# Motor on each wheel?



## StevenHansen (Mar 26, 2008)

Hey guys, 

My friend and I are building a "dune buggy" style EV with a homemade controller. I am thinking about using a nice 43kW constant power AC induction motor to power the drivetrain.

However, I have found many (a ridiculous number) of websites that reference using 4 (probably brushless dc) motors, 1 on each wheel. This seems to be way more complicated than using a single motor to power the drivetrain.

If you have 4 motors, wouldn't that require 4 controllers as well? Talk about extra space requirements, and / or extra weight.

Correct me if I'm wrong, but it just seems more difficult? Am I on the right track here? Any responses appreciated.


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## Mastiff (Jan 11, 2008)

It does not require 4 controllers.

There's a little thing called Series and Parallel wiring.

It basically involves wiring the motors to each other and powering them off of one higher power controller.

I thought we had a Wiki article on it but I can't find it.

In Parallel wiring (positive to positive and negative to negative) the motors run off the same Voltage but share the Amperage.

In Series wiring (Negative to Positive), the motors split the Voltage in half between them but use the same Amperage.
So if you had a 144 volts system with two Series motors they'd each only get 72 volts.

I forget what the advantages where to each method of wiring, but basically it allows both (or all 4) motors to run off one controller.


Now this would basically give you conventional 4 wheel drive, you'll only have control over the "total" speed of all the motors, you couldn't control them individually.


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## StevenHansen (Mar 26, 2008)

Ok, that's what I figured was going on. 

But like you said, you only can control the total speed of the system, not control each motor separately, so therein lies a drawback. 

Not only that, but the more parts inherent in a system, the more likely it is for something to break down. 1 Motor vs 4 Motors....

Hmmm. For now I think I may stick to using 1 AC induction to power my drivetrain. That way when I build a controller custom, I can have control over the quadrature and direct currents driving the motor (and thus have complete control).

Unless anyone can think of a reason why it is better (other than just 4WD) to use a motor on each wheel...


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## John (Sep 11, 2007)

I think the four hub motor approach represents a high ideal of high performance with minimum mechanical complexity through increased electrical complexity. The notion being that electrical devices are more reliable than mechanical devices, so you replace gearboxes, differentials, drive shafts, universal joints, and CV joints with brushless DC motors, electrical wires, and separate motor controllers. From a vehicle dynamics point of view having separate torque control over all four wheels opens up all sorts of possibilities such as active yaw force control and not only fore and aft brake bias on regeneration but also side to side brake bias. Some of what can be done would not be reasonable with a mechanical system. The four wheel drive allows the vehicles entire contact with the road to generate driving and regenerative braking forces for greater acceleration/deceleration before skidding. It also allows the division of the driving force between the front and rear axles while cornering increasing the total force available for acceleration or braking before any one contact patch becomes overloaded. The use of 4wd over 2wd doubles the available torque for similar sized motors, this is quite important for hub motor systems as they can be torque challenged.
It is an ideal and hugely complex and completely unjustified for vehicles of more modest performance.


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## 3dplane (Feb 27, 2008)

Steven! I'll agree with you on keeping it simple.A little bit on brushless dc and number of controllers:The only kind im familiar with thats more powerfull than a computer fan,is the three wire BLDC three phase sensorless permanent magnet motors.The only way one controller will run multiple motors is if they are absolutely sincronized(would not work in a road car)You knock one out of sinc and both stops due to the controller loosing....control.At any given time two out of the three wires going to the motor are energized and the third is used by the controller to detect rotor position,when it senses that the rotor moved (thru back emf) it switches to the next phase,to create the rotating magnetic field. So basicly it needs to see a clear picture.Even messing with motor wire lenght can cause false signals and the controller gets confused.All this example is from electric model aeroplanes but I've built a couple motors to power bycicles.(and they did)When they come out with powerful enough and affordable controllers.....I don't know enough about the other tipes of brushless dc motors or their controllers used in ev's(hub etc.) Good luck


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## epyon (Mar 20, 2008)

Why not put a motor on a differintail in both ends of the car ? Two 4.88-1 8.8 rearends might work with honda spindles for A-Arm's up front .


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## Bugzuki (Jan 15, 2008)

In a dune buggy you want the wheels and suspension to take up a lot of the bump. But if you were to put the motor in the wheel - that would add a lot of weight to the wheel. This works ok for street cars, but I am sure going over bumps quickly would make for a very rough ride.


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## Dennis (Feb 25, 2008)

> It does not require 4 controllers.
> 
> There's a little thing called Series and Parallel wiring.
> 
> ...




