StarWars robot design is somewhat "Dog-Like"
Keith Rowell Design

February Meeting Update

The mascot section of the February Club meeting brought some good feedback.
1. Motor Mount

The motor mount design was discussed. The virtues of using an added "plate" to attach the bracket to the gearbox was weighed against keeping the "boss stop" method that the gearbox originally used. The crux of the discussion revolves around wheather any weight is transferred to the gearbox. The general consensus is that the gearbox should "float" and that all the weight should be transferred to the wheel through the axle.

2. Articulated Frame

After discussing the modifications to the "umbrella folding baby stroller" and how to add shrouds and motors to drive articulation on such a frame, it was suggested that we abandon that frame and make one from scratch that suits our needs exactly. This sidesteps the difficulties of making the pseudo appropriate frame fit our critera, while serving as good reference material for a new design.
The in-ordinate ammount of play in the joints of the stroler frame is another source of dissatisfaction and new designs need to take this into account.
Many design mechanisms were suggested:

• rack and pinion
• drawer slider mechs
• scissor lift
• ball screw

I'll post some sketches showing some of these ideas applied to our project. I look forward to your feedback.

3. Paint

It appears that the wax (applied too soon after painting) caused the paint to crack. I didn't get many other comments about the silver painted gearboxes. Please provide some input as to aesthetic styles that you would like to explore for the mascot.

4. Reference material

I've included some references here that might provide some inspiration for our mascot's design.

Hoberman was a student of Buckminster Fuller's geodesic dome design principles, and has since created fantastic articulated shapes such as the Hoberman sphere that you may have seen in toy stores. These are amazingly complex expanding structures, definitely the kind of design I would consider to be "showing off" worthy. Here are a couple of his newest mechanical odities.

http://hoberman.com/fold/Switchkick/switchkick.htm

http://hoberman.com/fold/Braintwist/braintwist.htm

http://hoberman.com/fold/assoc/projects.htm#

http://hoberman.com/fold/sightings/clinton.jpg

Some standard off the shelf mechanical shapes:

http://www.hobbyengineering.com/SectionFR.html

http://www.8020.net/

http://www.beijingthc.com/conveyor_chain/carbon_steel_one_piece_chains.htm

http://www.partserver.de/frame.asp?firm=duffnorton&language=english

Mechanical linkages simulations

sphynx is an incredible spherical 4 bar linkage simulator, as is Synthetica. Try them out!

http://synthetica.eng.uci.edu:16080/~mccarthy/Synthetica1.0/Synthetica.htm

http://gram.eng.uci.edu/~mccarthy/SphinxPC/Sphinx.html

http://www.keypress.com/sketchpad/javasketchpad/about.php

http://www.brockeng.com/mechanism/index.htm

http://math2.math.nthu.edu.tw/jcchuan/java-sketchpad/jsp.html

http://www.enchantedlearning.com/physics/machines/Levers.shtml

Fictitious Designs

http://www.colinmackenzie.net/robots/amee/

http://mullenmj.astromech.net/T3M4Droid.htm

Real Designs

http://asl.epfl.ch/research/systems/Shrimp/shrimp.php

GearBox / Motor Mount Design for Folding Frame

motor mount
Keith Rowell Design

I've worked up some motor mounts based on the discussion in the January meeting. (held in Feb.) These are to mount the gearboxes onto the folding frame.

I was able to modify the folding frame to maintain it's width when closed, as per the meeting comments. It appears that the bottom "x"scissor brace controls closed width, and the vertical "x" scissor brace controls the angle of the vertical frame when fully open. I drilled out the rivetes and moved the connect points and achieved a configuration per saturday's comments. In the current configuration, when the motors are added the full width is 26.7" wide. That's with the frame's outer rails at 12.75". In order to bring the total width down to 24", the folding frame needs to be modified further to have a total width of around 10".

I don't have a camera handy today, I will post those photos when available.

motor mount front
Keith Rowell Design

The basics of this motor mount design are that the top is a clamp that compresses the frame's down tube. The weight of the bot is carried on the axle that distributes it out to the wheel, passing through the gearbox and coupler. The awkward angle on the motor mount corresponds to a boss on the gearbox, keeping it stationary under torque. It doesn't carry any weight.

motor mount side
Keith Rowell Design
We of course are looking for volunteers to build this part. There are two of them, identical except for the screw holes which should be mirror copy on the two parts. I have atatched a pdf of the part drawing on the listbot. Contact me if you need a copy...