# Dual motors driving front wheels independently?



## mattW (Sep 14, 2007)

My guess is that the wheel going faster will have more emf so more 'resistance' and less current, so the slow wheel will push harder (more current) but that may not necessarily be a bad thing. When you are accelerating on a corner you have probably already reached the apex and want the car to start straightening out anyway. If you are off the accelerator then there will be no effect.

But don't base it on my opinion... thats just a best guess until the big guns chime in.


----------



## bblocher (Jul 30, 2008)

A slower spinning motor of two connected in parallel would pull more current and generate more torque. 

The real question though, is there enough difference in rotational speed to even be noticed? Especially at high speeds, you won't have the front wheels cranked completely one way at 60, you'll barely move the wheel at all and the difference in roational speed is insignificant.


----------



## 1clue (Jul 21, 2008)

A brushed DC motor or AC induction motor won't much care.

An permanent magnet (PM) AC motor or brushless PM DC motor will care a lot. The controller in this case will generate a signal based on where it thinks your magnets are in relation to the windings.


----------



## kek_63 (Apr 20, 2008)

I would think that a greater safety concern would be possible loss of power to one of your front wheels if a motor crapped out. Might need keep a tight grip on the steering wheel. 

It's been a long time since I had Minis (I do still miss them), but I think that it would be fairly easy to modify a transaxle case and drive the tranny output shaft with your 2 motors belted or chained together.

Later,
Keith


----------



## PhantomPholly (Aug 20, 2008)

Sounds like a perfect place to implement CVTs, since you're using belts anyway. That might have the added advantage of the CVT reducing the adverse impact of any differences in current draw.


----------



## MalcolmB (Jun 10, 2008)

Thanks for all your replies, some good points there. I like your thoughts on accelerating out of corners Matt.

I'm sure this approach must have been tried before on front-wheel drive but I've not come across anything in my surfing. It's the effect on steering feel that I'm most concerned about, as my wife wants to drive this car as well. I reckon I'll just go ahead and try it anyway. If it doesn't work out I can always couple the motors together and use them to drive a diff.

I know there are benefits to keeping the existing gearbox, but I'm really keen to try and keep this conversion as simple as possible. I'll post some photos once I've made some progress.


----------



## sunworksco (Sep 8, 2008)

MalcolmB said:


> Thanks for all your replies, some good points there. I like your thoughts on accelerating out of corners Matt.
> 
> I'm sure this approach must have been tried before on front-wheel drive but I've not come across anything in my surfing. It's the effect on steering feel that I'm most concerned about, as my wife wants to drive this car as well. I reckon I'll just go ahead and try it anyway. If it doesn't work out I can always couple the motors together and use them to drive a diff.
> 
> I know there are benefits to keeping the existing gearbox, but I'm really keen to try and keep this conversion as simple as possible. I'll post some photos once I've made some progress.


The way to design the IRS 2-motor drive system is to use 2-controls and 2-battery packs independent of each other.I know that the ac motor control will control both motors as if there is limited slip differential.It would be better to design a single motor with a limited slip differential.I am designing a front wheel drive with this design and have located a limited slip diff shown in the attached image.


----------



## sunworksco (Sep 8, 2008)

Forgot to mention that this diff can be set up to use Porsche or VW axles.You can use late model front-wheel drive Porsche uprights/suspension/hubs.


----------



## MalcolmB (Jun 10, 2008)

sunworksco said:


> The way to design the IRS 2-motor drive system is to use 2-controls and 2-battery packs independent of each other.I know that the ac motor control will control both motors as if there is limited slip differential.It would be better to design a single motor with a limited slip differential.


Yes Quaife make some really nice units. I especially like this one: http://www.quaife.co.uk/Quaife-CD-axle-unit-and-drive-flange-for-chain-driven-cars. It solves a couple of problems at once, at a price.

I understand you need two controllers for AC, but what I'm aiming for is a bare bones solution. This project began when I found a pair of series motors cheap, so I'm just trying to make the best of what I've got and try out something a little different at the same time.

By the way, I love the Avion Blackjack – I came very close to buying one myself, but the British weather finally dissuaded me.


