draw, thrust, and components

Anything to do with Propulsion.
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scubersteve
Posts: 251
Joined: Jan 28th, 2013, 10:29 pm
Location: Milton, Florida

draw, thrust, and components

Post by scubersteve »

I think we need a thread where people can post their thruster specs all in one spot.
Tell/show us what you built maybe even with part numbers if so inclined and post the draw and thrust specs.

I am trying out a new thruster design and am building a test tank so I can quantify results.
However it occurred to me that no matter what numbers I get I wont know how good they are until I have something to compare them to. Anyone just starting into a build could benefit from such data.
I'll post mine here as soon as I get my tank finished... I would love to see other people's numbers here too.
Please feel free to add your data and part numbers to this thread.
I believe it can benefit us all.
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Last edited by scubersteve on Nov 17th, 2013, 11:15 am, edited 1 time in total.
scubersteve
Posts: 251
Joined: Jan 28th, 2013, 10:29 pm
Location: Milton, Florida

Re: draw, thrust, and components

Post by scubersteve »

so I'll go first...
So from left to right we have...
A hextronik dt700 with a GWS 64mm edf rotor.
It put out:
16 oz thrust @ 3.2 amps
25 oz @ 8.2 amps
It would draw more if I kept feeding it but the thrust output didn't increase which tells me a bigger prop is in order.

The next one is a AX2308N 1100kv with a no-name ebay 53mm rotor (item #321020534177)
It put out:
9 oz @ 3.1 amps
13 oz @ 5 amps
20 oz @ 11 amps where my ammeter cuts power because it is only rated at 10 amps.

When I switched to the GWS 64mm rotor on the AX2308N it put out:
11 oz @ 3 amps
14 oz @ 5 amps
21 oz @ 11 amps

The last one is a brushed 12v automotive washer pump motor modified to take one of the 53mm ebay rotors.
It put out:
4.3 oz max no matter what up to the 8 amps it draws if connected directly to the 12v battery.

All tests performed @ 12v. Brushless motors powered by a hobbyking 30 amp car esc controlled by a servo tester.
Test tank is 12x20 inches filled to 6 inches deep. Motor thrust line and scale attachment point are equidistant from pivot point so no calculations of thrust are required. Scale is a cheapie ebay luggage scale and ammeter is a harbour freight DVOM with a 10 amp limit although it doesn't actually cut out till about 11.25 amps.

Plrase feel free to add your test data and part numbers to this thread.
I look forward to seeing what you come up with.
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Last edited by scubersteve on Nov 17th, 2013, 11:17 am, edited 2 times in total.
duncan
Posts: 22
Joined: Nov 6th, 2013, 5:43 am

Re: draw, thrust, and components

Post by duncan »

This may be a dumb question but how are you setting up test tanks to measure the thrust?
a_shorething
Posts: 289
Joined: Sep 10th, 2013, 5:26 pm
Location: New Jersey Shore

Re: draw, thrust, and components

Post by a_shorething »

This thread is a great idea. I think it's going to at least give a ballpark estimate of what people can expect to see and determine what they need based on some kind of background instead of just doing the same tests over and over again that others have done.

While it's probably impossible to make identical rigs and eliminate every single variable that could be introduced by having different people attempt to do the same tests, there probably should be some description or definition of what makes a 'test'.

I think most people are testing in a 'tank' which is typically a tub with water in it and a thruster attached to some kind of arm that extends up out of the water to a force measurement device.

Alternately I just saw njs552 posted one that used an arm pulling on a force meter (a great jig, just different).

Some things that may affect the setup off the top of my head are:
1. The two parts of the lever arm should be the same distance from the pivot point or you need to show your math for how you arrived at the final result (if one arm is twice as long you need to divide or multiply depending on which way the force is going...)
2. Gravity should be eliminated from the calculation so measuring a force where one arm is horizontal and the other is vertical you should ensure the measuring device is zeroed out and that you compensate for the fact that the horizontal arm will be helped by gravity pulling down for the test, but not in a real situation.
3. Swirling: I think if all of the tests are done in a tub, the size of the tub should be listed because once the motor starts moving you are setting up a water 'circuit' that will help push the thruster. For most people a large enough test tank (like a pool or lake or whatever) is not an option but a small test tank will give readings that include the force of swimming 'with the current' if you will. It will be as if you're measuring the force of someone paddling a canoe downstream from shore instead of in a lake. The amount of 'pull' with relation to someone on shore will include the force that the river is exerting on the canoe relative to the shore as well.

