The CS:R NextGen Frame

Design Background
The frame is one logical place to start building a droid. Back in 2011 that's where my efforts started. What follows is the background information for how the NextGen design came about. If you are only interested in the design itself you can skip down to prototype design.

R2 is Not Designed for Accessibility
I realized even then that accessibility to R2's internal parts was going to be both important and difficult to achieve.
I wanted something better than the 'stand on your head' posture most of us have to take when working on R2's insides!

I wanted a droid where a rear panel could be lifted off for access to the inside (hinged was not necessary). That turned out to be more difficult than I expected.
In the CS:L frame I built a box beam that links the two shoulder plates together for strength. The cross brace pieces are set back from the edges because otherwise they would interfere with the ribs.

In order to add a removable rear panel to the existing design my original thought was to add a second box beam connecting the two ankle plates at the bottom of the frame.

Adding a second box beam at the ankle slice (the beam itself is not shown here) would have only further interfered with the already limited accessibility to the inside of the frame.

Just the opposite of what I was trying to achieve!

Over the intervening years a number of other things have also changed:

My plastics supplier stopped 'stocking' .250 plastic sheeting.  The 'new' .250 sheeting was actually .220 [and my supplier still calls it .250!] It forced a re-design in my existing plans, but at the time I considered that the thicker sheets were worth using (instead of doubling up a pair of .125 sheets) for both convenience and strength. I have heard from a number of builders who wanted to use my designs but were having problems sourcing .220 plastic.

The CS:R drawings were finalized and released. A major effort on the part of several R2 Builders the CS:R drawings represent the best representation of a "screen accurate" R2. The team had unprecedented access to studio props and drawings and put a lot of work into the effort. It represents a major change for the frame as there are measurable dimensional changes in a number of locations.

Putting skins on a Styrene R2 isn't easy at best. There are no 'mounting points' that are incorporated into the design, other than the rings and the vertical ribs. In my design that's a .125 thick piece of plastic. It would have been nice if it was wider. To further complicate things, there's no support designed in for the skin seam that runs on R2's sides under the shoulder. I wanted to fix that.
I need a better way to mount a Utility Arm Box that is much cleaner in design and implementation than the one I came up with.

A fellow R2 Builder, Ziz started offering CS:R Styrene Frame flatpack plans and instructions. He is using 3/16 inch (.1875 in or 4.76mm) thick plastic in his design for increased rigidity. The 3/16 plastic is more widely available than the .220 I've been using. Part of what I'm doing is to get designs out to other builders that they can cut them on their own. Particularly builders in Europe and Australia where shipping my parts packages adds significant cost. That's becoming possible as "hacker spaces" which offer cheap access to expensive machine tools are becoming more prevalent, but only works if compatible sheet materials are available too!

Finally, Andrew Radovich, who build Jenna's Droid R2-JE using my eggcrate frame, and other styrene parts, came up with an idea for a removable central core to make access and servicing the batteries and other electronics inside R2 easier. [Start at the Nov 20th 2014 Blog Entry]
I had met Andrew at DroidCon II where we jointly gave a talk on 3D Printing. Andrew is a clever designer who has been pushing both the 3D printing envelope as well as Droid construction to new limits!

He removed the cross pieces of my Shoulder Box and added a cylindrical center core - here a taped up version is test fit.

This finished version of the core has drawer slides attached to tie it into the frame

Finished core with batteries mounted and electronics installed

Finished core with dome motor mounted on top installed in R2-JE
Pictures here were downloaded from Andrews R2-JE Facebook page.
I didn't realize it at the time, but the idea of a center core provided the "missing link" to complete my new frame design.

So what's at the heart of the new design? 
I'm utilizing the concept of Andrew's removable center core as a way to reinforce the frame rings that are cut in order to make the door opening.

I'm starting with 1/2 inch schedule 40 PVC pipe with an edge cut off. 

