Multiple Motors vs Transmissions

Technical discussion on converting internal combustion to electric
Post Reply
User avatar
photomac
Groupie
Posts: 306
Joined: Tue, 17 Nov 2009, 21:56
Real Name: Matthew Clifton
Location: South Perth

Multiple Motors vs Transmissions

Post by photomac » Thu, 18 Feb 2010, 23:00

I am curious about the concept of individual, smaller motors on each drive shaft of a wheel rather than a singular motor going through a power hungry gearbox and differential.

My understanding is, it is feasible but controlling the motors to work in unison, is the problem. Making sure a wheel doesn't spin wildly being an obvious isssue. Hence choosing one motor going through a slip diff.

I wonder which clever people are combing the power of brake-assist and powered wheels (regenerative breaking) into the one unit. Ian Hooper - perhaps a patent there for you?

While some attempts to mount the motor inside the wheel is promising, the extra mass means greater demands on spring and dampening units. The Michelen wheel motor seems to have reduced that mass.

Anybody trying it?
Last edited by photomac on Thu, 18 Feb 2010, 12:01, edited 1 time in total.
Yes,   we can.   Image
Hyundai Kona 64 v1 Sept 2019 onward. 00016 up to 3850+
Mitsubishi PHEV v1 Apr 2016 to Aug 2019 14500 to 72000km
Nissan LEAF v1.0 Nov 2013 to Apr 2016 00035 to 36000km

antiscab
Senior Member
Posts: 2489
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

Multiple Motors vs Transmissions

Post by antiscab » Thu, 18 Feb 2010, 23:58

photomac wrote: I am curious about the concept of individual, smaller motors on each drive shaft of a wheel rather than a singular motor going through a power hungry gearbox and differential.

My understanding is, it is feasible but controlling the motors to work in unison, is the problem. Making sure a wheel doesn't spin wildly being an obvious isssue. Hence choosing one motor going through a slip diff.


the weight of a motor is roughly proportional its continuous torque rating.

so direct driving each wheel will require 2x bigger motors than a motor to diff requires.
thats why the tango needs 2 x fb4001's where as a single one would have been sufficient with a diff.

getting two motors (particularly DC ones) to work in unison is trivially easy.
in series they will behave like a open diff (torque through both motors is equal)

in parrallel they act like a limited slip diff (the two motor speeds try to stay equal).

the engineering does get a tad tricky when trying to mount two large motors together.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

User avatar
Thalass
Senior Member
Posts: 741
Joined: Sun, 12 Aug 2007, 07:29
Real Name: Ben Rypstra
Location: Perth, WA, AU

Multiple Motors vs Transmissions

Post by Thalass » Sat, 20 Feb 2010, 04:17

ProEV's Subaru Impreza uses two induction motors (with two VFDs). It's reasonably quick but built for motokhanas.

I'm hoping to do the same thing, eventually, but one controller with two motors in torque control mode. I think that's the mode that works.

*edit http://www.evalbum.com/464 <-- there's the link
Last edited by Thalass on Fri, 19 Feb 2010, 17:19, edited 1 time in total.
I'll drive an electric vehicle one day.

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

Multiple Motors vs Transmissions

Post by coulomb » Sat, 20 Feb 2010, 15:33

antiscab wrote: the weight of a motor is roughly proportional its continuous torque rating.
Sounds reasonable.
so direct driving each wheel will require 2x bigger motors than a motor to diff requires.
Can you help me understand that please, Matt?

Surely each small motor only needs half the torque of the big motor; the diff will split the big motor's torque in half [edit: to each wheel shaft]... except in unusual conditions. Is it the unusual conditions where you need the full big motor torque to one wheel?
Last edited by coulomb on Sat, 20 Feb 2010, 04:34, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
woody
Senior Member
Posts: 1715
Joined: Sat, 21 Jun 2008, 02:03
Real Name: Anthony Wood
Location: Mt Colah

Multiple Motors vs Transmissions

Post by woody » Sat, 20 Feb 2010, 17:41

I think Matt is assuming a diff reduction ratio of 4:1 ?

