04
Oct 2011
by larry

Aqua-Xtracycle, the Amphibious Bicycle

boating mode: the boat carries the bike

boating mode: the boat carries the bike

biking mode: the bike carries the boat

biking mode: the bike carries the boat

The Aqua-Xtracycle is a do-it-yourself amphibious electric cargo bike. This video shows how it works, and the photo gallery below shows a bit of our development process. In a future post I’ll describe how you can make your own Aqua-Xtracycle.

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  • http://lblackimp.com The Imp

    I was imagining propelling the boat with the pedals, not the battery. So you can get exercise. Will this be a feature of the Aqua-Xtracycle, version 2.0?

    • admin

      Hi Imp nice to see you. This question was also asked on the Youtube discussion, and I think it is a good question. There I wrote “I think the design could go two ways, either lighter and pedal-powered or heavier with more electric-powered features such as an electric air pump and solar panel. I think we have to get away from the idea that small vehicles are human-powered and large vehicles are gasoline-powered. With advances in electric motors and batteries there is now an electric middle ground that is largely unexplored. That said, I did try adding paddles to the rear wheel and I also plan to try a friction driven prop.”

      Here’s some more thoughts about why I chose electric propulsion. Note that the aquatic parts add 40 lbs to the bike. This is a lot of weight for a human-powered bike but trivial for my electric cargo bike, which I often use to carry hundreds of pounds. Because of the weight, I think a practical amphibious bike needs to be an electric bike. So if I am already carrying a battery and motor, it makes good design sense to have the boating mode use the same battery and motor as the biking mode. The current design shares the battery for both boating and biking mode but has two separate motors, a bike motor and a boat motor. A better design would be for the boating mode and biking mode to use the same motor.

      Another constraint is seaweed. This is what eliminated the paddle wheel idea. See the photos. The best analysis of Human Powered Boat designs I’ve seen is:
      http://www.recumbents.com/WISIL/hpb/hpb_faq.htm

      Another design constraint is that I wanted to be able to quickly remove all the aquatic parts so that I could use my bike as a normal bike when I wasn’t on a boat trip. This limits what kinds of propulsion I can come up with for the boat mode. With the electric trolling motor it is very easy to snap it on and off.

      The friction drive prop system I have in mind would be a combination of this prop:
      http://www.recumbents.com/WISIL/hpb/compact_drive.htm
      with this Xtracycle blender drive:
      http://www.recumbents.com/WISIL/hpb/compact_drive.htm
      Because my electric bike drives the rear wheel, this propulsion could be either human-powered or electric or both at the same time.
      Anyone else have a better idea?

      More questions please! Challenge me!

  • http://cargobiking.wordpress.com/ Derek

    Hahaha!! Pure awesomeness. I am inspired to do a little xtracycle inventing myself.

    • admin

      The biggest breakthrough I think is my idea of using handlebar stems inserted into the h-rack holes. I really struggled with finding a good way to attach accessories quickly and securely without having to modify the bike. The stem idea opens up all kinds of possiblities such as sidecars, snow plows, trike conversions, etc. Let me know what you come up with!

  • http://balandaeyes.blogspot.com/ David F

    That looks like fun!
    I’ve been playing with a few ideas for both my Xtracycle and my canoe (separately, to create an amphibious bike would require a whole lot more imagination, time and skill than I have!)
    Fantastic to see what you’ve done so far. I like the series of photos in this post too!

  • http://mark.stosberg.com/bike Mark Stosberg

    I would have been concerned about submerging the electric bike components. It looks like you found ways to address that concern.

    • admin

      Well the way I addressed that concern is not to be concerned. All electronics are high out of the water. And I’ve driven the bike on the water enough times now to know that it’s unlikely to sink without warning. And lastly I know from experience riding in the rain that just about all the electronics on my bike can get soaked and still work after drying out.

      I do take precautions however. When I was testing the first prototypes I removed all the electronics. I always put my wallet and cell phone in a plastic bag. I don’t go too far from shore. I do currently have a slow leak in the starboard pontoon so I have to re-inflate it every half hour or so. Ultimately I would like to get longer pontoons that have multiple bladders so if any one of them become punctured the others can still keep the Aqua-Xtracycle afloat. The ones I have in mind cost $1,000.

      I’m curious what would happen if my bike was completely underwater. I’m not about to try it but I did do a little experiment with a battery: a 1.5v battery connected to an LED continued to work underwater. I think most batteries will continue to work underwater. I measured the resistance of water in a bowl and it was between .5 and 1 Mohm. A 12v battery would only have a micro amp flowing through the water. When I added salt to the water the resistance went higher beyond the range of my meter. So lake water and certainly salt water have such a high resistance it’s unlikely the water could short out a small battery. (Corrosion is another matter.) It’s possible a large battery underwater could spark between two closely-spaced connectors. I know arc welding is possible underwater; it would be like that. How large a battery? I have a friend whose house current continued to work even when his basement was underwater in a flood. So apparently even 110v at 20a doesn’t arc underwater; a typical ebike battery is 36v at 20a.