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iRobot Scholarship idea : Pool Cleaner

I've seen mods for the roombas before, where the robots are water sealed, and then the wheels are turned into propellers. My idea is that I could water proof the robot in plexi glass, or something, and then a net on it, to collect all the leaves, dead bugs, and other stuff that collects on the surface of a pool. normal pool cleaners only vacuum the floor of a pool, and it takes days for floating leaves and other grime to sink to the bottom. With a robot like this, I could just set it in the pool, and let it clean everything up. What's nice is, when company is coming over, it's embarrassing to have a dirty pool...this modification would allow you to quickly clean up your pool-even on short notice. Update (for some clarification): What I would want to do, is make a case for it, so that you can simply remove the wheels, and connect the propellers/steering device to where the wheels were, then just place the roomba in the watertight case, and it would be able to swim around and clean! Also, i'm working on some sketches of how it would work. I'll post those when they are done.

Pool Skimmer.jpg
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Aug 28, 2007. 8:55 PMewilhelm says:
This might be a little late, but one of the tricks I know for building underwater robots is to pressurize the inside of the robot; so, if there are any leaks, air leaks out rather than water in.
Aug 3, 2007. 6:10 AMNachoMahma says:
> I need help finding rubber bushings . O-rings epoxied to the case? Would need to be a relatively loose fit or you'll lose too much power from the drag. . cooblades "grease seal" might work. . > Also, i'm seeing measurments on bearings such as 5x11..what does that mean? . I used to know that, but can't recall it to save my life. It's hell, getting old. Check out the web site of a bearing manufacturer (eg, Timken) and see if they have a page that explains it.
Jun 30, 2007. 12:44 AMSacTownSue says:
Mighty pricey! Yours is really interesting tho.
http://www.irobot.com/sp.cfm?pageid=316
Jun 21, 2007. 11:16 PMW_world says:
Really neat idea. Have you considered making it submersible? you could use a "swim-bladder" type system to ballast it. I think it would be cool if it could seek out debris in a 3D setting; you could use a camera to find the debris against the solid color of the pool walls.
Jun 20, 2007. 11:09 AMloubard says:
Isn't this similar to the Scooba product iRobot already available? Great CAD btw.
Jun 19, 2007. 6:57 PMNachoMahma says:
. That looks great - both the design and the drawing. I really like the funnel/scoop design. I think the prop needs to be closer to the centerline or it will go in circles - some bias on the rudder may handle it.
Jun 17, 2007. 7:45 PMNachoMahma says:
> How big/how many blades do you think a propeller for something like this would need? . If noone else has an answer, I have a friend that has a speedboat (and seems to know quite a bit about prop design) that I can ask for some tips. Not sure how well what he knows would scale down. I'm betting that the speed you will be turning the prop and the amount of torque/HP available will be the major factors.
Jun 18, 2007. 5:26 PMNachoMahma says:
. I talked to my friend and (after much discussion) he recommends getting a prop with ~18" pitch and a diameter of ~4". This will probably be too much prop, but he thought you should be able to chuck the prop to a drill and use a file to make the prop smaller and smaller until you get the speed you want - if it looks too ugly get a new prop of that size. He said you may want to start with a 3" prop, too many variables to be sure.
Jun 18, 2007. 9:03 PMNachoMahma says:
> do you think there's a way to water proof the bearing ... . Not that I know of. Most of the brgs I've seen that needed to work underwater either used a pressurized lube system or were designed to use water as the lube. I'd try it and see what happens - it'll probably last long enough to get your project built and a video shot. As cheap as they are, even a poor student can afford to ruin one or two. Silicone spray may help, but it's as expensive as the bearings. . . That's great having the hobby store nearby. I'd try browsing the aisles for ideas and inspiration. They probably have all sorts of gadgets, widgets, and gizmos that will come in handy.
Jun 18, 2007. 10:07 PMNachoMahma says:
. Have you tried seeing how the R/C boaters pierce the hull? Remember that my background puts me at a disadvantage at the scale you are using (when you're using a 100HP motor, frictional losses from a bearing shield just don't matter). This kind of thing is what keeps boaters up at night experimenting and I bet they have much better ideas than I.
Jun 17, 2007. 11:20 PMNachoMahma says:
. No idea on the specs of a Create. If you can't find the specs on the web site, try contacting someone at the company that might know.
.
. I'll talk to my friend and see about getting y'all together. I do remember him mentioning a web site called Scream and Fly. Just checked and sure enough, http://www.screamandfly.com/ is a site for "hot rod" boaters - try posting to one of the forums. They may even be able to tell you how to guesstimate. LOL
Jun 17, 2007. 11:32 PMNachoMahma says:
. Well... I went to the iRobot site, but everytime I'd get close to what I thought would be helpful I'd get a Flash not installed msg. The info seems to be on the web site, but I can't tell. If not, it appears that they have a few good ppl in the forums - maybe one of them knows (or can give you some ballpark figures). Wouldn't be surprised to discover one (or more) of the engineers hangs out in the forums.
Jun 15, 2007. 7:38 PMcooblades says:
Oh btw just to warn you water robots will always veer off course. Also the propellers will create a counter torque which will make your robot veer into the wrong direction so when you mount them, make sure they are not straight but at an angle to correct this. My guess if the propellers are anything like RC planes it should face the bottom right. Sensors will be a must if you want anything that does more than get stuck at the edges. Especially for a skimmer. The level of difficultly programming a water based robot goes from Crawler, Skimmer and Hovering being the hardest. Good luck!
Jun 16, 2007. 11:06 AMTheMadScientist says:
oh really? i always found that skimmer was the hardest, followed by hovering then crawler... always found that all of the challenges of actually being partially submerged in water far outweighed the challenges of keeping the hovercraft above water...
Jun 16, 2007. 2:12 PMcooblades says:
I meant hovering underwater in the definition "wavering between conflicting positions". In the video I posted the first robot is a hovering robot the second was a skimmer and the third was a crawler.
Jun 18, 2007. 10:03 AMTheMadScientist says:
ah, sorry, I mistook hovering as my favorite type of land robot!
Jun 15, 2007. 7:56 PMcooblades says:
Leaving it random sounds like a great idea you pretty much will save yourself the load of coding I had to go through.

