Introduction: Lobsterbot - a Simple LM386 Based Robot

About: I am a theatre designer and technical director. I work at Merely Players, a small non-profit theatre group in Southwest Colorado. Check us out on Facebook: Merely Players-Durango. You can also see some of …

Quite some time ago I built a Herbie Junkbot mouse.  I liked the simplicity of the op-amp chip and the relay to determine motor direction.  I was also looking at six-legged robots.  The original lego site with the leg layout has since disappeared.  Here is the closest site I can find now.

The design can also be seen in the six-legged kit addition to the Boe-Bot.  Jameco and others carry the kit.  There's just something about a multi-legged robot that is so cool!

So I decided to combine the Herbie brain with the Boe-Bot six-legged body and throw in feelers.

Step 1: The Chassis

First, I played around with the leg layout.  I made body and leg pieces from cardboard and attached them together with brass brads to test how the legs would work.

When I was happy with the mockup, I cut aluminum side panels from 5052 aluminum.  I think it's 1/8 inch thick.

Then I used pieces of flat brass to make the leg pieces. 

#6 bolts 1 1/2 inches long made the longest pivot points for the legs.  Looking at the top view you can see that I used other lengths of #6 bolts. 

I added lengths of brass tubing over the bolts to hold the body away from the leg joints.  When I got the legs aligned correctly, I used loctite to keep the bolts and nuts from loosening during walking.

Step 2: Parts - the Circuit

Parts List

1.    1x  2222A transistor (similar to 3904, black thing w/ 3 wire)
2 .   1x LM 386 low power amplifier (chip w/ 8 wires)
3.    1x dpdt relay (black w/ 10 wires)
4.    2x motors
5.    1x 1k resistor (brown - black- red bands)
6.    1x 10k resistor (brown - black -orange bands)
7.    1x 100uF capacitor (blue thing)
8.    1x red LED
9.    1x toggle switch
10. I used two plastic battery boxes, each of which holds 2 AA batteries
11.  double-sided sticky foam
12.  2x photodiodes - Jameco and others stock them

Here is a nice and simple one page description of the circuit.  It also goes through some errors in the Make magazine Herbie and the Instructable version.

I soldered my circuit together on a piece of perfboard that I measured to fit between the chassis and servos.

The servos were bolted to the chassis with 3/8" #6 bolts and nuts.  Then the two servos were attached with a piece of double-sided foam tape, which is remarkably strong.

I removed the "brain" in each servo and just soldered two wires directly to the motor.  This way you don't need PWM signals to run the servos, they just go!

Step 3: Lobsterbot Lives

Herbie the Mousebot uses a lever snap switch to determine if it has contacted something.  The circuit then puts the motors in reverse and backs up.

Lobsterbot uses whisker sensors.  Basically, they are just a switch.  When the whisker (guitar string) makes contact, it bends and touches the brass tube.  One sensor wire attaches to the brass/copper whisker support, and the other sensor wire goes to the guitar string.  The guitar string end has shrink tube around it so that the base doesn't contact the support brass tube.

There is a dead zone directly in front of Lobsterbot, so he can get stuck on things.  But no one is perfect!

I dipped the ends of the brass legs in Plastigoop, the stuff you can dip tool handles into to provide a better friction surface. 

I think that's about it.  Lobsterbot was fun to build, and I really like the movement as power is sent to the two servos.  It is fun to control him in a dark room with a flashlight.

Step 4: Lobsterbot in Motion

Here's a video of Lobsterbot exploring its environment.  I hope that you enjoy it.

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