----------



## sunworksco (Sep 8, 2008)

MalcolmB said:


> Yes Quaife make some really nice units. I especially like this one: http://www.quaife.co.uk/Quaife-CD-axle-unit-and-drive-flange-for-chain-driven-cars. It solves a couple of problems at once, at a price.
> 
> I understand you need two controllers for AC, but what I'm aiming for is a bare bones solution. This project began when I found a pair of series motors cheap, so I'm just trying to make the best of what I've got and try out something a little different at the same time.
> 
> By the way, I love the Avion Blackjack – I came very close to buying one myself, but the British weather finally dissuaded me.


 The Blackjack company does not want sales in the U.S.
I requested an invoice but they said no sale!
So I am building my own trike weighing 600lbs. in a single cockpit version.
The body will be similar to the attachment of the U.K. Rocket Car except one less wheel.


----------



## MalcolmB (Jun 10, 2008)

sunworksco said:


> So I am building my own trike weighing 600lbs. in a single cockpit version.
> The body will be similar to the attachment of the U.K. Rocket Car except one less wheel.


Seems like we have similar tastes. The Rocket is another of my bookmarks. Part of a fascination with fast, minimalist lightweight cars. I don't have the skills to build my own yet, but one day... My ideal would be a cross between the Rocket and a Cree Sam http://www.cree.ch/


----------



## sunworksco (Sep 8, 2008)

MalcolmB said:


> Seems like we have similar tastes. The Rocket is another of my bookmarks. Part of a fascination with fast, minimalist lightweight cars. I don't have the skills to build my own yet, but one day... My ideal would be a cross between the Rocket and a Cree Sam http://www.cree.ch/


I have images of the cree as well.
This is a very well engineered car.
The only things that could use improvement is the suspension and the rear trailing arm/wheel.
I'm using BMW F800ST motorcycle rear suspension with a Ducati axle and BST carbon fiber wheel(front wheels also).


----------



## MalcolmB (Jun 10, 2008)

Anyone have any more comments on my plan to use two motors for independent front wheel drive before I commit myself and start cutting steel? Does it seem feasible or is it likely to be a pig to drive?

I'm also curious to know what methods others are using to cut power to the motor in the event of a failure in the driveline. The most likely problem in my case would be a snapped drive belt. I'm electronically challenged so I'm looking for a fairly low-tech solution. The simplest I've found so far is to use an adjustable shift light (such as ebay item 110348393070) to provide a clear warning. The signal for the light could also be used to cut out the controller, but there are obvious safety implications there.

Your thoughts are welcome, positive and negative


----------



## sunworksco (Sep 8, 2008)

MalcolmB said:


> Anyone have any more comments on my plan to use two motors for independent front wheel drive before I commit myself and start cutting steel? Does it seem feasible or is it likely to be a pig to drive?
> 
> I'm also curious to know what methods others are using to cut power to the motor in the event of a failure in the driveline. The most likely problem in my case would be a snapped drive belt. I'm electronically challenged so I'm looking for a fairly low-tech solution. The simplest I've found so far is to use an adjustable shift light (such as ebay item 110348393070) to provide a clear warning. The signal for the light could also be used to cut out the controller, but there are obvious safety implications there.
> 
> Your thoughts are welcome, positive and negative


You will definately notice noise and power loss if your belt breaks but you can use a Kevlar reinforced belt which is mostly trouble free.Try to use a Kevlar belt that is mass produced , like the BMW F800ST motorcycle drive belt.It will be less expensive.
You can install an emergency/accident motion switch from a 1979 MGB under your dash for car accident disconnect and also a manual breaker.
The MGB motion switch is a simple affair of a steel ball bearing that drops out under a violent movement and disconnects the voltage.
You should use a motor RPM gauge which will tell you when a belt breaks.


----------



## MalcolmB (Jun 10, 2008)

sunworksco said:


> You should use a motor RPM gauge which will tell you when a belt breaks.


Thanks for the tips sunworks. I'll be connecting a rev counter to each motor – one calibrated for rpm, the other calibrated for road speed. That way the speedo serves a dual purpose. You're right, a drive belt failure is likely to make enough noise to alert the driver anyway.


----------



## sunworksco (Sep 8, 2008)

MalcolmB said:


> Thanks for the tips sunworks. I'll be connecting a rev counter to each motor – one calibrated for rpm, the other calibrated for road speed. That way the speedo serves a dual purpose. You're right, a drive belt failure is likely to make enough noise to alert the driver anyway.


