Before I can make my Roomba (I need to name this guy to make it easier to talk about him -- suggestions taken in the comments) hover, I should do some research into what it will take and how to actually go about it.
The simplest plans I've seen on line are found here: http://amasci.com/amateur/hovercft.html (better pictures can be found here: http://vip.vast.org/HOVERCFT/home.htm). These plans should scale down well to my Roomba since the plans call for a disk shape and the Roomba is already disk shaped. This is the design I will be basing my HoverRoomba on.
Obviously, I won't be using a leaf blower or shop-vac since the Roomba already provides this capability. The Roomba's vacuum motor is located in the dust bin and looks like this: http://www.roombaexchange.com/proddetail.php?prod=345252&cat=20. My main concern is whether this will provide enough "oomph" to get the craft off the ground. If it does, phase one becomes a pure construction project that should take a weekend to complete. Otherwise, finding the right fan that will work (powerful enough without too much draw) could become a challenge. For this project, I will be building this in a manner where my Roomba actually rides the overcraft instead of rebuilding the entire undercarriage.
The Roomba's critical dimensions are 13 inches in diameter and about 10lbs in total weight (including battery, brush deck, etc.). If weight becomes problematic, I can shed some of it by removing non-essential pieces (i.e. the brush deck as was done in the Airsoft gun mod) but I would like to aviod that because it makes the mod more of an "accessory" than a "rebuild".
From this link: http://scitoys.com/board/messages/1/2331.html?1203676370 we see that the critical factors are surface area (40.85 sq. inches) and weight (10lbs). In order to get off the ground, I need at least 0.245 lbs/sq in. According to this page: http://www.olshove.com/HoverHome/hovcalc.html I need to move about 1.8 cubic feet per second (184 cubic meters per hour).
I found a research paper (http://www.stevens.edu/ses/me/fileadmin/me/senior_design/2007/group01/) that names the fan motor as the Mabuchi FK-260SA-12300 ( http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=fk_260sa ). Using the picture of the motor listed earlier, we can see that the fan has 16 to 20 blades and should spin at around 7200 RPM and from the specs puts out about 0.002 HP.
So, what does all of this mean? Nothing really because I don't know enough about airflow, etc. to take it any further (and haven't had a lot of luck finding the formulas I need to see if it will work). In the end, I'm going to just try it. If the vacuum fan doesn't work, I'll have some numbers I can use to compare performancec stats against. I've looked at some PC fans and most of them are underpowered for what I'll need, but since the voltage draw of a PC fan is lower than what the Roomba motor will draw, it might be possile for me to use two PC fans to accomplish the task.
Next up, planning and materials.