This instructable will show you how to replace a tire on an iRobot Roomba vacuum cleaner, using only household items. It is not meant as an expert's advice on casting, and there are probably many mistakes. The goal of this project was to replace a tire using only items that were available on-hand. If you don't have a house and kids, then you might not have everything you need (although it can all be easily obtained for little money).

For some reason, it appears that iRobot used two different rubber compounds on my Roomba 400 series vacuum. On one side, the tire has held up magnificently. The other side is as bald as [insert funny analogy here]. I'm not sure why.

It seems like the bald wheel has a softer rubber compound that shreds easily, leaving black rubber dust on the floor, mostly right near our one carpet - a small mat near the back door.

On top of that, it had a noticeable list to the left.

// if you're only interested in the process, and not the back-story, skip the rest of this step

Because I'm usually quite busy, I tried to do a quick-fix. I took a piece of bicycle inner-tube, and stretched it over the bald wheel. Then I swapped the drive wheels from either side, and stuck 'em back on the machine. (I thought that perhaps there was more of a frictional load on the left side wheel).

It seemed to work, because the tire wasn't shredding itself any more. Unfortunately, the drawbacks of this fix were brought up with a comment from my wife.

"What are these black marks all over the floor?"

Well, they seem to follow the pattern of some kind of automatic floor-cleaning apparatus with a limp. Yup, room-bot's spare tire was not up to the task.

However, he remained in this state for several months. Then came my wife's requested birthday gift - a stick vacuum that's really light and works pretty well. Also, it doesn't leave black tracks all over the floor.

Step 1: A Little Light Reading to Get Started...

Now that we had another convenient way of cleaning the floor, I took advantage and took poor old room-bot apart. I knew that this process would take several days (and with several days in between when I had the chance to work on it, it would likely be a few weeks before room-bot had completed his recovery).

http://www.robotshop.com has a good set of pdfs documenting the disassembly/reassembly procedures. They also have reasonable prices on used and new parts, but I'm extremely cheap, so I thought I'd give it a try on my own. I referred to http://www.robotshop.com/PDF/roomba-disassembly-discovery.pdf and http://www.robotshop.com/PDF/roomba-drive-wheel-discovery.pdf through the repair. I also used clear tape to affix screws to parts in order to keep everything organized.

Because the assembly procedure is so well documented, in a much more thorough manner than I could do here, I have skipped the disassembly and reassembly steps. Just be sure to keep yourself organized, and it's fairly straight forward as to what goes where. If you can't keep track of that stuff, this 'ible is probably too advanced for you.

As you're disassembling, it's a good opportunity to get rid of any little hair clumps or dirt that's really jammed in there. With five hairy animals at home (and that doesn't include me), I periodically do this just to keep the machine running in top shape.

The possibility of doing this on my own without spending a bunch of money on specialized equipment was made clear when I read mikey77's 'ible on Oogoo. Turns out, I have everything I need to do this fix, without spending anything!

Finally, a small caveat to this instructable. This was my first time ever making a mold and casting a part. I made some mistakes. I will attempt to describe what I did wrong, and what I believe would improve the process, if you decide to do this. However, if you know better, or have different ideas, please don't take this instructable as direct instruction. It's intended more as a journal of what I did, and what you might want to try, as well.

Step 2: Organize Your Materials

Things you're going to need include:

Philips head screwdrivers; #1 and #2 - $0 (a part of any decent tool kit)
small paintbrush - $0 (I used a model paint brush, but you can use anything, even a Q-Tip)
white glue - $0 (I "borrowed" some from my kids)
vaseline - $0 (From the diaper-changing kit)
baby oil - $0 (from the bathroom)
baby-food jars or some other suitable vessel for mixing and storing - $0 (left over from feeding the little one)
play-dough or some other non-hardening modeling type clay - $0 (used some of the old, mixed-up playdough, and even returned it after I was done)
silicone caulk (I used GE Silicone I) - $0 (left over from re-caulking the shower)
corn starch - $0 (left over from Oobleck-ing with my kids)
maybe paint thinner, if you want - $0 (you don't even need this!)
old newspaper - $0 (used a free local paper)
paper towel - $0 ("borrowed" from the kitchen, 2 sheets in total)
elastic bands - $0 (came with some veggies)

I've got an air compressor, so I used it a couple times, but it wasn't strictly necessary. I just like playing with tools, really.

