[PSUBS-MAILIST] Brushless thruster test 2

Sat Feb 6 17:29:55 EST 2016

Thanks Alan.  To reciprocate, attached are our initial test last week.  The
variable pitch prop is not out of the machine shop yet so main goal was to
evaluate test rig with Minn Kota MKP-33 prop ( two blade, 4" pitch, 11"
diameter)  that matches with the MK-101 lower unit. We are going to use the
MK-101 and MKP-33 prop as the control for our new prop.  We also tested a
Kipawa 80/01 (3 bladed prop, 5"pitch, 11" diameter).  The Kipawa prop will
fit in my ducted nozzle so measured the bollard thrust with and without the
nozzle.  We are still analyzing the data but some initial results.  Bollard
thrust of the MKP-33 of 67 lbs is low relative to the 101 lb rated thrust.
A quick look on web shows that manufacture thrust rating are 30-40% higher
than a bollard thrust test.  Test rig is fully calibrated.  With the Kipawa
prop, the bollard thrust is about 10% higher when using the nozzle than
without.  BTW, this is an open water prop and is not designed to be used
with this nozzle. A ducted nozzle prop needs to have more of a square tip
to keep water from moving from the high pressure side of the blade to the
low pressure side.   Like you my initial reaction is that we could be
having the same boundary or end effect because of the proximity to the pool
wall.  We did prove the system worked. Not sure why both rpm and current
are dropping over time when the measured battery voltage is constant?
 Next week, we are going to repeat the test with the thruster oriented
along the long axis of the pool and see how the thrust compare.

On your test, a couple of questions:
1) How long did run each test point?
2) On the first test sequence, 3800W and 81 lbs bollard thrust for input HP
of over 5.  This seems like quite a bit of power to develop this amount of
thrust. Do attribute most of this to this boundary effect or recirculation
affect?
3) On each of these test points, your are stepping through higher and
higher power to the thruster.  For any one of these points, how repeatable
is thrust?
4) Thrust is proportional to density * n^2*Dia^4.  I think to be able to
make sense of data from different props with different diameters and
pitches, you need an angular velocity or speed measurement.  Can you
measure the motor speed with this type of motor.  For our test we use a
proximity switch and count pulses to measure speed.
5) Are you planning on testing any ducted props?

Cliff

On Sat, Feb 6, 2016 at 2:41 PM, Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

>
>
> ------------------------------
> *From:* Alan James <alanlindsayjames at yahoo.com>
> *To:* Personal Submersibles General Discussion <seaquestor at gmail.com>
> *Sent:* Saturday, February 6, 2016 11:18 PM
> *Subject:* Brushless thruster test 2
>
> This is mainly for Cliff's benefit, as he is going to be doing some
> thrust testing.
> Tested 2 different props out. One being the same as the first test, the
> yamaha 7&1/4" x 4" pitch
> & the second was a Vetus 6 blade 108 mm ( 4")  for 25kg bow thruster. No
> stats on the pitch but it
> looks about 180mm or 7".
> My watts measurement is done off the battery whereas other people quote
> their output at the motor.
> I am comparing my motors performance to statistics from commercial
> thruster brands but not sure
> where they are measuring there power from.
> Had some wacky results from the yamaha prop again. It was the more
> powerful & I think I am getting what
> is called a "short circuit" effect through having the motor about 28" out
> from the pool edge & in about 3ft
> of water. Short circuit is where an edi is formed & the water moves from
> the output to the input in a semi
> circle around the thruster. This is caused by water bouncing off a pool
> wall, or in my case the inlet flow
> bouncing off the wall or pool bottom.
> I was running off a 40V 5 amp  Lipo battery & the voltage dropped a bit
> during the tests.
> Ist test was 10 kg (22 lb ) at 500 W
> 2nd 11 kg at 1000 W & 39 V
> 3rd 15 kg at a huge 3,400 W
> 4th 37 kg at 3,800 W & 85 amps.
> As you can see some inconsistent results there, and some missing figures
> like amp draw, as I needed
> an assistant to read the figures.
> Next is the Vetus prop.
> 1st 10kg  547 W  39 V
> 2nd 11 kg  634 W  11 amps  37.81 V
> 3rd  15 kg  998 W  27 amps
> 4th  20 kg  1700 W  39 V
> 5th  24 kg  2500 W
> It's amazing what a difference a prop makes.
> In conclusion, I need to ditch this rig & buy a longer plank of wood to do
> tests in the middle of the deep end.
> I have a more sophisticated volt / amp meter that stores results & plots
> on a computer & I need to employ that.
> I need to buy a similar motor but a sensored version, as there was too
> much cogging at low speed.
> Sensoreless motors read the back emf produced by the motor to ascertain
> the position of the rotors & can stop /start
> & rotate backwards on low speed where there isn't enough back emf produced.
> I need to replace my motor controller with a sensored controller, probably
> Kelly & buy a bigger life po4 battery.
>    I also want to wire the motor to a WYE configuration which will give me
> .73 less rpm. So will gear it down a bit.
> Some good news is I have found people on boating forums adapting these RC
> brushless motors & an absolute
> guru who uses these motors for traction vehicles & has posted pages of
> information on them.
> Cheers Alan
>
>
>
>
>
>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
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