# 6x6 (four wheel steering) EV project



## Bgt2u48 (Jun 20, 2019)

Hello everyone. I am building a street legal 6wd vehicle, and l am seriously considering going electric. I was going to power it with a ZX14 Kawasaki Ninja engine, however if it is feasible, l would prefer it to be an EV. To be totally honest, I do not know the first thing about controllers, battery requirements, or the motor that l would need. I do know that l would want a range of 50 -75 miles on a charge, and it obviously would have to be powerful enough to drive all 6 wheels. Is this even possible? I am simply looking for some advice, on where to start, and what to start with. Any help, or suggestions, are greatly appreciated.


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## brian_ (Feb 7, 2017)

Six wheels don't really take more power to drive than four - it's just spread out among more wheels.

The photos show a chassis with chain drive and no differentials, suggesting skid steer rather than steered wheels. At the same time, the middle suspension appears to be non-steering, while the end suspensions look like they could steer but have no steering linkage. What would the plan be?

If you have an idea of how the vehicle would be driven and controlled, you can start to get an idea of how many motors of what size would be suitable.


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## Bgt2u48 (Jun 20, 2019)

Brian, after replying to you, l now see how l was supposed to do it. Sorry about that. Anyway, it is a front and rear steering chassis, that steers with front and rear wheels turned in opposite directions, sort of like a zero turn radius. It has a chain drive LSD differential (not pictured), and two steering racks, one at each end, that are set up to steer at the same time, in opposite directions. I would be using it for around town street use, and trails. Acceleration is not a major issue, although fast would be nice. I just would like it to have a range of at least 50 miles. The chassis obviously can be modified for whatever is needed to get it to work. I just simply need an idea of where to start, and what l might need for controllers, motor, batteries, etc. A few suggestions would help me greatly. Thanks again.


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## brian_ (Feb 7, 2017)

Bgt2u48 said:


> .. it is a front and rear steering chassis, that steers with front and rear wheels turned in opposite directions, sort of like a zero turn radius. It has a chain drive LSD differential (not pictured), and two steering racks, one at each end, that are set up to steer at the same time, in opposite directions. I would be using it for around town street use, and trails.


Thanks - that fills in the missing pieces. 

The system of only one differential plus separate left and right drivelines is reminiscent of the system in some old military vehicles.

In any turn the end axles will need to turn faster than the middle axle, just as the front axle must turn faster than the rear axle in a conventional vehicle. Just as a centre differential (or disconnection of one axle) is required to drive a 4X4 on pavement without excessive tire scrubbing and axle stress, this 6X6 will need another differential, or middle axle disconnect... or a separate drive motor for the middle axle so it can turn at a different speed. I suppose you could also use air suspension to lift (or at least unload) the middle axle on the street.

The significance of this drive system issue to the EV scenario is that, unlike a vehicle driven by an engine, it is practical to use more than one motor. The most conventional approach would be to use one motor per axle, each with a differential; this is the design used by current production AWD EVs (such as those from Tesla, Jaguar, and Audi). A more capable design is to use one motor per wheel; this is the design of proposed EVs such as those from Rivian and Bollinger.


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## Duncan (Dec 8, 2008)

The SENSIBLE approach is one motor plus a reduction gearbox and a diff per axle

The one motor plus gearbox per wheel is good for construction machinery but NOT for a road vehicle - it is a mistake to refer to vapourware as "more capable"


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## Hollie Maea (Dec 9, 2009)

Duncan said:


> The one motor plus gearbox per wheel is good for construction machinery but NOT for a road vehicle - it is a mistake to refer to vapourware as "more capable"


Don't be ridiculous. This has been done many times, for instance by Rimac.


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## Duncan (Dec 8, 2008)

Hollie Maea said:


> Don't be ridiculous. This has been done many times, for instance by Rimac.


Six or seven cars is NOT a production road vehicle! - and if the Rimac is any good it is despite the dopey arrangement and not because of it


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## brian_ (Feb 7, 2017)

Duncan said:


> The SENSIBLE approach is one motor plus a reduction gearbox and a diff per axle...


The easiest thing to do is to put one motor plus reduction box onto the currently existing hardware (feeding the single differential which is not shown), but what would the sensible approach be for inter-axle differentiation, since that design doesn't include this feature?  
Remember, this vehicle is supposed to be streetable. Anyone who has driven a part-time 4X4 (no centre differential or slipping clutch for one axle) stuck in 4WD on pavement should realize that driving all axles at the same speed isn't very streetable.