Total Cost: Nothing! Realistically, if you need to buy everything on this list, then why the heck do you have a roomba?!?! I would imagine that most folks with enough floor space to need a vacuum would have at least most of this stuff lying around. If not, you can expect to spend about $25 for it (and you'd probably be better off buying replacement drive wheel assemblies).

Step 3: Preparation

Now prepare your materials.

You'll need to dilute some white glue with a little bit of water to thin it out. I didn't use any ratios here, it's not too specific. The point is to get the glue to soak into the paper easily, and reduce its viscosity. I would guess that I used a ratio of 1:2 water to glue. That is, half as much water as glue.

You also have to mix up your mold-release. I can't remember where I read it, but in the course of researching, I found out that someone used a mixture of baby oil and vaseline as a successful mold release agent.So that's what we're going to use. I went with a good, eye-balled half and half mixture. Be sure to mix it thoroughly - it can be tricky.

I put a coffee stir stick into my drill at a slight angle, and ran it for about 5 minutes. Don't worry about any trapped air bubbles - they don't matter. Shake it, stir it, do whatever it takes to mix it up.

Step 4: Make the Mold

This step was by far the most time consuming, labour intensive part of the whole project. It's also one I would change completely if I were doing it over again, so take what I've written here with a grain of salt. If you know a better way of making a mold (using only what you've got on hand), please use it. In fact, post it in the comments, too, so other people won't make the same mistakes I did.

For this step, you will need:
- the wheel you want to duplicate
- white glue
- vaseline
- baby oil
- play dough
- two vessels to mix in (I used empty baby food jars)
- paper towel
- newspaper
- coffee stir sticks or some other stirring implement
- small paint brush

Remove the good wheel from the Roomba. It will be used to create a mold, and the new tire will be a duplicate of this tire. It worked out for me that only one tire wore out - if you've had both tires wear out, use some play dough or modelling clay to recreate the tread pattern before you make the mold.

I used paper-mache to cast a mold of my tire. Begin by filling in any areas that you don't want to have covered in paper mache using the play dough. For my purposes, that meant I had to block off the inner part of the wheel, and the holes in the hub. Next, I wrapped the middle of the wheel with a thick layer of play dough, and cut it along the halfway point on the side of the wheel. This will be the break between the two sides of the mold. I also made a notch along the side, which keyed the mold sides to one another.

Use the small paint brush and the mold release to coat the half of the wheel that you're going to cast. A thin layer works well. Now tear off small bits of paper towel, and attach them to the wheel.

I used the back of the brush handle to stick the paper towel to the tread first. I dipped it in the glue, then soaked the paper towel and pressed it into the tread pattern. This was a bit labour intensive and fiddly, but worked out in the end.

Once the tread is covered, use larger pieces to cover the rest of the wheel. You want to build up several layers of paper towel. Finally, cover the paper towel in a few layers of newspaper to stiffen everything up. Then put it aside for while to dry. I only attempted the second side after a few days had passed.

Now remove the play dough from around the side of the wheel (but leave it around the inner diameter). Coat the other half of the wheel, and the flange of the mold you just made, in mold release, and cast that side, too.

Unfortunately, I didn't get any good photos of the mold in-progress. They all came out blurry, glue-y, or both. But it's paper-mache. You get the idea!

What I did wrong: I used the glue mixture to "seal" the inner surface of the mold once it was totally dry. This re-hydrated the mold enough to let it warp slightly, making it out of round. Any time your mold needs to dry, stick it back on the wheel. It will take longer, but it will be worth it.

