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Electric vehical motor type help

  1. Mar 23, 2008 #1
    i want to make an electric vehical, problem is i cant decide on a proper motor. the vehical can weigh upto 300kgs so what sort of motor do i need to propel it at decent speeds. i can use a gearbox attached to the motor so the torque part can be solved to some extent.

    can u people send me some links for high rpm and torque AC and DC motors? somewhere in the 10 - 20 hp range.

    what sort of batteries will i need and will it be better to use AC or DC motors??
  2. jcsd
  3. Mar 23, 2008 #2
    What's your drive train and rolling friction?
    What grade should it manage, and at what speed?
    How much range should you expect out of a charge?
    How much acceleration?
    Does that 300 Kgs include the battery mass?

    Use a DC motor.
  4. Mar 23, 2008 #3


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    What is your level of understanding about AC/DC motors, batteries, controllers, and do you have a decent budget to work with ?
    Are you interested in outside the box ideas, or only off the shelf proven components ?

    I have a few links, depending on your answer, but i will have to get back tomorrow or the next day.

  5. Mar 24, 2008 #4
    actually i am a mechanical engineer so my knowledge on motors is pretty limited.
    i can fabricate a lot of the stuff including the body...

    i think the range will be limited by the batteries??
    i want to use lesser batteries as they are pretty heavy. lead acid is what i will use as llithium ion is out of the question.

    so the actual question is about the motor and the torque power requirements and number of batteries etc. then i can design the body according to that.

    budget is not too much i am afraid... i might be able to buy motors from scrap so that is where i can save. also 2nd hand lead acid batteries i can obtain as well.

    throw me all ideas what ever you can think of. i have only just started to think seriously about the project so there is plenty of time
  6. Mar 24, 2008 #5
    speed can be between 50 to 80 km/h... acceleration should be such that the vehical looks like its moving.. i am not making a tesla roadster!!
  7. Mar 24, 2008 #6
    planning on using a gear box (with several different speeds)? because a motor capable of both the high torque for initial acceleration along with the high rpms required for 80km/h is going to be expensive.
  8. Mar 25, 2008 #7


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    Once again too little time:smile:
    All too often first reaction of almost everyone, is why something won't work, or sounds too complicated, or too much expense for too little gain.
    These are important to any process, but in a lot of cases good ideas never see the light of day, and i would think that "fear of rejection" is high on the list of reasons why ideas don't surface until hard times. (now off the stump):uhh:

    Two ideas i have been preparing to work on (gathering materials and parts) but always too many other things that require first attention.

    1. Consider a multiple of smaller motors (example 10 PM/DC 3hp units). Without going into all the pros and cons, these offer some variations that can't be produced with a single motor. They can all drive a common jackshaft and produce about 30hp, easier to keep cool, and a grouping of 2-3 or 4 can be run in reverse mode, with the use of clutch bearings, and Thur a much greater gear ratio, can be 0-7 or 8 mph , then at a proper speed a next group can take over etc. this mixing and matching offers a lot of possibilities, and some fun if you do enjoy mechanical engineering. At full forward speed they will be running in same direction, and sharing the load.

    2. Designing a lead acid battery that is new and different, maybe not as powerful, or efficient as current design, but almost totally immune to failure, should be a worthy challenge.
    My starting idea is to have a large PVC water pipe (8" or larger, very thick walls) and each end being lead plates with very good seals. One side is positive and the other negative. Through bolts of stainless steel carry current to the proper end plate. The quantity of bolts will depend on how much current needs to flow, and they will be insulated at proper locations depending their polarity.
    Number of cells will determine voltage, and these can be a section of ? size filled with pure lead shot, as sulfating builds, the cylinder will be turned and the tumble action of the shot will produce a clean and maximum working medium for the battery.
    With fluid circulation the battery should be able to sustain a much greater rate of charge, and discharge, than standard designs.

    All cell seperators will be of material nonconducting and uneffected by sulfuric acid, and resistant to the shot tumbling.

    These ideas might not work as well needed in the manor presented, but they should serve as a start point to change where we are with all the exotic, and high price applications now being considered.

    Hopefully i didn't just kill another good thread, think i remember someone else talking about thread killing.:biggrin:
  9. Mar 25, 2008 #8
    I've been waiting for your post, Ron.

    I've heard vaguely about the 'economy of scales', which if applied to propulsion tells you that you are better off with one big motor rather than several small ones. But I've wondered, as well, about the possible advantages of multiple motor drive. It does work in electronics where smaller is better, For instanc,e power FET's that are designed using an array of many small FET's --but that's microelectronics for ya.

    I'm afraid no one has given much answer to saad ahmed khan yet.
  10. Mar 25, 2008 #9


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    http://www.motionsystemdesign.com/Issue/Article/38375/Clutches_brakes_and_inertia.aspx [Broken]


    http://www.evadc.org/build_an_ev.html [Broken]

    These are some links that have information i have found interesting, and a couple require a lot of search. I have other links more specific to electric cars, but realized they are on one of my other computers, or several hard drives i have switched out over the last few years:cry:

    With the price of copper on a steady rise, the cost are going to keep moving just out of reach of most DIY builders.
    My materials list is right at $4K US and if i can decide on the final connection point, the chain and sprockets will be my last needed parts.

    I bought the book "build your own electric vehicle" and a promising power train, is a DC start, and AC final drive.

