I want to build an electric go-kart for my children, to help them
learn about mechanics and electricity, and to have fun.  I want to
build the frame out of wood, instead of welded metal, to let the kids
do more of the work.

I know very little about electric motors, and need some expert help.

I want to power the go-kart with 1 or 2 12V car batteries, and I want
to use a commercially available, common motor, not surplus or junkyard
material (for easy spares, etc).

Can someone help me with the following questions:

(1) Where is my best source for electric motors that meet my goals
above?  Is there a mail order catalog?

(2) DC or AC motors?

(3) What particular model motors should I consider?  Order numbers?

(4) How do I control the speed of high-wattage electrical motors? 
What type of motor control electronics do I need to build or buy, in
order to control the motor speed, etc.  Where can I learn what I need
to know about power control for electrical motors?

(5) Given the power required to drive these motors, what sorts of
critical electrical or thermal design issues will I face?

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Clarification of Question by bkft-ga on 29 Mar 2005 13:45 PST

just4fun2-ga has thoughtful suggestions about gas engines, but I
really want to use an electric motor.  The point of this project is
not really to build a go-kart, but to teach the kids a little about
electricity and electric motors and power as part of a fun project.

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Request for Question Clarification by jbf777-ga on 29 Mar 2005 15:05 PST

bkft -

Thank you for your question.

I believe I found the source for the information you're looking for,
and it probably will address other future questions that could arise. 
However, it's about $20.  Would you like to decrease the price of this
question to $80, and I can post this source as an answer?

jbf777

---

Clarification of Question by bkft-ga on 29 Mar 2005 16:09 PST

jbf777,

That sounds great.  But, two clarifications first:

(a) I already purchased plans from "GA Products", an Australian
organization for an electric/wooden go-kart, so I don't want that.

(b) I would really like to understand the basic concepts behind
electric motors and the power control (item #4 in my original
question), and sources of electric motors (item #1 in my original
question), so the kids and I could build other electric motor projects
in the future.  If these are in the source you found, sounds great! 
But if this $20 source is just a "how to build a wooden go-kart" plan,
which doesn't address #1 & #4, I'll probably still be a little stuck.

Thanks!  Look forward to what you found!

Hello -

Thanks for the clarification.  I have researched further and found
different sources for information than I originally mentioned.  If you
need any clarification, please don't hesitate to ask.  Thank you.

The first question that needs to be addressed is that of your use of
"DC" vs. "AC" power.  In this application, you will be using DC power.
 Batteries, fuel cells and solar cells all produce Direct Current in
one direction.  The positive and negative terminals of a battery are
always, respectively, positive and negative.  Current always flows in
the same direction between those two terminals(1).

Learn more about AC and DC here:

(1) Direct Current vs. Alternating Current
    How Stuff Works
    http://science.howstuffworks.com/electricity7.htm

Your go kart will work very much like an electric car.  The
electricity from your battery source will flow through your
accelerator/pedal system, which will be attached to a potentiometer
(variable resistor).  As the pedal is pressed or released, the amount
of electricity sent to your motor (via its controller/drive) is
varied, and the corresponding speed is increased or decreased
respectively.

These above principles are excellently outlined and illustrated at a
different section of the same website above:

(2) Electric Cars
    How Stuff Works 
    http://auto.howstuffworks.com/electric-car2.htm


The same website has a section on how electric motors work:

(3) Electric Motors
    How Stuff Works
    http://electronics.howstuffworks.com/motor.htm


I think any DC motor above 2 HP would be appropriate for this
application.  Here's a pricelist of various horsepower motors from a
company called "Electric Motor Warehouse" that predominantly sells
electric motors:

Price List
http://www.electricmotorwarehouse.com/DC_motor_menu.htm


Here's another company selling a variety of motors:

Temco
http://www.electricmotorsale.com/


Typically the reference manual of a motor/drive should provide you
with technical details as to what requirements are necessary to
interface with it.  The manufacturer's technical support should also
be of assistance.  They will be able to provide you with direction as
to what thermal and electrical design issues you should be aware of,
as this may vary depending on the motor.


A company named ETI Systems makes several types of foot controllers
with potentiometers built in.  This may be something worth
investigating:

http://www.etisystems.com/footselect.asp


A consummate resource for all sorts of equipment that might be
relevant to your project is the Thomas Register.  Simply enter in the
product you're looking for, and the service will return manufacturers
specializing in that product:

http://www.thomasregister.com





Additional link:
  MFG Supply (Go Kart parts)
  http://www.mfgsupply.com/m/c/index.html?id=jLDv7rhi


Select search strategy:
  electric motors prices
  foot potentiometers

Decent answer to a tough question, along with interesting references
to parts suppliers.

Some of the answers were superficial (the AC/DC answer in particular
--- I know that several people recommend AC-DC conversion, though I
don't know the tradeoffs).  Also, I'm not 100% sure the suggestion
about resistive potentiometers will work for high-amperage motor
drives (too much heat loss), so I might need some kind of motor
control/power amp system, but I'm not sure.  No pragmatics about
thermal design.

However, the vendor references are great starts.

Not a total solution to my project, but some good leads I wouldn't
have already found.  Thanks!

This would be a lot easier with a small 5hp gas engine.  But, you
might consider using a starter motor.  On/off switch.  Run the output
to a set of different size pulleys.  Run belts between the pulleys. 
Have three or four clutch levers that tighten the belts for different
speeds.

Hi,

I've just come across this thread.

A central element in any efficient electric vehicle is the motor
controller, this is the electrical device which takes the nominally
fixed voltage output from your batteries and, in accordance with the
demand signal from a foot pedal or thumb lever, produces a variable
voltage supply to the motor(s). This is how speed regulation is
usually achieved. There are several manufacturers of these relatively
inexpensive solid-state bits of electronics but one in particular has
a very informative web site at www.4qd.co.uk - they sell directly to
individuals aswell as companies and the online info is provided to
help individuals understand and apply the technology. Very worth a
look.

My interest in electric vehicles can be seen at
www.buggies.builtforfun.co.uk - this isn't a sales pitch just an
encouragement to persevere - EV's are a lot of fun, quite and clean
once you get them going.

Good luck!

ianhopper-ga is correct.  You need a motor speed controller.  They
will sit between the battery and the motor, and have some simple
control circuitry.

the way they work is to turn the motor on and off very fast.  Imagine
just having a on/off push button, and using that to control the speed.
Now, do that like 10,000 times per second.  if you want more speed,
the motor is on more than it is off.

here's a more thorough description: http://www.evparts.com/faq/show.php?id=58

To select one, you need to know what voltage and current.  to do that,
you need to size the motor.  I'd recommend looking at the electric
bicycle web sites for a controller. those should be about teh
size/capacity you want.

You do know basic voltage and amp notation, right?

for reference, a car starter can run at like 200A, with a inrush peak
of 400-1000A.  you'd need a full size truck battery and you wouldn't
go very far,
but you'd go really fast! (as long as the restof the drive train could
hold together under the stress)  car starters are common among
"shopping cart drag racing" http://cmeyers.boilerbots.com/chair.html

In general, I'd say that you should do some research on electric
bicycles and cars, and that will give you a pretty good idea of what
to expect.

ianhopper/rightsock, thanks for the tips.

My next challenge will be to figure out the drive train.  I imagine I
will want to do some kind of belt/chain drive insread of direct drive,
but I'm not sure how best to engineer this...

Thanks for the help.  I'll hopefully nail the motor choice soon.