How to Design a DC Motor

Simplest is probably to use a starter motor from an old car.

Dear Sceptic, Thanks for your suggestion but, I skeptic about your idea. These motors are meant for short term high torque and draw heavy current, as much as 120 to 200A. May be it needs a bit of redesign.

Hi ganapa:

On reflection, I think you are right.

A starter motor is made for heavy, short term use, not sustained use.

I have seen one used as a motor for a trailer winch, which is what made me suggest it originally, but I didn't think it through .

Thanks for setting me straight.

regards

sceptic

are you going to design a dc motor or in place old gasline engine?

YESSSSS

This idea of using the gearbox with an electric motor always appeals to amateurs, but is not necessary.

An IC engine needs a gearbox and a clutch because its torque and low speed (minimum 1000 rpm or similar) characteristics + the fact that it has to be running all the time! Make any other arrangement quite difficult to achieve.

An electric motor has generally a wide speed range with good torque characteristics (if designed correctly of course!), does not need to be running all the time, so it can be directly connected permanently to the drive wheels, often inside the wheel(s) as a hub. Some cars achieve 4 wheel drive through this.....

A further problem is that a gearbox actually wastes energy, a lot of energy!!! So being able to throw the gearbox away (and in the case of cars the differential as well) means that the vehicle in question needs far less electrical power to achieve the speeds and performances required, than the size and power of the IC engine suggests.

I have seen figures that suggest that a well designed gearbox, in a good condition, can easily lose 50% of the energy input, particularly when not using the full power of the motor concerned!!!

This implies that if you need say 150 BHP to achieve the standard of driving that you require, a correctly designed electrical power train may only need 75 BHP!!!

I found an interesting web site, selling such hub motors and also discussing the energy losses associated with gearboxes here:-

Gearbox Mechanical efficiency

Dear AndyGermany, thanks for that link. I remember Sherlock Holme words THE PLOT THICKENS. I do will have lot reading and work. Thanks again for that wonderful link.

Dear Ganapa,

that's what we are here for, to help each other in a friendly manner whenever possible!

Stay well my friend and do inform us with a few pictures etc if you do "bite the Bullet" and build something interesting.

Regards

Andy G.

A wild suggestion:

If you have a 5 BHP 7500 RPM engine, take a motor of equivalent power 6 or 7 KW and base speed of 7500 RPM/ This way your normal gear box etc will work, you will be replacing the engine with the motor.

But a fully functional electric scooter will need an Induction motor with VFD and controlled converter for dynamic braking.

Wrong! variable speed is easy, and cheap with a DC motor. Pull your head out of the "cool" mode and look at what is possible with the "old" approaches.

I hate to put a damper on your enthusiasm, but you need a lot of experience and detailed knowledge to build something anywhere near useful.

A starter motor from a car is not a feasible way to go, why, well firstly the bearings are not up to continual usage, the current requirements are such that it could easily take 400 amps at 12 volts, overheating will become a problem within a few minutes!!!

Motors for electric vehicles of any sort are a highly specialised items, you might be able to make one, but you will need also the use of a lathe and maybe other expensive machine tools.....and the knowledge to use them......

Most electric vehicles are direct drive, with the motors in the wheel hub(s), they do not need to waste power in a gearbox. Where the engine and gearbox are now, you will need as a storage space for batteries.

The electronics need to be very refined, if possible also recovering electricity back to the battery when braking or going downhill, to allow maximum distance.

Lead acid batteries are not very efficient, only about 70% if I remember correctly, so other more modern (and far more ) expensive types will be needed if you want something that has reasonable performance in both speed and distance.....

You have not picked a simple job, but at least the motors can be bought on the internet.

Best wishes.

Given below is This is the specification of an electric scooter available in market.

Your petrol engine driven scooter also will look from outside exactly similar.

Now check the major difference from petrol engine.