I.E. 100Nm in the diff => 200Nm to each wheel
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

Squiggles
Senior Member
Posts: 742
Joined: Wed, 22 Apr 2009, 03:19
Real Name: Neil
Location: Newcastle NSW

Multiple Motors vs Transmissions

Post by Squiggles » Sat, 20 Feb 2010, 19:41

Assuming you want maximum wheel speed of approx 1000rpm and most electric motors spin to speeds in excess of 2000rpm you are going to want a 2:1 reduction of each motor. In effect the same result.

But how to get the reduction? Belt drive systems or compact reduction gears. Belt drives would give flexibility in mechanical arrangement.

User avatar
woody
Senior Member
Posts: 1715
Joined: Sat, 21 Jun 2008, 02:03
Real Name: Anthony Wood
Location: Mt Colah

Multiple Motors vs Transmissions

Post by woody » Sat, 20 Feb 2010, 20:06

A method used in the early Kombis and the Unimog is a gear reduction at the wheel end of the axles.

The michelin wheel motor system has a similar concept whereby a small, light, fast motor with a small cog drives the inside of the wheel which has teeth giving approx 10:1 gear reduction.
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

antiscab
Senior Member
Posts: 2489
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

Multiple Motors vs Transmissions

Post by antiscab » Sat, 20 Feb 2010, 23:42

woody wrote: I think Matt is assuming a diff reduction ratio of 4:1 ?

I.E. 100Nm in the diff => 200Nm to each wheel


yep, and no reduction for direct drive to wheels.

when i was talking to Tuarn a while back, there was discussion about using small industrial motors already coupled to a single ration gearbox, and driving them independantly.

that would be viable (though not sure about cheap)

but yes, going further,

the continuous torque rating of my x-91 motors is 20Nm
with my 4.1:1 diff, that means two of them coupled together gives me 82Nm to each rear wheel continuous (good enough for 100kmh cont)

if direct driven, it means only 27Nm continuous to each wheel.

the internal diff ratio is between 3:1 for high displacement engine cars (falcon etc) to around 6:1 for small rev happy engines.

for some conversions, using the diff directly is easier than going through the gearbox.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Multiple Motors vs Transmissions

Post by T2 » Sat, 08 May 2010, 08:52

Of course the Impact was the first pure electric concept vehicle to adopt twin motors.

The Impact was built around 1989 by Allan Cocconi et al. at Aerovironment under contract to General Motors USA.
A short video "Imagine the Impact" was released. It is probably on YouTube. It shows a competition run of 0-60mph in 8.0secs.

GM took the car and Hughes Electronics - who they had just purchased - redesigned the powertrain replacing the two motors with a single motor with conventional fwd transmission. Almost a decade later it re-appeared as the EV1. The EV1 was rated 137Hp 0-60mph in 8.5 secs.

The following is sourced from AEVA's own newsletter
Electric Vehicle News #66 February 1990.

AC Induction motor
Power        57 Hp
Torque       47lbs-ft to base speed
Base speed   6600rpm
Max speed   12700rpm at 75 mph
Effcy        90-95%
Voltage        400
Amps            159 A (per motor)
Frequency       500Hz max      

Transmission Integral Single Ratio planetary
              10.5:1
Battery pack 32 x 10v lead acid 42A-Hr 13.6Kwhr 870lbs
Rims           14"
Tires        P165-65
T2

Dean
Noobie
Posts: 12
Joined: Fri, 27 Feb 2009, 23:13
Real Name: Dean
Location: Aust

Multiple Motors vs Transmissions

Post by Dean » Thu, 13 May 2010, 02:00

photomac wrote: I am curious about the concept of individual, smaller motors on each drive shaft of a wheel rather than a singular motor going through a power hungry gearbox and differential.


So am i. More so the motor sizing in AC. Enginering them to fit is easy, rearwheel drive with half shafts.
photomac wrote: My understanding is, it is feasible but controlling the motors to work in unison, is the problem. Making sure a wheel doesn't spin wildly being an obvious isssue. Hence choosing one motor going through a slip diff.


