# Best range - high RPMs in 2nd or low in 3rd gear?



## chansen (Mar 13, 2009)

Just finished my conversion and I was wondering, should I try to keep the RPMs low to achieve the best range? I suspect low RPMs in 3rd gear might draw higher current and loss of range vs just letting the warp9 motor spin faster in 2nd.


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## Amberwolf (May 29, 2009)

Very basically:

Faster the motor spins, the higher the BEMF, so the less current it draws; letting the drivetrain do the speed-to-torque conversion to get similar power output to the wheels for less battery current used.

It could be explained a lot better by many others here, but as I understand, that's the gist of it.  It certainly works on my CrazyBike2 that way.
________
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## kek_63 (Apr 20, 2008)

Search the Wiki and the forum - this comes up often. 

Simplest answer - Low rpm = high amperage = low efficiency+heat

Keith


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## tomofreno (Mar 3, 2009)

I think that's a good way to look at it. Power is the product of torque and angular velocity. Running in a lower gear means the motor has higher shaft angular velocity for a given wheel velocity. The motor power is then the product of a lower torque and higher shaft velocity and is equal to the power at the wheels which is the product of a lower angular velocity and higher torque due to the mechanical advantage of the overall gear ratio of the vehicle. Motor torque is pretty much proportional to current, so less current is required to produce the lower motor torque. So as you say, for better efficiency you want to use the mechanical advantage of the gearing to transform a lower motor torque to a higher torque at the wheels, so less current to the motor is required. 

Tom


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## chansen (Mar 13, 2009)

I'm doing some "field" tests on this by measuring the DOD on multiple daily commutes (20 miles) in which I either use 2nd or 3rd gear for the whole trip. It will take me a month or two to collect enough data that it becomes statistically significant. I will post the results when I am done.

Thanks for the tips.


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## Bowser330 (Jun 15, 2008)

chansen said:


> I'm doing some "field" tests on this by measuring the DOD on multiple daily commutes (20 miles) in which I either use 2nd or 3rd gear for the whole trip. It will take me a month or two to collect enough data that it becomes statistically significant. I will post the results when I am done.
> 
> Thanks for the tips.


awesome...thanks chansen!


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## Astronomer (Aug 7, 2008)

Can't someone with a current meter on the dash just run a short course two times in two different gears and simply observe which requires more amps?


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## roflwaffle (Sep 9, 2008)

What are the 2nd/3rd gear ratios, axle ratio, and tire size? You should be able figure out what's best for efficiency from the Warp 9 map. Generally speaking, 2000-4000rpm is where you want to be.


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## Bowser330 (Jun 15, 2008)

roflwaffle said:


> What are the 2nd/3rd gear ratios, axle ratio, and tire size? You should be able figure out what's best for efficiency from the Warp 9 map. Generally speaking, 2000-4000rpm is where you want to be.


I think his setup is for 120V. The graph you reference is for 72V.

Does the voltage make a difference what rpm range is most efficienct?


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## E4mula (Mar 31, 2009)

Astronomer said:


> Can't someone with a current meter on the dash just run a short course two times in two different gears and simply observe which requires more amps?


I've run some tests like that. Constant speed over the same course through different gears. Average power consumption over the course increased when shifting into higher gears.


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## piotrsko (Dec 9, 2007)

E4mula said:


> I've run some tests like that. Constant speed over the same course through different gears. Average power consumption over the course increased when shifting into higher gears.


new question: which gear made you faster through the course and can you give some data as to watts per ET?


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## chansen (Mar 13, 2009)

I calcualted that for my transmission ratio, final drive and tire size the following RPMs for the Warp9 motor:

http://www.kabamus.com/garage/gears.html

in 2nd and at 45 mph => 5000RPM
in 3rd and at 45 mph => 3500RPM

So it seems that 3rd is the right gear for everyday driving, given the Warp9 info from a previous poster. My problem is that in 3rd, the acceleration from stop is slower than other vehicles on the road. I live in hilly area so I often stop on an incline.


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## roflwaffle (Sep 9, 2008)

Bowser330 said:


> I think his setup is for 120V. The graph you reference is for 72V.
> 
> Does the voltage make a difference what rpm range is most efficienct?


I don't think it changes it much, but I'm a layperson so take that with a grain of salt barring verification.


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## frk2 (Jan 2, 2009)

Ive done tests in my car from my home to office trip (8km). I would drive in third from stop on one trip and then 2nd-3rd (shifting). The 1rst option (3rd all the way) consumes marginally more energy (maybe 10% more), gives me far better acceleration and is all round pleasant. 2nd to 3rd actually results in bad acceleration for me since my 2nd gear is REALLY high (3.1:1) with a final 3.6 ratio so 10:1 gear to the wheels. 

I simply drive in third.


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## Bowser330 (Jun 15, 2008)

frk2 said:


> Ive done tests in my car from my home to office trip (8km). I would drive in third from stop on one trip and then 2nd-3rd (shifting). The 1rst option (3rd all the way) consumes marginally more energy (maybe 10% more), gives me far better acceleration and is all round pleasant. 2nd to 3rd actually results in bad acceleration for me since my 2nd gear is REALLY high (3.1:1) with a final 3.6 ratio so 10:1 gear to the wheels.
> 
> I simply drive in third.


So to clarify, the 2 to 3 shift option results in bad acceleration because the shift required takes more time than just leaving it in 3rd and flooring it...even though the lower gear (higher multiplication) gives you better INITIAL acceleration, the requirement of the shift bogs down the overall acceleration...do i understand that right?


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## frk2 (Jan 2, 2009)

Bowser330 said:


> So to clarify, the 2 to 3 shift option results in bad acceleration because the shift required takes more time than just leaving it in 3rd and flooring it...even though the lower gear (higher multiplication) gives you better INITIAL acceleration, the requirement of the shift bogs down the overall acceleration...do i understand that right?


Sorry for being vague - yes the shift bogs me down. Also although my VERY initial acceleration in 2nd is good - the power quickly tapers off as the motor enters high revs. This means that I have to quickly shift to third (this is due to my car's weird gearing). Overall its better if im driving in the lower (3rd) gear. Keep in mind that my 3rd may very well be your second - max speed in second = 35kmph and in 3rd = 65kmph.


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