I just had to enter GrabCAD’s latest contest. I couldn’t let a $2000 cash prize just slip away without at least trying a little. After a really busy week, I ended up with two days left before the contest deadline, and no model. My awesome family tried like hell to avoid me over the weekend while I threw my idea at Autodesk Inventor 2012.
I based the entire design in Autodesk Inventor 2012 Assembly Layouts, where I could use constrained 2D sketches to prove out my mechanisms BEFORE I proceed on to the component builds. Using sketch layouts are a great way to develop the moving components in a design without wasting any time with modeling.
I spent more time on some things than others. This is quite evident when you review the overall design. These are areas I focused in on the most.
The contest rules pointed out the difficulties of the existing screw knob actuator, and stressed the problems associated with the salt water environment. I have spent some time working with ocean going vessels, and understand exactly what they were concerned with. So, I chose a lever design: More torque to easily open when fouled by salt and compression to ensure better waterproof seal. After some substantial review, I decided on the j-hook over-centered design. It keeps the handle secure in either closed or open states. Additionally, this design was quite robust, however lacked the elegant appearance that one might hope for in a yacht cabin.
I needed a riser to keep most waves and water from entering the down-pipe. This was easy to accomplish, but reduced the airflow substantially. So I devised a simple approach. I used vanes and an open air base to trap the breezes on the weather deck, and direct them in a spiral toward the down-pipe. The bottom of the vanes were cut off to permit influent water to pass under the vanes following a path of least resistance and gravity.
The inner edge of the vanes (at the water cut-out) act as a vortex generator, and cause some of the influent air to climb up the lower edge of the vane. The vortex along the ascending lower edge of each vane will direct more air upward and over the riser instead of just bouncing about under the cover. This should hopefully provide more of a body of moving air to feed the cabin.
The vanes were also directed in such a manner that restricted any direct access to the down-pipe. All water (and air) must first travel along the vanes some distance in order to reach the inner chamber, and as a result will be slowed down, allowing gravity to do more of it’s job.
The vent must be waterproofed – not water resistant. I created a plunger that would both direct the air downward when opened, and seal off the down-pipe when closed. I used a press-on u-channel seal along the edge that presses both against the top edge of the down-pipe, as well as the top surface or the cover. This seals off the vent from water and air, and provides the spring-back that makes the handle snap into place in both the opened and closed positions.
I wanted the least amount of hardware that I could get in order to facilitate the easiest design to maintain. I used a clam-shell approach between the down-pipe and the ceiling register, and had 6 bolts inside the down-pipe. I didn’t want to scar up the deck with more holes than needed. The problem was no realistic method to be applied to mount the upper grate securely and still hold up to being accidentally kicked about. Inevitably, I added fastener holes along the base of the cover.
I wanted no springs and things that would break and fail. All plastic part joints were lined with standardized and commonly available stainless steel sleeves that are to be pressed (or molded) into the plastic parts.
Could Be Better
I am the worst critic on my own work. I have huge confidence in my engineering, but always find areas that I wished were better. I do like my design resulting from the items listed above, however, with 4 hours left to go, I started working on the ceiling register, and realized that I had overlooked some things.
With the lever centered like it was, it took up a substantial amount of area in the middle of the vent. I had wanted a cover in the middle that would cause the air to disperse horizontally along the ribs as well. However once the fastener mounts were added to the register, I realized that there wouldn’t be much center cover remaining. The fastener access holes and the operations lever chewed it all up. Rather than having a Swiss cheese cover, I just left it off.
I was totally jealous of a couple register designs, at least the elegance of them. This wouldn’t be the first time this happened, but I have a rule during contests and the like:
I never look at the competition’s work until I submit mine. This way I don’t end up stealing their ideas, even at the subconscious level.
Unfortunately, while I feel many aspects of my actuators are superior to others in certain instances, the beauty of some of the GrabCAD-ers’ entries is undeniable. Next time I’m teaming up with them. Take for example the fantastic rendering from Cemal Uslu. His design is just one of many in the contest that totally blew me away.
A weekend is not enough time to develop a thoughtful, robust, and elegant design. Other than my ceiling register, I am quite happy with my submittal. Based on some of the entries I saw last night, the judges are going to have their hands full. Good luck to all my GrabCAD friends. See you again for the judges results.
Derrek Cooper mentioned how cool it would be to run these things through Autodesk Simulation CFD 2012. I think I might just have to do that.