# Direct Drive efficiency improvements?



## electric_soarer (May 12, 2008)

How much energy is lost in the typical EV conversion through the transmission (friction, inertia etc)? Just wondering what sort of efficiency boost (I'm primarily thinking of range) to expect by removing the tansmission and somehow directly driving the wheels?


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## TheSGC (Nov 15, 2007)

I am not sure about efficency, but a direct drive is not good for dc motors. DC motors need to be in the thousands of RPMs because they have their effieciency at the higher RPM.

If you went direct drive, you would need some sort of gearing, like 5:1 to keep the DC motor from burning out. (Low RPMs mean excessive amp draw, and that will burn the motor out.) A 14 inch tire spins about 902 RPM at 60 MPH, and coupling a motor to that without gearing is not good.

I think in the end you would lose more efficiency using the direct drive than a transmission becuase of the extra amps needed to drive the motor at such low RPMs under load. 

Also some people has pointed out that direct drive means less top speed, and slower acceleration at higher end speeds.

AC motors on the other hand sometimes come with direct drive attachments that do quite well because of the large RPM range and other aspects of AC systems. And the built in regen probably works the best with a direct drive setup. It does come with a large price tag tho...


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## electric_soarer (May 12, 2008)

I was thinking of fixed gearing (a single gear) as you mentioned. Basically a larger version of a toy car setup. The motor with a small cog/gear driving a larger cog attached directly to the wheels. It would remove all the friction a gearbox would induce along with the extra energy required to turn all those cogs, bearings etc. If the loss is negligible then it's not worth the trouble.


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## Dennis (Feb 25, 2008)

All series-wound traction motors use class H (cheap ones use class F) insulation which is rated up to 180C (356F). So they can handle large speed decreases under heavy loading without letting out the magic white smoke. However, even at such a high temperature rating the insulation will start to wear from repeated high temperatures. So keep this in mind: smaller motors will heat up faster than larger motors due to their small size and their large efficiency decrease from demanding horespower well beyond their rating. So in single gear ratio setups it's best to go either with a very long motor or large diameter motor. A good motor for single ratio setups would be the Warp11" or 13" or GE 11", 13" diameter size series-wound motors.


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## electric_soarer (May 12, 2008)

Thanks for the input. So either a AC or larger DC motor. I guess the AC gives regen which adds toward the range I'm after. Still trying to determine if removing the transmission will give an efficiency boost (assuming the direct drive gearing doesn't overtax the motor at low RPMs). Removing the drivetrain would also reduce weight. My main goal is range over high performance.


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## theboy16 (Feb 28, 2008)

personally, i like the idea of the direct drive. a typical transmission has about a 15% loss due to internal friction. as far as efficiency, don't forget that the rear end has a gear ration, which can be changed to best suit the motor. so if your wheels are only turning at 1000ish rpms, a 4:1 gear ratio would have the motor spinning at 4000 rpm. the trick is to find the right ratio to give you the perfect balance of top speed and take-off torque

Steph


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## electric_soarer (May 12, 2008)

15% seems like a large enough figure to make it worthwhile to pursue this approach (if that translates to a 15% increase in range?) Add low rolling resistance wheels, reduced drag with aero mods... It must be possible to increase the range of the typical EV conversion (40-60 miles or less) to the 80-100 range. Direct drive is definately the approach the EV1 and tesla have taken, so it must be doable?


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## jeffey (Jun 2, 2008)

I have been wondering the same question, Why use a transmission with gears and fluid (oil, grease) = DRAG???

Then I found the perfect solution, even 1 or 2 steps farther than I could have imagined. Check out "Drive system" here: http://www.sunrise-ev.com/specs.htm. Then "Transaxel" here: http://www.sunrise-ev.com/kit.htm. 

Finding the correct ratio for the car/truck you are using might be a bit difficult, but you always have the option of using a Ford 8.8 diff.

It may cost a few hundred to build but seems to me the performance/range benifit would be worth the trouble!

Any other thoughts?


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## xrotaryguy (Jul 26, 2007)

Actually, you shouldn't lose much more than 15% through the entire drivetrain. This includes the tire's rolling resistance, the rear end's frictional losses, etc. The transmission probably only accounts for a fraction of that. Maybe 5%?


