New member with a very interesting paddle project.

[Jeff C. PSU]

Hi, My name is Jeff C, and I live in Portland Oregon USA. I am a Mechanical Engineering senior at Portland State University. I am working on a remote operated vehicle that is designed to operate in extreme environments. The hull is already made from aluminum, and measures 25 inches long, 15 inches wide, and 7 inches deep excluding the lid. The environment will be Boiling Springs Lake, in Northern California. The lake is about 300 m across, is primarily sulfuric acid pH=2, and is hot at over 80 deg Celsius. Because the water is so harsh, we have investigated a number of propulsion systems, but have settled on using a sidewheel because it provides excellent power transfer, and keeps all the moving parts out of the water (besides the wheel of course). It also has the added benefit of making the ROV semi amphibious. Basically, the current design will use 12 to 14 inch dia wheels, consisting of two round discs and 7 floats each. The floats will be mounted between the two discs evenly spaced, and will be approximately 2.5 inches wide. They will most likely be made from aluminum welded together. But I have some questions I can't find the answers to. First, I have noticed that no design seemed to use enclosed floats like this design. Is it because it would have been too expensive, or is there something I am missing? It seems like the enclosed floats will be more efficient because water can't escape out the side. Second, is there any other materials that might work well? Finally, we need a motor drive system, the two wheels will be independent.
Thanks for the advice,

[derekwarner_decoy]

Hi PD's & welcome Jeff C....I think this may be the first tertiary study question for PD's but here goes

1) Materials & Compatability
In OZ we tend to transport pure 100% concentrations of sulphuric acid in 'steel' containers but all/most lower normalities of sulphuric acid in glass or glass lined containers... concentrations of lower that say 96% I would have thought would eat your proposed Al hull overnight if not quicker : ... possibly a composite hull material selection could be considered =....assuming that your lake acid concentration could not be 100%

2) Paddle Design
You could read many postings on Paddle design, however essentially your closed design will drive equivalent fixed pockets of air down into the "fluid" - I am unsure what is behind this concept - when you draw the line of paddle element [or blade] you see the engagement at fluid level you will see the evidence of the fluid [SG of 2] effectively lowering the volume of trapped air in each space as the paddle rotates lower into the fluid, the back out toward the fluid level on completion of each sections immersion

3) Paddle Material
Again I would have thought a composite material as noted @ point 1) worthy of consideration

4) Propulsion Methods
In OZ & USA, automotive car or truck windscreen wiper 12 V dc motors have been used with great success - [may need a 10: 1 belt speed increase] however are very stable, very low current draw, hence low delta T during use, continuously rated due to original design, emit very low values of spurious electronic single

One down side of such motors is/are [again from original design] intentionally limited to singular direction.... they certainly can be reversed, however this reversal of magnet gauss draws the armature shaft off the singular fixed roller thrust ball & allows axial float which causes minute rotational variations in speed

I am sure other PD's will offer alternate comment

Derek in Australia  

[Brian]

As remarked above, as the Aluminium Alloy is apparently being used in an Environment which is "chemically hostile" it was wondered whether the aluminium would be treated by Anodising.

The process of anodising may be either SOFT ot HARD Anodising.

For Example: Aluminium alloy treated by hard anodising makes the surface of the treated aluminium so hard that it cannot be marked even by a Hardened steel scriber.

The aluminium component after anodising has an increase in its dimensions. Care should be taken to ensure the particular aluminium alloy being used is suitable for anodising/anodizing.

[Jeff C. PSU]

Thanks for the responses. There is always more to the story, and here is the rest of it. My team has inherited this project from a capstone team from last year. The hull is already built from welded aluminum (not my first choice either), so we are stuck with it. Our assignment is to just make it work as well as possible. Unfortunately, they designed a drive system that involved a complicated outboard like setup that will simply not work, so we are faced with trying to adapt a new system to make this boat go.

The reason behind the paddles being made from aluminum is so they will match the hull, which has passed a test sample being boiled in lake water for 10 hours. Although visible oxidation occurred on the surface, no catastrophic pitting or other damage has occurred indicating that the aluminum will be satisfactory for service. I have been advocating that we coat the hull (and paddles if they are made from aluminum) with fiberglass resin or epoxy paint to provide additional protection.

The reason for the enclosed paddles is for simplicity of construction, and strength for the amphibious feature. Air should escape from the top, but I am not an expert on the design of paddle wheels, so I value your opinion.
The ROV needs to operate at least 4 hours before recharging, and in addition to the drive system, it has 2 GPS systems, a Sonar system, and a 2L probe that takes water samples, measures temperature, acidity, luminosity, and pressure, so we need low draw motors. The wiper motor I have here for testing draws 1.5A and turns 166 RPM. This will give us about 2 hours on our current battery supply. Anyone use motors that draw less than an amp each and turn around 160 RPM? I will keep the search up for wiper motors that are a little more efficient.

The most important thing about the paddles is they be simple and strong. We do not have the time or the resources to make complicated paddle systems. For us, the main possibilities for making paddles at this time are aluminum with welded or riveted floats, or marine grade plywood coated with resin or epoxy paint, stapled or glued together. If there is another construction technique that might work and be very simple and easy to construct, please let me know.