If there is no inter-axle differentiation, then the current design shown (with one diff and chains linking the axles) is more capable off-road and equally non-streetworthy. It uses a more complex chain arrangement but eliminates two of three differentials, and eliminates cross-axle spinning (where, for instance, the left middle tire and both front and rear right tires all spin because the right middle suspension hits the compression limit going over a bump, leaving little driving force for any tire except as provided by limited-slip diffs).

It would be possible to set up a lockable or limited-slip "centre" differential, with one output driving the middle axle and the other output split (without a differential) to the end axles... but that seems like a lot of hardware. I suppose if you're an electric vehicle enthusiast who prefers complex mechanical systems to electrical systems, then it would make sense. 



Duncan said:


> The one motor plus gearbox per wheel is good for construction machinery but NOT for a road vehicle - it is a mistake to refer to vapourware as "more capable"





Duncan said:


> Six or seven cars is NOT a production road vehicle!


Even Honda uses separate left and right motors (in a common housing) on the electric axle of their hybrids. The Acura RDX and MDX "Sport Hybrid" and NSX models with this system are far from Honda's best sellers, but they're regular production models and the RDX and MDX are ordinary family cars, not exotics.

The Rivian and Bollinger vehicles are not yet in production, and may never reach production, but unlike "vapourware" (software which is promised but doesn't exist) these things have been built and drive around without motor control issues. If you can build one, you can build... well, one more but with six wheels.

One drive unit (motor with reduction gearbox plus differential) per axle is any easy solution, which is why all production AWD EVs are built that way... although this six-wheeler would need locking or aggressive limited-slip differentials to be useful.



Duncan said:


> ... if the Rimac is any good it is despite the dopey arrangement and not because of it


While I agree that much of what Tesla and Musk do is "dopey", I wouldn't put this feature of the design of the coming Roadster and Semi in that category.


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## Bgt2u48 (Jun 20, 2019)

I did forget to mention, that l have been considering leaving the center wheels in a raised position (approx 1-1/2", to 2") off of the ground, while it is on the street. The wheels would still roate, but not make any contact with the pavement. When off road, l would lower them, and use all 6 wheels. If l did this, would it be feasible to use one motor, with the LSD? I have attached a picture of the LSD this time, it is on the very back of my earlier chassis design.


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## piotrsko (Dec 9, 2007)

Y'All forget it has been done here before down in the offroad section maybe 7-10 years back in The Great White North, don't you know,Eh?


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## brian_ (Feb 7, 2017)

piotrsko said:


> Y'All forget it has been done here before down in the offroad section maybe 7-10 years back in The Great White North, don't you know,Eh?


It's not possible to forget what one never knew; 7 to 10 years ago is long before my time in this forum. 

There have been skid-steer 6-wheelers (not the same at all) and at least one Volvo 6-wheeler proposal (different powertrain, and none built). Do you have a link to save us the trouble of searching without even a good search term?


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## brian_ (Feb 7, 2017)

Bgt2u48 said:


> I did forget to mention, that l have been considering leaving the center wheels in a raised position (approx 1-1/2", to 2") off of the ground, while it is on the street. The wheels would still roate, but not make any contact with the pavement. When off road, l would lower them, and use all 6 wheels. If l did this, would it be feasible to use one motor, with the LSD?


Yes, that's what I suggested as an alternative:


brian_ said:


> I suppose you could also use air suspension to lift (or at least unload) the middle axle on the street.


It is certainly the simplest workable approach.


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## Bgt2u48 (Jun 20, 2019)

Okay, now that l have gotten much appreciated input, from many knowledgeable members, l believe l am going to go with the one motor, to differential, with lifting center wheels set up. Onn that note, now, l just need some input on what size/type/brand motor would be best suited for this set up, along with the suggested batteries, controller, and things of that nature. Also, my budget is about $3000 (depending on what mood, and state of sanity my wife is in...lol).


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## dain254 (Oct 8, 2015)

Looks like you have a couple of your functional requirements defined - it has to go 50 miles and cost less than $3k. The other two aspects that need to be considered in sourcing a power system is what is the top speed required and how steep of hill will it need to climb. One motor to differential means you will have a fixed ratio, so motor torque and RPM will govern how much climbing capability and top speed you have. If this thing only needs to go 25mph this will be easy. If you want 50 miles of range and 60mph top speed... quite a bit more difficult. Cool project by the way!! I really like seeing unique things built!!