 Here is an image of a front-wheel-drive limited-slip differential :


----------



## grayballs (Aug 27, 2008)

We have a similar project, in the shop, at this time. The plan is to use 2 72v Curtis controllers, 2 6.7" ADC motors, and 1 battery pack with a common bus (in a Geo Metro). The issue, at the moment is whether we want to connect both motors to a common differential, (separate belts to a common pulley) or to drive each axel separately. We have just recently torn down the trans and started looking at the pieces. Once we have dimensions and a plan we will plug them into the CNC mill and start making parts.
Most of the negatives that I have heard are " worst case I could think of ", not from practical experience. The best advice I can offer is if it won't bankrupt you, go for it. Some of the best ideas I've heard on this forum have come from people that stretched the envelope.
Best of luck,,, keep us posted. I know I will be interested in your progress


----------



## eao (Mar 6, 2009)

Wow. Great stuff all. How, without a limited slip differential would you compensate for the fact that the inside tire will turn slightly slower in a turn, therefore making one motor bear more load in a one-motor-per-axle design? Or is that load difference not significant enough to necessitate it? I guess I'm thinking of a hard acceleration from a stop while turning rather sharply..

Eric


----------



## MalcolmB (Jun 10, 2008)

eao said:


> I guess I'm thinking of a hard acceleration from a stop while turning rather sharply..
> Eric


Hi Eric. That's probably the most testing situation there is. It might be possible to overload the inside motor in that case. If the motors are torquey enough the inside wheel is likely to spin. I should really install an ammeter on each motor to check how they play together in different situations. One solution would be to limit the combined motor current to the "safe" peak current for one motor, whatever that might be. I intend to take things easy when I eventually get the mini rolling. I'm still working out the finer details of how to shoehorn the two drive pulleys, bearing carriers and CV joints between the uprights on the mini subframe. There ain't a lot of space.

Grayballs. Missed your post first time round. Thanks for the encouragement. I'm a little surprised that no-one seems to have tried this on front wheel drive before, so I'd be interested in hearing more about your progress too, especially if you go for the independent drive.


----------



## eao (Mar 6, 2009)

In south CA there are many big/busy intersections without a left turn arrow, so you have to dart through oncoming traffic... I think someone already mentioned it, but that torque/load difference would want to pull the steering straight also, I'd guess. But maybe not too much? It is a great design idea, regardless. Hope you can make it work! My sister has a mini. True, not much space there :- )


----------



## Telco (Jun 28, 2008)

Ya know, the only reason a vehicle needs a limited slip differential to allow the wheels to turn at different speeds is when there is a PHYSICAL connection between the two wheels. When both wheels are physically connected, cornering results in the solid mechanical connection trying to spin at two different speeds, which will cause one wheel to skip, or break parts. As long as the two electric motors aren't connected together via a common shaft there will be no issues with cornering as each motor will be able to spin at the speed of the tire it drives.

Now it might be worthwhile to consider a feedback circuit that will measure the current draw between the two motors, that can detect when one wheel has more draw like during cornering. Since the inboard motor will be pulling the outboard motor around, this should reduce the load on the outboard motor while increasing the load on the inboard motor. To counter it, the load balancing circuit would increase power to the outboard motor while decreasing power to the inboard motor, so that both motors see the same load at all times. This would also ensure a good grab on these fast left turns from a stop, since both motors would be turning with the same load. 

You'd also want a way to limit how much adjustment the circuit is allowed to do though, because unlimited this would turn the car into an "open differential" vehicle where one tire on ice would result in 100 percent power being dumped to the spinning tire while 0 percent power goes to the one with traction. I can't see there ever being a need to pull more than 5 percent of power off, but you'd have to experiment with it to see what the actual adjustment would need to be during normal driving.


----------



## dnattig (Jan 24, 2011)

Hi, 
Did you build it with two motors? I would like to know how it turned out (and if you tried the feedback loop). I would like to make a rear wheel drive car with independent motors this summer (I would like to use one controller for both, but have heard that two controllers would be a better way to go).