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## electric_soarer (May 12, 2008)

I'm leaning toward the small motors driving individual wheels concept mentioned in another thread. Of course without actually testing any of these ideas I guess it's learn as you go. It looks as if your project is already a fair way along. Would appreciate any insights you've gained.


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## electric_soarer (May 12, 2008)

jeffey said:


> I have been wondering the same question, Why use a transmission with gears and fluid (oil, grease) = DRAG???
> 
> Then I found the perfect solution, even 1 or 2 steps farther than I could have imagined. Check out "Drive system" here: http://www.sunrise-ev.com/specs.htm. Then "Transaxel" here: http://www.sunrise-ev.com/kit.htm.
> 
> ...


I'm leaning toward the small motors driving individual wheels concept mentioned in another thread. Of course without actually testing any of these ideas I guess it's learn as you go. It looks as if your project is already a fair way along. Would appreciate any insights you've gained.


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## electric_soarer (May 12, 2008)

xrotaryguy said:


> Actually, you shouldn't lose much more than 15% through the entire drivetrain. This includes the tire's rolling resistance, the rear end's frictional losses, etc. The transmission probably only accounts for a fraction of that. Maybe 5%?


If it's only 5% it seems less appealing. Although, I guess it's a combination of minor efficiency improvements that made the EV1 so successful?


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## aeroscott (Jan 5, 2008)

check metricmechanic.com he said 20 to 25% loss in the differential . the differential is not a spur gear but a hypoid smiler to a worm gear i.e. sliding friction. just try to turn one by hand .


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## electric_soarer (May 12, 2008)

aeroscott said:


> check metricmechanic.com he said 20 to 25% loss in the differential . the differential is not a spur gear but a hypoid smiler to a worm gear i.e. sliding friction. just try to turn one by hand .


If it's 20-25% then it's definately worth removing the diff and driving the wheels directly.


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## jeffey (Jun 2, 2008)

Now we have gone from a simple converion (pull the ICE and replace with Elec Motor) to a slightly complicated conversion (pull the ICE and Trans, replace gears in diff and connect Elec Motor with direct drive) to (pull ICE, Trans and complete driveline, replace with small motors driving individual wheels)! &%$^*#@???

I don't know about you all, but with me, cost and my ability to do the job are the most important factors. If I run out of money the Project is Dead and if I get in over my head, same, the Project is Dead. 

What I am saying is I Love the idea of direct drive at the wheels (= 0% loss) but I cannot concieve in my head how this would work, much less consider building it.

BTW, does anyone know were the post about "small motors driving individual wheels" is located?


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## eleven (May 28, 2008)

aeroscott said:


> check metricmechanic.com he said 20 to 25% loss in the differential . the differential is not a spur gear but a hypoid smiler to a worm gear i.e. sliding friction. just try to turn one by hand .


i find it very hard to believe that the diff. alone is losing 20-25% since that's more than most people consider "normal" drivetrain loss. usually for RWD vehicles you can count on about 15% drivetrain loss, FWD and mid engine RWD slightly less, and AWD slightly more, some in the neighborhood of 25%

but, a salesman said it loses 20-25%, so it must be so...


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## electric_soarer (May 12, 2008)

jeffey said:


> Now we have gone from a simple converion (pull the ICE and replace with Elec Motor) to a slightly complicated conversion (pull the ICE and Trans, replace gears in diff and connect Elec Motor with direct drive) to (pull ICE, Trans and complete driveline, replace with small motors driving individual wheels)! &%$^*#@???
> 
> I don't know about you all, but with me, cost and my ability to do the job are the most important factors. If I run out of money the Project is Dead and if I get in over my head, same, the Project is Dead.
> 
> ...


I'm not yet in a position to actually begin an EV project (no money) so for me this is all day-dreaming for the day when/if I can start on a project. The reason I'm interested in increasing efficiency/range is that I have a long commute so the usual EV range of 40 miles or so wouldn't be of use to me. I wish that weren't the case because I'd be more that happy to go with a straightforward conversion. Your design (I assume it's yours from the links you provided) looks pretty good. What are you needs for range etc? I think if your ready to start, go for it. I envy you.


