# [EVDL] design for direct-drive FWD conversion



## EVDL List (Jul 27, 2007)

Hello EVers,

Please provide some advice, I'm pulling my hair out (luckily i have plenty)
trying to decide on a drivetrain design for my FWD conversion vehicle, a '97
Saab 900ES, roughly 3000 lbs. I'm wondering about two options, in terms of
performance, reliability, cost, and time-to-complete. Both options assume
direct-drive (i don't want to re-use and adapt my auto trans, nor install a
manual), with roughly a 4:1 reduction between motor and wheels, with readily
available, popular, series-wound DC motor technology, of which, i'll want
about 200lbs worth, according to calculations, in order to meet my
performance requirements, for the following two options.

-- Option 1 --
Use a single, large motor, i.e. a warp11. This would feed a gearbox, with
reduction gearing and integrated differential, which, ideally, my two
half-shafts would plug right in to, without serious modification. I have
found commercially available units similar to this, i.e. from AZD, but
nothing that meets my requirements. Am I looking in the wrong places? Is
there something available, that I could adapt? Or, how about just find a
differential, with roughly the proper gear ratios, that can be adapted to
two half-shafts in a front wheel drive?

-- Option 2 --
Use two smaller motors, i.e. two 9 inch motors, each motor driving its own
front wheel, where each motor would have matching separate single-speed
gearbox's, ideally would look something like this,
http://www.sae.org/mags/aei/SAEWC/7953 ,but i don't think i can buy one of
these. Is there anything available? I can adapt?

The main problem with both options, is the availability of a suitable
gearbox, and secondly having to modify or renew the axles. Where can find
something? How difficult is it to build a custom one, using standard
off-the-shelf gears? I'm leaning towards option 2, because i like the idea
of having two motors, no differential. I read somewhere, can't remember,
that dc motors are ideally suited for this and can be optimally switched
electrically between series and parallel. i'm wondering, also, how closely
matched the two dc motors need to be? would they need to be the ~exact~
model, or would two very similar, i.e. two 9" ADC's manufactured 15 years
apart, motors work fine?

I realize the easy way out would be to adapt my existing automatic
transmission, or get a manual, but i'm not looking for easy.

I hope to see (and meet) some of you in Hagerstown this weekend.

Thanks in advance for advice, i'm sure many of you have pondered these
questions much longer than I have.

Cheers.

Ed

Edward L. Moore, Ph.D.
Software Engineer
Tolland, CT
cell: 908-249-3478
http://www.evalbum.com/3271
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## EVDL List (Jul 27, 2007)

> Ed Moore <[email protected]> wrote:
> 
> > Or, how about just find a
> > differential, with roughly the proper gear ratios, that can be adapted to
> ...


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## EVDL List (Jul 27, 2007)

Lots and lots of possibilities.

Make your own gearbox.
This could be as simple as a box doen like the rear of Gone Postal 
hard to find pictures of, but there is a good video
http://www.suckamps.com/index.php?page=life_of_the_postal_van

But if I could, I would get two motors coupled together at the drive
ends by a double motorcycle pully.
This pully drives a larger one mounted in place of the ring gear on a
stock differential mounted in a simple aluminum box you construct and
put some oil in.
Then adjust the length of existing half shafts to complete the drive system.

In some automatics, the final drive housing bolts on the end and could
just as easily bolt to a side plate of the box you make and then the
idler shaft you make would be hollow and reproduce the sun gear to drive
the diffy. You could use this if the diffy doesnt actually have a ring
gear (crown gear on FWD)

This gives you a preset input ratio on the motorcycle pullies and final
drive ratio of the diffy. You can modify both to suit the car.
This also gives you series parallel switching which works like a
transmission to give you two ranges.

The transmission can rest low and on the centerline of the wheels and
the motors can be above and fwd agaist where the radiator is(or back
against firewall), giving you a nice space for batteries.



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## EVDL List (Jul 27, 2007)

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## EVDL List (Jul 27, 2007)

Bill, hmm... a "garage queen". It sounds like I may want one of those 
Well, you've now given me some inspiration, i've been wanting to open up my
150lb beast of automatic gears, see what's inside, tinker, figure out how to
lock down a gear.