----------



## MalcolmB (Jun 10, 2008)

I got sidetracked and have just restarted this project, so haven't tested it yet. I still plan to use two motors and a single controller to drive the front wheels independently. I intend to test it with the motors wired in series and in parallel to see what difference this makes to low-speed control. My build log is here:http://www.diyelectriccar.com/forums/showthread.php?t=52461


----------



## ElectriCar (Jun 15, 2008)

I'd like to see how this works out. I agree with some that turning won't be an issue. You likely won't notice it at all. I found an article about an F150 truck with 4 wheel motors. This eliminated the transmission, rear drive shaft etc saving probably 600 lbs I'd guess plus you now have 4wd and a much more efficient one than traditional drive trains. Ever drive a 4wd on a dry road? The front and back wheels are turning at different speeds for some reason I understand.

I think this is going to be the future provided it works well. I think if you lost a belt or otherwise somehow lost one motor it won't be a huge issue as well as long as you have a way to kill that motor. And I wouldn't rely on YOU to be the one to shut it down as it likely will rev very quickly to self destruction speed.

One thing you could do in that regard is use a photo sensor that operates like those people detectors you see in business doors that ring a buzzer or such when someone enters. A company that makes a lot of photo sensors of various designs is Banner Engineering. You can get some with a converging beam that doesn't need a reflector behind the belt, it reflects light back from whatever it's monitoring. However with a black belt that may not work without a reflector behind the belt. And they make reflective tape you could use or a bicycle type would work. Only thing about a reflector is they get dirty and could prevent it from working. 

You can adjust it so that when a belt breaks or becomes loose over time and sage it would activate. You could install it in the 12V KSI circuit or tie it to an indicator light just to notify you (not advised). Look at the 3rd one down here. They even have them with fiber optic operation so you can mount the brains remote from your belts.


----------



## MalcolmB (Jun 10, 2008)

It's the simplicity that attracts me. Your photo sensor approach would be one way to protect the motors, but I was thinking of killing two birds with one stone and fitting a pair of tachometers with shift lights. The shift point would be set to +6000 rpm and the shift light output would be used to disable the controller (via a latching relay?).


----------



## ElectriCar (Jun 15, 2008)

Well that would work as well. I would be inclined though to use two controllers in case one had a fault of some type. I guess though you could disconnect the offending motor to get you home after a short stop. 

Here's an article I just posted last night about installing aftermarket tach's on vehicles that didn't come with one. I installed it yesterday while trying to follow football games. I finally drove it last night late and it works like a champ. I didn't get a shift light though. Those tend to be large and I have an S10 with limited room so the one I used is 2 5/8" and is pillar mounted.


----------



## MalcolmB (Jun 10, 2008)

Thanks ElectriCar. That info about your aftermarket tach is useful. I wasn't sure which type of proximity detector to look for.


----------



## michaeljayclark (Apr 3, 2008)

The tropica had dual controllers with a motor on each wheel connected by belts

i drove one and it had no problems making turns.. wasnt a particularly fast car anyway.


----------



## cyclops2 (Feb 12, 2011)

Dead stop. Parking & turning.
Try it with LARGE EMPTY cardboard boxes. 
As you turn the wheels & barely touch the pedal the 2 motors are LOADED WITH MAXIMUM TORQUE.  As power is applied to both equally. Excitement ?? Very possibly, as the motors both want to run at the same speed ? " In a sharp parking space turn ? "  How much current will the pivoting wheel pull ? The outside wheel pull.

That is why a differential is always used on road surfaces.


----------



## MalcolmB (Jun 10, 2008)

cyclops2 said:


> As you turn the wheels & barely touch the pedal the 2 motors are LOADED WITH MAXIMUM TORQUE.


That seems pretty unlikely unless the controller has failed.


----------



## cyclops2 (Feb 12, 2011)

Drag cars have both wheels turning at the same speed. Straight ahead drive under power.

Tight turns & parking require a differential. 

Street, locked rear axles, are very rare.
Dual front motors on 1 controler, or 2 controllers & 2 motors, without differential power control commanded by the steering wheel angles are in for a exciting parking space time.


----------



## ElectriCar (Jun 15, 2008)

If you turn the wheel and floor it then it's going to spin out if you have enough power. Except for extreme throttle I doubt there's any issue. I've read where someone drove a dual motor, dual wheel drive vehicle and it drove fine around corners curves etc, no sudden spins into the ditch!


----------