Keep the ideas coming, I will post some pictures of it running in a few months!
Thanks!

[Eddy Matthews]

Is the 1.5A current draw with the motor just running free, or under load with a similar sized paddlewheel immersed in water?

If it's under load I doubt that you'll get much lower than that with the intended diameter of paddlewheels - But if that's the free running current you can probably double or even triple it when the motor is loaded....

I don't know if you can get them in the USA, but keep an eye out for Buehler motors - Superb quality German/Swiss made units that draw tiny amounts of current. They are available in a wide range of sizes and also with superbly engineered gearboxes to give you the RPM you'll be looking for.

A friend of mine has two in one of his paddletugs, which admittedly only has 5" diameter wheels, but the two of them together only draw 300Ma

[derekwarner_decoy]

OK Chris....

1) you could coat the hull externals with glass cloth & epoxy resin to minimize oxidation/corrosion
2) 25"X15"XI7" = 2625 cubic inches or 25"X15"XI5" would provide 1875 cubic inches & give you 2" freeboard
3) weigh all of your components & do a bath test to check for available buoyancy
4) a 12 V 7Ah gel cell weighs in @ only 2.6 Kg
5) your vented/open topped paddle wheels will minimise turbulence, again if pre manufactured coat in epoxy resin
6) you can purchase 5 lb bags of lead shot [from sports/gun shops] [for the people that reload their own shotgun   :boom shells] this makes it very easy to use ballasting calculations  
7) if with all of your additional equipment you find you need more buoyancy, it would be a simple task to get a sandwich/offcut of surfboard foam, cut it to shape & epoxy resin/glass cloth bond to the base of the vessel
you may wish to do a material compatability check with the nominated acid fluid as stainless steel fully sealed roller ball bearings are available for shafts of sizes...1/8" ID to ......1/2" ID and are very in expensive  

One last point... recheck the actual output shaft speed of your wiper motor - 80  to 160 RPM is great for model paddlers, but examples of wiper motors in OZ seem to provide approx 60 RPM - Derek

[derekwarner_decoy]

Hi Eddy - when convenient, could you please repost these comments or postings from their current [introduce yourself] location to a more appropriate   :computer folder.. so we could all talk about them more.......... :gather ... thanks ....Derek

[dragincity]

Hi Jeff ,
A few years ago I went thru the process  of getting wiper motors installed in my very semi-scale model of P.S Industry.

Points of interest :

1) I used rear wiper motors from Ford Falcon station-wagon (ranch wagon  in USA ?) tail gate as these are smaller, but just as powerful as the front ones. Also consider door window units. Mazda has sone very nice units.

2) one motor to each paddle

3) simple home made motor control unit, built from local store components -- three position toggle switches, micro switches & two cheap R/C servoes
--- giving forward/reverse, left/right motor stop start.

4) by using forward on one motor , stop the other, easy turns are made, reverse the other  complete boat length rotation. The rudder is ineffectual !

5) controlled by very cheap 2 channel radio, channel 1 stop /start/ forward/ reverse, channel 2  steering and motor control.

6) the shaft bearings ended up being a simple 'block' of brass with a 1/2+" hole bored thru with a simple oiler hole for lubrication.

The paddles were very simple, each made in stainless steel, but any metal would do :
a) two lazer cut discs ( with nice spokes & rims), all holes laser cut so assembly is rapid.
b) simple 'U' shaped floats in bent s.s and pop rivited to the rims.
c) assembled wheel pop rivited to a drive shaft  'end-plate silver soldered to the drive shaft,  shaft made of 1/2" s.s. tube so that it fitted over the motor drive.
d) wheel and shaft easily removed from boat by removal of one (1) split pin.

In your case if the drive speed is 166 then you could easily direct drive the wheels making building/maintenance very easy. My original design was for this, but as I discovered  my wiper motor only turned at 30 rpm I had to 'gear' via a pulley drive.

I have written a (unpublished) article about my project and would be pleased to send you a .pdf copy if you think it might be useful. I also have many photos
of the project that show the wheel construction quite clearly.

Due to the very harsh sailing conditions I would stick with cheap ready to source materials and avoid any 'nice but fancy' gear as they are sure to dislike the sailing conditions!

BTW 1 : I did not find any need to incorporate motor speed control into the control system, 160+ rpm is so slow that stop|start|reverse was sufficient.

BTW 2 : a paddle wheel housing is not really necessary, but in your case it will help protect the topside equiptment from sulfuric acid splash !!

--
Yours,
Brett Hallett

[derekwarner_decoy]

Hey...    welcome back Brett S Hallet who says...

I have written a (unpublished) article about my project and would be pleased to send you a .pdf copy if you think it might be useful. I also have many photos of the project that show the wheel construction quite clearly.

So................... come on Brett & share your  :post  & :kewl with us all... there are plenty of Forum locations in this new PD's site - & good to see you haven't forgotten us.....regards Derek