I guess what I'm now really asking, is ~why~ is it such an expensive and
time consuming R&D effort to adapt an existing differential, as Zeke
suggested?? or, build a single-speed gearbox? or, find, and adapt an
industrial single-speed gearbox? I know this must be difficult, I would
just like to understand why? What am I up against? Conceptually, it seems
like a single speed gearbox is easy... off-the-shelf gears, bearings,
shafts, a little precision machining on a housing, off-the-shelf nuts and
bolts, some oil, lube, and wellah! what am I missing???

Ed Moore



> Bill Dube <[email protected]> wrote:
> 
> > Using a SAAB transmission of some sort is probably the most practical
> > solution. Ever other option will be much more difficult and much more
> ...


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## EVDL List (Jul 27, 2007)

Jeff! I like this. Belts and pulleys. Why couple the two motors? How 
about each motor use pulleys and belts to drive each wheel? What is 
the reliability and efficincy of belts versus gears? - Ed Moore

Sent from my iPhone



> Jeff Shanab <[email protected]> wrote:
> 
> > Lots and lots of possibilities.
> >
> ...


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## EVDL List (Jul 27, 2007)

> trying to decide on a drivetrain design for my FWD conversion
> vehicle, a '97 Saab 900ES, roughly 3000 lbs... direct-drive with
> roughly a 4:1 reduction between motor and wheels, series-wound DC
> motor technology (200 lbs worth, according to calculations)...

Direct drive is possible of course. It just takes a bigger motor and 
controller.

A 4:1 ratio may not be high enough. I used a Saab 96 front end in one of 
my EVs, but with a 5.17:1 Dana differential. It was directly driven by a 
big GE forklift motor, about 10" diameter and 16" long (which did indeed 
weigh about 200 lbs). It was a 2400 lbs. EV with an 84v pack. Top speed 
was around 55 mph (limited mainly by the low pack voltage). Hill 
climbing and acceleration were pretty good, but I had a contactor 
controller, which could easily hit 500-1000 amps at the motor.

I helped Mike Shoop with his VoltVette (1987 Corvette) conversion. It's 
direct drive (no transmission) with a TransWarp 11" motor, 156v pack, 
and Z2K controller. He tried using the stock 3.xx:1 differential, but 
acceleration was poor and motor current very high. He changed to a 
5.14:1 differential, which as proven to be quite acceptable.

> -- Option 1 -- Use a single, large motor, i.e. a warp11. This
> would feed a gearbox, with reduction gearing and integrated
> differential, which, ideally, my two half-shafts would plug right
> in to, without serious modification.

Can be done, but everything hinges on how much room you have, and how 
good your fabrication and part-finding skills are. On my old Saab 96 
setup, the inner ends of the half shafts had completely ordinary 
universal joints, just like you'd find in a rear drive car's drive 
shaft. They were very easy to adapt to the Dana differential.

As others have suggested, it's probably easier to keep the stock Saab 
transaxle, and just leave it in one gear.

> -- Option 2 -- Use two smaller motors, i.e. two 9 inch motors,
> each motor driving its own front wheel, where each motor would
> have matching separate single-speed gearbox's, ideally would look
> something like this, http://www.sae.org/mags/aei/SAEWC/7953 ,but i
> don't think i can buy one of these. Is there anything available?
> I can adapt?

This is mechanically a lot more challenging to build. I doubt you'd need 
two 9" motors, unless you're going racing. Two 9" motors in a 3000 lbs 
car puts you in sports car territory.

Belts or chains are one possibility. They might be easier to fabricate, 
and allow more options in motor placement.

>> how closely matched the two dc motors need to be? would they need to
>> be the ~exact~ model, or would two very similar, i.e. two 9" ADC's
>> manufactured 15 years apart, motors work fine?

