The Big Day

It's a very important day in every boy's life when he gets his dome:


Lots of work to be done on it. I'm starting to review everyone's blogs about the steps they went through preparing their domes.

MM

Extra Skirt for Sale

When I was building my skirt, I ended up cutting two bases. So I took a bit of time recently and got the second one finished up. Full disclosure: the full length of the piece is about 1/4" short from the specifications. But everything else fits fine. I'll sell it for $90, plus shipping. It's made of MDF. It's been sanded thoroughly and touched up. It should be very close being paintable. I can cut the center square out according to the plans for a retractable middle leg if you want.

Skins

I dove into the skins project this weekend. I had been thinking about how to proceed with the full size plans I got and getting them transferred to the sheets of .040 styrene I have. I tried copying them over with a pencil and ruler but this was time consuming and inaccurate. A pencil mark is pretty wide and sloppy. I also tried using some spray on adhesive and gluing the plans down to the styrene. The first try didn't work out. The stuff on the left from Elmer's leaves a residue and really screws up the styrene.



So I tried the stuff on the right. It's supposed to be lighter duty for tacking art pieces down. I also applied it to the paper not to the styrene. That seemed to help. There is still a residue left over when you peel it off. But denatured alcohol seems to take it off quite effectively. So I'll just rub down the droid when the skins are all on.

Styrene is cheap--$15 a sheet--so I am anticipating taking a few tries to get this right. There are a lot of alignment issues with the frame, the front and back skins, the second layer skin, and top and bottom edges, and so on. And a little screw up could be really visible. I am also trying to sort out which of the panels on which layer--inner or outer--I need to cut out. And I am going back and forth about doing a back hatch. I know that having one would be really handy for working on the robot's insides and electronics, but I know that alignment is going to be an issue and it'll be really hard to get it to look clean and good. Furthermore, in all of the pictures I have been able to check, the real R2 does not have a back hatch. So that big cut out rectangle on there is bugging me. The alternative is to access everything inside him through the top after taking off the dome. I'll know more about what I want to do once my dome gets here. So here's the inner front and back layers on, or at least, an early attempt at cutting them right:



Starting to look like the real thing.

After searching around town in every hardware store, plumbing supply, and lumber yard, I found some PVC that's about 3" outside diameter. It's really 2.87 or so, but there don't seem to be any true OD 3" pipes in America unless you special order some metric pipe from overseas or something. I'm not that patient. So on with the battery boxes.

I set up the band saw with the fence and a board on the other side (unlike the posed picture here), and sliced the pipe down the middle. No special tricks here other than trying to keep the blade from drifting and trying not to let the cut corkscrew in the pipe. I snapped a chalk line on the pipe, but I still had some drift. I actually cut the pipe all at once, also unlike the picture, and then I cut cross sections to fit the blueprint specs. These half pipes will form the end caps on the battery boxes.



Then, after figuring out the dimensions I'd need, I cut some side plates. Useful tip: Once I got my table saw crosscut jig set to cut the pipe lengths, I cut the lengths on these side plates at the same time. That way the end caps and sides are exactly the same dimension.



And I cut some bottom pieces. I carefully shaped out one piece to fit and then used it as a template for all the others. Then I sanded the curves onto them on the belt sander. My sander can flip up to 90 degrees so you can set your piece on the table and sand the edges. Very handy feature for this sort of thing. Again, Grizzly tools rock. I got this big ass sander from them several years ago. It's 220 volts, 6 inches wide, and 40 inches long, or something, and it completely rocks. I could grind down a car with it if the need arises. But that also means that I have to be very gentle with fragile plastic pieces like these.



Once I had all the pieces cut, I started gluing. I improved my PVC glue technique a lot here, and killed a lot of brain cells breathing fumes. On the side plates, I cut some 1/2" wide strips and glued them inside with half of them overhanging the edges. This overhang would go over onto the half pipe pieces. Sorry, no picture. That way I had a good gluing surface for the joint, and so that the half pipes and the side plates weren't just butt glued together. I also found that once I had slathered on PVC cement onto one of the gluing surfaces, the trick was to press the two pieces together--not too hard--quickly get them alligned, and then just hold them perfectly still for 20 seconds or so. That let's the cement get an initial setup. I would just lay the pieces aside than and try not to handle them at all for a few hours. The label says that the bond strengthens a lot in 24 hours and that seemed to be right.

