# Thoughts on a dual AC-50 AWD setup please



## Bowser330 (Jun 15, 2008)

So I have been learning a lot from the HPEVS owner's thread about the potential of the AC-50 motor controller setup. The pending advantage of the 144V and 650A controller is exciting.

My question is this....Would it be possible to install one AC-50 to the transmission RWD transmission (as normal) and then add another to a front differential directly.

So the front AC-50 would be a direct drive, and would be geared so that it would never run out of rpm and have any issues, maybe make 100mph @ 6000rpm (leaving 2000rpm window for motor safety)

Example:

@ 60mph the front motor could be spinning at 4000rpm where as the rear motor (through the transmission and rear differential) could be spinning at 5000rpm.

Is it ok for the speed via the road to connect the two drive systems?


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## jeremyjs (Sep 22, 2010)

Not sure what you're talking about on hooding it up to a transmission and differential. They need to both be going through a separate differential front and rear with a fixed and identical gear ratio or it won't work. If the gear ratio's aren't the same the motors will fight each other.


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## Bowser330 (Jun 15, 2008)

jeremyjs said:


> Not sure what you're talking about on hooding it up to a transmission and differential. They need to both be going through a separate differential front and rear with a fixed and identical gear ratio or it won't work. If the gear ratio's aren't the same the motors will fight each other.


sorry it was hard for me to describe what i was thinking.

Ok so you are saying the gear ratios of both motors need to be identical otherwise they will fight each other....hmmmm....ok.

I guess i figured, because they were not connected, and only connected through the road per say, that it they could spin at different rpms, because the speed of the car would regulate the rpm in each, albeit different rpm.

Thanks for the feedback, I guess connecting them via belt drive is the best way


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## major (Apr 4, 2008)

Bowser330 said:


> Ok so you are saying the gear ratios of both motors need to be identical otherwise they will fight each other....hmmmm....ok.
> 
> I guess i figured, because they were not connected, and only connected through the road per say, that it they could spin at different rpms, because the speed of the car would regulate the rpm in each, albeit different rpm.


Hey Bowser,

I don't see why the two motors have to operate at the same RPM. Each needs its own controller. Run each in torque control. They will each deliver torque upon demand regardless of the RPM relative to each other.

Regards,

major


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## Nathan219 (May 18, 2010)

Go for it, this sounds like a neat project, I want to see this running, I bet a lot of Subaru owners do as well. Don’t let naysayers discourage you smart people can find a way to make things work.


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## kerrymann (Feb 17, 2011)

Bowser330 said:


> So I have been learning a lot from the HPEVS owner's thread about the potential of the AC-50 motor controller setup. The pending advantage of the 144V and 650A controller is exciting.
> 
> My question is this....Would it be possible to install one AC-50 to the transmission RWD transmission (as normal) and then add another to a front differential directly.
> 
> ...


I have been thinking about doing something similar but not using the rear transmission and just going with direct drive to both diffs. Is there a reason you want to keep the rear trans (better off the line acceleration)? One thing to consider is what donor car you would use. I'd say 95% of AWD cars (or are you considering a truck?) are really a FWD with a drive shaft going to the rear. If you want a RWD trans then a BMW 325ix could be set-up the way you proposed is relaitivly light and cheap and cool. 

On the practical side you do have to ask if you are really going to spend $9000 on motors and controllers alone?


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## Bowser330 (Jun 15, 2008)

kerrymann said:


> I have been thinking about doing something similar but not using the rear transmission and just going with direct drive to both diffs. Is there a reason you want to keep the rear trans (better off the line acceleration)? One thing to consider is what donor car you would use. I'd say 95% of AWD cars (or are you considering a truck?) are really a FWD with a drive shaft going to the rear. If you want a RWD trans then a BMW 325ix could be set-up the way you proposed is relaitivly light and cheap and cool.
> 
> On the practical side you do have to ask if you are really going to spend $9000 on motors and controllers alone?


Well you have to start somewhere, and I am checking the technical feasibility of the setup with those who know more than I. And for your information, I have no problem spending on what will perform, i will leave it at that, if you want to ask me about my taxes next, please pm.

