[PSUBS-MAILIST] Brushless thruster test 2

Sat Feb 6 19:50:19 EST 2016

Hi Cliff,thanks for the data, am interested in any more you get.I wrote an email on testing with a link to a bollard test set up for a DPV. If you didn't get it I will re-send. I have missed some emails lately.The Vetus prop is a square ended prop designed for nozzles. I didn't tryit with a nozzle. They have a range of props.Vetus, 6 Blade Bow Thruster Replacement Propeller

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I am not sure whether you can get a left & right handed propeller.I didn't run the tests long. I had a smooth start option programmed in to my controllerso it was a bit slow getting to full throttle. As per the instructions in the email link I sited,it is best to get it up to full speed fast before you create a strong flowing current.This is most probably why your amps went down, as the water was initially stationary& then started flowing & lowering the load. Typically a displacement boat can have 50% propeller slip or more soyou could have been doing a bit of a wheel spin initially & getting the revs up, then they might have come downas the current flowed.I am not sure why I got the large 3,800 W & only 81 lb thrust unless something is shorting to the aluminium housingunder load. It could be boundary effect???I have measured the max rpm out of water but can't measure it in water at the moment. That willbe my stage two testing.The thrust results were repeatable on the yamaha prop up to 10 kg (22 lb) & then they seemed to go a bit haywire,so this indicates boundary effects.The 6 blade Vetus prop was more consistant above this, but maximum thrust was 24 kg at 2,500 W.How many Watts were you drawing from the battery to get the 67 lb thrust?I will need to re-think this & order stuff in from overseas & maybe make another housing before I test again.Cheers Alan
      From: Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Sunday, February 7, 2016 11:29 AM
 Subject: Re: [PSUBS-MAILIST] Brushless thruster test 2

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 somethrust 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 itlooks 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 surewhere 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 whatis called a "short circuit" effect through having the motor about 28" out from the pool edge & in about 3ftof water. Short circuit is where an edi is formed & the water moves from the output to the input in a semicircle 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 V3rd 15 kg at a huge 3,400 W4th 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 neededan assistant to read the figures.Next is the Vetus prop.1st 10kg  547 W  39 V2nd 11 kg  634 W  11 amps  37.81 V3rd  15 kg  998 W  27 amps4th  20 kg  1700 W  39 V5th  24 kg  2500 WIt'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 absoluteguru who uses these motors for traction vehicles & has posted pages of information on them.Cheers Alan

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