If I were doing this again, I would probably make a mold using some type of liquid - perhaps a coating of epoxy - to pick up the details, then cover that with the paper mache. The final tire shows all the defects in my poor paper-mache-ing skills...

After thinking about it for a while, if I had to make another mold, I would likely use a combination of modelling clay, a tuna-fish can (or similar shape), and a mixture of epoxy and paper fibers. Just a theory at this point, but if the new tire doesn't hold up, I may put it to the test.

Step 5: Remove the Old Tire

Now you've got to get rid of everything in the way of where the new tire will go. Take your wheel that you want to fix, and using a hobby knife or exacto, cut gently through the tire rubber. It is fairly soft, and cuts easily.

Now pull it away from the wheel. It wraps around the rim a little bit, but comes away easily. It is not adhered to the wheel in any way, so it comes off clean.

At this point, I washed and dried the wheel to ensure that it was completely clean. Pretty straight-forward.

Step 6: Prepare the Mold

Before you mix up your Oogoo, you want to be sure that your mold and the core (i.e. the wheel) are all ready to go. There are a few steps to prepping the wheel and mold to make sure that everything works well.

First off, test fit the wheel inside the mold, and think about how you're going to put it together when there's a bunch of sticky, goopy silicone trying to get out of the mold. I planned on putting some Oogoo into the tread area of the mold, and smearing some around the outside of the wheel rim, then smooshing it all together.

This should demonstrate where problems might arise. In my case, a lot of silicone was likely to ooze out and fill the interior of the wheel, making it difficult to get a clean cut on the inside of the rim. After some experimentation, it turns out that the back of the silicone tube is a little smaller than the inside of the wheel - and as I was picking old silicone off the plastic tube, I realized that this would work well as a form for the inside of the wheel.

Cut a good length off the back of the silicone tube. Make sure that you're not cutting into the silicone compartment! This was not a problem for me because I was using the remains of a mostly-used tube.

Now cover every part of the wheel that is not supposed to have rubber on it with the mold release. Do the same to the entire interior of the mold. This stuff is slippery and sticky, so make sure that you're careful to keep the casting surface of the rim clean (so that the tire sticks to the wheel).

Now you're ready to get mixing.

Step 7: Mix Up Your Rubber

For my tire, I used a mixture of silicone, paint-thinner, and cornstarch. In retrospect, I would have omitted the paint thinner as unnecessary and smelly.

I didn't do any measuring here - I just squirted a bunch of silicone into the pot (more than I thought I needed), mixed in some paint thinner to get it a bit more workable (which was a first timer mistake), and mixed it thoroughly. Then I mixed in about 1/2 of the volume in corn starch.

You can use a lot of corn starch. A lot. Read the Oogoo 'ible to learn more. I didn't, and for my purposes it worked out fine. I was casting a fairly thin tire, and probably could have omitted the cornstarch entirely. However, from reading about it, the cornstarch makes the Oogoo more solid, and less flimsy. If I were to do this again, I would probably put in a lot more cornstarch to get a tire that was approaching the solidity of the stock tire.

So, to sum up:
Silicone - more than you think you need.
Cornstarch - more than I put in - a 1:1 ratio worked for mikey77
Paint thinner - don't bother, it smells bad and doesn't do a whole lot.

Step 8: Get Mold-y

Now take your rubber, and smear it into the tread area of each half of the mold. Put a lot in there, and try to get a uniform thickness. The way my mold was set up, the inside flange was the depth of rubber that I was going for, so I just used that as a guide.

However, here's something else I did wrong - I didn't work the rubber into the mold well enough, leaving a few voids. Nothing I couldn't fix later, but do your best to fill every ol' nook and cranny with rubber.

Put the piece of silicone tube inside the wheel now. I didn't, and I should have. Trust me - do it now.

Now smear some onto the rim of the wheel. This is where things get tricky (and sticky) because you can't put the wheel down! Some creative finger-maneuvering will help out here.