The AC-50 setup is continuing to develop and improve, with the expected 144V upgrade each setup will be able to produce 100hp & 115ftlbs, so 9000$ for a 200hp, 230ftlbs, that's a good deal of power for an AC setup...Additionally other AC inverters may be released that can take advantage of AC-50's 200V [email protected] 150V * 650A =97.5kw = 130hp (each)

The following setup is 15,000$ and only produces 120kw peak due to the lower max amperage (360A) vs. the curtis (650A). Yes the motor linked below has a lot more torque but according to the limited specs provided it appears it drops off rather quickly, if the peak is 161hp (120kw).
http://currentevtech.com/Drive-Syst...ers/120KW-BLDC-Motor-and-Controller-p168.html


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## Bowser330 (Jun 15, 2008)

Thanks all for the encouragement and the thought provoking posts


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## kerrymann (Feb 17, 2011)

Bowser330 said:


> Well you have to start somewhere, and I am checking the technical feasibility of the setup with those who know more than I. And for your information, I have no problem spending on what will perform, i will leave it at that, if you want to ask me about my taxes next, please pm.
> 
> The AC-50 setup is continuing to develop and improve, with the expected 144V upgrade each setup will be able to produce 100hp & 115ftlbs, so 9000$ for a 200hp, 230ftlbs, that's a good deal of power for an AC setup...Additionally other AC inverters may be released that can take advantage of AC-50's 200V [email protected] 150V * 650A =97.5kw = 130hp (each)
> 
> ...


 
I was more asking about the $9000 for 200hp as opposed to a different motor controller combination. Dual warp 9's with Soliton1s would cost you about the same, just with a lot more power.  I take it you are looking at AC mostly for Regen? My thinking has been more along the lines of a AC-50 on the front axle and a series 8 or 9" on the rear. During acceleration you need more power on the rear and during deceleration (regen) the front would be the most effective. The problem I keep running into is that low max voltage on the Curtis controller (108). It keeps you from having a single pack that can run the really take advantage of the warp 9 and multiple packs get's complicated quickly. With them upping the voltage to 144vdc the idea is more interesting.

Just my .02 so take it for what it's worth.


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## Quantum (Jul 10, 2011)

Yes, but if you put the motors in torque mode, the rear one goes through the tranny and has quite alot of mechanical advantage, so the back would peel out while the front putters along. For torque mode to work (using the street as a synchronizer) you'd need direct-drive on both and identical gearing.

Also you'd need diffs with a shorter gear ratio, and few diffs have parts made to change that.

I'm thinking more along the lines of a 67KW Siemens motor on my 5,000 pound car (with ICE), mated to a tranny from FB Performance. Won't be AWD, but the tranny sure should make the motor powerful enough for that heavy of a car. Only thing I don't know is whether the tranny can cope with regen.


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## major (Apr 4, 2008)

Quantum said:


> Yes, but if you put the motors in torque mode, the rear one goes through the tranny and has quite alot of mechanical advantage, so the back would peel out while the front putters along. For torque mode to work (using the street as a synchronizer) you'd need direct-drive on both and identical gearing.


I don't think this is correct. And nothing says you must give each motor the same torque command.


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## Quantum (Jul 10, 2011)

You don't see how a transmission gears down and gives mechanical advantage?

Or how a lower gear requires less torque for the same work?

Or how in torque matching mode the controller keeps the torque (current draw) the same for both motors?


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## major (Apr 4, 2008)

Quantum said:


> You don't see how a transmission gears down and gives mechanical advantage?


Of course I know this. 




> Or how a lower gear requires less torque for the same work?


That statement might be loaded. Work is force times distance. Or torque times angular displacement. And also equal to energy. Right? So for the vehicle to travel a certain distance at a certain speed, it would do a given amount of work, or more correctly have the work done on it by the propulsion system and this amount of work is equal to the energy removed from the battery. How is the gear ratio going to alter this?

You say "for the same work". I guess you mean between the front and rear. So if the rear had a lower gear (higher numerical ratio), then the rear motor would have to run at a higher RPM and output equal power as the front motor. And yes, it would output lower motor torque than the front motor.

If for some reason you think it is required to have equal motor torque, front to rear, and the wheels all are at equal speed, then the motor running into the lower gear (higher numerical ratio) will do more work because it is turning faster. But this is just an arbitrary control method, not required.



> Or how in torque matching mode the controller keeps the torque (current draw) the same for both motors?


If you look at post #4, you will note that I said you will need a controller for each motor. He is talking about a specific motor system, AC50. That uses an induction motor and closed loop vector drive in torque control. So the two systems, one on the front (FWD) and one on the rear (RWD) do not have to operate at the same speed. And they do not have to receive the same torque command. So if the RWD had twice the ratio of the FWD and he wanted equal wheel torque, he could command twice the torque on the FWD. But it is not necessary to have the same torque on both axels.

He doesn't need the same ratio front and rear. He doesn't even need the same size wheels. He wouldn't even have to use the same motors for the FWD and RWD. There are a lot ways to skin this cat so to speak. 

Regards,

major

Edit: Doesn't the Toyota Highlander or Lexus SUV hybrid use a completely different motor and fixed ratio (direct drive) on the rear and the Senergy system on the front (variable ratio)?