Speaking of labels, I a few years ago when I was building something, I had a revelation. This is going to sound stupid--because for 20 years I was stupid about it--but if you just read the damned directions on the label of stuff, or the manufacturer instructions, you'll get a wealth of accurate information that will make the difference between a project that is a failure and one that is a complete success. On the flip side, the place you should not be getting any advice about how to build something is from some snot nosed, dumb ass 17 year old who works at Home Depot and why has never swung a hammer in his life. No offense if you are a snot nosed, 17 year old dumb ass who's never swung a hammer.

And while I am on the topic, the one question that every hardware store employee, lumberyard troll, or counter help asks and that drives me completely insane is, "What's it for?" That is, you come in asking for a piece of foam rubber, or some 1/4" PVC sheet, or, God forbid, a piece of pipe that has an outside diameter of 3", and the first thing they say is "What's it for?", as if whether or not they have will depend on what you're building. I resist the urge to say, "none of your goddamned business," and just try to get them to tell me where it is without my having to explain WHY I am building my own scratch built, fully remote control R2D2. If you tell them that that's why you need the item, they you're less likely to get them to tell you where the pipes are or whatever.

Ok, I'll settle down.



When are started on this phase of the project, I realized that the setup for the battery box parts was most of the battle, and that I could crank out pieces for more of them than I need while I was at it. So at each point, once I was set up I cut enough to make 5 pairs of boxes. I had it in the back of my head that I could sell these to the builder's group if there is interest. I've learned a lot from reading about everyone's experiences and some people might not have some of the tools I have. So email me if you want to buy a pair. I'll have pictures of the end result posted shortly.

A few other notes. As I was designing my cutting plan for the pieces, I tried to build them so that all of the edges that would need to be trimmed would be on the outside, instead of on inside corners. That way, I could easily get to them with the sander and save myself a lot of work.

Once all of the pieces--I think there are 14 total--were glued together, I roughed out the curves on the top with the band saw to save my having to sand too much material off. Then I finished the job with the sander. That worked out pretty well. I have started to put primer on one pair and it looks like they'll need a minimum of filling into any gaps between the pieces. More news on those shortly.

I'm looking ahead to building the shells for the outer feet. I got some 1/4" ABS plastic sheeting from Interstate Plastics today (www.Interstateplastics.com). I think that will be sturdier than the expanded cell foam PVC that I used on the center foot.

And I have been reading all the accounts on the web that I can find about the way people have constructed drive systems in the feet. There are some really ingenious systems out there from people with much better engineering skills than me. Jerry Green's drive systems are incredible, and I think they are selling for over a $1,000 now. As usual, Victor Franco and Mike Senna have come up with some really neat solutions to these problems.

Here are some initial thoughts. I think I want to use as much of the full length of the outer feet--14 inches--as I can for a long wheel base for my R2. That is, I want to try to put two wheels into each outer foot, and put them as far apart as I can. I think that will add to stability, and make the unit rock around less when he's moving. I don't want him rattling, bouncing, or tipping. But of course, the shells get shorter as you got out to the edges, so that limits things. For the same reasons, I am wondering about using the widest possible wheels I can find for the job. A lot of the wheels people are using are 5 inches or so high, and maybe only 1.5 inches wide. I am going to try to scrounge up some wider wheels. I would even sacrifice some diameter on the wheels, I think, for some breadth. But maybe someone should argue me out of that. I figure that wide wheels will help make him stable and ride smooth. But I know that bigger diameter will make it easier to get over door sills and things. I'll have to experiment with that, and I'll have to go through the McMaster-Carr catalog.

I'm also wondering about maybe setting the motor up to be direct drive instead of chain drive. But I know that there are serious space limitation issues with the shells and the battery boxes. A lot of builders are hiding their motors inside the battery boxes. I'm not CAD adept, but I am good at intuiting what will work and what won't once I get the materials and parts in front of me and get my hands on them.