Stick the wheel into one half of the mold. If you made your mold like I did (covering the flat side of the wheel), there's a round groove that you've got to fit the hub into. Do it now. Let it ooze out a bit - don't worry, you can fix it later.

Now the other half. Things are gonna get sticky, so just be ready to let it goop out onto a sheet of newspaper or something. Maybe your lap.

Finally, stretch the elastic bands around the mold. You want a snug fit. Now hold the back of the mold, and press down hard on the rim of the silicone tube to seat the wheel into the mold. You might see a few white "snakes" of rubber squeeze into the inside of the wheel - that's a good sign. It's showing you that your mold is all full, and the rubber's gotta find some other way out.

Now leave it for a while. At least overnight. I left mine for a day and a half.

Step 9: Get De-mold-y

Okay, maybe de-mold-y isn't a word, but it's what you're gonna do.

Take the elastics off.

The trick here is to pull the mold off the wheel, while leaving the tire behind. I used a compressor and a sports-ball inflator needle to squirt some air between the mold and rubber, and between the silicone tube and rubber, just to encourage release.

Pull gently on the mold parts, and they should eventually come off.

Before you take the silicone tube off, trim the excess rubber using a sharp hobby knife. It's easier to do it now, while there's something for the blade to press against.

Once all the mold pieces are off, trim off any excess rubber.

Step 10: Now Fix It

Okay, so with my mistakes, I had some fixing to do. You will probably not (hopefully).

I had some voids from my mold that I had to fill. I just took plain old silicone, straight from the tube, and smooshed it onto the voids in the tread. Then I stuck the molds back on for another day. When replacing the molds, I rotated them 90 degrees from how they were originally placed. I hoped this would mitigate the defects in the mold (and in the molder).

Easy fix. Hopefully you can avoid this step. If not, don't worry, the final product won't reveal your mess-ups.

Step 11: You're Almost Done!

Now that you've got your new, improved tire on the wheel, you're ready to put the wheel back on the roomba. Just reverse the disassembly steps, or follow the guide from robotshop.

Mount the wheel on the hub, then check that it fits properly and turns before you complete the reassembly. Easier to fix it now than to have to go through the whole rigamarole again!

While I was reassembling, I took the opportunity to blow all the dust bunnies out with my compressor.

Now test her out!

Step 12: Revel in the Glory!

If need be, recharge your roomba before you give it a test run.

Press the button, listen to the cheery little chirp, and then crouch down low on the floor and enjoy your handiwork.

Aaaaah. Life is sweet once again.

Step 13: Hindsight

Overall, I am really happy with the results of this project. Thanks to mikey77 for the Oogoo idea (the catalyst, so to speak, behind my decision to take on this project), robotshop.com for the helpful pdfs (so I didn't have to write them), and to the whole community here for being so pro-DIY.

I'm not sure how long this tire will last, because it came out softer than I expected. Next time I'll do things a bit differently (and post a second 'ible to update the crowd/cloud here).

In retrospect, there are a lot of things I would do differently. Here's a list...

1) Use something else to make the mold. The paper mache did not pick up the tread as well as I had hoped. I was thinking of using a coating of epoxy (pretty thick epoxy) before the first layer of paper mache. Maybe even with some paper fiber embedded in it to solidify it. Something non-water-soluble would've helped a lot.

2) Don't take the mold off the good wheel until absolutely necessary. I fiddled around with the mold, and didn't leave it on the form until it was entirely dry. It ended up out-of-round a little bit.

3) Don't bother with the paint thinner. I thought I would need my rubber to be more fluid than the Oogoo in the instructable, but it wasn't necessary. Also, my tire is smelly now. Not a big deal (unless you like smelling your roomba's wheels), but it wasn't needed.

4) Be really thorough when filling your mold. I rushed this a bit (it was late, I was tired, and I've never done this before). You'll avoid having to fix your mistakes the way I did.

5) Use a lot of cornstarch. You want your rubber to be firm, not floppy. I don't know how long my tire will last, but I'm hanging on to my molds just in case this version ends up too flimsy to last very long.