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## Bgt2u48 (Jun 20, 2019)

Thank you, l really appreciate the "cool" compliment. I am a retired Electro/Mechanical/Structural Engineer (notice the custom designed car in the background of the one picture). Anyway, that background offers me nothing in the area of building an EV.... so, l will continue to ask, and learn. As per your comment, this 6 wheeler will need an approximate 50 max speed, so l can keep up with around town traffic (no highway use). I also would never attempt to climb anything more than a 40 - 45 degree incline. Hopefully this information will give you a better ballpark idea, as to what l would possibly need.


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## dain254 (Oct 8, 2015)

One thing I've learned from driving around town is that on 45mph roads it's still nice to be able to do 60mph so a person isn't getting passed all the time since everyone drives 55mph anyway - would depend on how traffic is around your town. 

I've been recently fighting with one of the motor/controller combinations I use that would meet the needs of your project well. If I get it working right I'll share what it is but I can't recommend a product that I'm not having good luck with. For energy storage I think you'll want around 10-12kwh. There are many good options for batteries - a lot of it depends on the voltage you are going to use... Chevy Volt modules are still my favorite.


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## brian_ (Feb 7, 2017)

dain254 said:


> One thing I've learned from driving around town is that on 45mph roads it's still nice to be able to do 60mph so a person isn't getting passed all the time since everyone drives 55mph anyway - would depend on how traffic is around your town.


That makes sense; however, regardless of traffic I don't think I would ever want to go 60 mph in a vehicle which steers the front and rear axles equally - it's not going to be stable. My understanding is that this is primarily intended to be a relatively low-speed off-road vehicle.


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## Bgt2u48 (Jun 20, 2019)

Yes, it probably will prove to be unstable at anything close to 60 mph. If this proves to be the case, l will change the rear wheels from steering to locked at all times. I figure as long as the center wheels are raised slightly, (like mentioned before), lt would simply steer and drive like a normal four wheeled vehicle. I will have to just wait and see, and make any needed changes accordingly.


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## brian_ (Feb 7, 2017)

Bgt2u48 said:


> Yes, it probably will prove to be unstable at anything close to 60 mph. If this proves to be the case, l will change the rear wheels from steering to locked at all times. I figure as long as the center wheels are raised slightly, (like mentioned before), lt would simply steer and drive like a normal four wheeled vehicle.


If you lift the middle axle and steer only the front axle, it will be just like a regular 4X4... but still a part-time 4WD system locked in 4WD. By locking out the rear steering, you gain stability, but cause the tire scrubbing problem.


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## Duncan (Dec 8, 2008)

Four wheel steer cars like the Mazda usually steer the rear the same way as the front at speed for stability and the opposite way at low speeds for increased maneuverability


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## Bgt2u48 (Jun 20, 2019)

The Chevy Volt batteries are pretty easy to get, so that is a good thing. I originally was looking into the Nissan Leaf batteries, however from doing some research, it seems that getting around software issues seems to be a major complication. Are there issues like that associated with the Volt batteries? Well anyway, when you get your setup working, please let me know what parts you decided on, and maybe that would work for me, or get me close.


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## Emyr (Oct 27, 2016)

The long-narrow layout of the Volt battery looks like it might suit your project if you want to straddle it like a hex-bike.


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## dain254 (Oct 8, 2015)

For the budget, you will definitely not be able to use a complete Chevy Volt pack at 96S, not to mention the complete pack weighs 435lbs - although buying a complete pack would be a good start as you can sell the leftover modules. The Volt pack is made up of 7 2kwh modules and 2 1kwh modules (2011-2015 or 16). You will probably end up somewhere between 50 and 150V depending on motor selection. It is possible to parallel between modules with the proper BMS harness, I do this on two of my electric vehicles. Doing so will allow more capacity while hitting a certain voltage (in increments of 25.2V).


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## Bgt2u48 (Jun 20, 2019)

I can..........maybe, find some decent Chevy Volt battery packs on eBay. I just have to search around.l am a little confused by your comment on "25.2 volt increments". Is this the voltage of a single module? My next question is: What size, and or brand motor do you think would be most beneficial for my application? No worries, I'm not going to hold you personally responsible, if it's not perfect...lol.


