Solar Roach-Bot Project Updates

[Gopher]

Instead of posting updates scattered around in my old question threads (which have all received enough answers already) I decided to make an announcement thread.

Roachbot

Goal
To create a simple 6-legged, autonomous, solar/battery hybrid microbot capable of living out it's empty little cockroach life with minimal human involvement. Moreover, to create this system without the benefit of a microcontroller, as a pure hardware system.
 
Description
The Roachbot will be a novelty/toy, meaning it will serve no useful purpose. It's high-level behavior can be described as consisting of two states: "Hunger" and "Fear."  In the "Hunger" state, it will seek a bright spot to sit. Like a real roach, which spends most of it's time searching for food, the roachbot will spend most of it's time in this state, passively soaking up light to charge it's main battery. The bot will switch from hunger to fear in two ways. First, if it's battery is fully charged it will stay in "fear" mode, hiding in a dark spot; or when it hears a loud noise, it will switch to fear mode (unless it's battery is critically low). Switching back from fear to hunger will occur when the battery power drops below a minimum level, or when no noise has been  detected for a period of time. In addition to this basic behavior, it will have a pair of "antenna" which it uses to detect ledges. When a ledge is detected, it will back up and turn away to avoid falling. This allows Roachbot to be kept on a desk or table, making it an interesting conversation piece.
 
To add interest, I would like to add a set of dip switches allowing it to be switched between normal (autonomous) mode,  always-on (walks constantly, ignoring light but still avoiding ledges), recharge-only (no movement, but still charges battery from solar), and off.

Unresolved Issues and Potential Problems
Much of the design has been worked out, but a few major elements remain undefined
* Fear timer
Without a microcontroller and given the tiny scale planned, a real timer is impractical. I'll be playing around with ideas over the weekend (10/6/06).
* ledge-detection and avoidance
The thing that complicates this one is the "spastic" style of locomotion, which will not provide a very stable platform for mounting the sensors. I have a solution in mind, but it is unproven, and can't be tested until the base chassis is up and walking.

Status
I've bought most of my parts today, though a few key items are still missing, including voltage triggers, voltage comparators, photoresistors, and pins onto which the gears can be mounted. Tomorrow morning I will be going out in search of as many of these components as I can find. Any I am unable to track down will have to be ordered. Until I get at least some of these components, I am unable to start constructing the chassis or testing most of the circuitry, but regardless of what I find my principle task this weekend will be formalizing my circuit diagrams. This will allow me to calculate the actual resistance and load of the bot's circuits, which will tell me if the battery I'm using will be sufficient. I will also be able to produce a complete, detailed list of parts, which will allow me to calculate both the cost and the weight of the final bot.

Expect regular blow-by-blow progress updates.

[Charlie1138]

This sounds incredible. I want to build one too!

What do you roughly estimate all the parts will cost? Just a general ball park figure.

[Gopher]

Hard to say at this point; I'll have a better estimate after I put together my complete parts list. Yesterday I bought a lot more stuff than needed at Radio Shack, like 150 assorted resistors, 30 each of PNP and NPN transistors, etc. (When you can buy 3 for $2, or 15 for $6, it's kindof a no-brainer!) Also a new multimeter (I've got one somewhere, I think it's in the closet at my parents' house, but this one is a little nicer and it was still cheap) and all 4 of the ZZMT engine kits (I certainly won't need 12 motors for this bot, but it's nice to have extras and they were just so cheap!)

I think it's going to fall in the $40-$60 range. If you're not as clever at scavenging parts as me, might be more; if you're better at it than me (which isn't hard), you might build it for less. There aren't really any expensive parts, since it won't use a microcontroller.

I'm thinking about writing a couple of tutorials on the project if I get it all working; One on constructing the basic 6-legged walker chassis, one about the makeshift tactile sensors (I quickly figured out from my research that DIY seems to be the only way to go with tactile sensors for microbots, but it's a lot easier than you might think), and one about the brain that wires it all together.

Now I'm off to hit another radio shack, HobbyTown, Sarge's Army Surplus, and any other places I can think of that might have any of the parts I need.

[Charlie1138]

Sounds great. I seriously can't wait. This sounds like it would be right up my alley! Especially with a tutorial.

[Gopher]

Yeah, it should be an interesting and educational journey

Got a late start yesterday, and my shopping expedition was less than perfectly successful. I didn't have high hopes of finding voltage triggers or comparators, but the radio shack that was supposed to have photoresistors, didn't. Amusingly, they checked the computer and it claimed the location I went to the day before had them. Ended up going all over town, and didn't have time to do any work before meeting some friends.

:sigh:

Otherwise things went well; found the materials I needed to start building the chassis. Experimented this morning with ways of cutting and shaping the plastic and metal sheets, and now I'm going to start making parts. It's probably going to take some experimenting to get the gears mounted firmly and accurately enough to avoid twisting and slipping when powered, so this should keep me busy until I can get the missing electronic components.

