[PSUBS-MAILIST] Brushless thruster test

Sat Jan 30 17:54:12 EST 2016

Cliff,the prop is a 3 blade 7&1/4" x 4" pitch off a yamaha 2hp motor.The motor diameter is 63mm diameter x 74mm long (called a 6374) about 2&1/2'' x 3"About 3hp specs below.Turnigy Aerodrive SK3 - 6374-149kv Brushless Outrunner Motor

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| Turnigy Aerodrive SK3 - 6374-149kv Brushless Outrunner...Turnigy Aerodrive SK3 - 6374-149kv Brushless Outrunner Motor |
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To measure the thrust I designed a wooden apparatus that fitted to the steps of my nephews swimming pool.It is a beam that extends horizontally out over the swimming pool & has a vertical member going down in to the poolthat is hinged at it's half way point. At the bottom of the vertical member the thruster is mounted, & at an equaldistance above the hinge is an eye bolt for connecting a cable to some electronic scales. There is another eye boltnear the start of the horizontal beam & the scales are suspended between these two eye bolts.In my set up I can only measure forward thrust.Before I made the housing I did an initial test with no housing & just bolted the mounting bracket that comes with it to a similar test rig. It had lots of grunt despite the fact it was submerged as is, in fresh water. I had a little bit of rust on the magnets afterward & I think some crc would have helped.   If you want to get technical on the test, here is a good paper.http://www.tahoebenchmark.com/pdfs/2009/DPVBollardPullv2.pdf
   Some of my calculations on propeller size & motor hp were based on results from online propeller calculators.https://www.vicprop.com/calculator.htmbut the inputs referred to boats not subs so not totally accurate.  I was looking at variable pitch propellers yesterday & wondered if there would be any benefit considering thesmall speed range we operate at.  I was googling to try & find out the bollard thrust results for the 101, because I am not beleiving what they say.I have a theory that the Minn kotas are over sized to deal with the heat that builds up inside the can. I wouldbe interested in your results.Am pretty convinced that brushless & oil compensated is the way to go. If you grind metal hard out & it heats upyou can cool it instantaneously with water but if you leave it in air it takes a long time to cool. There is always an airgap in a motor between the magnets & rotor, but large gaps at the ends of the coils (front & back of motor) so oilcompensating would be a lot easier on the motor. Brushes can have problems lifting in oil, so the brushlessoil compensated motor seems the way to go.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, January 31, 2016 10:55 AM
 Subject: Re: [PSUBS-MAILIST] Brushless thruster test

Alan your thruster is coming along.  What is the pitch of the prop that you are going to use?  It is a little hard to tell the size of the unit from the pictures.  What is the prop diameter and what is motor diameter?
I am working with some engineering students on a new variable pitch prop for my boat.  They have also built a test rig to measure the bollard thrust, rpm, current and voltage of the thruster.  Hopefully in a week or so we will get some testing done a a MK-33 prop that goes with the MK-101 lower unit.
How did you measure the thrust on your thruster?  How did you calibrate the test rig?  What kind of duty cycle is this motor rated for?  What do think the final HP will be for your thruster?
Thanks for sharing your work to date on the thruster.
Cliff
On Sat, Jan 30, 2016 at 12:43 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hank, Tim.With a load on it should be about 1300 rpm.It was leaking just sitting in the pool. When I got homeI poured a low viscosity oil in the wire entry & it just flowedout the seal. It is quite a learning experience. There are some big gaps in my understanding of the maths of what is going on.I am getting a 1500W sensored motor with low kv & an operational voltage of 44Vmade up for me. The motors I have are sensorless & it is hard to find a goodspeed controller with reverse for sensorless motors.Alan

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Sunday, January 31, 2016 7:08 AM
 Subject: Re: [PSUBS-MAILIST] Brushless thruster test

Alan,That motor looks pretty nice!  I still think rpm is your enemy, seal wise.Hank 

    On Saturday, January 30, 2016 9:20 AM, T Novak via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Thanks for the update, Alan.It looks like your research is coming along quite well.Tim  From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Alan James via Personal_Submersibles
Sent: Saturday, January 30, 2016 1:47 AM
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Subject: [PSUBS-MAILIST] Brushless thruster test  I had an initial pool test of my brushless thruster yesterday.Thruster is on projects page http://www.psubs.org/projects/1235435392/brushlessthruster/A bit of a mixed bag. Firstly I was testing it on 36-37 V & not 44 that it was designed for,due to size restrictions on import of Lithium polymer batteries. I will buy the additional voltage.   I was getting 5kg (11lb) thrust off 150W & 10kg (22lb) off 515W, which is comparable &better than some commercial direct drive BLDC thrusters that I have specs on.However I got to 13kg thrust & the propeller seemed to slip at that point & even though it was running at 2,200W I wasn't getting any more thrust. I was only a couple of feet out from the pool edge when testing, so that could be contributing.Another factor could have been that the seal leaked badly & the motor was short circuiting through the water. Why did the seal leak? Possibly I damaged it hammering it in to it's housingor because I didn't polish up the propeller shaft. I have other motors I will be testing, so a lot more work & learning to do on this one.I did notice I had the same problem as  Cliff, with the motor wiring starting to wear throughwhere it comes out of the housing.Cheers Alan
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