TRKpoker wrote:I can envision several problems with the design. First trash.
Forgot to mention that the design does include a grate/mesh on the intakes. They're planned for both intakes and outlets. Just not shown in the model.
TRKpoker wrote:Second size under boat.
As mentioned before, we're most likely going to move the screws further apart and closer to the hull. We're toying with the idea of putting the mounting bracket on top the kayak behind the driver. I'm a bit hesitant to do this since I believe space is a premium for you guys. We're also trying to incorporate some adjustability into the bracket, for up and down and possibly forward and back. This would be to allow for shallowest draft at all times and address the launching issues.
Rik wrote:
Is the drive unit detachable while in the kayak?
As it is shown now, no. However, see above. We're working on it.
Rik wrote:How much depth will be required beyond the normal draft of a kayak?
Officially, we need to beat 12". Unofficially, I would like to draft much less than this.
Rik wrote:Will the pedal unit have any gears to reduce the number of pedal revolutions once speed is obtained?
The ratio we're shooting for is 1/5. One turn of the pedals would equal 5 turns of each screw. We based this on a 1 pedal rev/s cadence for cruise. That equates to 300rpm for the screws. We're considering using the tapered rollers shown to our advantage. By moving forward or backwards, you could get a variable ratio. Don't know how big an impact this would make yet. Not without more calculations.
Rik wrote:Could the drive unit be embedded in the hull to decrease the draft requirement? Not knowing how big around those pipes are, it seems they could be embedded, at least partially, and use the existing draft of the kayak.
The pipes are 3-4" PVc, most likely 4". We avoided anything to do with a tunnel hull since it would've added to our workload and would've been impossible for us to do with the equipment we have. For us to 'pass' we have to prove numerically everything we're doing. Accurately modeling the kayak hull would have proven too difficult, not to mention flows/drags of the hull. We basically took what Hobie owners told us, that a good cruising speed is 3.5mph. We did a rough calculation of the force produced by the Hobie. We then said if we could match this figure, we'd be in good shape. Another reason was that we were unofficially shooting for universiality. Anyone should be able to buy this unit and attach it to most kayaks. I think having to cut two tunnel hulls in their kayaks would be too cumbersome for most owners, but I could be wrong?!
Rik wrote:Has any testing been done on the augers to see how they'll react to normal stuff in the water such weeds, gorilla snot (not the technical term I'm sure but everyone on this forum knows about it), sand, oysters?
The research I've read said that Archimedes screws are advantageous for their debris handling capabilities. However, most enclosed screw setups I've seen are for hydraulic lifting, huge screws at an angle with 2/3 of the tube filled with air. I don't know how being parallel to the ground and totally submerged will change this. Hopefully, with the proper grate/mesh design, it won't be too big an issue.
GILs_GONE_WILD wrote:Pretty neat concept. I would only suggest to not put too much time and effort in a reversing mechanism as 99% of the time you'll be going forwards.
Reverse is not one of our official goals. But it would be nice. I'm really hoping to make the turning with opposing thrust happen.
GILs_GONE_WILD wrote:GILs_GONE_WILD wrote: Instead of a solid mounting bracket as in the pic between the two motors perhaps the design could "swing" both "motors" up to either side of the kayak but not too far as to impede the use of a kayak paddle.
Looking at it closer, perhaps you could move the "motors" to the rear of the kayak. Then, when you pulled "the/a" lever to raise the motors to just above water level, so as to eliminate drag, you wouldn't impede paddling at all.
The plan is to mount the screws just behind the driver. Once finals are done, I plan on finding the 'big idea' on how to mount them and still accommodate everything. It needs to be adjustable without making the driver have to turn 180 around. It also needs to not tear the kayak hull in case of an impact. Lastly, vibration isolation will be key, since we believe a kayak hull is like a speaker box, noise will reverberate.