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## Duncan (Dec 8, 2008)

You can lose a lot of that weight - and reconfigure the modules 

I used the mounting brackets but not the heavy metal bottom plate


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## brian_ (Feb 7, 2017)

dain254 said:


> The Volt pack is made up of 7 2kwh modules and 2 1kwh modules (2011-2015 or 16).
> ... It is possible to parallel between modules with the proper BMS harness, I do this on two of my electric vehicles. Doing so will allow more capacity while hitting a certain voltage (in increments of 25.2V).





Bgt2u48 said:


> I can..........maybe, find some decent Chevy Volt battery packs on eBay. I just have to search around.l am a little confused by your comment on "25.2 volt increments". Is this the voltage of a single module?


The two sizes of modules of the first-generation Volt pack are 6-in-series (22.5 V nominal, about 1 kWh) and 12-in-series (45 V nominal, about 2 kWh).

The second-generation Volt (2016 and later) has different module sizing, 12-in-series (45 V nominal, about 2 kWh) and 16-in-series (60 V nominal, about 3 kWh).

https://media.gm.com/content/dam/Media/microsites/product/Volt_2016/doc/VOLT_BATTERY.pdf


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## brian_ (Feb 7, 2017)

Duncan said:


> Four wheel steer cars like the Mazda usually steer the rear the same way as the front at speed for stability and the opposite way at low speeds for increased maneuverability


True. And their maximum rear steering angle is usually small compared to the front even in the low-speed mode, and even smaller in the high-speed mode. And if they are 4WD they have a centre differential or clutch to allow different front and rear wheel speeds.

4WS was somewhat popular for a while - mostly in Japanese cars but there was even a "Quadrasteer" GM pickup truck - and had made a bit of a comeback, but it is still rare. This time around, it is in luxury and exotic cars. I can't think of a Mazda with it since the MX-6 of two decades ago. Those systems did provide good examples of what can work; although most use complex computerized control systems which I don't think this project is considering, Honda had a clever all-mechanical system in the Prelude of the 1980's (which wouldn't suit this 6X6 at all, but it was still clever).


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## dain254 (Oct 8, 2015)

The motor that I'm using and currently fighting with in one of my EV's is a Motenergy ME1507. I don't think the motor is at fault for any of my issues, I believe it is a programming issue that I am working with the controller manufacturer to resolve. They make a liquid cooled version of that motor as well that is likely what you will need. Both of those motors run at around 100V which is just 2 of the 2kwh Volt modules in series. To gain more range I parallel another 2 modules giving me a total of 8kwh. in my vehicle this is good for nearly 50 miles (700lb autocycle called the CozE). 

When I said "25.2V increments" as Brian said they packs are broken into 6 cells series which is the 1kwh modules and 12 cells series which is the 2kwh modules. 25.2V is 6 cells at peak charge, which is not recommended. I charge my total pack up to 98V which is a little less than 4.1V/cell. Some will argue that this is slightly more over but it is convenient since the Elcon charger I have is able to be programmed to that value. 

The motor controller I'm using is a Kelly 96601-8080IPS, I believe there are other controllers out there such as a sevcon gen4 that someone else may be able to comment on.


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## Telco (Jun 28, 2008)

Question, is it a requirement for you that all 6 wheels be under drive? If the answer is no, I have a solution that might solve both problems. Use one motor, and use it to only drive the center wheels. This would solve the problem of dealing with 6 different driven tires spinning at different speeds by reducing it to two driven wheels, which can easily be handled by a limited slip differential. This also eliminates the need to raise any tires, which simplifies things and keeps you from adding power robbing weight. You can also eliminate quite a bit of that chain hardware that's on there. The 4 outside wheels can freewheel, and only be connected by the steering linkage. You would wind up with a lighter, faster rig, which would allow you to get your range and speed easier. The only downside to this is fewer driven wheels means it would be a little easier to get stuck off-road, but a little care in driving would avoid that.


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## brian_ (Feb 7, 2017)

Telco said:


> Question, is it a requirement for you that all 6 wheels be under drive? If the answer is no, I have a solution that might solve both problems. Use one motor, and use it to only drive the center wheels.
> ...
> The only downside to this is fewer driven wheels means it would be a little easier to get stuck off-road, but a little care in driving would avoid that.


I can't speak for the builder, but I can't imagine wanting a 6X2 off-road vehicle. Even on-road three-axle trucks can almost all drive both rear axles. Off-road, it wouldn't be just "a little easier" to get stuck.

Certainly driving only one axle is simpler. It just makes the six wheel design pointless.


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