Friday, 8 July 2011

Current Thoughts.

So I am currently undecided about a few things.

Do I keep the gas motor for lift or do I buy a ducted fan?
I will need to buy various things for the gas motor and it would require much more work for mounting. It is also messy as there is no muffler so it just spits unburned fuel and exhaust everywhere.
The ducted fan seems to be in the 20-50$ range for something pretty reasonable. The benefits of having the ducted fan is that I wouldn't require the bonnet. I could just glue the whole top section together and just have it mounted on rods to the lower section as it wouldn't require the ease of access into the air chamber as the gas motor would. Its the lowest and most forward component so that there may be the occasional slight spray hitting it or if it stops on the water it may sink sightly and the that component is destroyed.

How do I go about completing the top of the lower section?
I have a few options here, I'm not sure if its worth using foam as it is only about 5mm high in places and with the expansion It would just have too much excess. Fibreglass, I can fibreglass the whole float, this is messy and time consuming but it would provide a structurally sound piece and would be pretty light. Remote controll plane film,  this is basically just a heat shrinking contact sheet, its light but it wouldn't add a whole lot to the structural integrity.

What does everyone think?


Monday, 4 July 2011

Main Body, Float

Sorry for the absence, I have been to the coast for a camping trip.

I finished cutting out all the balsa for the rest of the top structure and glued it all together. Then using the same taping method as the bonnet I taped it all up and filled it with the remaining foam. I started to trim it up but left it reasonably proud as it still needs a bit of foam.  One more canister and all the foaming should be done. I am leaving this section for now so that I can make any adjustments so the pieces fit together before filling in the remaining foam.

Under side of the motor mount.
Bunnings finally had some in stock so I purchased 5, 2.5mm pieces and 3, 5mm pieces to begin constructing the lower frame. $4.65 for a 5mm piece is much better than craft store prices. I also had to get more glue, I decided to try Selleys Liquid nails. I also bought some Selleys Plasti-Bond to try out.
The build so far.
When I got home I started cutting out parts for the buffet/float skeleton. I began with the area for the motor mount and then extended from there. This was mostly because it was the highest point and also needed to be very solid. I didn't worry about printing anything out for this as it was easier to just work out from the centre and then taper it to the required thickness. This only required the lengths of all the sections off the Catia model. I chose to leave the middle section open so that when I glued the 2.5mm sheets underneath this would allow for a bit of adjustment.
I then started a separate section for the rear whilst waiting for glue on the front section to dry. When both sections were dry I joined them together, I still chuckle each time I can see a representation of the actual size and what I have taken on.
After this was all dry I began to stick the sheets of 2.5mm on the bottom. These sheets should give me something to mount the skirt to and the whole section should allow it to float and keep the electrics dry should it die on the water. I began by sticking the first two sheets in the middle and this allowed me to mark out where it needed to go so the front could be adjusted an the back would be down the centreline. Working out from the centre I would just glue a sheet on each side. I then added in small pieces to make the surround as be seen from the picture below.
Weighted down to dry.

Whilst waiting for the glue to dry (about 30 mins - 1 hour depending on room temp) I started making other smaller parts out of the balsa off cuts. I started making a tower for the drive motor so that I could learn how best to work with the Plasti-Bond.


Monday, 20 June 2011

Build - Bonnet cont.

Day 3 -
This morning I sanded back the left half of the bonnet. With a flexible kitchen knife it is easy to cut through the foam. So I worked the shape down until it was roughly where I wanted it then with a light sand it was pretty easy to shape. There are a few gaps and larger air bubbles in the foam so I will need to find some putty or filler on my next trip to Bunnings to smooth out the shape. This evening I had nothing to do so I succumbed once again to art store prices and bought 3 sheets of 5x100x915mm balsa for 24$. 

With one of these sheet I completed the remainder of the bonnet and fixed the right skeleton to the left foamed section. I then used the same tape method as before and then used the remainder of the second foam canister to fill what I could of the right half. I also cubed up some of the off-cuts of foam from earlier today so that I could try and get as much filled as I could. Unfortunately it came up a bit short so I will leave this until I have to foam the rest of the top. After setting the bonnet aside to dry I printed out the remaining sections I would need and  traced out some of them onto one of the sheets of balsa before cutting it all out.
So far with this project I'm impressed with how light and sturdy the whole structure will be. It still amazes me that balsa wood is so easy to cut with a Stanley knife yet when teamed with the foam it is extremely strong. I am still undecided how I am going to get the bonnet to seal to the rear section and also around the tubing. I am thinking about using a tongue and groove set up for attaching the 2 sections and then having bolts running down through to the foam base.

Almost Complete.

Sunday, 19 June 2011

Build - Bonnet

At the end of the first day of building
I had the initial structure of the left part
of the bonnet all pinned in place.
Day 1 -
I printed out some of the parts I would require this morning then forgot about the project for most of the day. After a trip all over Sydney I finally found one lone piece of 6.5mm balsa wood in bunnings, it had been trod on and was a little scrappy but it would do as with the small selection I had I could begin the project. I came home and began to cut out some pieces. After a shopping trip for dinner I purchased 2 pieces of 5x100x915mm balsa for $8 each from a craft store, it was very expensive but it would allow me to continue as I had almost run out already. 

Day 2 -
 Bottom of the L-Bonnet after taping.
I began the day by finishing off the balsa structure of the left half of the bonnet. I initially just pinned it together before looking for more balsa wood in bunnings. They still hadn't got stock in so I just purchased some masking tape and sand paper. I also searched for some tubing to join the 2 sections together. There   was only 50mm PVC pipe so I decided that I don't have any tools to melt and bend it so I needed some flexible tube. They only had 40mm diameter clear vinyl tubing so this would have to suffice, it was a bit expensive at $16 for a 900mm piece.
Top of the L-Bonnet after taping.
When I got home I decided to super glue the skeleton together before taping up the top in preparation of spraying foam. I had a 340ml can of foam but didn't see the fine print saying that the 3x expansion occurs over time. So I sprayed it all in to a few of the compartments before running out. I then decided to make a quick trip to buy another 340ml can for $8 and whilst there noticed the expansion over time clearly printed on the larger cans. After racing home to salvage it I scooped as much as I could into the other compartments and topped off the remainder with the new can before setting it to dry.
I hoped to begin shaping the foam this evening but after cutting into the foam the centre is still gooey so it will have to wait until the morning.

<  After first can of foam.

 After foam expanding and drying. >

< After removing the masking tape.

Using masking tape to cover the top worked extremely well, as you can see from the 3rd picture above the foam comes out pretty close to the final product.

As always, tips and tricks for the blog or project are always welcome. 



With university exams looming I decide I need a project to take on.
Many years ago I began toying with remote controlled hovercraft, initially a rubbish bin lid with a vacuum motor and decided that now I'm in uni I need to make something that reflects this.
I began by messing around on catia to get a model of what I wanted and after about a week I had a shape resembling what my initial idea.
My knowledge of Catia initially was limited but along the way I discovered various new techniques for creating what I wanted. This meant that after working for a while on one model I restarted to redefine what I wanted and get the modeling process to go more smoothly.
After getting the 3d model I used the drafting component to get sections to print and then translate into balsa wood.

Below is the design that I had come up with.

Underside of Catia Design

Exploded view showing all the individual components. 

Here is an excellent resource for building your own Hovercraft.
Its full of information on how to build a hovercraft capable of holding a person.