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Old 04-17-2009, 02:41 AM   #1 (permalink)
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need hypothetical numbers for project

I'm just doing some very early homework on a possible engine/tranny combo for an EV build. I'd like to see what you guys think about the motor size. voltage, trans type and weight. I'm not really looking for anything more than 50 mile range and scalding fast performance. Here is my parts list so far. Please tell me what you think with this limited amount of information


9" warP 9 motor
6spd manual trans from a hyubusa (sp?)
72v (12 6v golfcart batteries)
1200lb curbweight

It looks good to me from a power/weight standpoint but only because of the ultra tight gear ratios in the trans. I think I'd be shifting quite a bit to keep it on boil but is 72v enough to make IMPRESSIVE power and still maintain a 50+ range? My thinking is that the drivetrain will allow for much lower cruising rpms (and less power consumption) while still providing me with the top end I'd demand (80+mph)

I've seen several high quality EV-beetle kits that use the 9" motor but they run 96v. I'm unaware of their vehicle weight but the performance is NOT anywhere near what I'm looking for.

I've been discussing it locally and some people think the transmission will make all the difference in the world and some (me) only know "more batteries = more power". Who is right?

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Old 04-17-2009, 06:24 AM   #2 (permalink)
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I'm no expert, but I think given the relatively flat torque curve of electrics that two speeds is all that is really required. The Killacycle uses a direct drive it seems but "shifts" by switching its two motors from series to parallel, FYI.

On the other end of the spectrum, for my bicycle sized machine I'm thinking something along the lines of retro-direct, to make sure I can have decent top speed and still climb hills.
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Old 04-17-2009, 01:48 PM   #3 (permalink)
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I've noticed that most EV's either don't use a transmission or they only use a simple 1-2 shifter. I think (aside from the tesla) these all suffer acceleration problems though don't they?

I'm not working on a killa-cycle budget or know-how! I just thought mating a big 9" to a motorcycle manual would allow me gobs of power down low (400:1 ratio in first) but the ability to cruise at 70+mph without much power drain. Does the logic sound solid?
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Old 04-17-2009, 02:45 PM   #4 (permalink)
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Quote:
Originally Posted by Electric Frenzy View Post
I've noticed that most EV's either don't use a transmission or they only use a simple 1-2 shifter. I think (aside from the tesla) these all suffer acceleration problems though don't they?
I really don't know what that assumption would be based on. My understanding is that more gears are needed with a gasser because the torque isn't even. To keep the gasser near peak torque (and acceleration) you have to have lots of gears (and slip the clutch when getting started). To keep the electric near peak torque you turn it on
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Old 04-17-2009, 03:07 PM   #5 (permalink)
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Here is a diagram (guessing it starts at 0 rpm) though it may be a little exagerated, you get the idea:


Slow EVs just dont have the power to accelerate fast would be my guess, but they also tend to be much more efficient too.
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Old 04-17-2009, 03:44 PM   #6 (permalink)
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I'm no expert; but I'd bet that 7" motor would have more torque than the Busa transmission can handle.

More Voltage = more Power; if you are looking for power go 144 volts +++
Try looking at 12 volt batteries rather than 6 volts.

More batteries (wight of batteries) = more Range
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Old 04-18-2009, 01:11 AM   #7 (permalink)
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I appreciate the discussion so far but I'm not getting the clear answers I was hoping for.

1. would the 9" motor and motorcycle transmission be a good match for blazing performance?

2. Is 72v enough power to be fast and have good range if you're using a multi-gear transmission?

3. Is 72v enough power (running through a 9") to move 1500lbs (vehicle + passengers)

4. What other options would I have for running a large motor to a single rear wheel if the motorcycle transmission isn't a good choice?
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Old 04-18-2009, 04:21 AM   #8 (permalink)
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Well, the calculations aren't all that tricky for best performance. F=M*A covers most of it. I don't mind giving it a try, though I could be completely off.

lessee, we have to know :
1. The torque of the motor @ 72 volts
2. The rpm range of the motor w/72 volts available.
3. The gear ratios of the transmission you are interested in
4. The overall gear ratio and tire size
5. the weight of the vehicle.

Given the flat torque curve, it should accelerate at a fairly even rate, excluding drag.

But I don't know enough to talk about it in general terms, I need a specific example.