As long as they are the same basic motor, matching won't be necessary.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377	| There is a crack in everything
leeahart earthlink.net	| That's how the light gets in -- Leonard Cohen

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## EVDL List (Jul 27, 2007)

Oops, I can't believe I said pully, I meant sprocket and motorcycle chain
Chain is by far the strongest and most eff.
Gears to handle torque of chains are heavy and large
If you do look up gear strength, remember you are allowed to multiply
rating x2 or x3 for electric vs gasoline. Smoother torque, much less
fatigue.

Gears are 1-4% loss per mesh, but multiple gears in parallel(like
planetary) is not as bad as it seems. Becasue the load is reduced. It is
gears in series that waste a lot.
A well oiled chain is 99% eff
Gears only distribute load across a few teeth at a time making a
possible weak point.
A preloaded sliding contact gear is quiet and can handle more torque,
but is lossy (hypoid)
A straight cut non-prloaded gear is noisy and weak, but more efficient
The oil in a gearbox adds losses.
Grease can make losses as high as 8%
oil ads < 1%
At high rpm oil can cause losses up to 4% and can cause hydraulic
ingof gears and breakage.
At this point a dry sump and spray nozzles is employed.

( I have worked on a few racing trannies)
(Shot peening and cryogenic treatment of gears can make them stronger)





> Jeff! I like this. Belts and pulleys. Why couple the two motors? How
> about each motor use pulleys and belts to drive each wheel? What is
> the reliability and efficincy of belts versus gears? - Ed Moore
>
The two motors was for series parallel switching. The weight you
mentioned makes me thing a single 9 may be on the light side and so as
not to over rpm it by gearing it to low, a series parallel of two 8"
motors (or 9") would give you enough power to gear it higher and keep
the rpms in check for cruising.

I was guessing a High Voltage system and series parallel also allows
higher voltage to the motors as each see half in series mode.

> Sent from my iPhone
>
>


> Jeff Shanab <[email protected]> wrote:
> >
> > Lots and lots of possibilities.
> >
> ...


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## EVDL List (Jul 27, 2007)

Watch out for this trickery, GM does it, i don't know if on the metro

There is an input ratio on the transmission input chain and a final
drive ratio, but they simplify their specs and list the final drive
ratio's with the input ratio factored in.
So a grand am and a Grand pree show Final drive ratios, but have the
same final drive partnumber, it is the input ratio that actually changed.

Lucly, it is easy to check with a sharpy and a little quiet time


> I just got back from the junkyard, and took apart a Geo Metro
> automatic trans. The differential is driven by a gear that
> could be relatively easily powered directly by the electric motor.
> Then you get the 4:1(ish) gearing and drive two axles and reduce the
> trans weight significantly. Even could use a belt drive to drive
> the diff gear shaft, another gearing to get maybe 6:1.
>
> That said, the Geo metro 5-speed trans is only about 40lbs,
> it doesn't add much weight at all to an full EV.
> So unless you're building some super lightweight vehicle that
> uses few batteries, the weight savings isn't too significant.
> 

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## EVDL List (Jul 27, 2007)

Why not use an existing transmission?
US Electricar converted at least two types
of vehicles for which it was easy to get a
manual gearbox, but proceeded to mount them
in a vehicle that used to have an automatic.
They also locked the gearbox in second gear
just to give them a fixed gear reduction
matching the (AC) motor they used and this
allowed an operation as automatic with a well
matched gear reduction so they could hit the
motor redline of 9,000 RPM at a decent max
speed (72MPH for the S10, about 90 MPH for
the Prizm) while also keeping a good acceleration.

The automatic gear selector was modified to just
operate a switch selector and in P drop a pawl
onto the starter ring to lock the transmission.
For a series DC motor your choices will likely
be different wrt the gear selector.

Regards,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Ed Moore
Sent: Friday, June 04, 2010 10:25 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] design for direct-drive FWD conversion

Bill, hmm... a "garage queen". It sounds like I may want one of those 
Well, you've now given me some inspiration, i've been wanting to open up
my 150lb beast of automatic gears, see what's inside, tinker, figure out
how to lock down a gear.

