Originally posted by: Alexstarfire
The battery you suggested is terrible. A 2-3 year life span for a $2000 battery, that's insanely expensive. The battery I have in my Prius is said to last 10 years and costs like $5000-$7000 and I still think that's crap. Let's just use some simple math to show you how bad your battery would be. I believe they say that the average person drives 15,000 miles a year so I'll just use that for comparison.
Ok, that took a long time to write so I hope I put everything in there correctly.
All of your mathematics are correct. My design would not be using the high-caliber battery management technology in the Prius; it would just have all the batteries wired in a big series/parallel configuration.
My idea was to show that you could go fast on an electric vehicle - not how it would be practical. Battery technology has not come terribly far in the last five years - I've seen a maximum of maybe a 25% increase in power density, if even that - but with a bit more work (or a lot of the nastily expensive Saphion non-exploding lithium cells), an electric car or motorbike is not just a possibility - it can be made.
Were you able to use Prius-grade battery management, battery life expectancy would be very similar to that of a Prius - at least six years or so, depending on conditions and how much you drive it.
Also, the price would be much, much lower. Thanks to dropping prices, a battery pack could be made for perhaps $800 for a dual-motored vehicle - possibly less - using the high-grade lithium cells.
Finally, what I've designed is intended to act in place of a very small car - it's essentially a faster, lighter, and cheaper version of those funny little cars at airports.
The top-end version of the motors are capable of 25-30mph. I'm honestly not sure how fast such a vehicle would go - my estimate is that it would weigh about 30% more than the electric bicycle for which they were intended. However, instead of one, there would be four - hence, four times the torque and four times the overall horsepower. Imagine a go-kart with four of these - you could hit 50mph with ease, and corner in a manner that would make 2wd gas kart owners green with envy! (And high-end karts are serious buisness - people spend thousands on them.
EDIT:
The price of a 2-wheeled "mini-truck" for moving about town could be dropped a great deal.
1. Motors, 2x $400 - these are made in a very small quantity. Sell one hundred times as much, and they could be made for $150 - maybe less.
Of course, we can just use the RoadRunner 4820 motor. Although performance is somewhat anemic, one must consider the fact that they're:
A. $225 each
B. Two of them would be used.
C. The total weight they would be pushing is not that much greater than the bicycle for which they would be intended.
2. Speed controllers. If this is a 3-phase brushless motor - and I think it is - a pair of homemade 40A at 36v ESCs can be made for under $50. See here:
http://www.speedy-bl.com/spdy1684-e.htm
http://www.speedy-bl.com/schema-e.htm
All that's needed is to upgrade the FETs to larger, higher-voltage models. (They're IRF3205 HEXFETs, which essentially means that you can replace them with with bigger HEXFETs that cost $2 each, and use a cheap heatsink (old socket370 heatsinks work well) to cool them.)
If you're wondering, reversing the motor is the simple matter of switching one lead (there's three) with another, which is really easy - the whole thing's controlled by a PIC microcontroller.
Note that each ESC would be capable of a power output much larger than actually required.
3. The battery.
Lithium cells are all very nice, but NiMh Tenergy 10,000mah D-cells (1.2v) are $4.75 each.
http://store.shorelinemarket.com/1dni10reba.html
A 48v 30Ah pack of 120 cells (3 cells in parallel x 40 cells in series) would cost about $550, and weigh about 35 lbs. It uses the exact same battery chemistry - actually, almost exactly the same cells - as are found in the Prius. I'd expect at least 3 years off of this pack with basic battery management technology. (By "basic" I mean something bodged together with a PICmicro and some FETs.)
This pack should give at least 30 miles on a charge, likely more - I can't see the efficiency chart of the 4820 motor, but they advertise 20 miles on a charge with a single motor on 10Ah - each motor would have 15Ah (50% more) and would be pushing a much lighter load than the tested 36v motor (there's two of 'em). I would say maybe 40-45 miles if driven at about 25mph (local traffic) over a flat road.
So, here's the "new price breakdown":
$450 - front wheels/motors.
$50 - diy ESC
$550 - D-cell NiMH pack
$100 - other bits
Total: $1150.
Not too shabby, if you ask me. Remember, this would be for a 4-wheeled bicycle style vehicle capable of carrying a passenger or a good-sized amount of stuff. In other words, it's a noise-less, smog-less, gas-less moped that can carry things.
Finally, as a side benifit, remember this:
1. No power is used when the car is stopped in traffic or at a light.
2. You can turn off the engine when moving downhill - it's largely friction-less.
3. It's front wheel drive with two seperate motors - essentially, a limited-slip differential on steroids.
4. Ground clearance that SUVs envy - roughly 12".
5. Add knobbly mountain-bike style tires (these are bike wheels, after all) and you can tackle rain better than anything else on the road.
6. While tires will not last as long as car tires, they also cost a tiny fraction as much - $60 for a set of four versus $600 for a set of four. Maintaining a vehicle like this only requires replacing the wheels and tires, which you can do yourself in about twenty minutes. Everything else just needs a bit of grease once in a while.