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## electric_soarer (May 12, 2008)

Here's the link to the motor for each wheel thread
http://www.diyelectriccar.com/forums/showthread.php?t=14209&highlight=wheel+motor


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## electric_soarer (May 12, 2008)

eleven said:


> i find it very hard to believe that the diff. alone is losing 20-25% since that's more than most people consider "normal" drivetrain loss. usually for RWD vehicles you can count on about 15% drivetrain loss, FWD and mid engine RWD slightly less, and AWD slightly more, some in the neighborhood of 25%
> 
> but, a salesman said it loses 20-25%, so it must be so...


Would be interesting to know the definitive answer on this


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## DVR (Apr 10, 2008)

eleven said:


> but, a salesman said it loses 20-25%, so it must be so...


It must be true cos they wouldn't lie would they?

LMAO!!

I remember years ago being in a VOLVO truck yard and seeing a brand new, just uncrated prime mover diff sitting there. My mate who worked there as a deisel mechanic saw me trying to turn the UJ by hand and commented "Good luck. That takes 50hp just to get it moving"
That still sounds a bit high to me but my point is that any effort required to work a mechanical device is effort lost. Only what you put in beyond that, makes it out the other end and does work.

All mechanical devises incur loses, be they gear boxes diffs or whatever.


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## aeroscott (Jan 5, 2008)

eleven said:


> i find it very hard to believe that the diff. alone is losing 20-25% since that's more than most people consider "normal" drivetrain loss. usually for RWD vehicles you can count on about 15% drivetrain loss, FWD and mid engine RWD slightly less, and AWD slightly more, some in the neighborhood of 25%
> 
> but, a salesman said it loses 20-25%, so it must be so...


just look at the site please ! then tell me he is just a salesman. if we as a group can do 10% of what he has done I would be happy! for more then 20 years I have been asking about this , the dyno guys all seam to confirm high losses in the rear end . same for my "x"


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## mattW (Sep 14, 2007)

Couldn't you just compare the horse power and brake horsepower of various cars to give you the efficiency? I'm sure there would be plenty of cars with measures of power at both the engines and the wheels.


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## eleven (May 28, 2008)

i did look at the site. that's how i determined he was selling something. selling something makes you a salesman by definition. Maybe he's totally right that the BMW rear ends lose 25% but that would mean a stock E46 M3 would lose 83hp through the differential alone, let alone whatever is lost through the transmission, weight of the driveshaft, and the unsprung weight (brakes, wheels, etc.)
it may be that it loses more due to it being an IRS as opposed to a solid axle, and the limited slip as well, but i find it hard to believe that BMW can't accomplish today what Ford has been doing since the 60's, which is make ENTIRE DRIVE TRAINS that lose less than 25% of their power


and for the record, I typically consider myself the resident hater of Blue Ovals


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## eleven (May 28, 2008)

mattW said:


> Couldn't you just compare the horse power and brake horsepower of various cars to give you the efficiency? I'm sure there would be plenty of cars with measures of power at both the engines and the wheels.


the hp at the wheels will encompass more than just differential loss... there will be transmission losses, driveshaft losses, wheel losses, brake rotor losses, etc.

plus, the atmospheric conditions as well as wear and tear not only on the engine, but all of the drivetrain will give several variations in the dyno results. i guarantee no one has dynoed, then pulled the engine and put it directly onto an engine dyno


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## jeffey (Jun 2, 2008)

OK, we've established the fact that there is a loss! May be 10% or even up to 25%. The question is how to minimize or eliminate that loss.

The origional question was direct drive, eliminating the transmission. If the transmission were eliminated and you could achieve the correct ratio would that work and what other obsticles would you have to deal with?

BTW, This ( http://www.sunrise-ev.com ) is not my site. When I said "I found the perfect solution" I ment I found a site with the perfect solution. Although it probably isn't perfect. Just Better!


