of the voltage and all of the amperage, whereas in series each motor would see 1/4 the amperage and all of the voltage.


Hey Ana,

I think you have this backasswards.

major


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## Anaerin (Feb 4, 2009)

As many people have pointed out, I was in fact wrong (Which I finally worked out for myself once I seriously thought about series/parallel switching in drag racers). I was thinking about thing from the motor-s POV, rather than the controller's. Here's the corrected version:

Motors connected in series produces an open differential effect. Motors in parallel produces a "Limited slip" differential effect.

If you have a single *very* high voltage controller you could connect all four motors in series (Each motor then receiving 1/4rtr the voltage, full amperage). This would be equivalent to a 4x4 with "open" differentials.

If you have a single *very* high amperage controller you could connect all in parallel (Each motor receiving 1/4rtr the amperage, full voltage). This would be equivalent to a 4x4 with "locked" or "Limited Slip" differentials.

If you have a high voltage and high amperage controller, you could have the wheels in series/parallel, with each left-right pair connected in parallel, then those pairs connected together in series, or vice-versa. Each motor would then receive 1/2 voltage and 1/2 amperage. This would be equivalent to a 4x4 with "locked" front and rear differentials and an "open" centre differential, or if reversed, "open" front and rear differentials and a "locked" centre differential.

Or you could use 2 controllers, one for the front pair, one for the back pair. (High voltage mid amperage if in series, mid voltage high amperage if in parallel).

Or you could use 4 independent controllers. Though using more than 1 controller will mean ensuring that all the controllers are running at the same level and balanced.

Of course, you could also use a metric tonne of contactors and have the setup dynamically changing series/parallel connection too, but that would be very complex indeed, and would also need on-the-fly switching of voltages and power levels within the controller (and potentially within the battery pack also).

This is assuming you're using DC here. ACIM or BLDC will _*require*_ one controller per motor, because each controller is explicitly connected to the exact rotational position of each motor.


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## bruceme (Dec 10, 2008)

Kewl... as long as we're all learning


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## chenying (Jul 25, 2011)

OK so then it is possible to derive the differential effect with certain configurations of the controller and motors but now my question is what are the advantages to having 4 electric motors to one? Considering the fact that certain configurations require more controllers (AC) why would a company like jaguar use 4 electric motors at each wheel?


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## aeroscott (Jan 5, 2008)

A single controller is like my Dodge 4x4 , no advanced traction control . Unless you add it to the braking system , this works OK . But you can feel it's ruff and lots of steps and cross talk to engine ,trans , brakes and brain / sensors . With 4 controllers and brain/sensors wheel speed is very predictable and much more direct . Also we are not overheating our brakes to get control . It can also steer or power vector.


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## ken will (Dec 19, 2009)

chenying said:


> why would a company like jaguar use 4 electric motors at each wheel?


More precise control.

But, Mostly because it sounds more intense and Cat like.

I want to be the first person at my Country Club to have a car with 4 motors!!! That will make me special!!


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## aeroscott (Jan 5, 2008)

If you get on slippery road it could save your life . I just rolled my Dodge because of a soft shoulder , 18 years with out a problem .


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## pyroboy1080 (Sep 14, 2011)

bruceme said:


> Cost... you need 4 controllers and 4 motors, but it can be done.


I would also caution anyone planning on experimenting with this to be very thorough in your design for the hubs/wheels/assembly. I feel like impacts like railroad tracks and potholes could smash up your coils and magnets.  I'm sure there must be a way to circumvent this, but I haven't put much thought into it, and the efficiency of the motors may be affected by doing so.
HOWEVER I for one would think this would be a bitchin' setup, especially if zero turn was a possibility, even if it was just a concept vehicle that didn't go highway speeds


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## aeroscott (Jan 5, 2008)

staying with cv shafting will keep the motors happy .


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## Ziggythewiz (May 16, 2010)

pyroboy1080 said:


> I feel like impacts like railroad tracks and potholes could smash up your coils and magnets.


I second this. Anyone working on a non-sprung system(and all road construction workers) should spend some time driving an un/crappy sprung car. 'Small' bumps like train tracks or even gaps between pavement blocks can feel like a kick in the teeth. I guarantee you would not regularly kick or drop your control boards etc during development, why do it after it's completed?


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## Bowser330 (Jun 15, 2008)

aeroscott said:


> staying with cv shafting will keep the motors happy .


+2, keep the motors tucked up into body/chassis and use cv shafts to directly drive the wheels. 

Problem is what motors to use, you need to have some gear reduction for commonly used DC and AC motors. There are some wheel motors out on the market but they only output 30kw peak and I am not sure of the torque. They are also only suppose to support a weight of 500lbs, so unless your car is only 2000lbs the manufacturer won't condone the use...ev-propulsion.com

1300$ motors and the Kelly controller is 1000$ so 2300$ * 4 = 9,200$ for 
30kw * 4 = 120kw peak, not sure about the torque.

Then again you could always convert an AWD car and replace the motor with a Warp11HV & Soliton1 (6,500$) and have ~300ftlbs of torque & ~280kw


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