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Exploring the Hobby of Building your own ROV - Imagine, Create, Inspire.
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 Post subject: Topside Battery
PostPosted: Jun 17th, 2013, 8:15 am 
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Joined: Jun 17th, 2013, 6:36 am
Posts: 8
Hello All,

I am planning to build a dual arduino controlled ROV, with brushless motors running wet. I do not have any experience of ESCs or brushless motors and am wondering if it is possible to run the ESC and Motors from a topside GEL lead/acid battery. Safety is a concern as I plan to use the ROV off of a petrol boat. I am a bit nervous about batteries ! particularly the LiPos. I am hoping for a 30 -50 metre tether,

Do you think the ESCs would be tolerant of the voltage drop from the tether or is it a better idea to put a GEL battery onboard. Would an ESC accept a GEL battery or do they require LiPo ?

Finally, Do ESCs accept 12 volts ?

Thanks, probably silly questions...


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 Post subject: Re: Topside Battery
PostPosted: Jun 17th, 2013, 9:39 am 
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Joined: Aug 30th, 2012, 11:43 am
Posts: 391
Location: Currently: NW Suburbs of Chicago. Originally: NE Wisconsin
Northwind wrote:
Hello All,
Do you think the ESCs would be tolerant of the voltage drop from the tether or is it a better idea to put a GEL battery onboard. Would an ESC accept a GEL battery or do they require LiPo ?


Hello Northwind,
I think you will find that you really need to consider onboard batteries if you are going brushless. I cant remember where i read it, but i seem to recall that most Hobby ESC need to have less the 500mm of cable between the ESC and the Motor.

I am not positive on the battery type. I seem to recall that you can use NiCad batteries or LiPo on most ESC... but again, would be worth digging up more data before proceeding with that.

LiPo batteries can sound a bit scary, but if you are careful, and don't cut any corners, their benefits far outweigh their risks! And these days, they are getting safer and safer!

Ryan
"KR2_Diving"


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 Post subject: Re: Topside Battery
PostPosted: Jun 17th, 2013, 1:45 pm 
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Joined: Mar 14th, 2013, 6:36 pm
Posts: 48
We have an ROV in the works that will use a single power line in the tether (12AWG stranded). This will feed four ESCs on board. However, tether is only planned for 20m.
A second power line in the tether will power the onboard Arduino, sensors, and cameras.

Bench testing says this length and arrangement works. I don't have the exact figure or what all was hooked up during the test, but the voltage drop over 20m was not a negative impact. Again, just a dry test so far.

If you were thinking battery, controller, ESC topside and then running wires down to motors...no I would not suggest that. If doing that get large bilge pump brushed motors and run each power supply separate. As said, the wires between the ESC and motor should be fairly short.



We use deep cycle 12V AGM batteries topside. I don't think any device cares if the power is from a LiPO or NiMh, etc - more about voltage and amps. Most ESCs I can think used for ROV would take anything from 5V-20V...but check the data sheet for your ESC to be sure. If using LiPo, get a ESC that has a low-voltage cutoff, as LiPos can die when used under 3V or so.


And I agree with KR2, while LiPo has made for some headlines with explosions and flames...if properly cared for, charged, and monitored...they should be fine. IIRC, most mishaps have occurred during charging, not usage.


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 Post subject: Re: Topside Battery
PostPosted: Jun 17th, 2013, 4:39 pm 
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Joined: Jun 17th, 2013, 6:36 am
Posts: 8
Thanks guys,

That helps a bit. I have a 12 volt supply on the boat so it's attractive to do it that way. With the arduino,ESCs on the ROV.

Have you by any chance any thrust measurements from brushless motors with 5 or 6 cm props (with Kort Nozzel) ? An idea of expected thrust with say something like these would be great. I haven't been able to find any indications on the web. It would be nice to have a speed of 3knots (1.5m/s) ! Am I dreaming ?

I'm thinking small seabotix type hull. (fairly streamlined, only round acrylic tube facing sea.)

http://www.hobbyking.com/hobbyking/stor ... Motor.html

Thanks again for your time.


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 Post subject: Re: Topside Battery
PostPosted: Jun 17th, 2013, 5:09 pm 
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Joined: Mar 14th, 2013, 6:36 pm
Posts: 48
You might search thru the archive Tech Reports of MATE competitions. They often will list their max submerged velocity. I peaked at one with some big trolling motors and a pretty sophisticated control mechanism and they listed only a 1.0 m/s.

Hobby style brushless probably would need a pretty small and sleek design. Don't forget about open water current. You may need a fair amount of power just to overcome current and stay alongside your surface vessel.

http://www.marinetech.org/tech-reports/


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 Post subject: Re: Topside Battery
PostPosted: Jun 17th, 2013, 6:18 pm 
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Joined: Jun 17th, 2013, 6:36 am
Posts: 8
Thanks,

That's a great resource. Had some fun reading through some of those. I didn't come across any brushless use yet but I did notice that the bilge pumps get a couple of pounds of thrust at 3 or 4 amps. Is anybody getting a couple of pounds or more! thrust from brushless at similar amps.


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 Post subject: Re: Topside Battery
PostPosted: Jun 17th, 2013, 6:54 pm 
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Joined: Feb 28th, 2013, 6:01 pm
Posts: 383
Location: Australia
Northwind, just so happens that yesterday I did the first water-test of my prototype ROV, and I am using the same motors as you linked to. Running off a 7.2V ni-mh 3300mAh, and turning Turnigy 5030 props cut down to about 75mm diameter, I would guess at 1m/s but certainly not more. Lots of draggy appendages in the form of brackets and wires, and the vertical duct/shroud, though this and the port and starboard prop shrouds and hull are 90mm stormwater drain. Overall length and beam 620 by 490. I do not think a Seabotics http://www.seabotix.com/products/lbv150-4.htm type hull would do 3 knots with these motors, but something of smaller cross-sectional area, properly streamlined, certainly would. Sorry no video but some stills..


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 Post subject: Re: Topside Battery
PostPosted: Jun 17th, 2013, 7:00 pm 
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Joined: Jun 17th, 2013, 6:36 am
Posts: 8
Well done Rossrov. That looks great. You've just given me great confidence to proceed. Look forward to seeing more. Thanks


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 Post subject: Re: Topside Battery
PostPosted: Jun 18th, 2013, 1:48 am 
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Joined: Aug 30th, 2012, 11:43 am
Posts: 391
Location: Currently: NW Suburbs of Chicago. Originally: NE Wisconsin
Hey Ross,
Looks great! I like the props!
How did the forward vs reverse thrust balance out?
Don't suppose you checked how many amps you pulled with the motor running in the water?

Again, congrats on your first sucessful dive!

Ryan


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 Post subject: Re: Topside Battery
PostPosted: Jun 18th, 2013, 5:52 am 
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Joined: Jun 17th, 2013, 6:36 am
Posts: 8
Hi Ross,

Would it be possible for you to give an indication of your battery size and expected run time ?

I have been looking at these lifepo4 batteries http://www.hobbyking.com/hobbyking/stor ... _Pack.html

They sound safer than the lipo's, although the voltages are a bit weird and not sure if they work with the aforementioned motor. Interesting though.

Sean


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