Oh btw here is a video of a underwater robot I built for a conference. (the first one). Its made from Lego Bricks and a programmable controller.

http://www.youtube.com/watch?v=J5ndxtPJ6Bw
Jun 15, 2007. 7:36 PMNachoMahma says:
. cooblades, that is AWESOME!
. Weissensteinburg, if anything I say contradicts cooblades, I think you know who to listen to - I'm not even in the same league (maybe not even the same game).
Jun 15, 2007. 8:15 PMcooblades says:
Thanks!
Jun 15, 2007. 7:29 PMNachoMahma says:
. It may turn out to be negligible, but the effects cooblades describes may cause the 'bot to "huddle" toward the middle or a corner. I'd keep an eye out for it.
Jun 16, 2007. 4:10 PMNachoMahma says:
. Have you done any prototyping of a mag coupling yet? The more I think about it, the more problems I see for a DIYer on a tight budget and short schedule.
. It will need some type of thrust bearings to keep the magnets apart. The bearing mounts will need to be sturdy, which may present space or aesthetic problems. For your use, plastic/plastic or plastic/steel may work, which would make them easier to fabricate, ie, no "real" bearings, just pick low-friction materials.
. Alignment may present problems.
. The distance between the magnets (hull + 2 airspaces) may require larger and/or more expensive magnets that don't fit your space or budget.
. These may not be a problem for you, but I think you need to do some experimenting before you get too far with your design.
.
. While I think the Cool Factor of a magnetic coupling is orders of magnitude greater than cooblade's grease seal, the grease seal should be much more practical. Very easy to seal the hole in the hull and it shouldn't be too hard to find a "grease" that won't leave a slick.
Jun 16, 2007. 5:21 PMNachoMahma says:
. But they will be strongly attracted to each other. If you don't force them apart, they will slam into the plexiglas and not rotate. . There will have to be an air gap between the hull and magnets (or they can't turn, see above) with a little extra thrown in for manufacturing tolerances. A pretty big gap considering the scale. If you were using the 4-6" magnets I'm used to, the extra distance wouldn't be a big deal.
Jun 16, 2007. 7:34 PMNachoMahma says:
. Exactly. With the magnets I'm used to, 1/2" gaps (magnet coating, barrier, etc) were the norm, but this was with much stronger magnets.
. I'm not trying to talk you out of it - I think you can do it - just that I'd run some proof-of-concept tests before trying to design around it. It's shape/config may change drasticly before you nail it down. Maybe hold a couple of good disc magnets about 1/4" apart and see if it feels like enough torque can be transmitted.
Jun 16, 2007. 7:53 PMNachoMahma says:
. I'd try to make the test as close as possible to the design in your head. . Not sure how bar and disc magnets compare/constrast (other than the shape). I'm just assuming that since the ones I've seen use discs, then discs are better.
Jun 16, 2007. 8:15 PMNachoMahma says:
. LOL So many options, so little time. . If your plexiglas is in short supply, use plywood (or something similar) to make your "first drafts." If an idea doesn't work out, you haven't ruined the plexiglas.
Jun 16, 2007. 9:01 PMNachoMahma says:
> I think I would use card board and hot glue...
. Great idea! That should float long enough for testing and the price is right. A good coat of paint/varnish/wax/etc and it might float for days (and would probably make it more rigid, ie, more like plexiglas, also).
.
> *really hopes to win*
. Your's is the most practical idea I've seen.
. The thiefbot comes close. Very high Cool Factor (especially with the right appearance and sound effects), but finding/acquiring random objects may be difficult to implement even if he's not picky about what gets picked up.
Jun 15, 2007. 4:38 PMcooblades says:
I've done marine robots before. If you are worried about water proofing, try a motor shaft in a long narrow tube with some grease in the middle. That should prevent a lot of water from backing into the motor. For your other connections try using Marine Goop, it is used to seal boats connections and its pretty affordable. Magnetic coupling is going to cost you some energy due to friction if you plan to use it so be careful what you choose. For floatation you can use home insulation foam boards (approx 1-2" thick). They are sold in large sheets and very cheap at Home Depot. A hot wire cutter can help you cut that to some pretty nice shapes.
Jun 15, 2007. 6:45 PMcooblades says:
Sounds like it would be pretty good. My family owns a fish pond and we grow lily's. To ring in the lily's so they look nice we cut a rubber tube and use a extending joint to join the two ends for an airtight seal. The trapped air is enough for it to float.

