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?

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.

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?

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 :)

Here is a diagram (guessing it starts at 0 rpm) though it may be a little exagerated, you get the idea:
http://www.evehicle.com.au/i/torque-curve.jpg

Slow EVs just dont have the power to accelerate fast would be my guess, but they also tend to be much more efficient too.

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

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?

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.

I'd go with No
since you said Blazing performance I'd say no
48 volts will do that; very slowly, but it will do it.
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.

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?

Max speed will be wherever your forward thrust equals drag and is vehicle and drive system determined. A bigger motor will give more thrust but requires more lead and more $. Lower drag is all gain, so smaller, lighter, sleeker, etc. is a big help.

Max range is the ratio of kilowatts-hours of usable battery you have on board to average watt-hours each mile consumes.

If you burn 100 Watts / mile and you have 5KW to use, then you'll average 50 miles. Watts/mile is mostly a matter of vehicle drag and drive system efficiency. Usable battery is limited by how deeply you want to discharge the batteries. The depth of discharge affects battery life.

So many choices.

Ok, sorry to bump this after a week or so but I've been thinking about some earlier discussion.

It was mentioned on here that the 9" motor has a ton of torque and a flat torque curve that wouldn't require a transmission for performance or top end. It was put to me that "piston engines use them because of their limited powerband. EV's don't have that problem".

Ok my question is this then: Why do the (IMO) very professional looking EV beetle kits maintain the factory transaxle with a 7" motor and 72v?? I saw a video of a beetle kit driving around town and it was HORRIBLY sluggish with hardly any top end (62-65mph TOPS). It took forever to get up to cruising speed on the interstate (which would get you killed here) and had a very limited range (about 23miles as quoted by the driver).

I don't know if this due to the smaller 7" motor used or the 72v available or the weight of the conversion (can't be THAT bad) that made it a horrible performer but even WITH the transaxle it was slow.

I don't see how having a 6spd manual wouldn't help make it much faster with lower cruising rpms which would in turn provide longer cruising range and higher top speed. I understand how weight, drag and rolling resistance are all important factors (as is gearing) but something just does add up to me with the previous comments.


Let's assume this cost $0 to build and you could fabricate anything you wanted. Would you guys PURPOSELY stay away from a 9" motor coupled to a motorcycle 6spd powered by 72v? Would you add more volts?, direct drive w/ 144v?, what?

I'm really looking for some good discussion on this so I can start making some plans ASAP. I want something unique like this but it HAS to be fast and at least get me 40-50 miles on a charge. Help a noob out.

Well, I tried.

Here is a rare good answer in yahoo answers
How do I do an electric vehicle conversion without using the transmission? - Yahoo! Answers

They also mention the killacycle approach of using two motors switched into series for torque and parallel for speed, but otherwise that is direct drive. Ac system is nice too, think that might be the next controller project :)

no no no, I'm not saying you're not helping out. I'm just saying that I want to get multiple inputs and varying ideas. I have a lot of questions and the more we discuss it the faster I'll learn.

I'll check out your link now.

It looks like, from what I read, that the transmission is necessary for reverse and as a stepper gear for low speed and then high. I also noted how they mentioned that you pretty much had to choose one or the other (hill climb or top end). I live in Alabama and climbing a hill is a must. So is freeway speed.

Looks like I'm back to my original question: Do you think a 9" motor coupled to a 6spd manual will have enough gearing to make it fast AND cruise on the top end with only 72v?

Methinks you still need to go through the exercise of thinking about what the ideal gearing should be, and not just hope your existing tranny and sprockets will do the job (if your tranny will even handle a 9").

Think about these questions:
What do you consider fast? i.e. 0-60 times.
What do you want for top speed?
How far do you want to travel and at what speed?
What is the steepest incline you need to get up?
What is the frontal area and CD of the bike?
What will the bike weigh with all that?

All these questions are pretty much interrelated. My gut feeling is that a 9" is not the limiting factor on a bike, but there is no reason to speculate. Pick a motor and a battery pack and a controller and do the math, and play with the gearing, rinse and repeat till you find a combination that can deliver what you want, then see if it is in your budget. It is a lot of number crunching. Less talky, more mathy ;)

Think about these questions:
What do you consider fast? i.e. 0-60 times. 5s or faster
What do you want for top speed? 80mph
How far do you want to travel and at what speed? 40-50miles @ 45mph
What is the steepest incline you need to get up? 26* grade
What is the frontal area and CD of the bike? I have no idea but it's frontal area is very small. Very pointy, not teardrop shaped.
What will the bike weigh with all that? Estimated at 1100lbs without driver

The math is what I don't know right now. I don't have the gear ratios for the bike transmission but I do know that the rear sprocket is something I could easily buy aftermarket to adjust a small amount. I'll call a bike dealer and see if I can get some more concrete info on the gearing.