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## eleven (May 28, 2008)

jeffey said:


> OK, we've established the fact that there is a loss! May be 10% or even up to 25%. The question is how to minimize or eliminate that loss.
> 
> The origional question was direct drive, eliminating the transmission. If the transmission were eliminated and you could achieve the correct ratio would that work and what other obsticles would you have to deal with?
> 
> BTW, This ( http://www.sunrise-ev.com ) is not my site. When I said "I found the perfect solution" I ment I found a site with the perfect solution. Although it probably isn't perfect. Just Better!


you could probably reduce SOME loss, but obviously not all loss. most of the drivetrain loss is actually noticed from the unsprung weight of the wheels and brakes. you could do a custom Independent suspension setup with dual motors, CV joints and custom half-shafts to the rear wheels (or front if you really wanted FWD for some reason) but you'd still need some sort of reduction gear to make the power useable, otherwise it would be like driving a regular manual transmission vehicle in 4th gear at all times


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## jeffey (Jun 2, 2008)

Holy Moly!!! Based on this calculator it would take a rear end ration of 20:1 to go 50mph with an 84" circumferance tire at 4000 motor RPM!!

http://www.free-online-calculator.c..._speed_calculator/road_speed_calculator.shtml

Input Parameters Are the Following:
Differential Gear = 20.00 to 1 
Transmission Gear = 1.00 to 1 
Tire Diameter (Inches) = 84.00 
Engine RPM = 4000 
Computation Results:
Computed Vehicle MPH is 50 

Does this seem right?


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## eleven (May 28, 2008)

jeffey said:


> Holy Moly!!! Based on this calculator it would take a rear end ration of 20:1 to go 50mph with an 84" circumferance tire at 4000 motor RPM!!
> 
> http://www.free-online-calculator.c..._speed_calculator/road_speed_calculator.shtml
> 
> ...


the calculator asks for diameter, not circumference... that's your error... try something more like 21 inches


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## eleven (May 28, 2008)

here's mine...

Input Parameters Are the Following:


[*] Differential Gear = 4.00 to 1
[*] Transmission Gear = 1.00 to 1
[*] Tire Diameter (Inches) = 21.00
[*] Engine RPM = 4000
 *Computation Results:*

 Computed Vehicle MPH is 62 

with these figures, you'd probably need a pretty massive motor to propel the car from 0-62 in 4000rpm with no transmission... it would take a LOT of torque down low


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## SuperChuck_A11 (May 29, 2008)

jeffey said:


> I have been wondering the same question, Why use a transmission with gears and fluid (oil, grease) = DRAG???
> Then I found the perfect solution, even 1 or 2 steps farther than I could have imagined. Check out "Drive system" here: http://www.sunrise-ev.com/specs.htm. Then "Transaxel" here: http://www.sunrise-ev.com/kit.htm.


i looked at those specs and they say:
Transaxle: 
A Ford 8.8" differential from the donor car is used, with new gears for a 5:1 ratio. That is a really steep rear gear. 

This is a very strong part, often used in drag racing. ahhh usually it is ditched for a 9 inch. But it is pretty strong.

Dry sump lubrication is used with lighter weight oil to improve efficiency. 
I hope they are directly lubing the outer bearings on the axles.....and i wonder if the oil pump they use is mech. or ele. ??


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## aeroscott (Jan 5, 2008)

eleven said:


> you could probably reduce SOME loss, but obviously not all loss. most of the drivetrain loss is actually noticed from the unsprung weight of the wheels and brakes. you could do a custom Independent suspension setup with dual motors, CV joints and custom half-shafts to the rear wheels (or front if you really wanted FWD for some reason) but you'd still need some sort of reduction gear to make the power useable, otherwise it would be like driving a regular manual transmission vehicle in 4th gear at all times


very old idea by Laturno he belt electric weel drive heavy equipment the off road dump trucks etc. they have planitary gear reduction in the hub . it could be on the motor side of a cv type . but planatray gear is 95% eff.


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## SuperChuck_A11 (May 29, 2008)

aeroscott said:


> very old idea by Laturno .


LeTourneau, 
Say it outloud, Layyy ...TOuR..NO ..makes the LARGEST stuff you have ever seen. 
All driven, as areoscott says, by Electric motors. Check out the web site you will be impresses at the size.
The TIRES used on the dump trucks....have a used market all their own. they are so big you can haul ONE on a 18 wheeler bed.

http://www.letourneau-inc.com/


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## eleven (May 28, 2008)

aeroscott said:


> very old idea by Laturno he belt electric weel drive heavy equipment the off road dump trucks etc. they have planitary gear reduction in the hub . it could be on the motor side of a cv type . but planatray gear is 95% eff.


true...

although, a quick search online showed that most people consider about 5-6% loss through a typical GM 12 bolt rear diff, and about 17-25% for the entire drivetrain depending on other options...so, using the rear diff alone would be about the same and a LOT easier (not to mention cheaper and lighter) to implement with a very similar end result


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## jeffey (Jun 2, 2008)

> the calculator asks for diameter, not circumference... that's your error... try something more like 21 inches


Duh!! Thanks eleven.

