# Keep the gear and adapt it to electric power



## Simon the Frenchie (Nov 13, 2012)

Hi,
You can find my presentation at:

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http://www.diyelectriccar.com/forums/showthread.php/peoples-said-its-polite-present-yourself-80902.html
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In a EV we need a powerful and fast engine, engine that you can find in any EV parts suppliers for a amazingly expensive price (compare to the cost of building it or even to industrial electric motor). But witch choice do we have? None?
Let's take look to the transmission, by the direct drive you're at 1:1, by the gear you can expect 0.7 on the 5th or 6th gear of your original gearbox, knowing that you're loosing power through it.
But what if we change the bevel*? Keeping the gearbox but modified to be appropriate to electric power instead of gas?
It would allowed you to buy industrial motor with amazing power and torque but lower rpm for a much much lower price.
Would it work?
Maybe it's stupid maybe not, what do you think?

*Because my technical vocabulary is poor I'm not shure that bevel is the right word, I'm talking about this;


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## subcooledheatpump (Mar 5, 2012)

You mean to change the final drive gear ratio?

In a truck, SUV, or van, the rear differential is driven from a ring gear, which is driven from a pinion gear. The picture you posted shows those two, which form a hypoid gear drive. 

Anyway, I'm not sure but I believe changing the final ratio is fairly difficult. I've looked into changing the ratio in my van, seems like once you take the differential case apart to change the gear it has to be reassembled carefully and precisely or the van will develop noise or damage to the gears.

If it were easy and simple to do, it would be a great help to be able to change the gear ratio


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## Simon the Frenchie (Nov 13, 2012)

The picture is not the same as I got in my car, I just took it from google images, it comes from a quad gear. So the english name of it is?
I guess it's difficult but I've been looking and found that we can buy different pieces to change the car ratio, so it can be done. But those available pieces are for 1:1, 2:1, 4:1 etc... We would need more 1:2, 1:3 etc...
It may can be build by manufactory especially for your EV, as it's not such a complicated piece shouldn't be to expensive.... I guess..... I hope


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## Karter2 (Nov 17, 2011)

Exactly what type of...


> .. industrial motor with amazing power and torque but lower rpm


......are you thinking of ?



> I've been looking and found that we can buy different pieces to change the car ratio, so it can be done. But those available pieces are for 1:1, 2:1, 4:1 etc... We would need more 1:2, 1:3 etc...


 No.. car final drive bevel gear ratio's are generally in the range of 3:1 or 4:1 with a motor speed of say 5000rpm
If you plan on using a industrial Emotor at say a 1800rpm a ratio of something like 1:1 -1.5:1 would be needed.
But to install that gear set would require a complete ne axle & differential assembly to be used.

Also, ..The gear set you show is only used in cars with rear wheel drive, and since most cars are now front wheel drive, that type of bevel gear set is not relevant. !


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## Simon the Frenchie (Nov 13, 2012)

You are exactly saying the same thing as I said in a other way , I know it's not relevant, as I said it was just for explain what I was talking about because I wasn't sure "bevel" were the right word (should I notice that I'm french-speaker?). For the motor it's about the rpm I though, but 5:1 isn't too much? Wouldn't be something like 9'000rpm at 1:1 ratio (1'800x5=9'000)?


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## Karter2 (Nov 17, 2011)

These are speed REDUCTION gears ( road wheels turn slower than engine speeds) so a 2:1 ratio means the output (wheels) turn at half the input (engine) rpm
And i was suggesting a 1.5 : 1 ratio...not 5:1
IE motor at 1800 and wheels at 1200rpm

Which would be similar to a normal 4:1 ration with an engine at 5000rpm
IE motor 5000rpm and wheels at 1250rpm
All numbers are approximations.

but as i said , making that sort of gearing change is not simple or cheap.

So, which cheap industrial motors are you thinking of ?


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## Simon the Frenchie (Nov 13, 2012)

Hoo sorry, in France it's midnight and I've been calculating all day along, this was stupid...
I haven't got a special motor in mind because I wanted to know if it could be possible to do it first.
A other question, if you are in direct drive it's more efficient that a simple 1:1 ratio because of the bevel took out?


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## Karter2 (Nov 17, 2011)

Simon, 
I dont believe there is any difference in efficiency between a 2:1 bevel gear and a 1:1 bevel gear.
The ultimate goal would be to eliminate ALL gears in the drive line , and have a true direct drive with the motor connected to the wheels ( hub motors ?)

Go to bed !


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## Simon the Frenchie (Nov 13, 2012)

yeah you're right time to sleep!
I'll see tomorrow about direct drive benefits.


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## shortbus (Sep 27, 2011)

Here's a link to a calculator to figure gear ratios and motor RPM to MPH.

http://wahiduddin.net/calc/calc_speed_rpm.htm


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## Simon the Frenchie (Nov 13, 2012)

Thanks Shortbus great link.


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## TigerNut (Dec 18, 2009)

subcooledheatpump said:


> You mean to change the final drive gear ratio?
> 
> In a truck, SUV, or van, the rear differential is driven from a ring gear, which is driven from a pinion gear. The picture you posted shows those two, which form a hypoid gear drive.
> 
> ...


The difficulty of changing gear ratios depends on how the rear axle goes together. Most Toyota rear axles as well as the venerable Ford 9-inch have the gear assembly in a separate casting that unbolts from the banjo housing as a complete unit after you pull the axles out from each side. So you can do the gear setup on the workbench rather than under the car. You can also swap ratios without ever disassembling either the old or new gear-sets.


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## Karter2 (Nov 17, 2011)

TigerNut said:


> The difficulty of changing gear ratios depends on how the rear axle goes together. Most Toyota rear axles as well as the venerable Ford 9-inch have the gear assembly in a separate casting that unbolts from the banjo housing as a complete unit after you pull the axles out from each side. So you can do the gear setup on the workbench rather than under the car. You can also swap ratios without ever disassembling either the old or new gear-sets.


 Sure a competent mechanic can swap out the gear ratios in most diff housings,....but swapping a typical 3.5:1 ratio out and installing a 1:1 or similar , ratio is never going to fit into any standard rear end assy/ housing .
The physical difference in size of those gears is just too much.


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