I suggest all tests should include a description of the test equipment used so if someone is testing a different way or wants to compare them he can. This should include a description of the volt, amp, and force measuring devices in addition to a description of the testing procedures. It doesn't have to be longwinded or really detailed, just:

Tub test: Fluke Digital VOM meter, 15 gallon test tub, using 90 degree arm and digital scale. Distance from thruster to pivot point and pivot point to scale is 80cm...

EDIT: this is the test jig they are using at OpenROV:
Image
Last edited by a_shorething on Nov 19th, 2013, 10:20 am, edited 1 time in total.
scubersteve
Posts: 251
Joined: Jan 28th, 2013, 10:29 pm
Location: Milton, Florida

Re: draw, thrust, and components

Post by scubersteve »

An excellent point on specifying the test equipment.
I have edited my post to include that information.
njs552
Posts: 61
Joined: Jun 10th, 2013, 6:22 pm
Location: Sacramento, CA

Re: draw, thrust, and components

Post by njs552 »

Hi, njs552 here, and I thought I should move my results into this thread so they are all in the same place. Great idea!

Motor setup:
NTM Propdrive 750: http://hobbyking.com/hobbyking/store/__ ... _140w.html
with a 43mm aquaprop: http://hobbyking.com/hobbyking/store/__ ... x9mm_.html

This combination produced about 4.5-6.5 newtons of force, so about 1-1.3lbs of force, 16-22oz, with 1.12(18oz) as the average.


There were 2 different test setups, one with a 1:1 arm that lifted a weight off of a scale, and the other was using a force meter.

I went with the scale first because that was all I was able to find. I am not sure how accurate the results were because the weight was off to the side of the scale, and there was a lot of friction around the rod (see video). After I finished that test I got a force gauge and found a PC with the right software. This was far more accurate because the motor stayed vertical, and did not move around as much as the scale test did. However, both tests were almost the same, with about >500g thrust measured with the scale, and ~5 Newtons measured with the force gauge.

Test tank dimensions are 19"x13", with about 7" of water in the tank. See the video below for more details.



Please let me know if you have any questions or if you think I should change some part of that setup.
Thanks,
njs552
scubersteve
Posts: 251
Joined: Jan 28th, 2013, 10:29 pm
Location: Milton, Florida

Re: draw, thrust, and components

Post by scubersteve »

I turned over my thruster test rig to the student rov team I'm mentoring and they tested an old thruster off of last year's entry. It is a 500gph bilge pump motor with a very large (I'm guessing around 75mm) two blade boat prop.
Connected directly to 12v (which is the way they ran it last year) it drew 4.6 amps and produced 13oz of thrust.
They then tested my dt700 and got the same results that I mentioned in my previous post.
I believe they will be switching to brushless on this year's build.
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a_shorething
Posts: 289
Joined: Sep 10th, 2013, 5:26 pm
Location: New Jersey Shore

Re: draw, thrust, and components

Post by a_shorething »

scubersteve wrote:I turned over my thruster test rig to the student rov team I'm mentoring and they tested an old thruster off of last year's entry. It is a 500gph bilge pump motor with a very large (I'm guessing around 75mm) two blade boat prop.
Connected directly to 12v (which is the way they ran it last year) it drew 4.6 amps and produced 13oz of thrust.
They then tested my dt700 and got the same results that I mentioned in my previous post.
I believe they will be switching to brushless on this year's build.
<><
Ha ha, sweet. I'm curious though, did they find that they felt they had enough thrust to move about and maneuver before? If so, what was the size and weight of the ROV and the configuration of the thrusters? I'm trying to get a sense for what is 'enough' and what is overkill (of course I want overkill, I just don't know if I need to hit 11lbs of thrust to be at that point, or if 4lbs of thrust per thruster will be more than I need). :)
a_shorething
Posts: 289
Joined: Sep 10th, 2013, 5:26 pm
Location: New Jersey Shore

Re: draw, thrust, and components

Post by a_shorething »

I thought I'd post the OPENROV results here too since, well, that's why they call it OPEN ROV, right? :)

I didn't see anything about the actual motor they're using. The test was to see how different props would work in their already chosen design.

Here's the complete write-up:
http://openrov.com/profiles/blogs/preli ... cy-testing

Here's their plot:
Image

They did it in grams, and it looks like to me that they hit 1200 grams at 6.8 amps.

1200 grams=2.64lbs of thrust.

Image
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olegodo
Posts: 222
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Location: Bergen, Norway

Re: draw, thrust, and components

Post by olegodo »

This is the link to the motor they use for the OpenROV.
Info taken from their BOM list.
http://www.hobbyking.com/hobbyking/stor ... oduct=8622
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