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Old 04-18-2009, 04:34 PM   #11 (permalink)
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Quote:
Originally Posted by Electric Frenzy View Post
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.

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Old 04-25-2009, 05:17 AM   #12 (permalink)
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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.
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Old 04-25-2009, 11:52 AM   #13 (permalink)
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Originally Posted by Electric Frenzy View Post
I'm really looking for some good discussion on this
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
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Old 04-25-2009, 01:01 PM   #14 (permalink)
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Originally Posted by dcb View Post
Well, I tried.
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.
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Old 04-25-2009, 01:51 PM   #15 (permalink)
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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?
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Old 04-26-2009, 06:49 AM   #16 (permalink)
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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
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Old 04-26-2009, 04:14 PM   #17 (permalink)
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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
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Old 04-26-2009, 04:17 PM   #18 (permalink)
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Quote:
Originally Posted by dcb View Post
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
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.
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Old 04-26-2009, 06:30 PM   #19 (permalink)
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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
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Old 04-26-2009, 08:25 PM   #20 (permalink)
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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!

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