I'm also thinking about ways to engineer an aluminum frame for all these motor/wheel/chain contraption that will integrate well with the shells and use the space effectively. Since I am building the shells now, I can design in some features to tie them to the drive train chassis. I am also hoping that I can figure out a way to effectively fabricate/bend/join aluminum. I've learned a lot from Dan Baker's method, and Franco's and others. I'll buy a brake from Harbor Freight tools if I have to, but maybe I can do better. When I roofed and installed gutters and aluminum siding years ago, we always had these big fancy brakes that could put all kinds of complicated bends into the materials. If I could only get my hands on one of those again.

More soon.

MM

Trickery

Ok droid fans, lots of developments today.

After some trial and error, a couple of false starts, and some cursing, I made some headway fashioning the top of the boot for the center foot today. I cut the trapezoids out of PVC sheet (1/4"). All the angles are complicated. It was probably obvious to someone with more experience reading blueprints than me, but the height measurements given for the feet are for the height of the profile, not the actual height of the pieces. Since the sides of the feet are angled back towards the center, their actual height is taller. Some math with the Pythagorean theorem helped me get the measurements.

Once I had the ziggurat assembly cut and glued up, I came up with this trick to cut the slot through the foot where the connection to the leg will go. I flipped the piece over, set my tablesaw up, and made several passes through to remove the material:



This trick saved me a lot of trouble because calculating the angles and cutting these notches out of the pre-assembly pieces would have been a lot of work. With the saw, it took me 30 seconds to get it all perfect. I also cut it so that the pieces that go in to fill the notch would overlap out onto the face of the foot:



I cut these three pieces a bit long so that once they dried I could sand them down on the belt sander to be exactly flush with the rest of the assembly. If the joints had been on the inside, it would have been a lot of work to get them smooth.

Next, I tried something new with the legs. I want the painted finish on them to be as smooth as possible when I'm done. I don't want any wood grain showing through. So I am trying a coat of grain filler. It's a goopy, wet sort of filler that you wipe on. It fills all the really small crevasses in the grain. That's how they get those mirror finishes on fancy French dining tables. I am hoping that with a coat of this before the primer, I'll get good results. We'll see. I'm sure there are experts out there who could really fill me in on how to do this right:



Next challenge: On the curved and angled pieces towards the bottom of the legs, there is a little slot that is cut out of the angled face. Look here on the real McCoy just above the ankle cylinder:



Getting that little slot cut out has made serious headaches for lots of builders, I think. Here's what I came up with. I have the curved, beveled piece already fashioned out of stacked and sanded MDF. I set up my router table with a 1/4" bit, sticking up about a 1/16" (.060 in the plans, I think.). I flipped the piece over onto the beveled side and ran it all the way through, cutting a groove across the whole face:






Sorry that one's blurry.


But of course, it needs to be a little rectangular inset, not a slot cut across the whole face. So I trimmed down a scrap of MDF to fit snugly into the slot with some extra. I glued those into place carefully to fill in the slot where it is supposed to be flush:



The glue dried fast--it's hot as hell here in Sacramento now. And I carefully put the pieces to the belt sander to trim off any excess and get the pieces down flush. The results were just what I wanted and once their primed and painted, the added pieces won't show:



That's some sneaky ninja shit right there.

Next I have some devious ideas for building the little skirt that goes around the bottom of the feet with all the little rectangles cut out. Coming soon.

MM

Leg Hubs and Axle

Today I got the leg mounting hubs attached to the frame. I put them on with the axle and the legs to get them located. I did a bit of sanding to get them to fit nicely on the frame. Then I clamped them into position, drilled counter sink pilot holes from the inside, and sunk some screws into them. With the screws located, I could take them off, put glue on them, and then put them on with glue too. I've found that no joint is better than glue and screws. By putting the axle through the hubs and checking the level of the pipe with the level of the frame, I could confirm that they were located in the right spots. I wouldn't want my R2 to drive in circles from crooked legs.



Once those were dry, I squeezed the mounted legs together on the frame with a clamp so that they were sitting were they should on the body, then I drilled a hole down through the two pipes (one inside the other) on the inside. I don't know much about drilling or machining metal, and I am sure I wrecked my bit. I used some motor oil to lubricate it up and keep it a bit cooler. Once I had a hole all the way through, I could insert a little king pin I rumaged up at Home Depot through. This will hold the two legs onto the body and ideally it will hold them locked into the same plane of movement. R2 doesn't need independent leg movement on the big legs. But even after all this trouble, I still had some play in the two legs. The hole I had drilled was a tiny bit too big, I think. I'll think about what to do next. Another pin, as Senna suggests would probably do the trick.