1.Battery: 48v/38ah silicone

2.Motor power: 1500w

Let us consider that you can use your existing transmission and gearbox along with body replacing the petrol engine, carburetter,petrol tank and in it's place fix an electric motor that is readily available in market and battery . Now the modification required will be the motor starting and speed control replacing accelerator assembly & wire and kick starter . All these things are very difficult job but not impossible. If you take it as a challenge you can do it with some investment.

An electric scooter make already available in market

Specification of An electric scooter make already available in market

1500W Electric Scooter with EEC & EPA (HS50QT-17

Electric scooter
Dimension: 1700*555*1170
N weight/ G weight: 115/136kgs
Max speed: <60km/h
Battery: 48v/38ah silicone
Motor power: 1500w
Load capacity: >85kg
Brake: Disk brake FR, drum brake RR
Mileage for one charge: 80km

Do you really think , designing of DC motor is such a simple thing that I can just write hear in few sentences. Even the simple motor design book take 50 to 100 pages to explain the theory of magnetic and electrical design calculations and details pertaining to materials required. To become a designer study hard and get down to the work.There is no shortcuts.

Dear Abraham, should I express my proudness for being a fellow Indian or I am termed selfish by my technical friends from other countries. Yes they are right, in a technical forum/discussion it is one world. However thanks for your technical reply and bit advice given about designing DC motor etc. I do not wish to buy a new electric scooter for my daughter and meanwhile let my petrol scooter junk away. May be in few years I may not be able to find spares LML 150 scooter. This idea has some selfishness that I dont want my daughter roam around whole day taking friends as pillions etc. Address me a Gana or Ganapa.

Hi Gana,

I was really happy when you brought the idea of coveting your scooter from petrol engine to electric engine in CR4 . My LML 150 is also lying idle in my garage for the past six years un used as really there is no one to drive it and I am scared to drive a scooter in Pune as the traffic is so dangerous. But the idea of converting petrol driven scooter to electric engine was very much in my mind way back in 2004 before I disposed my 1970 model Lambretta scooter to a scrap buyer but could not venture in to it because I was too busy and I did not have the required initiative . During those time when price of petrol was shooting up I thought of designing a conversion kit similar to Petrol to gas conversion kits for motor bikes and cars. In those days no one in India dreamt of making an electric scooter. Now there are electric scooters and cars available in Indian market. In Bangalore itself there is an electric car manufacturing factory which is a great success.They are gong for export of their cars to Europe. So technical knowhow and electrical parts are available in India to make your dream project a success. Think of making it a conversion kit for scooters and motor bikes. So do not get disheartened must go ahead with the idea, with motors and other required components which are available in Indian market.You do not have to design a motor for that purpose. If successful you can even get a manufacturer to buy your product to manufacture it commercially.

Dear Abraham thanks a lot for the inspiring words. May be we can work together on this by exchanging ideas. I wish to start this work in the month of March and will try to collect as much info as possible before doing the practical part.

See the Models of electric scooters available in market for your guidance

http://www.made-in-china.com/showroom/chengjinzhong/product-detailyqemjUJlaQDP/China-1500W-Electric-Scooter-with-EEC-amp-EPA-HS50QT-17-.html

If you are really interested to design a DC motor read the link and find weather you can make out something from the links below and search in Google to get lot more reading materials which are ailable there, before starting your project. Best of luck

http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee3/bdeee3_5.aspx

http://lancet.mit.edu/motors/motors1.html

I think reply #6 is the best start you can have.

Check the power manufacturers use first, then go from there to build your motor, or better to source it from somewhere (electrical appliance scrap, etc).

good luck.

I have no intention of disappointing you but if you want to make something that's worthwhile the effort the tech you need to put in is something a hybrid car has.

Use a specially designed motor or a car generator and work on the electronics to turn it into something useful! Later you could rewire the generator to get the best out of it, may be with not much better result.

With this arrangement you could get energy returned in battery during braking if the electronics is designed like that.

e-bike wheels with BLDC Controllers are available in markets You just need to replace rear wheel with it. And scarp all gear box's etc.

GA from me!!