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Discussion Starter · #1 ·
Here's a newbie question. If I chuck out the transmission in my EV conversion project, how do I gear down the revs from the motor to the wheels? Are there off the shelf single speed "gearboxes" with a 3:1 or 4:1 ratio or thereabouts?
 

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Discussion Starter · #6 ·
You use a differential - like the one in the back of a Subaru - or a BMW
Or most rear wheel drive vehicles
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Most diffs are about 4:1 - just right for using a DC motor at normal highway speeds
Yes, the question is from someone who (at least tentatively) is planning on using the front and rear final drives of a production 4WD vehicle, and that's what I meant by this:
... assuming that you still have the final drive reduction and need an additional stage before that...
The reduction of a typical final drive is enough if you are using a motor which only goes to perhaps 3,000 rpm. If you want to use a broader speed range of a higher-speed motor, more reduction is required - that's what an additional gearbox would be for.

It is also possible with common final drives ("diffs", "axles") to change the ring and pinion gears to get a different (typically more reduction) ratio, but the choice depends on the specific brand and model.
These are great answers people.. Thanks so much.
I will be keeping the final drives( front axle & rear differential). I hadn't realised that the ratio in a final drive was that high. Should be adequate for the pair of forklift DC motors I plan to use.
 

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Discussion Starter · #7 ·
Here's a newbie question. If I chuck out the transmission in my EV conversion project, how do I gear down the revs from the motor to the wheels? Are there off the shelf single speed "gearboxes" with a 3:1 or 4:1 ratio or thereabouts?

More details would help. Front wheel drive? Rear wheel drive? Lower RPM DC motor(Duncan's specialty)? Higher RPM AC motor(more and more popular)?
So sorry, I forgot to mention - it's for a 4wd using a pair of DC forklift motors. I'm trying to avoid cost and complexity.
 

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Discussion Starter · #12 ·
DrGee, when you skip to a new thread, on the same build, you need to bring the rest of us up to speed on the basic info from your original thread.
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Most of us(except maybe Brian?) have a life outside of this forum and can't read and parse every post that's ever been written.
LOL

But seriously, the 4WD scenario is of particular interest to me, I had responded to the main thread, and it was recent, so I happened to remember it.

... Better yet, try to stick to one thread to avoid the confusion.
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Another option might be to reference your previous threads or posts.
To be fair, the question in this thread is a distinct and specific topic, which would be reasonable without the whole context - all it needed to include was the use of the original final drive unit (diff).

There is an advantage to keeping a thread to a more narrow topic - it is less likely to get sidetracked and become a massive pile of discussion in which no one can later find anything. A link to the other thread "for anyone wanting more background" would work fine for me.
Thanks for your reply Brian!

I decided to move my questions about the transmission to the other thread - AC Vs DC, in "DIY wiki discussion"
 

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Discussion Starter · #16 ·
Rule 1: If you live in steep or rolling hills, stick with a transmission.
Rule 2: If you are going direct drive with no clutch or transmission, the lower you are below 2500 Lbs the better.

Rule 3: Simple is best. EXAMPLE: My car is 1,900Lbs. I live in a flat area, but still have a powerglide. I can drive around in high gear all the time, but if I want to zip ahead sometime, that low gear is awsome......

Rule 4: Gear your EV as you would a gas motor. Motor RPM / Tire height/ desired road speed.

EXAMPLE: I have an AC50 @ 6,500 RPM. My tires are 32" tall, SO I have a 6.14:1 rear axle ratio. It gives me a normal speed range.
Okay Mizlplix,
Great details & very relevant points.. Love it!
Now,
1.I live where it's flat as a pancake- fortunately..
2.The car is a Jeep Grand Cherokee - about 2 tons.
-but if I use two forklift DC motors as planned, does it change #2?
3. Can you describe your powerglide?
Cheers!
 

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Discussion Starter · #18 ·
In the Grand Cherokee, the central transfer case can be separated easily from the 6 speed automatic box. Here's a consideration -
I remove the gearbox with the ICE and do a direct drive from a single large motor to the central transfer case. All-time 4x4 will be retained & no need for two motors.. Any comments?
 

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Discussion Starter · #20 ·
In the Grand Cherokee, the central transfer case can be separated easily from the 6 speed automatic box.
I assume that we're still talking about a 2011 (model year) Jeep Grand Cherokee WK2. If Wikipedia's list is correct, this has a Mercedes 5-speed or Chrysler 5-speed (depending on engine), not the later Chrysler 6-speed. The number of gears isn't important, but different transmissions may come with different transfer cases, which may mount differently. All should detach reasonably easily from the transmission.

I remove the gearbox with the ICE and do a direct drive from a single large motor to the central transfer case. All-time 4x4 will be retained & no need for two motors.
Fundamentally, it should work.

You gain the simplicity of a single motor and single controller, and don't need to coordinate front and rear motors, but then you must carry the weight and complexity of the transfer case and live with whatever it does for front-to-rear power distribution (which may depend on the transmission controller that you don't have any more, although it may be independent).

Gearing is then fixed (as it would be in any solution not using a multi-speed transmission) to what the transfer case and final drives include. There were at least two different transfer cases, one with a single ratio (presumably direct) and the other with two ratios (presumably a low and direct). The low and high ratios may not be usable as a routine first and second gear, as frequent shifting between them is not expected.
I've decided to use my 2005 WK Grand Cherokee. It has nearly 200,000 miles on it, but still runs flawlessly. (Couldn't justify searching for a 2011 with a blown engine, when I've already got my '05 which I know so well).

You're right about the gearbox - it's a 5 speed.
I believe you're right about the two types of transfer cases too. Mine is the the single speed NV140. It has an electronically controlled clutch pack & splits torque 48/52, front /rear. So both speed & torque are fixed, but I don't mind.
I wonder if the electronic control will be an issue since the sensors might be unhappy without the ICE..

Both front and rear differentials are conventional ( not limited slip). They've got a ratio of 3.07:1.
I may need to increase the ratio at these final drives, but this all depends on the characteristics of the mighty motor I'll need (rpm at what safe voltage etc). I'm going to enjoy finding one. Let's see if I can better Damien..
 
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