    If this thread continues a while I'll try to put in the links as i find them again.

    Last edited by a moderator: May 3, 2017
  11. Mar 26, 2008 #10


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    I have not used a combination of motors yet, but the most recent heavy duty application (one motor) that has been worked with, is a 250gallon air tank that i loaded with 150 pounds of gravel, and tumbled the gravel to clean the inside so that it would reveal any excessive rust pits. the entire setup weighed around 800 Pounds. It was rotated using a pillow block bearing at each end.
    I used 120vac, a 15amp router speed control, a 600v 25amp rectifier to get dc current. I never calculated the ratio but 12amps is the most the motor pulled at any time, i ran 6 or 7 most of the time.

    These are 3hp continuous duty motors. At 59.95 each i think 18hp for $360.00 compares to an Advanced DC 20hp for over $2,000 and makes a try worth while (and they might not last for one run) i would think that is purely a matter of AMP control.

    Not sure if any of this helps anyone, but putting a few tidbits out might bring out a few answers and maybe some other methods to consider.
  12. Mar 27, 2008 #11
    Thanks for the links.

    In my own investigations, I'm focusing on direct drive--the friction bothers me a great deal. But the power band becomes very narrow and ground clearance is an issue. Some diesel-electric trains once used direct drive with provisions to reduce uusprung mass.


    I stand corrected. AC motors seem to run at far more mass per horse power than DC. Can you tell me where AC has advantage over DC?
    Last edited by a moderator: Apr 23, 2017
  13. Mar 27, 2008 #12


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    First thoughts that come to mind are that each has certain advantages over the other.
    DC shines in the slow speed high torque applications, but as the speed and power increase, the brushes, and commutator have to handle this high voltage and current.(high wear, and heat losses) A real bottleneck for power.

    AC is good in higher speed, larger power output, using much smaller wire gauge, and lite weight ? controllers.

    An EE might step in at this point and give a better, and more in depth answer to your question.

    Last edited by a moderator: Apr 23, 2017
  14. Mar 27, 2008 #13
    net problems...

    this multiple motor idea is a good one.
    yes i will be using a changeable gear box.

    i am thinking i might as well use a transmission right out of a car.... does any one have ideas as to what model and make of car might have a usefull transmission?
    making my own gear box will be complex and right now i am still in 4th semester.. havnt studied gears as yet.
  15. Mar 29, 2008 #14
    I think you want something closer to a large motorcycle transmission for a vehicle of that mass. If you are then constrained by your transmission selection, the next consideration is the required Kv of the motor.

    DC motors are specified, by a few basic parameters including power rating:

    Kv -- RMP per volt
    Kt -- Torque per ampere
    Io -- no load current
    Rm -- motor resistance
    Vo -- no-load speed

    These are not independent constants. Kv*Kt = 1352 in English units.
    Notice that Kv*Kt = (Torque * Shaft Speed) per (Volts * Amps) = power/power. Sometimes the manufacture or textbook will use different constants. Instead of Kt, they will use 1/Kt.

    Kv is the first thing you need to calculate.

    To pick some numbers out of the air (I'll have to use English units), assume

    40 miles per hour top speed, (59 feet per second, 3520 feet per minute)
    15" diameter tires, (3.9 feet of circumfence)
    6 to 1 total transmission and gear train reduction in high gear, and
    2*12 volts from the batteries.

    This is 900 RPM at the wheels and 5400 RPM from the motor.
    Kv = 5400 RPM / 24 volts = 225.

    Say you want to deliver 10 peak horse power for acceleration. 10 HP = 7460 Watts. That's considerable Amperage.

    For a motor manufacturer's tutorial on how to select a DC motor try
    Last edited by a moderator: Apr 23, 2017
  16. Mar 31, 2008 #15
    what about all the conversions projects that people carry out.. they take out the engine and put in a motor.. is it really that easy??

    and they use the original transmission of the car... so i was thinking along those lines. fabricate a buggy type vehicle and use a transmission taken from a small car..
  17. Apr 1, 2008 #16

    for sure, it's simpler to start where you don't have to reinvent the whole wheel. You wouldn't get much distance between battery charges though...

    Are you in India or Pakistan? They have some very cool vehicles that are the modern evolution of a lory(sp). Something like that would make a good conversion to electric, I would think. A top speed of 50 km/h might be ok, but 80 km/h is way high.
    In any case, it's a good idea to start simple and learn from what you can do. (KISS, ya know. It means "keep it simple, sir," or something like that.)
  18. Apr 3, 2008 #17
    i am in pakistan.. 50 is a bit low for city driving. its not a small city. i was thinking of something that could take me to university daily. and what vehicals are you refering to?
    cars are very expensive here unlike usa where you can pick up a car from junk for almost no cost. even 20 year old cars here cost upwards of 2000$.so definitely new cars are out of the question. i will keep looking though...
    still not sure about AC or DC. from what i have read AC are for higher speeds and the wire guage will be lesser. but the controller is difficult?
  19. Apr 5, 2008 #18
    Im calling a lory(sp) is a three wheeled vehicle. Like a tricycle motor cycle.

    I'm afraid I've about exhausted my knowledge on applying DC motors to vehicles for your particular problem. AC motors are a mystery to me. You might need RonL for that.

    But I did find this motor equation for DC motors,

    Power_in = VI
    Power_out = (V - IoRm)(I-Io).
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