You are going fast enough that you don't get to skimp on the Frontal Area and Coefficient of Drag estimations.

You have to start somewhere, so let me suggest

Figure out the CDa (and rolling resistance), you can determine how much horsepower needed to maintain 80mph with that.

That will give you tell you roughly how many watts you need (746 watts per hp)

Pick a motor that is a good %20 over that rating. Note RPM at that rating.

Figure out the motor power requirements at 45mph (in volts and amps, depends on gearing too)

pick batteries that can deliver the amps for top speed and can supply amps for an hour @45mph without losing more than half their capacity.

Note where you are at with the weight now (including driver) that you have a first guess on batteries/motor/bike/controller

determine your zero to 60 times at that weight/CDA/power level. If it is acceptable call it good, otherwise you need more motor/batteries.

Pick gearing (based on max motor rpm and tire size) to get you to 80mph.

See if that gearing is sufficient to get you up a 26* grade hill. If not you need more motor/batteries, or less weight (fancier batteries), or a lower gear that needs computing.

No promises, never been here before, just thinking out loud :)

now THAT is what I'm looking for! I can use those points to start getting the right numbers to figure out what it'll look like in advance.

It's going to take me a little while to compile all this so don't expect an update right away!

Depends on how much the motor is going to put out. The Hayabusa has it's primary ratio between the crank and clutch I believe, and it's something like 1.7:1. Then comes the transmission.

I know for a fact some people boost up to double the HP of the stock engine without even touching the transmission. So that is perhaps, 300+ ft lbs on the input shaft?

But then again, I see gears only as a necessary evil of gas engines. :p

Also: AC! Better than DC. :)

yeah but AC = much more $$ than DC.

I think we're just going to mock it up in a simple chassis and see what it feels like on 72v. It feels impressive then we'll just build it. If it needs work then we'll sit down and crunch the numbers. It would be easier to build the adapter plate to mount everything up than it would to track down specs on every gear and do the math.

FYI, I was digging through some Tesla info, it has no gears either. But it does have lots of torque down low w/gear reduction and a wide rpm range.

1. Single speed
2. 0-60 in 4 seconds
3. claimed 160mpg equivelant
4. ~230 mile range (lithium ion)
5. top speed 125 mph (electronically limited)
6. 2723 lbs, fully charged ;)

Battery: 6,831 standard 18650 Lithium-Ion cells (400volt system)

Motor: 3-phase, 4-pole AC motor - unique design
215 kW @ 7,000 rpm (288 bhp)
Max torque (350 Nm) at zero rpm, max speed 13,500 rpm
Weighs 50 kg

Transmission
Single speed double reduction bespoke transmission
Reverse? - reverse motor direction!

So if you could halve the weight and the CDA of the tesla, you could have similiar performance with half the motor and batteries, and no gears, I think :)

If you could live with 1/5th of the 230 mile range, you could maybe use 1/5 of the battery pack (if the remaining batteries can still deliver the performance).

edit 683 of those li-ion batteries would be like 70 lbs!, the tesla is carrying about 700lbs of them, there is an easy weight (and cost) cut there.

more specs on that battery:
Specifications: Nominal Voltage :Average 3.7 V Nominal Capacity :2350mAh, Minimum 2300mAh Max. Charging current: 2.4A Max. Max. Discharging current: 4.6 A max. Dimensions: Diameter 18.3 mm (Max 18.4), Height: 64.9 mm (Max 65.1) Weight : 46.5 g (1.64 oz) Internal Impedance: Internal Impedance: less or equal to 90 mohm (with PTC) Cycle Performance: 80% of initial capacity at 300 cycles

So that 7 strings at 400v would be 756 batteries. Which could deliver 32.2 amps @ 400volts or ~17HP. Scaled up that would "only" be 170 HP so I think that tesla either has better batteries, is over pushing them a bit, or has more motor than the batteries can fully utilize.

ok bear with me here. I'm trying to follow everything you've said.