So take the 9" warp: Shock EV | NetGain WarP 9 Electric Motor
  • 9.25” diameter, series wound DC motor
  • Weight, approx. 156 pounds
  • 32.3 HP (72 Volts, 335 Amps
  • 70 Ft. pounds torque*
  • 5,500 RPM's

You have guessed 1200lbs

And lets assume your batteries are "standard" T-105s
Golf Cart Batteries and are in good shape to deliver 335 amps.

and lets assume the rear tire is 24" and revolves 840 revs/mile

You stated an overall ratio for 1st gear, 400:1 (???)

So lets run the numbers for that,

so basically the torque on the rear wheel in first is 70*400 or 28000 foot lbs. Since the radius of the tire is 1 foot, you basically have 28000 pounds of thrust. But it is turning 400 times slower than the motor too, so when the motor redlines in first at 5500 rpm, your rear wheel is going 13.75 rpm, or about 1 mph, and now it is time to shift to second. I don't think most hyubasa owners shift at 1mph

On the other hand, if you want top speed to be 70mph @ 5500 rpm, your top overall ratio needs to be 5.6 to 1. And the tire will be pushing the bike with 392 pounds of force (70 * 5.6), which sounds reasonable to me.

So lets start there and add some gears (I'm gonna ignore aerodynamic load for now)

convert to metric, 392 lbs = 1744 newtons, 1500lbs=6672newtons, 70mph=31.3 meters/second

With direct drive, 1744/6672 = .26 = A , so 31.3/.26 = 120 seconds to 70mph

lets add a 11.2 ratio first (overall) and a 5.6 2nd. So acceleration has doubled to 35 mph. This first gear should be our biggest time gain, the rest will be diminishing returns. So off the top of my head it looks like 90 seconds to 70mph. 4 gears might get you down to 75 seconds.

So if I were a gambling man, I'd say the limit, assuming infinite gears and zero shift time, would be 60 seconds to get to 70mph.

Not exactly "blazing", and I could be completely off the numbers here, but I don't think a close ratio box is going to help matters.
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Old 04-18-2009, 08:33 AM   #9 (permalink)
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Quote:
Originally Posted by Electric Frenzy View Post
I appreciate the discussion so far but I'm not getting the clear answers I was hoping for.

1. would the 9" motor and motorcycle transmission be a good match for blazing performance?
Quote:
Originally Posted by dremd
I'm no expert; but I'd bet that 7" motor would have more torque than the Busa transmission can handle.
I'd go with No
Quote:
Originally Posted by Electric Frenzy View Post
2. Is 72v enough power to be fast and have good range if you're using a multi-gear transmission?
Quote:
Originally Posted by dremd
More Voltage = more Power; if you are looking for power go 144 volts +++
since you said Blazing performance I'd say no
Quote:
Originally Posted by Electric Frenzy View Post
3. Is 72v enough power (running through a 9") to move 1500lbs (vehicle + passengers)
48 volts will do that; very slowly, but it will do it.
Quote:
Originally Posted by Electric Frenzy View Post
4. What other options would I have for running a large motor to a single rear wheel if the motorcycle transmission isn't a good choice?
Automotive transmission
Reduction housing built to go on a tail shaft
Industrial transmission
Direct drive is cheapest.
We can do the math to see what kind of performance is available. Have you tried eve's ev calculator?

What is the target vehicle? I hear 1500 lbs, Motorcycle, passangers so I'm not really sure what we are working with.
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Old 04-18-2009, 01:27 PM   #10 (permalink)
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now THAT's what I was looking for! Sorry for being difficult!

I can't go into TOO much detail about the project just yet to say basically what I have already said. I can offer up some more info on general stuff though.

1. uses automotive drive wheel in the back 17" about 7-7.5" wide. Will run a low profile tire (45series or lower)

2. it's not using a motorcycle swing arm, rather a custom assembly to house the wheel, hub, trans.


I'm obviously very new to this but I'm a quick learner so I appreciate the in depth answers.

As for the gearing in the transmission I was told that since a transmission is basically a torque multiplier that even with the low power of the 72v 9" motor I'd have "blazing fast" performance. It made sense to me at first but after seeing your numbers it looks like there is no way in hell. Maybe it's because of all the hypotheticals?

Does anyone happen to know what kind of range, speed, top-end I could get if I went with an 11" motor, direct drive and 144-156v? Would that be a better way to get more performance and save on weight and complexity?

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