# newbie question "how to calculate top speed range etc.."



## BobDeere (Jun 24, 2014)

Hi all !
Bob from a cold Sweden "yes even in the summer"
ill like to convert an old micro car "isetta" to electrical.
the car have 2 front wheel and 1 rear where the motor sits
what i would like to know how big engine i have to purchase beased on those specs.
size of vehicle approx 250 cm weight with batteries passenger "1 person" 
etc at least 400 kg.
on ebay i found some chinese 10 inch hub motors 3000 watt /84 volt
would that be enough to be used on my car?
il would like to achieve a top speed of around 40-50 mp/h
and a range of 20-40 miles.. but im know those figure can be hard to achieve
is it any easy formula out there i can use for calculating top speed , range etc?

Thanks
Robert


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## elevatorguy (Jul 26, 2007)

A resource you may wish to check is the wiki on this site, lots of information and formulas that you can use for the conversion.


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## BobDeere (Jun 24, 2014)

thanks for the info ..
now i have my afternoon secured


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## madderscience (Jun 28, 2008)

if you want a belt driven setup a perm 132 pancake motor running from a 72v traction battery through an alltrax controller would be a good setup for an isetta. Given the relatively low weight a 60ah, 72v battery would probably give you the range you look for and a 100ah 72v battery would be tons of range, but I haven't done the math but guessing around 100wh/mile (60wh/km). In both cases it is about 24 LiFePO4 cells, quite compact. Although a bit more complex to install than a hub motor would be, you get the advantage of being able to adjust gear ratios, as well as more flexibility in the traction battery voltage and controller options. Main disadvantages of a DC system are no regen and motor brushes to wear out or get fouled. A lot of the hub motors I have seen have matched pair controller so you don't have a lot of flexibility there.


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## BobDeere (Jun 24, 2014)

Hi Madderscience !
ill to tell a little more background about me
im a scooter/micro car guy. i have a shop where we make scooter parts
bd-scooters.com
so scootering and micro cars is my thing.
my dream is to take a scooter/micro car and make the conversion as easy as possible without affecting the original look and if possible make it so it can be re-made back to the original specs..
so the hub motor is like the easiest way..
the range is not that important since vehicles like that are more use for runs or rides usually 10-30 miles is more then enough.
the could also be used to commute to work sometimes " if you live near work" 
what is more important is the speed.. at least 40 mph for the micro car, ill love if i could come up to 50-60 mph " but there is also more space for the batteries"

when i speak tot the chinese manufacturer ..here is a link:
http://www.ebay.com/itm/200936028288?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

i dont get much data.. they just say " it will go like hell "
yeah sure.. " and i believe in them.." they just want to sell the damn crap..

btw..
i own since before 2 sinclair C5 "1 tuned.."


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## BobDeere (Jun 24, 2014)

i went down to my garage
the diameter of the 10 inch tyre is 135 cm or 54 inch
rpm for the engine is around 750/1000
im trying to get a formula for calculating topspeed but no luck..
can anyone tell me how "in theory" the top speed woud be?

cheers
Robert


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## PStechPaul (May 1, 2012)

I have an EV Calculator that includes calculation of speed based on motor RPM and wheel diameter, so the only other variable you would need is the gear ratio from the motor shaft to the wheel shaft. At 80 km/hr (50 MPH) the wheel will be 314 RPM so if your maximum motor speed is 1000 RPM (actually most motors will easily do 3000-5000), your gear ratio will be about 3:1. At 400 kg and a 3% grade, with all other values as default, the power required will be about 9 HP or 6500 watts, and you can expect to use about 131 Wh/mile. But on flat roads you will need only 5 HP (3800W) and you should use about 77 wh/mile. Those should be considered minimum values and much will depend on component efficiency and driving technique. But a small vehicle as you envision should be able to do about 100-150 Wh/mile average and your 30 mile range would use 3000-4500 Wh. Lithium batteries cost about $0.50/Wh so your pack might be about $2500. This is all theoretical but my results for other vehicles generally are close to real world reported values. Good luck and have fun!

[edit] I see that you plan to use a hub motor in which case there will be no gear reduction and at 1000 RPM on a 54 inch wheel you will be "going like hell" at 160 MPH! But you need to consider the maximum torque of the hub motor which for 1000 RPM and 3000W it will be about 21 lb-ft or 28 N-m. On a 6% slope at just 50 k/h (38 MPH) you need 185 lb-ft of torque and 158 lb-ft even at just 5 k/h. An electric motor can produce about 3x rated torque for a short while, but that will still be nowhere near enough. This is why hub motors have proven mostly impractical without some sort of reduction gearing. They work OK on a pedal-assisted bicycle where you can provide the start-up torque while the motor kicks in at higher cruising speed, but for hill climbing and acceleration, torque is the key, and a 54 inch wheel is practically impossible for a hub motor.


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## BobDeere (Jun 24, 2014)

Thanks Paul !
you helped me put a lot.
i own since before 2 Sinclair C5 and im aware that is the start that is most 
consuming/torque..
so if i understand you right the hub motor of 3 kw is way to small for that size of vehicle..
so know im thinking.. since its a small hub motor made for 10 inch wheels..
maybe i should 2 in the front and only have a "free" wheel at the rear?
or maybe have all 3 wheels with hub motors?
that should help.. or?


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## BobDeere (Jun 24, 2014)

please look at these site
http://www.gngebike.com/electric-scooter-motor

they have lots of different motors . kits etc..
what do you think?im most interested in the 10 inch hub
but they also have a "trike kit"..


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