Next, I took the plunge and carefully trimmed off the extra length I had left on the center leg on the bandsaw. With some careful sanding on the belt sander, I got the top all flush and flat. Then I fashioned a mounting plate for it from 3/4" plywood that would fit down into the square hole in the bottom of the frame. I put rabbet edges on the plate to make it fit, and I routed out a space for the leg to mount in. This whole assembly will fit down into the frame and be visible from underneath.



I've tried a lot of different spray paints on this project trying to get the right results. I put a coat of Rustoleum primer on this plate, then a couple coats of Rustoleum satin white No Rust paint and the results seem to be better than anything else I've tried. I'm always impatient and put too much paint on and get drips. It seems to help to put on more lighter coats, and to get the piece to lay down flat as much as possible.

Three Legs

I wanted to get the center leg put in there temporarily so that I could see some of the big relationships and solve some problems. As you can see in some of my earlier posts, I had purposely left the body of the center leg very long.



My idea was that I might be able to rig up some sort of retractability function inside the body and use that extra length. Now I see that there's no room for that--the leg goes way up into the body. It'll get in the way of batteries, electronics, and everything else:


That's why on some of the aluminum R2s with 2-3-2 function, they have the center leg raising on a platform--to preserve some space for R2 guts.

It took me a bit to figure out from the drawings just how high up the center leg rests for the 3 leg position. Then I realized that the top of the center leg is supposed to be flush with top side of the bottom of the frame. (Think about that for a minute.) So I figure I'll chop off the extra length, and mount the center leg on a piece of 3/4" ply, cut to fit the opening in the frame, and mount it there semi-permanently.

Up in here where I've got the temporary cross bracing. (Here's a couple of angles you don't usually see)





I've got a dome ordered from Ron Barklay. And I figure I'll start roughing in the feet next. Originally, I thought I would fashion them out of aluminum--I even bought some to get started. But I'm liking the idea of using something they call expanded cell PVC now. I've got a piece from Interstate Plastics. It seems workable, stiff enough, and pretty easy to manipulate. We will see.

Leg Axle

I pondered how to attach the legs for a long time. I finally settled on a method not far from Victor Franco's and Mike Senna's. I rummaged around at Home Depot and found pipes and fittings that would let me have a 3/4' diameter pipe on one side, mounted to the leg with a floor flange, and a slightly larger pipe on the other side that would fit over the 3/4" pipe inside the R2. I routed out the inside surfaces of the legs to hide the floor flanges, and did some cursing and grinding on the two pipes to get a nice fit. But eventually I got the legs to fit onto the body.






You can see the two pipes coming together inside the frame here. You can also see the big round plugs that I built as mounts that go between the legs and the upright plates in the body. I had to trim the tops and one is rotated down in the picture. Nothing is secured here--I was just checking for fit.





I'll attach the mounting plugs with screws from the inside, and I'll put a pin through a hole drilled through both pipes inside the body, as Senna and Franco suggest. That'll allow me to take the legs off later if I need to disassemble the droid for transport or something.

One problem that I haven't read about solving by anyone is how to set up this axle or the legs so that they do not rotate past the 18 degree angle that they are supposed to form from the body when R2 is in the 3 legged position. I can imagine several ways to do it.

If you're going to go for the full 2-3-2, fully automatic and motorized R2 function, then this will be solved other ways. If you're building a fixed, three legged R2, then you'll just screw the legs into the back, locked position. I am not going to have full 2-3-2 auto function--that's too hard to do with so much wood, and without a full machine shop. But I think I would like to have the option of putting him up into the upright 2 legged position manually for pictures or display, or whatever. (It does worry me how unstable he must be in that position.) So I'd like to do both. Right now I'm thinking that I'll put a pin through the frame, the mounting block and into (but not through) the shoulder of the leg from the inside. That'll hold the leg in position. Then if I want to change it, I'll pull the pin, move the legs, and put the pins into another set of holes. But I'll have to think about it.


