"Also the control of such thrusters can be wasteful
depending of
>the
>electrical configuration of the motor (i.e.. 3
phase brushless
>motors, or
>straight DC motors). Is anyone using
PWM to control their
>motors?
Anyone
>using brushless motors?"
I've for some time, have watched the
development of a new type of electric motor, called a Thin Gap
motor.
http://www.thingap.com/
http://www.thingap.com/technology/tgadvantage.htm
This company had developed a special motor for
a ring thruster meant to be used in the air. Since I'm interested in ring
thruster designs in general, I looked into this company. They have some great
electric motors that should make your given power supplies last longer.
Here is a quote from there site.
"The innovation of OEM products made possible
through the use of ThinGap motors is growing substantially month by
month. When your competitors begin offering longer life between battery
charges, higher torque in handheld power tools, and ultra smooth operation,
chances are there?s a ThinGap motor inside. Our motors are used in a
wide range of applications that require high power output in a small package,
high efficiency, high power-to-weight ratios, non-cogging operation, high
continuous and peak horsepower and torque.
Our patented electromotive coil technology is
changing the paradigm for brushless and brush motors and generators.
Your products become more powerful, efficient, responsive, controllable and
precise. Our technology enables your products to pack more power in a
smaller package that weighs less then a conventional
motor.
By replacing the iron core and wire windings of
conventional motors with a precision machined copper sheet, we have eliminated
such issues as hysteresis, cogging and iron losses, while substantially
reducing the impact of eddy currents and back emf. The copper sheets
allow higher copper density and a higher copper to total volume ratio,
creating a very high power density motor.
Our motors deliver a wide range of speed and
torque; and generate less heat and electrical resistance. These cool
running motors have a wide operational bandwidth and surpass conventional
motors in almost every benchmark.' End quote
I like the idea.....unfortunately most builders
wouldn't want to invest in these motors for a regular dc brushless motor (3
phase) would also save a huge amount of power.
For controlling these motors and other systems,
here is a very interesting link for motion control devices.
http://www.a-m-c.com/
I have a friend that installs and
works on computer controlled electric stepper motors for manufacturing
machines. From what he's told me, the stepper motors can be controlled very
precisely, and that they use allot less energy as well. I will ask him how and
if, a small or large stepper motor could be used to control thrusters,
compressors, high pressure pump motors for VBTs and sump needs, as well as
other control surfaces. Since they can go forward or back in precise amounts
there could be some good applications for them. I'm going to see if any of the
Thin Gap motors can be used as stepper motors to further increase there
efficiency.
They are basically a stepper motor.
The main difference between a stepper and a brushless dc motor is the amount
of coils made into it's casing(well there are actually many more things
different.....but for this discussion, it's not that important). A stepper
mostly has four (sometimes 6)windings to propell the armature around. This
means each winding is engergized in sequence to make the armature turn( always
pulling). Once you have reached number four(six) you just start over. To make
it turn backwards you energized the windings in reverse sequence. A stepper
motor moves only so many degrees per coil energizing. Some can be as low as
1.8 deg per step. This is where the problem lies with steppers, there is a
maximum speed at which you can drive a stepper (with any amount of torque)
without a huge amount of amperage to energized the
windings.
A brushless motor on the other hand
is built different internally. The motor is designed to make a revolution with
only three coils being energized. But they are phased. They are actually meant
to be powered with positive and negative power. One winding pulling,
another pushing(at any given time). This is why they are so effecient. They
can also achieve much higher torque loads and higher speeds. The controller
actually does the splitting of the power and controls the pulse phasing, hence
the reason the controllers are so expensive.
"Flying surfaces(dive
planes/rudder):
>
> This is the
area.....I'm especially interested in. I've gone
>through it
>in
my head....and an electrical actuator would be my first choice to
>control
>the dive planes/rudder. The failure of the through hull
is less
>likely to happen with a stationary item. The control
coordination of
>the
>actuator would then become a problem. The
actuator would need to
>know it's
>position to be efficient in
it's operation.
Other options perhaps could be some
thing like an electric Lenco marine trim tap actuator to move control
surfaces. I'm not sure yet what kind if any depth rating can be had or
modified to have. But if they control the control surfaces from inside by way
of through hulls it should work.
I was actually trying to stay away
from any thing moving "through hull". The water and air move through
pipes that are stationary, but linkages move through a seal that could fail at
the wrong time. Not that something else couldn't go wrong.....I mean look at
what we are designing here. I just don't like the idea of a moving object that
passes through the passenger compartment hull.
Here is a great quote from
Lenco.
"Lenco Trim Tabs
Powerful,
reversing, low-voltage motor, in combination with the ball-screw provides up
to 500% more usable power with much lower amperage draw (only five amps) then
either of the two best selling hydraulic systems.
Precision Comparison, Electric Vs.
Hydraulic
Lenco Trim Tabs are powered by a
single wire from the helm. Synchronization is precise.
Hydraulic Trim Tabs require pumps,
hoses, and fittings that are susceptible to leaking. When a hydraulic leak
develops, the tabs will drift. This requires constant repositioning.
Hydraulic synchronization requires same length hydraulic lines. Heavy amp
draws puts additional demands on the boats electrical system. Fluctuations in
a voltage occur as a result of heavy amp draw.
Lenco Trim Tabs lock in position if
they should ever loose power. They can't move or drift. The self-locking ball
screw keeps tabs from drifting or pulling under when backing down. With
hydraulic trim tabs, a major leak can result in a sudden, rapid movement of
the tabs. This can seriously effect a boats operaion, especially in a turn,
and can even cause a boat to flip over. Hydraulic trim tabs are known to drift
of pull under when backing down."
Here are some pics I took a couple
of days ago, of an interesting propulsion arrange on a home built steel
boat. They used Lenco trim taps, MotorGuide Machete weedless props, and what
looks like a saltwater type Minn Kota like the Riptide ST
motors.
http://www.frappr.com/?a=viewphoto&id=2628470&pid=7077049
http://www.google.com/search?hl=en&rls=com.microsoft:en-US&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=motorguide+machete&spell=1
http://www.cabelas.com/cabelas/en/templates/pod/horizontal-pod.jsp?_DARGS=/cabelas/en/common/catalog/pod-link.jsp_A&_DAV=netcon&rid=&indexId=cat400009&navAction=push&masterpathid=&navCount=3&parentType=index&parentId=cat400009&id=0044153
Hydraulics could be used....but then
we have to worry about the
>possibility of environment contamination.
Pneumatics are also
>available.....but even harder to control with
respect to position."
The yellow 50 passanger Voyager
Subs built in Seattle and then sent on to Hawaii, used peanut oil
for all ther hydralic fluid, to protect the environment and the passangers in
case of a leak. I don't know how well it lubricates the hydralic systems or
how often if needs to be replaced, but I can find out from Sam Brown who was
the main guy in charge of building Voyager I and II.
Hmmm.....peanut oil, I know it does
have some lubricating properties, but I'm not sure how much. That is a very
interesting bit of information.