From what ive read, controller for every motor and linked together adding weight. I did find a Japanese formula type car on the net but cant find the link again used one controller very light and small motor's.
photomac wrote: While some attempts to mount the motor inside the wheel is promising, the extra mass means greater demands on spring and dampening units. The Michelen wheel motor seems to have reduced that mass.
It does and gets rid of alot of extra weight (diff, half shaft, bearings, unijoints). Here we go into unsprung weight at the wheel..another problem.
photomac wrote: Anybody trying it?


I would....I dont want to steal the thread but if you could do two AC rear wheel drive motors how would you guys go about it?

Tritium_James
Senior Member
Posts: 683
Joined: Wed, 04 Mar 2009, 17:15
Real Name: James Kennedy
Contact:

Multiple Motors vs Transmissions

Post by Tritium_James » Thu, 13 May 2010, 14:09

You need two motors and two controllers. The 'electronic diff' type action between them is trivial, just tell both controllers to do the same motor current, and you get the same motor torque.

It's a very elegant way to go, but currently nobody is doing it because of the cost. Two smaller motors cost more than one bigger one. Two controllers cost more than one (duh!). Most cars already have the diff for free.

There's also the efficiency aspect. Smaller motors are less efficient than big ones, so this partially cancels out the efficiency gains you get from not having a mechanical diff.

However, if you want to build yourself a road rocket, it is most definitely the way to go.

Dean
Noobie
Posts: 12
Joined: Fri, 27 Feb 2009, 23:13
Real Name: Dean
Location: Aust

Multiple Motors vs Transmissions

Post by Dean » Thu, 13 May 2010, 21:21

Then lets design a road rocket that does 200kmph and does 200km at 1200kg mass, 2 motor's to 2 half shaft's rear wheel drive.

"However, if you want to build yourself a road rocket, it is most definitely the way to go."

Im looking to improve the image of the EV (not half brids)where do you start.

Hell yeh.....Inform the young street machine'ers.... Make it fast.

Needed....How do you convert the older.... Give it distance.

Walk to shops....Every one else is a daily comuter who needs 80Km tops. Home, work, home, shops.

Im interested and have the means. I just want knowagable options Motor and controller wise?

Tritium_James
Senior Member
Posts: 683
Joined: Wed, 04 Mar 2009, 17:15
Real Name: James Kennedy
Contact:

Multiple Motors vs Transmissions

Post by Tritium_James » Fri, 14 May 2010, 00:20

Where to start? >$100k available is probably a good place :)

Having the top speed at 200km/h will compromise performance unless you have a multi-speed gearbox. Settling for even 160 (100mph) would make a big difference.

For top performance each motor would also require a fixed reduction, probably around 4:1 or so. This makes better utilisation of your motors. Spinning them to only the wheel speed (~2000rpm) isn't making full use of their capabilities. A 4:1 reduction means the motors spin to 8krpm, which is quite likely to be better. This could possibly be done with a silent chain / belt type drive, not necessarily a gearbox.

You'd be looking at two of our Wavesculptor200 motor controllers :)

You'd also need a very high performance battery pack, capable of sourcing both large capacity (for the 200km range) and the ~350kW of power required at the high end of the speed range. This will not be trivial or cheap. I'm guessing at least 40kWh (ie probably around 400kg) and capable of 10C sustained discharge rates. This is probably a $50-60k battery pack...

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Multiple Motors vs Transmissions

Post by T2 » Sun, 16 May 2010, 16:29

Look fellas,
            could we follow this thread only to vehicles that meet current posted speed limits +15mph. So as not to stretch motor RPMs ?
Particularly as most are not going to be driving even at 80mph.
      
The Impact (EV1) was limited to 75mph. Although it was geared 10.5:1
The Prius was limited to about 100mph. The 2010 Prius is now ~10 : 1

Clearly a 10 : 1 ratio with base speed of 6600 as the Impact uses gets the power to max around 42mph, from then on it is constant(maximum) Hp

I am looking to put a planetary on the bell housing then out to the half shafts.This needs planetary to be part of motor, it also needs a short axial length motor but maybe 4kw. Two 4Kw will be harder to overheat than one 8Kw btw.