This technique does not work with AC induction motors. Only DC brushed motors. AC motors require current separation from the inducing currents and from the torque producing currents using Clarke transformations to control the current responsible for torque. Simply wiring an AC induction in parallel or series to another AC motor will not work. Another risk is there can be out of phase issues which can really cause havoc on an AC system if regen was used for multiple AC motors.


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## StevenHansen (Mar 26, 2008)

Thanks for all the great info. This is really helping my decision making process 

Now, one more question. I am very sure that BLDC or ACIM is the way to go (at least for me). But all AC motors (technically, BLDC IS an AC motor) I can find so far are very expensive.

I was checking out Metric Mind's stuff, along with the Brusa ASM810 25kW nominal ACIM. However, I just saw a price listing for the Brusa ASM810 at $19,000  

That seems ridiculous to me, as I can buy a much cheaper (although heavier) ACIM from Reliance, or any other industrial motor supplier. In fact, I could get a 100kW from Reliance for only $600, as opposed to Brusa's $19,000 for only 25kW.

What is the deal here? Am I just looking at the wrong companies?


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## Bugzuki (Jan 15, 2008)

That seems to be the reality at the time. The controller for electric vehicles is quite a bit different then the industrial controllers. Right now they are only sold in low quantities, so nobody has put the effort into developing a mass producable controller. It is like nobody wants to take the plunge with the risk of not selling any of them.

So, they keep charging outrageous prices and keep selling low quantities.

Also the motors designed for automotive use are usually designed lighter then industrial motors. Who cares how much the motor weights that is sitting on a cement floor in some huge factory. While an automotive motor usually has size constraints as well as weight.


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## Dennis (Feb 25, 2008)

> That seems ridiculous to me, as I can buy a much cheaper (although heavier) ACIM from Reliance, or any other industrial motor supplier. In fact, I could get a 100kW from Reliance for only $600, as opposed to Brusa's $19,000 for only 25kW.
> 
> What is the deal here? Am I just looking at the wrong companies?


You know you have brought up a good point that many have also. An industrial AC induction motor is cheaper than an EV AC motor AND a DC brushed motor.....




> The controller for electric vehicles is quite a bit different then the industrial controllers. Right now they are only sold in low quantities, so nobody has put the effort into developing a mass producable controller. It is like nobody wants to take the plunge with the risk of not selling any of them.


That is not entirely accurate. The are variable speed drives that can also do flux vector functions as a automotive type can. Here is a brochure of Reliance's variable frequency drives: http://www.reliance.com/pdf_elements/d2950.pdf The downside to these controllers are weight and size constraints are not an issue to them as they intended these for industrial use.


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## StevenHansen (Mar 26, 2008)

Well, I would have no problem buying a Reliance inverter duty induction motor, but they are too heavy and the sizes are not exactly made for an electric vehicle, as Bugzuki pointed out. 

To me, it seems their are plenty of problems...err...challenges to building a custom electric vehicle/dune buggy/whatever. 

The controller is not that big of a deal to me, as I have been building my own 400A 1200V IGBT controller for a few years now. Here are the main 2 problems I've encountered with even the idea of building an electric vehicle:

1) The batteries are way too heavy (20 Optima YellowTops (for 240V) = ~600lbs+)
2) The motors are way too expensive (unless you go with brushed DC). But with crappy batteries, you want the best efficiency possible (ACIM, BLDC)

I really think when battery technology gets to a new level, some really really cool EVs will be built!


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## aeroscott (Jan 5, 2008)

our freedom will not come from letting others control technology . all we need do is look , listen , ask and share what we find .


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## Madmac (Mar 14, 2008)

Down side to industrial AC induction motors

Heavy most parts manufactured out of steel
Air cooled usually with fan attached to shaft.
No provision to add water or forced air cooling
Rotor design not optimised for starting or low speed
Windings not designed to deal with high frequency PWM drive


Advantages

High volume product hence low cost
Can withstand being overdriven for short periods 

Because the construction has high thermal mass you could use a smaller motor and during acceleration overrun it. The cooling system then needs to make sure that whatever power it is then run at will not result in the temperature of the windings being exceeded. (by that I don't mean try and run a .5HP motor at 50HP)

Using multiple AC or BLDC motors, one per wheel, requires that the control electronics for each motor have an external control loop to keep the drives in sync. So if you want to go straight each motor drives the same. For a production vehicle this extra loop means that it is easy to apply traction control and other systems people expect these days. 
For the home builder this extra control electronics needs a fair bit of engineering and is probably not practical. Either use multiple straight DC or a single AC / BLDC motor.

Madmac


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