Propeller Selection - Choosing a more efficient propeller+nozzle for the ROV

#1

The current props for the ROV work great, but are designed for a different fluid (air) that is just a tad less viscous than water. So armed withthe thruster testing rig I plan on both charcterizing the existing propeller+nozzle, a bunch of OTS R/C boat propellers, and sourcing/fabricating the ideal propeller+nozzle.

Useful text all about marine propellers and propulsion

http://www.scribd.com/doc/30889292/Marine-Propellers-and-Propulsion

(the book is $200+ on amazon btw)

Choosing a nozzle

For the V2 ROV, we want to maximize the the bollard pull (thrust from standstill). By adding a Kort Nozzle, one can increase bollard pull up to 40%; however there are many nozzle profiles to choose from. From "Marine Propellers and propulsion", it seems that a fairly optimal Kort Nozzle is the MARIN no.37 profile, which isn't as efficient as the standard MARIN no.19A in the ahead direction, but is more optimal for both ahead and astern (forwards and backwards) operation (see page

The cross section of the No.37 nozzle is a bit hard to find (you are supposed to pay MARIN a bunch of $$ to get access to them), however I was able to find two grainy scans of it (scan 1, scan 2) and together they form the full picture of the cross section. I plan on making a parametric CAD model of it, so we can make nozzles of any size we want!

Another fitting nozzle design is the Rice Thrust Nozzle, which performance-wise is a bit better than the no.37 profile. However, since Rice has all the patents on it, I'm still searching for a diagram of the cross section.

Turns out that Seabotix uses the No.37 nozzlefor all of their thrusters, and from the looks of their thruster they use a Kaplan type prop.

random websites with info:

http://www.splashmaritime.com.au/Marops/data/less/Mano/Kort%20nozzels.htm

http://www.solarnavigator.net/kort_nozzle.htm

http://www.propellerpages.com/?c=nozzles

I'll continue to post my research/progress here on this page

#2

This is perfect! i had similar ambitions, but i havent had the time to build a jig.

i have alot of propellers from graupner that i was thinking of testing (http://www.cornwallmodelboats.co.uk/acatalog/propellers_plastic.html)

i also bought some DT700 motors from hobbyking to try out. http://www.hobbyking.com/hobbyking/store/__6246__hexTronik_DT700_Brushless_Outrunner_700kv.html these motors are very common on tri and quadcopters.

One thing i've noticed with these motors is that they run ALOT smoother than the 2213N kit motor. seems like the axles are better adapted to the bearings. a downside is the added weight.

#3

Hi Thomas

I was just looking at the DT700 and noticed that it may not have reverse windings, but maybe I am wrong., thought I would let you know just in case you missed that.

Regards

Dave

#4

what do you mean with reverse windings?

there is no diffrence among brushless motors if they can for "forward" or "backward". the motors go the way they are commuted by the esc. if it goes the opposite way of intended, change around two of the three phases. this changes the direction.

#5

I finally got my ROV in the water and quickly found out that I need to switch the props to reduce current loading on the ESC's. I am using 4 esc's, motors & 88mm duct fans and had a 15AMP fuse on my power blow when all motors were engaged. I changed that fuse to 25A and it now works ok but the esc's look like they are shutting down with over temp with only a short run time. So I need to reduce the size of the prop down to 65mm and use the G2609.65 & G2609.65L to increase thrust and reduce current. I use two vertical thrusters and I notice that using the vertical motors caused the ROV to spin so I need to use a clockwise and anti clockwise prop.I will do the same for the two rear thrusters. I have been looking all over the web to find a source to buy these from and I am not having very much luck. Does anyone have a source that I can purchase these from? Also the motors I am using have a 5mm shaft and was wondering if the inserts in these props can be changed,if so then maybe I could use the G2308.65 & G2308.65L and install inserts that will fit the 5mm shaft. Any help with this would greatly be appreciated.

#6

I coulnt find anything that is called 2609.65, are you sure its not the 2309.65 props youre after?

you'll find them here:

http://www.cornwallmodelboats.co.uk/acatalog/plasticm5.html

#7

Thanks Thomas you are correct it was a typo on my part they should be 2309.65

and that web site looks to be one that will ship to North America. That model seems to be out of stock but they have the 2308.65 in stock.

#8

Thanks again Thomas I have ordered up the props from Cornwall.

I also ordered 3mm & 5mm Bushings in hopes that I can remove the screw type bushing and insert a shaft mount bushing that uses a set screw.

I did this because I may have to change my motors to the 2213N the same ones you use which only draw a max of it think 9A vs the motors I have D3530 which are a max of 22A. The shafts are different sizes 3MM vs mine which are 5mm.

I may try to add a small fan to cool the esc's to see if that helps the shutdown issue or maybe a bigger heat sink. I am thinking the motors are just drawing to much current with the big duct fans I have and the esc's are rated a 18A.

Then there is the nozzles which I will leave for another day ,this is still very much a learning curve for me, but fun.

#9

I found this site has some props in stock if anyone is looking for them. Finish language but there is a British icon to convert to English.

http://www.hobbypeople.com/shop/index.php?main_page=index&cPath=34_161_257&sort=20a&page=6&language=en

G2308.65 is out of stock

G2308.65L is in stock

G2309.65 is in stock

G2309.65Lis in stock

I got a right and left G2308.65 prop now installed on my ROV and what a difference it makes, The esc's don't thermal shutdown on me and not blowing fuses anymore, I am a happy camper.

#10

Did you use the bushings you ordered

#11

Hi Martin

I did use the adapters but not in the way I had intended.

The Bushings I had ordered would not fit in the props but I did manage two solder two together to make one to go from 5MM motor shaft down to 4MM Prop screw and it worked ok but had an issue keeping them centered so as not to get any wobble in the prop. I also cut them to make them as short as possible.

These are what I had used:

http://www.cornwallmodelboats.co.uk/acatalog/couplings-modular.html#aC8011

Brass will solder very nicely as well with a propane torch and Flux.

I just ordered up these to replace the ones I had soldered together. http://www.gliders.uk.com/prodinfo.asp?number=G3374

and I think they will work for my application as I have a 5MM Motor shaft, I am just not sure how long they are, the shorter the better to keep the prop inside the housing.

I have not found one to go from 3MM to 4MM as this is what you would need but again I was only looking for my required 5mm to 4mm coupling, you may just find them out there.