Randy said:
This is an experiment in Torque.
I'm building a motor from a different point of view. Instead of
rotating the coil in a magnetic field, I'm mounting the magnets
(1"x1/8" NEO disks) on the rotor and spinning the magnetic field.
I want to use the coils, mounted in planetary fashion, like spark plugs
in an engine with an adjustable "distributor" (armature) for energizing
the coils mounted on the rotor. When the rotation of the magnets reach
approximately 75 degrees to the coils, The coils (electromagnets) will
energize wrenching the magnets toward 90 degrees but will de-energize
before the poles try to cog on each other.
I think the ideal place the magnets should be with respect to the
coils is that the coil should be exactly half way between two opposite
magnet poles when the coil current peaks. That way, one magnet pole
is pulling toward the coil and one is pushing off it. The coil
current is ideally zero as the magnet pole passes directly beneath it.
If the coils have iron cores that extend toward the magnets, there
will be cogging, just because iron is attracted to a magnet. This can
be reduced if there is a different number of magnet poles and coil
poles. For instance, you might drive a pair of magnet poles with 3
coils. That way, all 3 magnets do not cog at the same time. The
current switching arrangement gets more complicated, though. You
might look into hall effect switches as a means of detecting rotor
position to switch the coil currents. That is the way brushless
motors are made.
At this time, I have no Idea what the RPMs will be so time for me is a
best guess. I'm thinking low milli for about 13 degrees of rotation.
For first effort, since you don't have a speed goal, I think you
should forget speed and try to maximize stall torque per watt of DC power.
The adj. feed is to time for maximum torque and to compensate for my
shortcommings;-)
It is commonly used to advance the coil voltage timing to get the
current peaks where they are needed in spite of the inductive delay,
at rated speed. This is like adjusting the timing on a gasoline
engine to produce maximum power. There is a best setting for each speed.
You should be able to come up with a mathematical expression for
winding resistance versus turns, based on the dimensions of the
winding volume and your wire gauge. Ohm's law converts that to
current. Pick a DC power and you have the current allowed for a given
DC voltage.
Current times turns gives you flux which is proportional to torque.
Combining the ampere turns with the power formula gives you torque per
DC watt.
It should come out that above some number of turns, the coil diameter
is so big that the resistance is going up faster than the flux, so it
may not be best to fill all available space with coil.