Figure 2-4b: Mask placed on Head with facial attachment (but no back-of-head attachment)
The attachment of the face to the head is difficult at best and very finicky. It is surprising just how difficult such a seemingly simple task can be. The act of moving the backside of the mask and producing a meaningful movement on the outside surface of the mask is very challenging. Most motions simply make the mask contort in a fashion that is useless for meaningful expression creation.
When it comes to developing a project like a robot head, it is not always best to start with a preexisting frame. We found that having to remove the components that were already attached to be difficult and time consuming. It would have been faster for us to design and develop our own frame rather than having to test, adjust and/or remove components that were already attached.
We also recommend keeping a logbook of designs and research. This logbook is useful for planning out the more complicated designs, such as for eyelid movement. This logbook can then be used to keep track of what worked and what didn’t.
The work should be organized by figuring out what there is to work with, and what the final product needs to look like. It is a very good idea to plan out the steps needed to complete the entire project. From the initial research and design through full movement. This is necessary when attaching servos for the motion, you need to know what kind of movement is wanted before the servo is attached, since the kind of movement required will dictate how the servo is attached to the frame.
We found it helpful to have weekly meetings in the robot lab. The designs were worked out individually, and were then attempted as a group on the “skull”. These meetings lasted about 3 hours, and were fully concerned with working on the robot – talking was done while pieces were being either tested or adjusted. This was very easy for us to do, since there was just the two of us working on the head. This worked for us, since the individual parts of the entire robot could be broken up into three different major components and worked on at different times as different groups. About once a month, a quick meeting between all the groups was done to make sure that we were all on about the same page.
2.2.1 Hardware introduction The design of the base for the robot involved several considerations. The structure was the first consideration, the base needed to be easily reproducible, robust, and capable of the integration of multiple additional components including the arm/hand module, head module, and laptop housing while still having room for future additions. The second component to consider was the control system that needed to be implemented.
2.2.2 Components and Subsystems For the first component, the base structure, we used the TETRIX system designed by Pitsco because it is a readily available set of components that would make reproducing the robot easier. Since the dimensions of the head were already available this helped to define the robot’s width and the length. For movement, since the center of gravity would be changing around the front of the robot as the arm moves and lifts items, we decided on a front wheel driven system with rotating casters to support the back
To design our base structure we first created a list of our specific design requirements based on the given design parameters and extended goals:
The second component, the control system, proved to be much more of a challenge. The difficulty was manifested in the communication required for interaction between the software which controls the sound and head gestures and the NXT Intelligent Brick which controls the movement of the base and arm. We were able to resolve the communication between the main system and the head subsystem with the use of a virtual keyboard adapter which can be used to call functions within the head control program. We used a PSP controller to wirelessly control the base, as well as the arm.
As of the writing of this paper, the Tetrix base kit (structure only) was available from the Pitsco website for US$399. The complete kit can be found at the educational Lego website for US$897.95. The perforated aluminum was available from onlinemetals.com for US$39.60 for a 24”x24” sheet. The rotating casters are available from any hardware store for around US$4.
Individually, both the controller and the NXT Brick can be found at the Lego Education website. The controller specifically can be found at legoeducation.us for US$79.95, and the NXT Brick can also be found at legoeducation.us for US$144.95. Both of these items are included in the overall kit found at the educational Lego website for US$897.95 as well. Pertinent documentation can be found at their websites linked in the text above, or via the reference numbers provided. While the included 3Ah battery is functional and convenient, we found that we quickly ran out of power when controlling both the base and arm modules. We designed the battery housing to be able to hold a 12V/7Ah sealed lead acid battery which can be found with a charger at amazon.com for US$30.
We found that the PSP-Nx (v.3) adapter for Playstation 2 controllers worked perfectly in this instance since it also comes bundled with a 2.4GHz wireless controller. We found it available from mindsensors.com for US$59.95. Documentation and sample code can be found on the link above, and in the appendix below.
18.104.22.168 Base Assembly
Since many of our design considerations were relatively unknown at the beginning of the project, we needed to create a versatile base for our team. We began our design with what was known (the head dimensions) and used that to determine limitations on the arm design. The existing support structure for the head that we were provided to work with required that our base have a width of at least 41cm, and enough room to support a laptop, batteries, and Tetrix hardware.
Fortunately, as the Tetrix kit provides 416mm structural channel pieces, we were able to use that length to define our structural width. Then, for optimal stability, we decided on using the remaining 416mm channels to complete a square base structure. This allowed us to easily integrate Tetrix components into the rest of our design and make ready accommodation for the arm assembly since it was also to be constructed using Tetrix components.
Our design was finalized in a way that was efficient and cost effective using parts from the Tetrix base kit, including motors, motor positioning sensors, motor & servo controllers and wheels. Some pieces that were not available in the Tetrix base kit included the rotating caster wheels and components necessary to provide a secure place for a laptop. We found that a perforated aluminum sheet provided a suitably sturdy yet light weight platform for both the laptop pad and internal surface area. Unfortunately, we did not have enough material on hand to use the perforated aluminum for the internal surface area. Instead we ended up using a plexi-glass sheet which also turned out to work acceptably.
Our initial design consideration resulted in the following model: Fig. 2-5 Robot Base 3D Model
Notice in the final product that the Aluminum sheet covering the center ended up being plexi-glass. For a larger view, see "3D models and Structures" in the Base Appendix.
We ended up using most of the components in the kit. If the reader is building one from scratch, it would be wise to order an entire kit. The ordering information can be found below in the Ordering and Documentation section above and a detailed parts list is outlined below:
(56) 4mm nuts
(52) 4mm x 8mm bolts
(4) 4mm x 38mm bolts
(4) 416 mm Channel
(2) 96mm Channel
(2) 12V DC Motor & Mounts
(2) 101mm Wheel
(2) 70lb Rotating Caster
(1) 230mm x 450mm x ~2mm perf. Al. sheet
(1) 410mm x 350mm x 10mm plexi-glass sheet or perf Al. sheet
(4) plexi-glass bolts or (4) 4mm x 8mm bolts if using Al. sheet base