Gears and Circuit

It looks like I’ll get to this blog once a week or so. More than that seems like it will absorb too much time. I like it though as a rhetorical device (is that the right term?) to keep track of how I’m progressing, and what I’m thinking. I’ve also been keeping track of hours and tasks. You can see that here:

http://spreadsheets.google.com/ccc?key=0Al76QWdTTgR-dE1pd1RPUVZJRmtBLW5NekRxQXBKcWc&hl=en

Last week, I started to seriously consider the specific size of the robot. It should be bigger, big enough that it can impose upon the viewer if desired. But how big is that? This is a worthwhile aside… Most of my projects begin with an idea that appears to be Out There (for lack of a better expression). This means that the invention is novel both in terms of premise and design. It is like realizing a bit of science fiction or fantasy in the here and now.  But such far out devices are by definition difficult to make. I’ve learned through multiple failures to translate vague concepts into specific designs by implementing techniques that afford the desired aesthetic results, especially behaviors. Outward forms (those that are usually considered of primary importance in aesthetics) then are selected for their ability to support the techniques. This is in keeping with the near-century old Bauhaus design principle: Form follows Function. You can see evidence of my work being forced into this approach with the blanket project.

Early Version of the Blanket Project

The early version of the robotic blanket looks like a real blanket. Unfortunately the cover was somewhat restrictive and cut back on the machine’s ability to move. After several versions, and shifts in what I thought significant I arrived at the current version.

Current Version of the Blanket Project

In this version, the robot has been reduced to a padded skeleton, covered in a light veil only to give an allusion to blankets. This version allows the blanket better movement. It still is relatively comfortable to touch, perhaps more comfortable, because now the padding is made for the machine’s specific shape. And in fact, it is consequently a more interesting design…at least more original, & less obvious. So the methodology is, I think, effective for determining appearance. I wouldn’t say it’s the best way, but it is no doubt useful when trying to simply get something to work properly.

To close the aside then, in moving from a general desire to increase the emotional impact of ADB to a specific design, it seems likely that increasing the robot’s size would afford a greater variety of impressions. Not too big though, ADB should still be able to be handled by a user, either on their lap or on the floor…body sized. Following this I started to look at technologies for help. I found a motor which has decent torque, low-voltage, and affordable, and then almost as inquiry started to mock up some designs around this part. You can see the beginnings in last week’s post. But those mock-ups left an impression on me, and gave me something to build on, though I hope it’s not premature (this is where project management skills could help). With some initial dimensions proposed, the following sketches were printed based on those scales.

Full Scale sketches of ADB v.2

After some discussion with my beautiful girlfriend!! I was still unsure which size was preferable, so I moved from these sketches into modeling the module with the motor in Solidworks. What I found was that the larger of the two complete sketches seen here is the smallest that I can go with this motor! That’s a big robot, at a minimum.

Cross Section of Module at Minimum Size

Starting to think about how things fit together further allowed consideration of how other parts could fit into the module. On the bottom of the module in this model is the motor, just above that in the center is a slip ring. On the shaft of the motor is this gear sourced from SDP-SI, which mates with another that would be coupled to an adjacent module. There is 2:1 gear ratio, such that the speed of the motor would drop to a max of 25 rpm, but more likely 15 rpm on a 3.6V li-ion battery. But I would get twice the torque. It’s a trade I’m willing to explore at this point because I really want these things to be able to lift.

After this much was figured out about the mechanics (I know I’m glossing over a bunch of important details, but I gotta get off this damned machine already), I turned my attention to the circuit design. This I think will be somewhat easier than the mechanics (knocking on wood). I’m more experienced with electronics and the first version of the circuit mostly worked. In one of my more recent contracts, I designed a circuit which was remarkably similar to the one I envision for ADB. It is battery powered, with capacitance sensors and zigbee communication. Having the PCB’s on hand, I killed two birds with one stone and started assembling those circuits in order to test the concepts. That went smoothly enough until I ran out of parts, and so I spent the better part of the last two days searching for electronics and gears online.

Last thing…I dropped by Creatron this week and Lawrence told me that the motors roughly have a torque of 14kg*cm which is about 195 ounce*inch. With doubling it I’ll be getting nearly 400 ounce*inch!! not bad.

That’s it, that’s all I can say right now. I’ll try to get up a post describing how all the mechanical stuff fits together soon. But for now movie time!!