Being asynchronous they should be able to share the same VFD as rotor speeds will be extremely close. Most here are educaated enough to realise that any motor that starts to slip will automatically reduce torque as its electrical slip reduces as per normal induction motor action.
T2

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

Multiple Motors vs Transmissions

Post by Johny » Sun, 16 May 2010, 18:13

I'm too lazy to work it out but I think the speed difference between inner and outer wheels on a U-turn would be in excess of 8%. The motors will be fighting each other with one in motor and one in generator mode.
You also will not be able to use a vector mode in the VFD - you will be relying on v/f mode.

User avatar
woody
Senior Member
Posts: 1715
Joined: Sat, 21 Jun 2008, 02:03
Real Name: Anthony Wood
Location: Mt Colah

Multiple Motors vs Transmissions

Post by woody » Sun, 16 May 2010, 19:03

~10m turning circle FWD:
outer wheel radius 5m
inner wheel radius ~3.5m
30%
RWD would be worse.
Possible solution is disconnect inside wheel motor when cornering.
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

a4x4kiwi
Senior Member
Posts: 772
Joined: Thu, 03 Jan 2008, 19:04
Real Name: Malcolm Faed
Location: Australia
Contact:

Multiple Motors vs Transmissions

Post by a4x4kiwi » Sun, 16 May 2010, 19:46

As TJ mentioned elsewhere, if you run the controllers and motors in variable torque mode, you don't need to worry about it.
Silicon is just sand with attitude.

Blog: http://malfunction.faed.name

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Multiple Motors vs Transmissions

Post by T2 » Mon, 17 May 2010, 13:00

I see no reason to abandon the single controller with two motors model.

It would be necessary for each of the two motors to have its own encoder. A possible strategy would be for the controller to provide an output which would be preferential to the slower motor. When an opposing differential in speed is detected between the two motors a decision is made, with an inverse time characteristic such that the larger the difference the faster the changeover, the switch is made and the controller continues on to again service the slower motor.

It would probably be convenient to invent a new part, the encoder processor. This part would feed the single encoder port of a conventional controller.   

The encoder processor card, upstream of the controller, would monitor both encoders and make the decision to switchover to the slower motor with a two input multiplexer. This could be done seamlessly by waiting for both encoders to be outputting the same code and then make the switch, done that way the controller is prevented from seeing a bad code.
The ability to monitor current in both motors is lost of course but there is no reason that temperature monitoring in both cannot be made. Should either motor overheat the system can go into a limp mode.

The twin motor system gives ability for a series/parallel operation to be performed for the cost of a series parallel mechanical switch.
Perhaps I should ask you to curb your enthusiasm for twice the current and therefore the torque for a minute.
The more important considerations are :

The original controller is then able to output its FULL rated power over an extended vehicle speed range. This option isn't limited to the multiple motor scheme any single motor with two sets of identical windings can be reconfigured when on the fly.

Is this is an absolute must have, depends on the performance you can reach with affordable technology. If 0 to 60mph in 8.0secs plus 75mph top speed also acceptable then the Impact/EV1 did this twenty years ago with no electrical switching.

If it is an absolute must have, then the Tesla which was at the limit with 850Amp transistors certainly. Their motor would do 0 to 60 with 14.4:1 ratio @ 13500rpm AND 120 mph with 7.4:1, until the dual ratio gear box became inoperable with use. A larger frame size to generate more torque while staying with a single 7.4 ratio was an option to meet this spec and with the transistor current maxxed out already, a two stage winding would have sufficed. This would have extended the max power from 2500rpm instead of 5100 rpm which would have secured the 0 to 60 in 4 sec benchmark. Don't post me about the extra motor expense. The company spent a million on the gearbox debacle plus it delayed the roll out and secured bad press for all players. Everything is an expense.

Twin motors at the rear of this vehicle would also work. With series parallel they could have even have had a manual "gear lever" action that made sense.

