Pedal Boat Design

BG,

Man, you're disappointing me! Look at the legend at the top -- the green arrow indicates total thrust -- and that's on the hydrodynamic view, not kinematic, btw.

You might have to spend more time staring at this thing than I did!

I don't know what the maintenance schedule is like for these things, but the whole lower case -- the part with the levers and cams and such -- has to be filled with oil. I suspected this when I started examining the longitudinal section, and I was right.

 

Wouldn't be the first time I have disappointed...as long as it's not the ladies =)

I am busy staring at all these tiny parts. Not really sure I can make the knuckles and pin joints strong enough at this size. Not sure I could at full size in something thin and hydrodynamic either...

Anyone have any thoughts on what is going to happen in the tracks the 3 point cam followers travel in when they fill with water? On the plus side they stay cool and lubricated... what about fluid locking and all that nasty business? Realistically its a very small volume of water though. Maybe a non issue beyond the increased load on the afore mentioned parts.

 

Hey, I found the good stuff on the Voith props!

From this page,

http://www.voithturbo.de/publications-media.php3

scroll down in the "Market Division/Product Goup" box and click on "Market Division Marine" near the bottom. Click "show" and it will limit the results to the props and such.
Then, click "next" below the selection boxes, which will take you to the second page of brochures. Scroll all the way down and find


G 1849 | Special Print
Paper The Voith Schneider Propeller Current Applications


Click on the PDF icon to download the paper.

It has everything!!! All the details of the mechanisms, all kinds of specs, neat diagrams of how the blades move -- the whole works!

Check it out!

 

Wow...the mother lode lol.

Check out figure 10. See where the dead zones on propulsion or thrust are?

12:00 and 6:00 or 90 and 270 degrees. AKA TDC and BDC.

There IS also an articulated shaft on a ball joint, but its the central drive shaft and not the individual blades, as I thought.

Also, they say the whole system works at very low RPM so the wear is not so bad. Still looks like the things must weigh a LOT compared to a regular prop.

Cool beans Curtis.

 

Rick--

I am finding that the down strut assembly is going to be much wider then your thinking (maybe). Hard edges on an 8" diameter version are at LEAST 2" beyond the forward and aft (say 3 and 9 on your clock example). Then maybe 2 more inches for fairing them. Your looking at 14" to 16".

I will have the 1/3 scale design pretty close by weeks end for some peer review. Then I can order in some styrene and get going.

G

 

BG
Fair them to a wedge both front and back that is 2X length to width.

The more buoyancy you can get into them while keeping the volume down the better they will act as stabilisers. So any space to be filled with low density foam or sealed void.

The attached shows the Cd you could expect for the shape I describe. It is quite streamline. I have also done one with slightly longer wedges. You would need to check if the lower Cd offsets the increase area.

The side struts will cost around 12W each at 12kph. Not insignificant but if they also acts as the stabilisers by being buoyant then it will be tolerable. Off course the thinner and shorter you get them the better.

Suggest you mount the outriggers off the side rather than the top to get the maximum leverage from any above surface buoyancy.

Rick

 

BG
As far as peer review goes I would like to see the actual blade angles at the o'clock positions to confirm they match the curve. I amy want to refine this after I check the net lift force. It is important the lift is positive to ensue self stabilising once moving. It could mean a slight adjust mean to the cam path for pitch control.

Rick

 

Yeah, there's not much difference between theirs and yours, except that theirs always have the foils oriented LE-first.
They do also mention a high weight penalty to accept the heavy torque loading. I suspect that a double-ended rotor would lessen this, though. I also suspect that their complex system of control levers could be replaced by a track system like yours, but I'm not positive about that. If so it would lighten and simplify it further.
That shaft with the ball joint is not a drive shaft; it only controls the steering center. I don't know if it even rotates; it could, but doesn't necessarily have to. Drive power is through a pinion gear.

Batten down, man, Ike's at your doorstep!