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## Nathan219 (May 18, 2010)

You can do it build the thing and let see what it will do. This is a hobby and supposed to be fun right?


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## DawidvC (Feb 14, 2010)

major said:


> Edit: Doesn't the Toyota Highlander or Lexus SUV hybrid use a completely different motor and fixed ratio (direct drive) on the rear and the Senergy system on the front (variable ratio)?


You are on the ball, Major. AFAIK both use a seperate motor for the rear, no mechanical link at all. I see no problem with a tranny setup for rear, and direct drive for front at all, but I have no idea how it will perform in low tractio environment (eg snow). This is quite similar to an idea I entertained for my own conversion using tranny and DC motor rear and direct drive ac motor front.

In this case, with two identical motors, I would want to have the front motor at 5% more torque for higher efficiencies at highway speeds, but even that is not necessary.

Good luck with this build!

Dawid


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## Quantum (Jul 10, 2011)

major, but the point is to coordinate the two motors so they share the load _equally_. It would be all but impossible to dynamically coordinate the two motors all the time, if different gear ratio, different inverters, different motors, without a special computer with very special software constantly monitoring and adjusting. 

I wouldn't trust that day-to-day, would you? For your very fundamental traction? Even the slightest wheel slippage would do terrible efficiency and wear. As ppl here often say, 'sure it can be _done_... with unlimited money and resources'. This is the point. We want practical.


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## major (Apr 4, 2008)

Quantum said:


> major, but the point is to coordinate the two motors so they share the load _equally_.


Hi Quant,

This might be your point, "share load equally", but I don't see it as a requirement, or advantage. And it was not indicated by Bowser who started this thread. Why do you attempt to force your concept on him? Give it as your opinion and let him choose how to design his project. 



> It would be all but impossible to dynamically coordinate the two motors all the time, if different gear ratio, different inverters, different motors, without a special computer with very special software constantly monitoring and adjusting.


Again, this is your opinion and contrary to my experience. It is very easy to blend motors operating in torque control with other sources of torque in the system, be it friction brakes, IC engine in a hybrid or another electric motor. It can be done without a front end computer; however simple algorithms can be advantageous.

Regards,

major


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## toddshotrods (Feb 10, 2009)

Subscribed. Darn it Bowser!


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## aeroscott (Jan 5, 2008)

many 4X4's use 40/60 or other power split .


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## Quantum (Jul 10, 2011)

I see these asymmetric power splits alot, but the purpose is to bias traction to front or back for stability. There is 'give', or liquid coupling, to allow for differences in tire travel, cornering, etc.

But when a motor is direct coupled to the back and another to the front (whether through a tranny or not) there is no mandatory 'give', causing tire slippage on the road and strain on the drivetrain. If the back gets 51% and front 49%, it is a problem with the front skidding down the road.


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## major (Apr 4, 2008)

Quantum said:


> But when a motor is direct coupled to the back and another to the front (whether through a tranny or not) there is no mandatory 'give', causing tire slippage on the road and strain on the drivetrain. If the back gets 51% and front 49%, it is a problem with the front skidding down the road.


This is simply not the case. The situation we are talking about has no driveline mechanical coupling front to rear on the vehicle. It is only the road through the wheels which forces the front and rear to go the same speed. So the propulsion systems, front and rear, have the RPM relationship dictated by their respective drive ratios. You can apply any proportion of torque from either front or rear. It will not cause any slippage when within the limits of tire traction.

Just as in your regular 2 wheel (single axel) drive vehicle. The front and rear wheels are only speed coupled by the road. In this case, you have a 100/0 torque split. No slippage. You could add a motor to the non-driven axel and do a 90/10 torque split, no slippage. Or a 50/50 split. If you can comprehend negative torque, the same thing happens when you bias brakes front to rear. Equal speeds, unequal torques.


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## Ziggythewiz (May 16, 2010)

Simple experiment. Take the wifey out and push the car up the driveway. If she fails to push as hard as you do, will her feet slip? I think you'll do most of the work, but you'll both get to the top at the same time, no harm done.


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## aeroscott (Jan 5, 2008)

Well put Magor . when a motor is loaded it slows down , even a 60 cycle drops from its 1800 rpm to 1740 or so , do to slip . So as long as we not running to far out of sink on the power output it works .even with ac ,which we can program in the amount slip .if to far out one motor powers the other into a slight regen state ,pushing power into the bus . In DC , is not frequency dependent . If DC is a pm , a voltage difference will cause some regen , if large enough .


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## Quantum (Jul 10, 2011)

Alright, I give up.