Anyone have some input on manufacturing a suitable planetary on to the C face of a motor where space is a premium ? Anyone ideas out there ? What doesn't work ? Mech Eng is not my field but I have access to CMC technology and people who are motivated. We know 10:1 needed, we know helicals will give lateral thrust perhaps stick with straight cut. Should use an off-the-shelf internal gear into our own housing. Have a slo-syn example. I thought it was a single stage but it seems to use a (concealed) second planetary on the other side of the planetary carrier to provide balanced torque power to the output sun. Thoughts here ?   
T2

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

Multiple Motors vs Transmissions

Post by Johny » Mon, 17 May 2010, 15:24

a4x4kiwi wrote: As TJ mentioned elsewhere, if you run the controllers and motors in variable torque mode, you don't need to worry about it.
ControllerS (plural) - agreed. A single controller won't cut it though, regardless of how you play with the encoders. Woody's idea of only running one motor under certain conditions (requires contactors) is one answer but you would lose traction.

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Multiple Motors vs Transmissions

Post by T2 » Mon, 17 May 2010, 19:59

-woody,johnny,

yeah, you turned me. I figured that a sharp 180 degree would only be undertaken at low speed. The low frequency and low excitation voltage could be less effective and the likelihoood of large circulating currents between stators quite small. The induction generator itself could be pushed over its breakdown torque by the momentum of the vehicle together with torque from the inside motor. Regen would then drop rapidly of course. That would be something to try later on but I agree two inverters in torque mode now looks the best approach.

    In which case a dual inverter design could perhaps have savings over two individual inverters. It would have the flexibility to better utilise a single set of bus capacitors by means of a biphase technique. This involves triggering the PWM generator off of alternate phases of a common carrier clock.

OTOH There is merit in having two identical inverters. Reliability through redundancy as always, together with a lower carrying cost if the holding of a spare module is required.

The real problem comes down to driving the wheels with the least amount of mechanical intervention so that the inefficiency of a multi- ratio gear box and differential can be dispensed with. The Impact did it the hard way on the front. I am sure the rear is the easier - but how ?
T2

unheardofinstruments
Groupie
Posts: 86
Joined: Tue, 26 Jun 2012, 15:08
Real Name: ron Berry
Location: Nimbin
Contact:

Multiple Motors vs Transmissions

Post by unheardofinstruments » Sat, 02 Feb 2013, 06:23

It also occurred to me that a permanent magnet dc motor with suitable overclocking could get 10 times the torque with no reduction drive at all but a pretty large diameter might be needed. I would have to build them myself it seems but it is possible and not overly hard. Getting the right magnets is harder.
Twin AC motors adds up in frame/rotor axle weight substantially as do DC so axial flux pmdc seems the go weight wise and Agni have a 300mm higher power version in the wings, already prototyped.
I too thought that a purpose built twin controller could work out cheaper than two separate ones. They would have half the rated current of a single motor so it should add up to the same amount of transistors and caps, just an extra pwm low voltage section which could share the box, supply, etc. Maybe 150% of the price of a single controller project?
I am saving the concept for my next conversion...ha!

User avatar
carnut1100
Groupie
Posts: 334
Joined: Tue, 24 Feb 2009, 16:39
Real Name: Greg Milligan
Location: Brisbane
Contact:

Multiple Motors vs Transmissions

Post by carnut1100 » Sun, 14 Jul 2013, 20:46

One of my dream projects is an offroad 4x4 with 4 smaller motors and no differentials or transfer box or any of that stuff at all...no diff locks needed, no traction control or LSD or any of that stuff...and all that lovely room in a large engine bay and under body where the trans and transfer box were for batteries and controllers...
Based on a Land Rover Discovery you can ditch the thirsty V8, weak auto, fragile diffs, and they have a huge rectangular fuel tank as well as optional long range sill tanks...and a massive engine bay....
Fabricated axle housings with portal drive for reduction = increased ground clearance as well as reduction drive.....
Really nice V8 Discos are worth nothing nowadays...and they are an excellent 4x4 while they are running.
Lots of room for a small portable generator in the back for longer trips in the bush...run solar panels on the roof rack as well.

Just need a lot of $$$$$$$$$.......
Last edited by carnut1100 on Sun, 14 Jul 2013, 10:48, edited 1 time in total.

Post Reply