Fwiw..
Everything affects everything in motion control trains.
This is exactly the same in cnc machine tools, as in caterpillar
earthmoving, as in boats.
By far the most EV boats so far are low-mass, low-load situations, ie
not heavy or large or large-wind-surface-area ocean-going displacement
craft.
Relatively little actual *power* is actually needed to move even heavy
ocean-going craft.
Old rule of thumb was 1/2 hp per ton of displacement - for trading
ocean-going cargo ships. Around 1930 or so.
With pretty inefficient engines, props, hulls.
But pretty robust, heavy mechanical components.
E.
Old train engines had == 100 hp, but very heavy large diesel engines of
3000 kg mass or so.
E.
A human being can easily push/pull/drag a 70 metric tons 24 m steel
vessel, with no-or-low waves/wind.
But any small wind easily overpowers a human being (200W or so).
The best solution, imho, theory:
At the moment, it is easy and cheap to make high-efficiency motors, at
high rpm, and fairly cheap to make high-ratio transmissions for same.
Look at any modern vfd driven washing machine.
Typically less than 1 hp, 1:10 belt drive, 20.000 rpm or so at motor.
Light, cheap, lasts a long time.
Or Tesla cars.
70 hp cont. but at 1:11 transmission, incredible torque and peak power
of 700hp. Just like any (modern) servo drive.
But..
Many of the best motors in the world, today, are direct-drive servos
optimised for 0 or very low rpm, and high accuracy positioning.
These are used in the best, most-accurate lathes in the world, as
direct-drive spindles.
They are also extremely efficient.
Typically 25 kW, or so, output, forever, 24x7x365.
What this means is that high-torque electric motors can be made, they
are not very large, they do not heat up under 100% use.
At the moment, for heavy and larger (16m+, displacement) boats, the
mechanical transmission from ice engines is big, heavy, inefficient,
heats up, needs very large oil volumes and coolers.
The same mostly applies to electric motors today - not because it needs
to, but because most-all motors were made to run at fairly high rpms.
Because it is very easy and very cheap to make powerful electric motors
of high rpm- and 99% of the commercial ie $$ market is there.
Any transmission will work for 1:5, but belt drives are mostly limited
to 1:3, 1:4 at most.
The big-end pulley gets too large, the small-end gets too small with not
enough belt wrap, the belt gets too long, whole package gets too big, on
power-traction stuff.
Washing machines get around this with huge pulleys big end, tiny motors,
tiny small end pulleys and timing belts.
The tesla EV cars do about the same with mechanical gears and clever vfds.
I don´t have a practical recommendation.
My post tries to comment on the sota, costs, of todays
electro-mechanical engineering.
Cost is very material.
E.
I have a very old Bridgeport milling machine head, and original 3-phase
motor.
M-head, 1/2 hp, output, 3-phase.
It is very heavy - by todays standards. 18 kg.
It is very good - even by todays standards.
Likely made 1940 or 1950.
The motor was extremely well made for its day - and was very expensive
to make - then. About 3000$ in todays money.
Probably been used 10.000 - 50.000 hours in the last 60-70 years+.
I use modern ac brushless servos on cnc kit.
Compared to the best-in-the-world old Bp motor:
A 400W ac brushless servo, 60V, 3000 rpm, 5000 count, nema 23, is about
0.8 kg in mass. A drive+motor+cables == 290€ with 24% eu vat tax.
The motor == 140€ no tax.
At 22x less mass, 20x faster acceleration, 100x better positioning, 2-5x
better smoothness.
10-25x less cost.
My general opinion is to use modern motors, bigger, very cheap from used
surplus industrial dealers.
A large modern motor is extremely efficient, even at very low power
output vs peak capacity.
So a 25-50 kW industrial motor, used at 1 kW, might lose 10% efficiency
vs when run at 50-60%.
But it will be barely warm in use, will last forever, and might cost
50-100$.
And will save more than 100$ in transmissions (noisy, space/volume).
I perfectly understand the desire to use "stuff" You have.
I did so, for 10+ years.. until I learned better.
The Bp is a good example - and was an excellent learning opportunity for me.
--
-hanermo (cnc designs)
Posted by: Hannu Venermo <gcode.fi@gmail.com>
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