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## kerrymann (Feb 17, 2011)

So now that we have established the answer is: Yes you can do it. The next question is: Bowser, when are you going to build it?  Because I for one would love to see it done!


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## Bowser330 (Jun 15, 2008)

kerrymann said:


> So now that we have established the answer is: Yes you can do it. The next question is: Bowser, when are you going to build it?  Because I for one would love to see it done!


I'm a dreamer for now...still thinking about the ideal setup to pop my DIY EV cherry with and aligning my resources to help me through the process.


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## Overlander23 (Jun 15, 2009)

Quantum said:


> Alright, I give up.


Think of it this way... In your ideal 50/50 setup, the ends are mechanically identical and are delivering an equal amount of torque to the front and rear.

If the front motor lost power, the vehicle could still continue at the same speed if the rear motor had enough power to maintain that speed. Your torque split goes to 0/100. The front motor freewheels in this situation. It certainly doesn't lock up and scrub the wheels.

Feed power back into the front, and to maintain the same speed... torque will slowly shift from 0/100 back to 50/50... or however you want it allocated, all with the vehicle doing the same speed.

If you agree this situation is viable... it also means that the differential action between the front and rear axles is irrelevant. After all, they're not mechanically linked anyway. A motor not under power will just freewheel.


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## jeremyjs (Sep 22, 2010)

ok so I guess if it does work wouldn't potentially really bad things happen if you use regen? Since the torque multiplication between the motors is different couldn't you potentially get in a situation where one motor is doing full regen and the other isn't doing much of anything?

If this is the case it could be really dangerous and would largely eliminate the advantage of going with ac motors.


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## Overlander23 (Jun 15, 2009)

jeremyjs said:


> ok so I guess if it does work wouldn't potentially really bad things happen if you use regen?
> 
> If this is the case it could be really dangerous and would largely eliminate the advantage of going with ac motors.


It kind of depends. From a technical standpoint, since two controllers are used there wouldn't be a problem... but the amount of regen power you've got on each axle could be problematic.

If you decide to commit a lot of regen to the rear compared to the front that will lead to unstable "braking". Rear braking tends to allow for oversteer (bad, mostly). Most cars bias the braking power to the front of the vehicle which creates understeer (or no steer) which creates predictable braking.

Remember, the controllers are separate so the regen settings are separate. You'd just setup up the amount of regen per axle (via the individual controller) to appropriately setup your "braking" balance, or regen ratio. After all, regen doesn't just happen... you can control how strongly it can be applied.

As with standard braking practices, though, you want the balance to be correct front to rear.


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## jeremyjs (Sep 22, 2010)

Overlander23 said:


> It kind of depends. From a technical standpoint, since two controllers are used there wouldn't be a problem... but the amount of regen power you've got on each axle could be problematic.
> 
> If you decide to commit a lot of regen to the rear compared to the front that will lead to unstable "braking". Rear braking tends allow for oversteer in braking (bad, mostly). Most cars bias the braking power to the front of the vehicle. which creates understeer (or no steer) which creates predictable braking.
> 
> ...



Yes, but the problem is the rear has a gearbox so there's no way to set the regen and have it be consistent; since the ratio will change every time you change gears. I guess the question is how much.

From what I've seen it's usually about a 70-30 front to rear braking ratio; because of the things you mentioned and the fact that a large percentage of the weight shifts to the front under heavy braking.


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## major (Apr 4, 2008)

jeremyjs said:


> but the problem is the rear has a gearbox so there's no way to set the regen and have it be consistent;


I can think of several ways off the top of my head. Not sure it's needed. When I worked with a 3 speed hydramatic using an induction motor, regen was limited to 3rd only. That's where the most benefit was (at high speed) and regen torque was sufficient enough you didn't need to downshift anyway.


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## Overlander23 (Jun 15, 2009)

jeremyjs said:


> Yes, but the problem is the rear has a gearbox so there's no way to set the regen and have it be consistent; since the ratio will change every time you change gears. I guess the question is how much.



Ahh yes, true... Wasn't thinking of changing ratios. Well, in that case just regen on the front. Hard braking would be semi-hydraulic (mostly) anyway, in which case you've got the rear helping out. But for just reasonable decel/regen only using the front doesn't seem to be too much of a liability. Or, work out variable regen rates for different gearing. So, as major points out, regen at a specific rate in third... but expand it to all the gears. The ratio of a particular gear and the other axle will always be constant.

Of course, this will require knowing what gear the vehicle is in. Easy with an automatic, not as easy with a manual since you'd have to probably rig a sensing switch somehow.


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## ngrimm (Oct 19, 2007)

Would this vehicle be driven on slippery roads?


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