I used my 3D printer to create circular guides that would fit the PVC pipe and mount on the edge of a styrene sheet.

for this 'proof of concept' test I only used guides at the top & bottom of the sheet. In the actual core design the guides will be installed at ring locations on the frame. PVC pipe will be used on each side of the area where the removable back panel will be as well as other locations on the frame.

One lesson from the proof of concept: The edge of the guide needs a slight taper to make inserting the core easier! Even though it doesn't look it, it's not possible to 'pop' the guide out of the pvc pipe by pulling on the plastic sheet!
These interlocking components will provide both strength and rigidity. With both the back panel and the core removed access internally to components that a droid builder might want to install in the frame, will be unimpeded. Similarly, access to control electronics and batteries mounted on the core is simplified as well.

The CS:R NextGen Frame

Prototype Design
Here is where the design is as of 07/04/15. If you want
the design background jump here. As usual with my website, the images are linked to 3d.pdf files that allow you to move them around, make parts transparent, and otherwise see more of the detail. I've posted a 2d.pdf drawing of the various parts (with supplier information for extras, like the magnets)  so you can get a feel for what's in a parts package and assembly details for the new frame design and it's components. If you want to build your own download the construction drawings.

This is the the full frame, viewed from the rear left side.
It includes:

The "dome motivator" - a gear drive mounted on a Rockler Bearing.

The removable core insert that ties the frame together mechanically. It has been replaced by the Tab Core Insert. see R2.CSR.Tab.Core Warning: The balance of the NextGen Frame instructions will show the now obsolete PVC Core Frame

The removable rear door frame

The removable CS:R Utility Arm Box (new)

As a result, this image is a little cluttered with detail. The images will become progressively simpler as I strip away parts.
The Dome Motivator is a Pololu gear motor (I understand that there is an alternate, cheaper, source for the same motor) and hub attached to a gear drive.

There's nothing new in the design of this part. What's not shown, and is a work in progress, is a dome ring design that will accommodate rings of varying sizes and provide a clean mount for the dome itself.

Note: the Pololu gear drive motor & the Rockler Bearing are shown for illustration. I do not include mechanical parts in my parts packages.
CS:R Frame with removable Rear Door Frame and removable Core Insert.

Frame bottom is a pair of ring panels, ribs only penetrate the top panel (ring1) leaving the bottom panel (ring 0 - the base of the skirt) without holes that need to be filled. Ring 1 has cutouts to accommodate parts that need to be mounted on the bottom edge of the skin (Power Couplings & Octagon Ports)
Eight full height ribs (in purple) support the removable core. Four of those have to be trimmed at the bottom to provide clearance for parts mounted on the skin.

This is a partially filled out version of the original PCV Removable Core Insert. It has been replaced by the Tab Core Insert. see R2.CSR.Tab.Core

Unfinished Items:
There are 4 more pieces of conduit on the edges in the obvious places.

Note: the Pololu gear drive motor is shown for illustration. I do not include mechanical parts in my parts packages.

CS:R Frame with removable Rear Door Frame

Features: Shown here in orange are the 3D printed pieces that slide inside of the conduits on the insert (called sliders). While the top edge of the slider is chamfered. The top set should also be slightly staggered in height so that the insert only engages one at a time. That should make the insertion process easier.

Unfinished Items: additional Sliders will be placed lower on the ribs around the area of the frame rings to couple the frame into the insert in the areas of maximum stress. See the assembly instructions for more details

CS:R Rear Door Frame

The Rear Panel is actually 3/16" short. The skin will extend below the bottom edge of the Frame and cover the exposed edge of Ring 0 (the skirt base)

The Door Frame ribs are only 1/2 the depth of the Frame Ribs in the rest of the frame that was done deliberately to enable wiring to be routed into the back of the Core from the rest of the droid (see below)
CS:R Frame with Rear Panel Removed

Now that you've seen how the parts fit together, it's time to look at the assembly details.