[PSUBS-MAILIST] Thruster Test

[Alan via Personal_Submersibles]

Hi David,
the extension ladder worked but was a bit of an effort pushing it out
with weight on it. I will grease it before the next prop test.
As for thrust to watt ratio; I measured this at intervals from 18V to 44V.
18.2V, 13.2W per lb. of thrust.
26.8V, 19.5W per lb.
33.6V, 24.4W per lb.
38.4V, 29.9W per lb.
44.6V, 37.6W per lb.
So definitely a loss of economy as you open the throttle. The Vetus prop
is designed to work in a tunnel & I didn't have one on it. It will be interesting 
to see how the other props fare in this respect, & if these figures differ much
when I put a kort nozzle / prop guard on them.
Alan


> On 6/12/2018, at 3:58 AM, David Colombo via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Hi Alan, l never thought of using a ladder as a test rig. Was the thrust to watt ratio the same base at different speeds?
> David
> 
>> On Wed, Dec 5, 2018, 2:03 AM Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> Just did the first test on my latest brushless thruster version.
>> I started with a Vetus bow thruster which is normally housed in a tunnel, but
>> to simplify things I am testing several different propellors without nozzles first.
>> I have a 10mm prop shaft & the various off the shelf props need either drilling
>> out or sleeves made to fit them.
>>    I was getting 38.5 lb. thrust from 1,152 Watts & 45 lb. off 1,694 Watts, which
>> is comparable with some commercial thrusters but not with others. Some 
>> manufacturers are quoting thrust per Watt figures I find hard to believe.
>> Will see how the other props work.
>>    Testing came to an end when the automatic pool cleaner (which I had just
>> moved to the end of the pool) came down & knocked my prop off while I was 
>> jotting down notes. First swim of the summer finding the shaft pin. The prop
>> was held in place more or less by the force of the prop thrust & a tight fit.
>> Picture below is from left to right; load cell mounted on the vertical stationary
>> side of black test jig, motor controller, 48V rectifier with oil compensator on
>> top, grey load cel display, servo tester to control speed & laptop with Vesc Tool
>> program displaying data. 
>> The oil compensator is just for the testing, a much smaller & different system
>> will be on the sub.
>> Alan
>> 
>> 
>> 
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