I found this calculator: 
http://www.csgnetwork.com/circlecalc.html

Punched 86 in circumference ( I measured my ICE S-10 tire last night ) and got 27.375. 

Precision Gears Site:
http://www.precisiongear.com/ford88.htm

Put that in this calculator:
http://www.4qd.co.uk/faq/roadspd.html

2000 RPM
Input Parameters Are the Following:
Differential Gear = 5.13 to 1 
Transmission Gear = 1.00 to 1 
Tire Diameter (Inches) = 27.37 
Engine RPM = 2000 
Computation Results:
Computed Vehicle MPH is 32

4000 RPM
Computed Vehicle MPH is 63 

4500RPM
Computed Vehicle MPH is 71 

1st question for those of you that have an EV: Do you use the clutch to start the vehicle moving. I would guess this is not necessary, but I am asking so I don't have to guess. 

If clutch is not needed than direct drive is feisable.

2nd question what motor would work best within these RPM ranges ( 2000 - 4500 )?

Are there any Power/RPM spec sheets for different motors available online?


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## aeroscott (Jan 5, 2008)

eleven said:


> true...
> 
> although, a quick search online showed that most people consider about 5-6% loss through a typical GM 12 bolt rear diff, and about 17-25% for the entire drivetrain depending on other options...so, using the rear diff alone would be about the same and a LOT easier (not to mention cheaper and lighter) to implement with a very similar end result


I like simpler and cheaper if 5 or6% great , plus the added advantage harmonic damping that is inherent to hypo id . just got off the phone with Letouneau wow , wow, they have into this for a mear 60 years (wheel drives).they use SR drives for the last 9 years . what is this . it's a 3 phase igbt controlled induction sort of but not quite , the stator has 12 poles each phase has 4 coils at 90 deg. so 12 ,3,6,9, o clock followed by the next phase at 1,4,7, 10 , o clock , next phase 2,5,8,11, . now the rooter has no bars and is scalloped like ruff gear teeth .8 teeth for the 12 pole motor.it works on attraction instead of repulsion ( induction motor ) they can get full torque at 0 rpm with little heating of the rooter. motor has no slip.the control is the big secret and full breaking at 0 rpm .


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## SuperChuck_A11 (May 29, 2008)

Where are you going to get a 5.13 Rear gear ??

Most Diff. Carriers won't hold a ring gear that big...you will haveta buy a carrier to put in MOST production rears.


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## eleven (May 28, 2008)

SuperChuck_A11 said:


> Where are you going to get a 5.13 Rear gear ??
> 
> Most Diff. Carriers won't hold a ring gear that big...you will haveta buy a carrier to put in MOST production rears.


did a google search, clicked the first link i got, and you can get up to a 6.50:1 R&P in a ford 9" at this site

http://www.metropartsmarket.com/catalogs/fordrearend-c1s3.html


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## dfwheelman (May 15, 2008)

You could look at this chart for GM rear ends to find one with correct ratio

http://www.drivetrain.com/GMtrkratio_posidata.html

I think a direct to DIFF would be a lot less loss than either an auto or manual transmission/transaxle and you could do it in a front wheel drive car just as easily as long as their is room.

another idea for my idea box.


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## jeffey (Jun 2, 2008)

The link to Precision Gear is right on the post. They also have a 4.56 for the GM 7.5 ( S-10 ).

Precision Gears Site:
http://www.precisiongear.com/ford88.htm

Did some calculations on that ratio and it also get pretty close to where it needs to be!

Now for the questions:

1st question for those of you that have an EV: Do you use the clutch to start the vehicle moving. I would guess this is not necessary, but I am asking so I don't have to guess. 

( I actually found the answer to this one here - http://www.diyelectriccar.com/forums/showthread.php?t=14163 )

If clutch is not needed than direct drive is feisable.

2nd question what motor would work best within these RPM ranges ( 2000 - 4500 )?

Are there any Power/RPM spec sheets for different motors available online?


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