MrSpectaculous wrote:It would be good to see the props inside the the hull enclosed drawing water thru a tunnel and forcing it out the rear. Also if the drive could be powered by the existing foot pads rather then a set of pedals or wheel. Personall I would rather it be permanantly installed in the kayak so light weight maerials would be a must.
No tunnel hull for us since it would require "designing a kayak" which would've been difficult to do in the time allotted. Initially, we had foot pedals like the Hobie setup, working piston/bellows. The numbers didn't make sense to do this. The reason we went with the unicycle was that we could purchase it as a unit. Although I've never been kayak fishing, I fished off my buddy's 18' flats boat in the St. John's for years. I was going to get into kayak fishing when I decided to go back to school instead. When I suggested this idea to the group, part of my justification was that with gas prices, taxes and the economy, kayak fishing must be reaping the benefits. Also, this if Florida, fishing central. So finding sponsors would be easy. Right? WRONG! Sent out many, many letters. Only a few replies and two companies willing to help us out. So we're basically self-funded, which translates to poor. We're trying to do this the cheapest way possible and still pass the class and have a working product. That's why almost every piece is based on something you can buy off-the-shelf, like a unicycle.
BigFlyReel wrote:Couple issues:
1) Mentioned before: draft.
2) Steering. Are you planning to use a hand-operated rudder? If so, you want to balance the distance between the screws, both fore-and-aft and spacing from centerline. Assuming direct drive from your illustration, it appears the screws will counter-rotate. Testing those distances, and rudder size/shape, will tell you about rudder flutter and effectiveness in any drive stream eddies, etc.
Instead of feeding the screws power directly from two drives, you could always feed a dual friction transmission that allows you to direct more "power" to one screw or the other, and thereby provide some steering. Very simple mechanically, low maintenance... combine that with the rudder, and you may not need the reversing screw.
BFR
Draft was covered. We're not sure about the rudder. Technically it's not a requirement. However, in our interviews, turning radius was a concern. If we can figure out a way to turn faster than a Hobie (opposing thrust) then it would be a good thing.
The way the drive design stands now, we thought about pushing the caliper from side to side. If you had opposing springs holding it, it would want to return to center every time. This would allow for one screw turning, the other side disengaged. Don't know if this would provide the turning moment for a tight turn? Hopefully, after finals, I'll figure something out that will allow for the opposing thrust with ease of operation.
krash wrote:What about moving the drive mechanism, (an idea I been tossing around for a few years for an electric option), actually up into the rear end of the hull like a JetSkii intake water from directly below into the tube with either a directional output nozzle like a jet ski or fixed with a rudder. The rudder idea leaves out the reverse option, but a gated metal peice like JetBoats use to force the thrust down could be easily added for minimal reverse thrust.
Looking at the current design, I'd wonder if you could actually get good enough bite on the rollers to wheel into the drive cables to get the power transfer towards the screw-drive with out simply twisting the cable itself into a knot.
We stayed away from electric due to cost. We stayed away from jetskis because of the pump nature and the required power and also having to 'tube' a kayak hull. The rollers are planned to provide enough friction to operate the mechanism, but give way under extreme resistance, a safety feature if you will. So you're cruising along and an oyster gets into the blade for whatever reason. It will come to a complete halt, but your feet won't. Rather than snap some component, the roller will just slip. On the cables, we've found a rotary drive cable company that offers cables far above our power/torque requirements, in both directions as well.
Rik wrote:Will the screws create any suction so they could be mounted above the water line?
Not without losing most of the thrust, which in our case is volume related. As mentioned above, they will lift water. However, in those applications, there's not need for pressure at the top. Once the water gets to the top, it gravity feeds to whatever it goes to. Also, when lifting, the volume of water decreases immensely. It then becomes like separate buckets of water being moved.
Thanks for the input and keep it coming. I hope I've answered your questions with minimal confusion. If not, let me know.
And, having the pedal part be closer to the mirage drive, this may solve the issue of backing up.. 