However I think you are confused with what I was talking about earlier. Here is a link to clear things up
http://www.owenscorning.com/around/insulation/products/insulpink.asp
These boards are NOT fiber glass. They are Polystyrene and pretty safe to use for hobby work such as this. Here is a link of someone who used this to make a game icon. You can carve very nice models using a Hot Wire Knife

http://oz.games-workshop.com/games/40k/daemonhunters/terrain/icon/default.htm
Jun 15, 2007. 5:12 PMNachoMahma says:
. I like your grease seal, but would it have less drag than a mag coupling? The only drag to a mag coupling is the bearings. Grease can be pretty sticky. . Would the grease stay in place well enough not to leave an oil slick on the pool? If it will, your idea would probably be easier to implement.
Jun 15, 2007. 6:57 PMcooblades says:
Primarily we add a small amount grease or oil as a lubricant so it reduces friction. Whether or not it is less friction than a magnetic coupling depends on design features out of my control so I wont give you a definite answer on which is more frictionless. Regarding contamination I wouldn't worry too much about it. Oil and greases don't dissolve or mix well with water. Plus you're only using a drop and there are many safe and clear greases you can use. In the past I have used petroleum jelly from the store cause it was easy and cheap. The greased axle design is really simple and cheap. Go to a R/C hobby store and you can buy the tube, axles and grease there. Its a pretty basic technique in RC boating.
Jun 15, 2007. 7:03 PMNachoMahma says:
. OIC. You weren't comparing the two, just something to be aware of. . Since this project is for a swimming pool, I'd think contamination would be pretty important - who wants to swim in an oil slick? But, as you point out, it should be easy to manage. . It'll be interesting to see what he does. Wouldn't be surprised if he finds another (better) way to do it. ;)
Jun 29, 2007. 12:39 AMaarone says:
I don't think Radioshack'll carry anything like that. Try a hobby store.
Jun 15, 2007. 7:32 PMcooblades says:
I order them from tower hobbies. Their cheapest are about $1.15.