You can also see that I've screwed the skirt onto the frame here. I'll glue a piece of white styrene onto the bottom of the frame, between the frame and skirt eventually. The underside isn't very visible, but I want to have some nice, clean finishing details there when I'm done.

Leg Glue Up

I was anxious to get the leg pieces all glued up. Before I was committed to having them together, though, I wanted to do any work on the individual pieces that might save me headaches later. This means the little cut outs in the arm pits, right below the shoulders. There's just no easy way to do this, but cutting the inner piece of plywood before it was glued helped. Then I traced that outline onto the outer and inner pieces of plywood, and chiseled the material out to spec with my mortiser, and a some work with a sharp chisel and hammer. Some putty, sanding, trimming, and carving got the whole little pocket into pretty good shape before the glue up. Sorry no pictures of this part. Email me for more details.

A few tricks to share about the gluing process. First, when you glue pieces of wood together and clamp them under pressure, then tend to drift and slide around on each other, messing up your alignment of the edges. I glued two pieces at a time. While they were dry, I would clamp them together aligned exactly right. Then I would put a screw through the two pieces from the inside where it wouldn't show. Then I'd unclamp them, take out the screws, glue them, and put them back together. Then I"d put the screws back in carefully so that they went right back into the original holes. That way when I started clamping, the screws would keep the alignment perfect. If you've ever tried to desperately keep drifting pieces aligned while glue quickly dries, you'll see what a huge labor saver this is. In some cases where nothing could show, I would put a blind pin in between the two pieces by cutting the head off of a little finish nail, drill a little hole in one board, and then pressing other one onto it while keeping them aligned. This way there's no screw head showing. Sorry no pictures.

I think the tendency for a lot of people is to over clamp wood pieces. A couple of things. First, get an nice even thin coat of glue on both pieces to be glued. You want a small bead of glue to ooze out of the sides when they are clamped and drying. A lot of clamping pressure isn't needed. You'll drive all of the glue out of the joint and weaken the bond. Let the glue, not the clamps, do the work. Second, use some scrap pieces of wood under the clamp heads to prevent marring of your surfaces. If you do put a clamp dent in it, you can wet the dent thoroughly and then gently iron it with a hot iron. The water in the wood fibers will expand and the dent will swell back out. You'll be amazed at how big a repair you can do this way. Third, put the clamps on one at a time on opposite sides and slowly start to build up even pressure across the whole pieces. You can never have enough clamps. Get a bunch, and evenly distribute them around the edges. Put some newspaper underneath for the drips.

When the glue is about half way dry---about an hour for many wood glues and depending on the heat and conditions--you can gently scrape off the oozing drips on the edges with a chisel. It'll be clean and easy if you wait till then instead of doing it while the glue is runny. Sorry no pictures here either.

Legs!

After a lot of reading up on other people's methods, I got started on the R2 legs. My general approach follows Dan Baker's and Victor Franco's. I stacked up different thicknesses of good birch plywood to rough out the general shape of the legs. Home Depot and the plywood manufacturers are cutting us even shorter for our dollar now by offering only 18mm plywood. So it took some scheming to get the combination right.

One trick I learned from cabinet making is to set the saw up once for cutting these blanks and do them all at the same time without changing anything. That way they are all exactly the same width--makes for easy alignment and much less sanding later.


Kinko's will print up the pdf files from the club blueprints at full size. But it will cost you a bundle. What I really needed though was the main layout of the leg to save my having to copy all those measurements over. Kinko's was able to crop out just the part I needed and charged me only for that--maybe $2. Then I used some spray on adhesive to mount it directly to the plywood. How cool is that?





Here's another trick that worked out well. I mounted the pattern in the center of the blank. Several of the cuts on the leg pieces are straight cuts, parallel to the edges. So once I got the saw fence set up for one of those, I could run the cut, flip the piece, cut the other side, and then do the same for all the other leg pieces. Again, setting the saw up once insured that all the sides would be parallel and exactly the same. This saved me a lot of the messy, noisy routing that lots of club builders are doing to make leg pieces.



Then I did the same for the curved cuts. I set the bandsaw up with the circle jig, and with a little hole in the center of the radius of the shoulder cuts, I could quickly mount each piece and make matching curved cuts.



The resulting stack of pieces--5 for each leg--took about 2 hours to crank out this way.



More about the gluing up process next.