[Gopher]

Well, the metal wire I bought to mount the gears on was the strongest and least flexible I could find. It's called Music Wire, something I was previously unfamiliar with. Holy crap, this stuff is hard to cut! I did a little research after it notched my largest pair of wire-cutters. I did manage to cut the wire eventually, with a lot of grunting and straining, but it was playing hell on both my hands and the cutters. I needed a better way.

My research online informed me that to cut Music Wire requires a cutting wheel or carbide jaw cutters. As I don't own either of these, I had to improvse. Took an old pair of needlenose pliers that have a pair of cutters close to the joint. They're relatively useless for cutting, as they're not really very sharp, but I had an idea. I set the wire between the blades and held the tip under my shoe. By bashing the handles of the pliers with a hammer, I was able to cut through the wire. Not sure I would recommend the procedure, but it got the job done; the cuts were surprisingly clean, too.  If you do try it, be sure to do it on a solid surface (I did it on concrete myself). Unlike me, you might want to wear safety goggles - the cut pieces flew off with some serious force behind them!

Upshot: I now have everything needed to mount my gears. After a few experiments it seems I've chosen my materials well, I don't think getting the gears mounted/aligned is going to be as tricky as I had feared. I forgot to bring the gears with me to the store, but through a combination of genius and dumb luck I got exactly the right diameter to fit the bore of the gears.

[Charlie1138]

Sad that with all the power of the internet these people can't get their inventory straight!

I need to do some research.. I'm not familiar with the parts you listed. Sounds interesting though! Do you have a digital cam? I'd love to see pics of your first steps. Diagrams would be cool too. Or if you want to wait until it's done to post it that's cool too. Maybe some of us could offer ideas while you are working, though. I have a lot of ideas -- that's about all I'm good for, sadly.

[Charlie1138]

My research online informed me that to cut Music Wire requires a cutting wheel or carbide jaw cutters.

You know what would be good for cutting that? I am thinking a hacksaw with fine teeth cutting blade or a file! I think that will work well... at least until you can get a dremel or rotary tool.

(I did it on concrete myself). Unlike me, you might want to wear safety goggles - the cut pieces flew off with some serious force behind them!

haha I like your resourcefulness.. but be careful!

Upshot: I now have everything needed to mount my gears. After a few experiments it seems I've chosen my materials well, I don't think getting the gears mounted/aligned is going to be as tricky as I had feared. I forgot to bring the gears with me to the store, but through a combination of genius and dumb luck I got exactly the right diameter to fit the bore of the gears.

That's great.. sounds like you are making extremely fast progress. I am very slow.. I always need to do a lot of pondering when I make my contraptions. Maybe I think too much? hmmm

[Gopher]

I'd already spent every idle moment pondering and sketching for the past week, actually. I actually have a dremmel, but all of my bits are for working wood or plastic. I guess going to buy a bit might've been a better idea, but there was something satisfyingly visceral about bashing the pliers with a hammer.

[Charlie1138]

but there was something satisfyingly visceral about bashing the pliers with a hammer.

haha I bet!  I like to get "medieval" with my tools too. haha 

[Gopher]

Missed this post before...

Sad that with all the power of the internet these people can't get their inventory straight!

I know, but what can you do? It can't be easy; from the riffled-through nature of the component drawers and the large number of open packages, I'm guessing shrinkage is a big problem for them.

I need to do some research.. I'm not familiar with the parts you listed. Sounds interesting though! Do you have a digital cam? I'd love to see pics of your first steps. Diagrams would be cool too. Or if you want to wait until it's done to post it that's cool too. Maybe some of us could offer ideas while you are working, though. I have a lot of ideas -- that's about all I'm good for, sadly.

I'm not really documenting the prototype, aside from what you're reading in this thread. I do plan to document the construction of the final version thoroughly, though, including pictures every step of the way. For that version, I plan on using nothing but specific parts that can easily be ordered by themselves, rather than the Frankenstein approach of part-scavenging I'm using on the prototype.

I'll have to borrow a camcorder from somebody,  I will try to post vids to youtube of the prototype in action once I get it walking around.

[Gopher]

Well, the work-week has begun, so not much time to work; a few developments from sunday night I haven't documented, though.

First, accomplishments: put together one complete side motor/gear mount. No circuitry, but tested it out and all 5 gears hum along pretty good. There's an incredibly annoying high-pitched squeeling from the metal axles rubbing on the plastic strip they're mounted to, but otherwise works well. Just need to finish the piece up (do final securing and cut off excess length from axles and clean up the rough edges on the base), then I just make the legs and the top piece with the leg guides. Then I do it all again, and I can do my first tethered walking tests. Hopefully I'll have pics next weekend.

[Charlie1138]

How's it going, Gopher? Looking forward to another update!

[Cognaut]

I just saw this at Edmund Scientific.

http://scientificsonline.com/product.asp_Q_pn_E_3082403