http://www2.towerhobbies.com/cgi-bin/wti0093p?&C=BGF

If it were up to me I would just take apart the irobot and rip the connections off the motor and use a external motor to power the boat. It costs more but its easier. However your pipe idea is very novel, I would love to see a video if it works.
Jun 18, 2007. 12:25 AMcooblades says:
I bought the LXE473 because it fit onto a Lego axle. Honestly for something like this you can't go wrong ordering a few different styles and just use trial and error.
Jun 18, 2007. 1:08 AMNachoMahma says:
. For the heat-shrink, I'd try a local electrical/electronics supply house (where the local electricians go to get their parts) or hobby store (eg, Radio Shack) - shipping will eat you up on something like that. Explain what you're doing to a manager and you might get some stuff for free - especially if you promise to put their logo on your 'bot (check the rules first). . Try something similar at an industrial supply house for the bearings and other mechanical parts. They may be able to make some valuable suggestions, too. . cooblades is probably right about the prop not being that critical. I wouldn't think that speed is that important for a pool cleaner as long as you can produce enough thrust to push a full net around. An R/C boat site might be the best place to ask if you want a definite answer. I'll try to track my friend down tomorrow, but I have the feeling that what he does won't scale down very well and all he'll be able to provide is generalities.
Jun 15, 2007. 8:01 PMcooblades says:
Cool, keep it modular!
Jun 16, 2007. 11:07 AMTheMadScientist says:
woot, modular robots FTW (trade that gatling gun out for a rocket launcher ASAP!!!!)
Jun 15, 2007. 7:09 PMNachoMahma says:
> Where can I get a pre made propeller? Radioshack, maybe? . I'd start looking at radio control (R/C) sites. Shouldn't matter if it's boats/planes/cars/whatever. Their equipment is designed to be light and rugged, if not always cheap. Should be able to find all sorts of props, gears, levers, cams, servos, etc. Don't know if a ducted fan design would work for the prop, but it would look cool.
Jun 15, 2007. 7:24 PMNachoMahma says:
> I'm volunteering at my temple . Kudos for volunteering and Shalom. . . I'm guessing here, but I don't think a computer fan will work well - too many blades and designed to run at higher RPMs than what I think you're looking for. Might work for proof-of-concept, but I'll bet you need a "hydraulic prop."
Jun 16, 2007. 2:21 AMNachoMahma says:
> What do you mean by hydraulic prop? . One designed to move water (vs. one designed to move air).
Jun 16, 2007. 2:55 PMNachoMahma says:
. ROFLMAO! As you can probably tell, I'm trying to apply what I've learned in an industrial environment. It wasn't my money and efficiency is not as important when you have a 480V/3-phase power source. You seem to be doing a good job of translating what I suggest to The Real World.
Jun 16, 2007. 3:42 PMNachoMahma says:
. Not at all. I would not have sent the PMs if I didn't think you had a pretty good head on your shoulders and have a real good chance of making something that works well and is practical. . And you seem to know what you can and cannot do with the knowledge/resources/time you have available. Some of the other proposals are very good, but I doubt that the proposers are accurately appraising their capability to actually build it (particularly time and money).
Jun 15, 2007. 9:13 AMTheMadScientist says:
erm, a little bit of a suggestion, think submariene-like, adding ballasts or something like it, allowing your bot to skim any part of the pool, top, bottom, or anywhere in between.
Jun 15, 2007. 2:01 AMNachoMahma says:
. By using a magnetic coupling, you won't have to breach the integrity of the waterproof case.
Jun 15, 2007. 3:30 AMNachoMahma says:
. I've never actually seen a mag coupling as small as what you need, but have to believe they are available (probably pretty easy to build). The ones I've worked with were on pumps used for pumping very hazardous fluids and you didn't want to take a chance on a leaky mechanical seal. It's just two disc magnets with your hull between them. You should be able to find what you need at a magnet specialty store. I think I've seen some stores mentioned in a few on the iBles. . I'd try using rubber bands to hold the wheels against an axle that spins the coupling.
Jun 15, 2007. 3:32 AMNachoMahma says:
. I'm not sure how these things steer, but you may have to use two axle/coupling/prop assemblies; one attached to each wheel.
Jun 15, 2007. 1:52 PMNachoMahma says:
. OIC. Then it may be simpler to use a single axle. . . Going by the mag couplings I've seen and the Theory of Operation found in some of the manuals, it's just two disc magnets with a gap. I don't think you'll need a lot of torque, even when your net is full, so you shouldn't need the expensive "super" magnets, just some good "regular" ones. I'll guess that somewhere around 1/2" to 1" in diameter would work well; depends on how thick your hull is and how strong the magnets are.
Jun 15, 2007. 2:19 PMNachoMahma says:
. Since navigation is random, I don't think steering will be a big deal as long as you don't end up going in a circle. Rudder placement is probably not critical (though fore or aft would probably be best) as long as the prop thrust is not off-axis. I think what you have described will tend to go clockwise because of the offset thrust/drag. . It might be too complicated for a short deadline, but maybe you can combine thrust and steering by making your prop mount rotatable. Like what modern ships and tugs use.
Jun 15, 2007. 2:36 PMNachoMahma says:
. If it makes it to market (I have no problem seeing this on a late-night TV commercial - "Call now and we'll include a free pair of sunglasses. All you pay is shipping." heehee), don't forget your Ol' Uncle Nacho. :)
Jun 15, 2007. 3:52 PMNachoMahma says:
. If I see this on one of those annoying, hour-long "infomercials" I will track you down and kill you ... slowly. LOL . Seriously, I think it would sell as a stand-alone unit. Slap at PV cell on top of it and it won't even need batteries, it'll just sleep at night and work all day.
Jun 15, 2007. 1:41 AMtrebuchet03 says:
In case you didn't know.... iRobot does make a pool cleaning robot -- the Verro ;)
Jun 15, 2007. 2:14 AMtrebuchet03 says:
Ahh, gotcha -- you mean a skimmer. We had this very same problem when we first moved into our house.... I fiddled with the water jets a little to make sure the surface was flowing (in a circle :p) to make sure the built in skimmers were doing their jobs.
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