Pedal Powered Boats

Just provide me a hand drawing with the details you need (in metric if possible) and what profile the hub should have.

Stainless steel is more expensive for printing, but they show the price online when uploading the design. Maybe there would be no additional price when you print all parts together, as they charge for "packages" like cm³ with size restraints.

EDIT: Price is 8$ per cm³ with a minimum price of 35$ for stainless steel. Price for Nylon is 15$ for anything which fits inside the printable area (20cm cube) and has below 125cm³.

Just give me the sketch for the hub and I will tell you afterwards. The resolution is about 0.1mm.

Best regards, Andreas

 

Does anyone know of a variable pitch assembly appropriate for a 1:1 geared pedal boat.

It seems to be the way my design evolution needs to go.

Even if it's just the design for one, not necessarily a finished product...

 

Just google for RC helicopter tail rotors. This design is used for aerobatic RC planes (see below) and model ships too. Even a real airplane prop company is using this system for a cheap and lightweight system.

http://www.woodcomp.cz/en/varia170.php

The trick is simple: the blades are mounted in a way they can be twisted and set by a push-pull-rod which goes through the hollow axle. The angle can be set from the rearside of the hub.

See this too:

 

3D-printed prop

The hub is 24 cm long and 272 cm³. I could go with a smaller version that is 18.4 cm long and 122 cm³. If the hub is going to be 3D printed I should include the bolt hole and slot for the folding prop also. I'll experiment with Excel and see if I can export the shape to build a 3D model. I attached the hub shape.

Thanks, Dave

 

At 1:1 gearing you'll need a drive shaft that is quite stiff in torsion, especially in a sprint. Otherwise you'll be limited in how much power you can deliver through the shaft.

Dave

 

Why don't making it hollow with ribs? This makes it cheaper and lighter.

You can also make it in three parts, with the middle one in stainless steel and a polyamide fairing.

There is no need for making a model, I can make it for you from a sketch.

 

Ah, the Carmichael Bulb

The Carmichael Bulb makes an appearance!

 

Coach Dave,

Thanks for that.

Yes, a robust drive train but no sprints.

This is a long term flier.

30 minutes vs 30 seconds.

Designed for duration, not speed.

 

I made a 2D sketch that I hope you can follow. If it is mostly hollow with ribs it will be less than 125 cm^3. The first attachment is on a 1 cm grid. The slot will need a lot of material around it because it has to handle the torque of a 20" prop. I'll extend the slot toward the tail to make room for the prop to fold so that area needs to be solid.

The second attachment contains the x, y coordinates for the hub profile. You might be able to import the profile into a modeling tool then rotate it axially. If not I can try converting the csv into a dxf file.

Thanks, Dave

 

Hi Dave!

3D-model took 10 minutes with solidworks. At the time I tried only the full solid version:

970€ for stainless steel
79€ for Nylon

At these prizes, its not very interesting. I will do the hollow one tomorrow and keep you updated.

 

3D-printed prop

Thank you for building the 3D-model. It's good to know that stainless steel is available but it is out of my price range. The prop is where I really need the strength of stainless steel and they are easy enough to cut, twist and grind into shape. Arranged on a diagonal the hub will fit in a 20 cm cube and 125 cm^3 if enough of it is hollowed out so I am hoping the price will drop substantially.

Please post some views of the hub like you did for the props you are designing. Are you investigating a low drag hub for your props? I am working with a hub shape that supports laminar flow.

Dave

 

I am sorry, but the prize won't go down so much, even if hollow. The process is very complicated and therefore "cheap" is relative if you are a company which needs it very fast and a man-hour costs 100$++.

I have included a "tank-test" of your hub, it looks quite good at 3m/s.

My prop (for my wave interference project) has also a fairing, which is NACA 66-xxx. I included a pic of that too.

Sorry it didn't work out.

 

Hi Andreas,

I really like the pics of the hub. Thank you for generating them! The hub attaches on the end of a drive shaft the same diameter as the flat spot on the front of the hub. That would eliminate the yellow area in the "tank-test". The flow would be even smoother if I use a quadratic or cubic spline to transition from the drive shaft to the slope on the nose of the hub.

I think I'll be using a lathe to make the hub shape.

Thanks, Dave

 

Scheny:

Thanks for the post. Wonder if the "tank test" gives hints about the best shape for very short hulls....

Porta

 

the "bob" trailer cataraft

My bicycle cataraft system is evolving ......

I'm ditching the idea of the xtracycle long tail cargo bike bolt on extension conversion in favor of the "Bob" (beast of burden) single wheel trailer.

Is seems I am ahead of my time and the longtail conversion isn't a commercially available item yet.

The bob trailer on the other hand has some interesting possibilities!
For one it's much easier to modify
http://coastkid.blogspot.co.uk/2011/04/fatbike-trailer.html

http://coastkid.blogspot.co.uk/2011/04/fatbike-trailer.html

other benefits are I get to keep the original wheel base and use it as a regular bike for general normal use around town times.

for my sandcastle lesson on the beach I can put all my gear into the trailer and never have to worry about parking. it also would be great advertising as well.

but the big deal here is that I can use the trailer as the frame for the cataraft.

Now the trailer doesn't have to be exactly like this off the shelf model but it does need the hitch and basic idea. Modifying the existing trailer would be easier though. I can mount the bike on top of the trailer which has the attachment points all in place for a quick step. the cross bars for the pontoons can have built in attachment points, again making for a quick set up.

Next comes the drive system, and here is where I need some suggestions!

I'm thinking about using an internal 8 speed shifter so that should make things easier in a lot of ways.

Could I use a two ring sprocket up front to attach the prop drive chain to?
Or could I use the rear wheel in some manner to get the prop drive from?
Yes, there's lots of options here ....... more ideas?

the internal 8 speed shifter:
http://www.shimano.com/publish/content/global_cycle/en/us/index/products/0/nexus.html

the fat bike I'm considering:
http://www.fatsandbike.com/

the bob trailer:
http://www.bobgear.com/ibex

oh, one last thing, it all has to be boxed up to fit onto the greyhound bus.
I'm also going to be carrying lots of drinking water and camping gear, and of course the cataraft.