 

Rick--

12w each? With 4 of them thats 48w lost to the down struts. If I can recess half of the center pair into the hull thats still 36w =(

I am making the whole assembly as a sandwich that is screwed together with small stainless screws. If you want to try several cam loops to see how different AOA curves do it's as simple as cutting the new cam shape in a 1/8" layer of styrene and swapping it out with the old one. I am posting the entire thing for inspection before I cut anything so no worries there.

Hatches are battened down lol. We have already lost TWO roofs this year and there is something like 80 days left in the season.

 

Ouch! Hope you fare better in this one (and whatever others blow in)!

 

OK. I have the drive down strut with the 3 point cam follower track, the control arm bay, the chain/belt drive bay, and the wheel side bay all designed out. The problem now is how to present it so it is not so confusing lol. I know Rick has SW installed so he can view eDrawing files. Did the rest of you install the little free edrawing viewer? That would be easiest because you can see how the layers sandwich together in an exploded view. Post it in a bit.

 

There it is in an eDrawing. Once you have it open you can move the different layers by clicking and dragging them, or make them vanish by right clickong on the layer and selecting hide component. To return the part to its opening state just click the big home button on top.

All the layers are either 1/8" or 1/16" styrene plastic. From the back side, there is the pulley and belt bay which I made translucent so you can see inside.

Then the yellow 1/16" layer is a base layer that forms the bottom of the cam track and is a barrier between the cam area and the belt area.

Next is the green 1/8" layer that forms the walls of the cam track.

Next is the rose layer that is also 1/8" and provides the pocket for the control arms to move in as well as a lip that keeps the followers in the cam channel.

The 1/8" gray layer is the inner cover and well for the wheel rim.



The wheel rim is 2 layers of 1/16" and is shown in blue. Screwed to this wheel rim is a flanged axle that feeds through the assembly to the belt and pulley or sprocket cavity. That cavity will hold the upper pulley/sprocket attached to the cross axle and a lower pulley that transfers power out to the wheel.

The cam followers are shown in orange, the control arms in yellow.

Total thickness is .625"

Not shown are the 2-56 screws that keep the sandwich together, the drive pulleys/sprockets, or the blades.

I also did not add a fairing as it just gunks up the drawing. The tape measure button will allow you to measure from any point or line or face to any other point, line, or face.

Thoughts?

Looks like it doesn't take eDrawings. You can grab the file here.

 

BG
I cannot read chinese or whatever code that is!

My understanding with the wheel struts was that 2 off them will be faired into the hull. Also you have it thinner than I thought so expect better. I will check when I can see dimensions.

As far as the cam plate goes. It could be a longer loop to increase rotational speed. This helps efficiency.

Actually that Voith paper shows all the detail I have in my spreadsheet as far as angles go. One thing to note is that you have a very easily driven hull so the change in blade angle is much less than the Voith prop. Also the track of the blades does not have the little loop. Your blades will always have forward motion - never backwards in normal operation. At start up they will go backwards and torque will be quite high. Your prop will not be high thrust but will be efficient at speed.

Rick

 

Not sure what you mean about the Chinese.

http://geno.boxgods.com/drive_end_assembly.EASM

That should get you the edrawing file without any Chinese...

As for a longer cam loop, I tracked the LE location and mid point location through the 12 positions and built the loop to those locations. How would I make the loop longer? Do you mean make the arms longer?
As an interesting aside, I can almost run the thing with the control arm cavity. If I were to make it longer and kerf it like the followers I bet it would run.

As for the thickness...keep in mind thats for the 1/3 rd scale boat. the full size will be 1" to 1.5" thick if this works.

 

Impressive as hell. I feel like I did when I watched the first moon landing. Didn't understand THAT technology, either, but it was still fun to be an observer.

That file didn't want to open for me, either, in the program I downloaded earlier. I Googled for eDrawing2008 and downloaded that - it worked great.