Amphibious Bike Propulsion Problem

[Bohring]

Hi Guys,

I've made an amphibious bike, shown below. Basically, it's a bike which you can use to cycle along the road, down the slipway into the water with litle/no changeover, and then pedal off through the water.

It all works, and floats, but I'm struggling to find a way to propel it in the water, without just using an electric outboard!

Here are my thoughts so far:

• Flipper - best solution so far, but it's too slow in the water.
• Paddle Wheel - can't find a way of powering in the water, or disconnecting power when traveling on land.
• Making rear wheel a paddle wheel by placing metal sheets inbetween the spokes - can't find a 'safe' way to make the forks wider.
• Propellor - can't find a way of powering it, or lowering it into the water.

Any thoughts would be very much appreciated!

 

[sophiecentaur]

Great project!
I have seen a good demo that a screw beats a paddle. Adam Hart Davis, in a TV prog about IK Brunel. Couldn't find it on Youtube, unfortunately.
You could mount a shaft along one rear fork and put a prop (screw) on the end, just behind the wheel. It could be driven from the back tyre, using a roller. You would need a worm drive or equivalent to get through the 90 degrees. The roller could be engaged / disengaged with a lever but it would press, naturally, against the tyre when in operation (useful). You would need to brace the arrangement somehow but, perhaps the whole thing could be actually on the existing float frame, which would be easily strong enough - the only contact with the bike would then be the actual roller. The wheel bearings seem to be just under water so the screw would be almost at the right level if the shaft were tilted down slightly.
Let's have some pics when the system is going - whatever you choose.

 

[Bohring]

I'm liking the idea of a screw system! I'm using a flipper system at the moment, which is shown in the photo, but it's just too slow.

I did try a roller system, but I think you'd need two rollers, as with one, it would spin the wrong way. The main problem though it is works brilliantly on land, but when you go in the water, the wheel gets wet and loses all friction with the roller.

I'm thinking that a chain drive system would be best, as you'd get most power. But I can't think of a safe and easy way of engaging and disengaging the chain system!

Cheers,

 

[sophiecentaur]

If you want to drive from the chain (a better engineering approach), why not have a sprocket on the other side of the back wheel? I once had a bike with a fixed wheel sprocket on that side so you could use the wheel either way round. To engage / disengage, you could have a dog clutch as part of the right angle drive system. That bit would involve some serious metalwork, though.
Would an electric distribution system be out of the question? They do it in many high powered vehicles. It would solve the angle and control problems - but then there's the water to consider!