I guess what I'm now really asking, is ~why~ is it such an expensive and
time consuming R&D effort to adapt an existing differential, as Zeke
suggested?? or, build a single-speed gearbox? or, find, and adapt an
industrial single-speed gearbox? I know this must be difficult, I would
just like to understand why? What am I up against? Conceptually, it
seems like a single speed gearbox is easy... off-the-shelf gears,
bearings, shafts, a little precision machining on a housing,
off-the-shelf nuts and bolts, some oil, lube, and wellah! what am I
missing???

Ed Moore

On Fri, Jun 4, 2010 at 12:44 AM, Bill Dube <[email protected]>


> wrote:
> 
> > Using a SAAB transmission of some sort is probably the most practical
> > solution. Ever other option will be much more difficult and much more
> ...


----------



## EVDL List (Jul 27, 2007)

High performance belt drives using toothed belts/pulleys are *more *efficient
than chain and sprockets. See Gates data. for more info. The only real
disadvantage is if the belt gets an object on it's track , so don't use open
belts!!
The weight of belts for equal strength is also lower than chain and doesn't
need lubrication, a major advantage.Also no stretching, so once adjusted,
the tension stays OK. Disadvantage is alignment must be much better than for
a chain drive, and side flanges are needed, although I have used a very
slightly cambered idler to achieve good tracking. I almost forgot; belts are
much quieter than chain too.
I have a design for a variable speed drive using only a toothed belt drive
system, it is not a continuously var. drive but can offer a large
incremental gearing ratio. Anyone interested, please contact me off line as
this is still proprietary information without patent protection. Many years
ago I made a system using this for a pedal powered bike and it worked fine.
I also have a good source for custom pulleys made in steel or aluminum,
again, off newsgroup please. I am not using this group to advertise
directly.



-- 
When all else fails, remember failure is the success of knowing what not to
do.
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## EVDL List (Jul 27, 2007)

FWIW, if you use an Eagle Pd belt like I have on my Gizmo the pullys
don't need to have flanges. Alignment is critical, however.




> ron doctors <[email protected]> wrote:
> > High performance belt drives using toothed belts/pulleys are *more *efficient
> > than chain and sprockets. See Gates data. for more info. The only real
> > disadvantage is if the belt gets an object on it's track , so don't use open
> ...


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## EVDL List (Jul 27, 2007)

Well I knew I would catch a few up with that statement. It is kinda like
the IGBT vs MOSFET discussions.

There are belts that are more efficient in certain cases, But in general...

Also the air getting compressed in the teeth at high speeds eats power,
but gives blowers that sweet whine. Drill hole sin the roots of the
pully for the air to escape to reduce it.

Claims are just that claims. Gates makes great belts but chains have a
long history of going over their rating. Kinda like theyare rated for
the max load they can carry continuously and toothed belts are rated
where they break.?? I dunno but ask Rod about chain vs belt 

The high performance belts and pullys are more expensive but they do
less damage when they let go.
A chain should be used inside an enclousure also.

There are motorcycles using drivlines,belts and chains out there, I
wonder what those people say about them.

While I have seen a lot of ICE motors use belts for valve train, a lot
use chain.
The chain drives last longer and let you know when they are going.

All power transmission in cars has been gears and chains to my
knowledge. WHile I admit there are a few belt drives, I can say all with
99.99% accuracy 


> High performance belt drives using toothed belts/pulleys are *more *efficient
> than chain and sprockets. See Gates data. for more info. The only real
> disadvantage is if the belt gets an object on it's track , so don't use open
> belts!!
> The weight of belts for equal strength is also lower than chain and doesn't
> need lubrication, a major advantage.Also no stretching, so once adjusted,
> the tension stays OK. Disadvantage is alignment must be much better than for
> a chain drive, and side flanges are needed, although I have used a very
> slightly cambered idler to achieve good tracking. I almost forgot; belts are
> much quieter than chain too.
> I have a design for a variable speed drive using only a toothed belt drive
> system, it is not a continuously var. drive but can offer a large
> incremental gearing ratio. Anyone interested, please contact me off line as
> this is still proprietary information without patent protection. Many years
> ago I made a system using this for a pedal powered bike and it worked fine.
> I also have a good source for custom pulleys made in steel or aluminum,
> again, off newsgroup please. I am not using this group to advertise
> directly.
> 

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