draw, thrust, and components

[a_shorething]

Sweet setup Bubbles, can you tell us more about your housing and shaft seal? Looks like a professional thruster!

+1

Very nice setup and great numbers. Looks like reverse is quite a bit weaker than forward, but I imagine that's still plenty.

I would really be interested in seeing how it works out for you in operation.

If you don't mind, that looks like quite a pricey endeavor. How much do you think the materials for each motor cost?

How about heating, was there any noticeable warming of the outer housing? I'm wondering if prolonged running at full power will cause a problem (and maybe the solution is as simple as setting up your controls to send 60-70% power and no more like a rev-limiter in a car).

Really nice design! (I need to do the conversion for weight, I have no idea how much 850 gr weighs )



..... about 1.9 lbs each. That's quite heavy, but maybe that just means your ballast is built-in, right?

[Bubbles]

Sweet setup Bubbles, can you tell us more about your housing and shaft seal? Looks like a professional thruster!

+1

Very nice setup and great numbers. Looks like reverse is quite a bit weaker than forward, but I imagine that's still plenty.
True.Reverse is a bit weak.But i think is still ok.
I would really be interested in seeing how it works out for you in operation.

If you don't mind, that looks like quite a pricey endeavor. How much do you think the materials for each motor?
Each thruster cost me about 200€.The price include aluminium,acetal,motor/esc,magnets,lathe.Plus painting which I know price today.

How about heating, was there any noticeable warming of the outer housing? I'm wondering if prolonged running at full power will cause a problem (and maybe the solution is as simple as setting up your controls to send 60-70% power and no more like a rev-limiter in a car).
I didn't notice any heat.At my next test I will use a temperature sensor in the hull to check it.
Really nice design! (I need to do the conversion for weight, I have no idea how much 850 gr weighs )
..... about 1.9 lbs each. That's quite heavy, but maybe that just means your ballast is built-in, right?Correct !

[TigerShark]

I have nearly the same setup as kenl yet my thrust numbers seem to be off by a factor of 10 on the low side. I have an equal length lever arm so I am at a loss to what I am doing wrong. I checked the scale and it is accurate at least in the vertical position. It is the same small digital luggage scale some others have here. I have it on its side so the only thing I can think of is that maybe it has to be on its back. Any ideas?

So I did more testing using 16ga wire and the problem is gone, now I am drawing much less current and getting more thrust. Wire gauge is really important even over these short lengths!

[scubersteve]

I just tested three more thruster setups...
A HexTronic DT700 with a Graupner 2308.65
it put out forward:
14.5 oz @ 2A
31 oz @ 5A
43 oz @ 8A
and reverse was:
9 oz @ 2A
16oz @ 5A

The second one is a Turnigy dst-700 with a 2308.65
it put out forward:
16.5 oz @ 2A
30 oz @ 5A
40 oz @ 8A
in reverse:
9 oz @ 2A
15 oz @ 5A

The third one is my shallow-depth waterproofed Turnigy dst-700 with a 2308.65 mentioned in another thread.
It put out the same specs at 2 and 5 amp as the exposed one so apparently the power loss caused by the drag of the seal is negligible.
The interesting thing is that as I approached 8 amp it would create a whirlpool in the tank and cavitate. I suspect that it is due to the decreased shrouding of the prop by the motor due to the increased distance between them. This should result in better thrust numbers at the upper end providing sufficient water flow can be provided to the prop.

The same test tank setup was used as in the first post of this thread.
I couldn't test above 8A because my ammeter would start cutting out above that.
A 50A continuous wattmeter is on order from ebay.

[olegodo]

Tested this EDF fan as a potential propeller:

EDF Ducted Fan Unit 6Blade 2.75inch 70mm


All @ 12v with the NTM Prop Drive 28-36 750KV

2 bladed prop:
1kg = 6,5 amps
1,95kg = 23 amps (max speed)
Reverse:
0,9kg = 23amps (max speed)

3 bladed prop:
1kg = 5.5 amps.
2kg = 25 amps (max speed)
Reverse:
1kg = 25amps (max speed)

5 bladed prop:
1kg = 8.6 amps
1,8kg = 27amps. (max speed)
Reverse:
1,2kg = 26amps (max speed)

And the famous Graupner 2308.65
1kg = 5amps
2,2kg = 13amps (Max speed, but sucking some air so not really reliable)
Reverse:
0,9kg = 12.5amps (max speed)

[olegodo]

Graupner 4 blade 70mm prop (2311.70)

@ 12v with the NTM Prop Drive 28-36 750KV

1kg = 7,5 amps
1,8kg = 14,5 amps (max speed)
Reverse:
1,3kg = 14,5mps (max speed)


And for fun:
Two props on same motor.
Numbers were the same in forward and reverse as one would expect.
1kg = 10 amps
1,5kg = 18amps. (max speed)

[scubersteve]

See, this is good data.
Notice the Graupner 2308.65 had approximately the same numbers on your 750kv motor as on my two 700kv motors.
So we could assume that someone using that prop on a motor in the 700-800kv range could expect to see similar numbers.
Putting it in a shroud could change things of course...
Anyway, good data.

[olegodo]

Yes, the numbers I got for the 2308.65 also matches the OpenROV test data.
About the shroud tho, I remember Doug from SV Seeker saying that the graupner props did worse in a shroud.
But I can print one and post the numbers.

[scubersteve]

what sort of profile are you going to go with on your printed nozzle?

On one of the openrov posts they were talking about the efficiency of differing shapes.
http://openrov.com/forum/topics/propell ... ler-nozzle

And did you test the 2308.65 inside the ducted fan housing or mounted outside like your double prop setup?

Also, I just re-watched the SV Seeker video on prop testing and didn't see where he tested the Graupner prop in a housing, just exposed.

[olegodo]

Hey scubersteve,

I havent testen any shround on my graupner props yet. And you are correct, the SV Seeker video did not show that they do worse in a shroud, he just said that they did.

However, my time has been spent on a slightly different project. I randomly searched Thingiverse (thingiverse.com thousands of things you can download and print) and I found this prop:
http://www.thingiverse.com/thing:338127

As you can read in the description, the creator claims 14N of force @ 6amps, 12volt on a 750kv motor. in both directions! This is above graupner forward performance. And in both directions.
I tried to print this prop, but as it is printed "flat" it needs to be printed with support material witch is slightly more difficult and requires a lot of work afterwards to get a good enough finish where the support material has been removed.

So I made my own version with modular blades. It is now very easy to print. One complete prop took about 55mins to make. To print a set of four blades takes 40mins.
The one I have tested has a diameter of 69mm so it fits the shroud that came with the EDF fan I tested earlier. I can also very easily test different pitch, diameter and twist in the blades.

Tested the first prop now, straight from the printer:

As you can see in the pictures below, the prop doesn't sit deep enough in the shroud so the performance was a little bit bias to the direction where it pulls water through the shroud and out on the "propeller side"

1kg = 5amps
This is pretty much the same as the graupner 2308.65 and quite a bit better then the 4 blade 2311.70 prop.
But, where the graupner 2308.65 prop maxed out at 2,2kg while pulling 12.5amps. This printed prop went to ~3.9kg @ ~22amps (!)
That is a lot of amps, but also a lot of push if you need it Also, it shows that the performance is quite linear! My tank is a bit too small for the max speed, so the readings are somewhat unstable.

I am sure I can tweak this further, both in the geometry, surface treatment and maybe number of props. But even at this point I believe this prop design beats pretty much everything, especially since it will be pretty close to equal in both directions once the shroud problem is taken care of.