1. You're suggesting I mimick the Tesla Roadsters motor and battery pack but scale it down by 80%?

2. The CDA is what exactly? Coefficient of drag?

3. You're saying with 1/10th of the battery pack they're using I should be able to go 46miles per charge? for about 70lbs worth of weight (in the batteries)

4. "Transmission=Single speed double reduction bespoke transmission" I'm not familiar with these. I don't understand how gear reduction transmissions work as they relate to electric motors.

5. I'f I'm using a DC motor I'd still need a trans for reverse as I wouldn't be able to just reverse the polarity of power going to the motor. Is that correct ?


I'm loving this discussion. I'm learning more every day.

Check this out and see if I'm following you correctly.

This is a link for an AC electric motor. It's 3phase and rated at 10hp and 3600rpms. That seems awfully low for a vehicle. Obviously I'm not looking at the right item but am I on the right track?

01036EP3E215T - WEG ELECTRIC CORP MOTOR 3PH 10HP 3600RPM 215 T 208-230/460V


Here is another motor rated at 20hp @ 1800rpms. It costs $1000 but that is VERY cheap compared to others I've seen. It seems with this type of low rpm motor I'd NEED a transmission to compensate for that. Sure I wouldn't need 6 gears but maybe 3.

http://www.galco.com/scripts/cgiip.e...pnum=U652-MARA

50%, lets say you keep the battery pack at 400 volts, but use half as many cells as the tesla (and half the motor).

And you can do that because you figured out how to reduce the coefficient of drag(CD) multiplied by the frontal area (a) in half (or CDa) so top speed will be similiar

And you also figured out how to halve the weight of the vehicle so you have half the mass of the tesla, and half the power, so acceleration should be similar, though rider weight will have a larger influence.

The tesla batteries are at their max for these acceleration figures, the 1/10 pack numbers didn't work out, sorry. 1/2 the number of batteries works, and is a healthy bit of weight to lose still. You'll just have to live with a 220 mile range :)


A couple gears, you can't shift them but they make more torque at the rear wheel. According to the specs it is 8.28:1 overall ratio. It would be like having a 10 tooth front sprocket on the motor connected to an 83 tooth rear sprocket, not that those are practical sprockets, but sprockets are fairly simple to make too (lots of drilling)

We are in the motorcycle section. Who cares about reverse? ;) How will you reduce frontal area substantially if you have more than 2 wheels? OR the weight? We are talking about a bike right? But DC motors are reversable, just got a bit more controller expense though. Might use 2 motors (each at 1/4 the tesla motor outout) and use the killicycle series/parallel shift for possibly more performance, but still direct drive.

Another approach might be to thumb through the EV album for motorcycles till you see some specs that you like and see what equipment they have listed.

EVAlbum: Search Results

Like this guy with 50 mile range and top speed of 100, and acceleration of "very fast". It looks like you can go buy one of these today for ~$16k from their website. Go hitch up the trailer :) Looks like it is in Charlotte (400 miles from you)

http://www.evalbum.com/img/2508/2508a.jpg

reverse is mandatory. What I'm wanting built is a fully enclosed 3 wheeler which is LEGALLY a motorcycle. I like the one pictured above but I have a 250cc if I need some 2 wheeled fun.

I've been doing some searching and I'm finding numerous 3ph AC motors with 20hp and rpms ranging from 1800-3600. I don't know if these will work but if so they are priced reasonably and would allow some extra money to go towards battery packs.

Speaking of Batteries..... where would I go to research and price custom built LiIon battery packs like you mentioned needing above?

p.s. I've checked out that link you posted to the electric motorcycle company. There is a lot of debate on other forums about how legitimate they are. They make a lot of claims that seem HIGHLY dubious. (30minute charging of LiIon and 80mile range with stellar performance) No'one else can do that and certainly not for that price.

I actually called the guys. They have a base price, and you can add 20 miles chunk of batteries for like 5 grand (that might have been for the car) and up to 8 or 10 5k chunks of batteries fit in the car. And they have a controller upgrade for a few hundred. Looks like they use several chargers at a time to get the times down or something.

$16k would be a nice write off, and look at all the advertising space on that two wheeler :)

Sorry, I can't get excited about a three wheeler though, have fun :)

I already have a nice 2-wheeler. It doesn't get any attention....not like a trike would!

What can you tell me about my LiIon battery questions and where to buy them? I'm trying to crunch the numbers you've given me on the project but need to find suppliers and get more detailed specs.

I don't know squat about suppliers dude. google for part numbers "price" etc.