April 15, 2012
This part of my mini R2D2 project. i'll post all the updates on the main body in this blog page.
This is the first bit of frame with some extra bits. Those pieces are for two doors: one large one that covers allmost the whole back and a small one in the front.
I decided not to make too many panels into doors, because that will make the body less strong. So only a large back-door to access the inside of the droid when it is assembled and one small door in the front to hide a few buttons and a USB or serial plug.
The small door will cover the rightmost opening of the three in the front.
On the right you see the top part of the frame. About 4cm under the lower ring, a bottom plate will be placed. because the middle leg comes up through that plate, I chose to mount that later on, after the lifting construction is finished.
The whole frame is glued, not skrewed. I hope I am making the right choice there, because when some of my previous bots had an accident, the PVC broke near the skrew. Using glue only, I'm hoping that the weld will break leaving the PVC pieces intact.
These pictures to the left show the inner skin (that covers most of the body) and the outer skin (that just adds nice detail to the body).
I started cutting the skins out of 0.3mm PVC. This is great stuff, because you can use scissors to cut it. Most of the cuts however were done with a knife. Because of the small panels, the skin will bend in an ugly way during manoeuvering of the scissors.
I just finished both inner skins and the front outer skin. Oh Boy, is this a lot of cutting! Note that most of the panels that were cut away, need to be trimmed down and placed back. This is really much more work that I thought. My muscles are hurting from pressing the ruler down to guide the knife.
You can see that with both layers on top of each other, this starts to get a real R2D2 look.
Sticking them together will have to wait until the frame is done. The layers need to be bend when they're glued, because the curve will stretch the outer skin a tiny bit more than the inner skin. So if you glue them before you bend, that will put a lot of strain on the weld between the skins.
Update May 13th 2012: The picture to the right here of the skins for the back give a better idea of the dimensions.
The back door is quite large, but not large enough to make alterations on the inside when the rest of the body is covered. If I am to do any work on the inside after the skin is finished, the skin has to be removable. One way that may be feasable is to use screws on the inner skin and glue or thin double side tape to attach the outer skin. On the places where the inner skin is screwed, only tape is used so the outer skin can be pealed of a bit to reach the screws... Have to think on that for a while...
The frame as it is seen here, is only the part that is covered by the skin. Underneath that part, another layer is added with a smaller diameter. On the R2D2 blueprints and the builders websites they call that bit "the skirt".
The frame is now allmost ready. The shoulder Hubs still need to be mounted and the fixtures for the doors, circuit boards and motors have to be made. I have no idea where everything will fit, but I image there will be plenty of room.
Today the skins where more or less attached to the frame to see if it fit. I used thin double sided tape, but that didn't hold very well. Especially when the outer skin was also adding to the strain. You can see my hand is needed to hold the left part of the skin to the frame.
Todays fitting was just for the pictures and for fun, but a few valuable lessons were learned:
Lesson 1: Glad I didn't attach the shoulder hubs yet. As can be seen in the picture to the left, the silver hub is not thick enough: you can see behind the hub. An extra 5mm is needed (and of course sanding and painting)
Lesson 2: The skin fits well and goes right up to the markers halfway along the horizontal disks and the openings for the front door and front ports are right where they are supposed to be. Still need to see how it goes with the back skin added too. Vertically the skin sticks out a small bit (less than 1mm) but still anoying.
Lesson 3) The legs and every other visible bit of expanded PVC needs to be painted. The two shades of white are just too far apart. Hopefully I can find a spray can with a color that is close enough to the white of the skin. That way I don't have to paint all the other white parts as well.
Update May 23rd: After a lot of contemplating and overthinking a lot of options, fears of ruining the carefully cut panels were put aside this weekend as I got started on preparing the skins for painting. Last week I experimented on the back door using the primer and white paint I had. This did not turn out well. The primer is flaking and the white paint is not very white, but milky beige. Funny thing is, that the flaking off-white paintjob makes the backdoor look like it came of a very old robot, which isn't that bad considering lots of people buildign R2 units go out of their way to make their creation look battered and dirty.
Still I went to the DIY hobby shop to ask for advice on painting that shiny PVC and I think I got the right paint now. The primer I have is for painting laminated kitchen cabinet panels. I've used it before when i wanted to turn the side of my fridge into a chalkboard. I had to give up on spray cans for the white paint, because all the spray cans were off-white. One advantage of using old fashioned brushes, is that I can paint while the skins are near areas of other colors. With the spray paint, everything has to be removed or taped up before painting. we'll see how it goes..
Today the skins were mounted on the frame. The picture on the left here shows how I did it. I used pins to align the panels and keep them in place. You can see the pins on the left of the picture here. After the alignment, which was more tricky than expected, the pins were replaced with small screws.
The back half of the inner skin (on the right here) needed a lot of extra fixation points because of the large opening. So that half is permanently attached to the frame as the outer skin is glued over the screws. This makes the screws less visible.
The front part of the skin was a much better fit that only really needed pins on the sides of the body. Keeping in mind that I would prefer to be able te remove the skin later on, the front outer skin is glued on and both the inner and outer front skins are fixed with screws on the side.
As you can see here, there is plenty of room for maintenance inside the body even with the skins attached. Maybe they will never have to come off.
Also in this picture: the PVC is not thight to the frame. This because all the vertical pieces are made from leftover bits while the rings of the frame are more accurately cut from plates.
Even with everything carefully measured, the PVC doesn't fit perfectly. I need to trim bits and pieces and I had to make some adjustments. All in all I am pretty pleased with the result at this moment.
Another puzzle has been laid before me. Actually an older puzzle that I have been putting off for a while: "How to attach the back door panel and the front door panel?"
Update july 21st 2013: Just closed up te body. The back panel is attached with 2 magnets for cabinet-doors. That holds it very tight, but the edges do not allign very well.
Also made an attempt to make the two vents in the front. The tiny pieces of plastic are covered in blobs of glue, but they are fitted in the body nonetheless. I'll figure out a way to make better vents later. Right now it will have to do. I intend to mount an SRF02 range finder behind the top vent. Hopefully the vent wont desturb the ultrasonic signals too much.
Also finished the skirt. It's mounted on the bottom and will hold the lifting mechanism for the middle foot. The skirt is done by cutting small pieces of plastic to more or less look like the endresult. It is made tidy with a plaster that is used to repair laminated floors. It is smooth, but still a bit course for my taste.