Shawn,
You have asked way many more questions than you realize. As I don't
expect you would understand compete and accurate answers, I will post
short answers in line (I hate doing this). The only other solution
would be to lend you to you the text books from the electric machinery
courses that I took.

Shaun Van Poecke wrote:
just some general questions here to try to get my head around DC motors....

is there a direct relationship between max RPM and torque for motors of the
same wattage?
No, not maximum, but there is for rated load.

ie. if you have 2 ungeared motors that both draw 500watts and
one has a max 300RPM the other has a max 1000RPM, will the 300RPM motor have
more torque?
If the 300 & 1000 are rated load speed then the one will produce three
times the torque at its rated speed. (speed*torque/5252=hp)

is maximum pull really available from zero RPM?
That is motor design dependent. A series motor can provide a torque
curve that is this way. Traction motors used on locomotives are this
built that way.
many people say this, but my experience with small DC motors
(cordless drills etc) doesn't point at this being true.
Does the nature of the controller have an effect?
No, the battery stack falls on its face and lets the motor power off.
Don't try this with a good cordless drill, you will hurt your hand.

can all DC motors be wired up in reverse to go backwards?
By and large - yes, but because miniature motors are missing lots of
windings, most are designed to run in one direction

Are they really a 'free voltage' device, can i use a 12VDC motor with 24VDC,
or a 36VDC motor with 48VDC? am i shortening the life of the motor by doing
so? some motors that i have seen specify operating voltage from say,
48-144VDC....
DC motor design gives little consideration to operating voltage. The
internal design is all based on ampere-turns. If you run a 12v motor on
24v it may run faster and have a higher power output, but it may not be
able to accommodate the thermal load and over heat. If you have seen a
motor with a rating you mention, it is a variable speed motor and
actually designed for the maximum source voltage listed.

For two motors of the same given rating say, 500W, if i have a 24VDC and a
48V motor, will they actually have the same operating characteristics?
That is motor design dependent.

Will the 48V motor have more power than the 24V one, even though they
consume the same amount of power?
NO

Does current draw remain the same as the voltage goes up, or does it drop?
That is completely dependent on the load that the motor is driving

Some manufacturers say that as the voltage goes up,
so does the HP... ie. 8hp@48V, 12hp@60V etc etc....
Remember the ampere-turns thing??

is one specific type of design more efficient than any other?
Permanent magnet field motors are generally more efficient as they do
not use supplied power to create the stationary field.


Thanks,
Shaun

I don't know what you are planning to try to do, but I suggest that you
learn a lot more about electric machines before you spend much money on
anything. If you get a motor that has a different rating than you
believe you need, do not count on being able to push the curve and make
it work.
Good Luck Guy
Matt Colie