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My second take at a 2-motor walker design

After biting off more than I could chew with Protowalker, I took a step back in mechanical complexity and built the ModWalker. Here, I got rid of Protowalker's mid-body hinge and variable-geometry front motor, and just concentrated on making experiments with different head, leg, foot, and drive circuit designs (this ought to be enough challenge for now).

ModWalker is built using Mac floppy eject motors, with the front motor mounted 45 degrees off vertical; I plan on building him a brother with a different front motor geometry.

Later, I'll likely build yet another model of ModWalker -- this time with BG Micro lens motors.

ModWalker -- not built for looks

The basic ModWalker layout is compact, to aid balancing:

The basic idea behind ModWalker is (as the name implies) modularity. The idea is that by easing re-arrangement and replacement of various things, I can more-easily experiment with performance benefits of various changes. ModWalker's modularity comes in 5 forms:


  1. Provision for quick mount / dismount of a head (although this mount can be used for other purposes, as shown to the right)

  2. Provision for quick mount / dismount of the drive circuitry on a "daughter card"

  3. Provision for quick attachment / removal of motors (they're attached via "cable ties"), though the structure is really optimized for Mac floppy eject motors

  4. Provision for quick attachment / removal of legs

  5. Provision for quick attachment / removal of feet

The ultimate expandible 2-motor walker (just add circuitry)


The "bare" ModWalker, though, is just structure, power supply, and motors. Here are some views of a ModWalker before anything else (battery, daughter card, head) is attached and plugged in.

ModWalker "unplugged" from left / front

ModWalker "unplugged" from right / rear

ModWalker "unplugged" and in pieces
ModWalker "Unplugged," left side

ModWalker "Unplugged," right side

ModWalker, exploded view

The body cards provide structural support (for motors and any head), as well as providing signal routing for the front motor, and power supply circuitry (reducing the 9V battery's supply to a regulated 5 V). There's a flat plate located just above the top of the front motor to allow for mounting various head designs -- this plate has two "nuts" epoxied to its underside to speed head (dis-)mounting. My only real complaint with this walker is that I put the head-mount plate on "copper-side-up" (this really limits what I attach here, since the copper can short out traces placed against it).

The drive circuit is on a daughter card, quickly swappable (via the 8-pin interconnect I'm growing to appreciate more every day). Two "nuts" are epoxied to the underside of the main body card to ease daughter card swaps. So far I've run this walker with both Walker 2:14:1 and 2:14:2 daughter cards (the latter gives ModWalker the ability to reverse; right now I'm running ModWalker with the 2:14:2 card along with a Sharp IR proximity sensor head).

In one definite improvement over Protowalker, the "umbilical" connecting the daughter card to ModWalker is now made from "wire wrap" wire (this is much more flexible than the ethernet cable wire I used on Protowalker ). If you're going to go this route, I'd suggest you make the "umbilical" longer than you think you'll need -- I built it long enough to give me about 1/2" of slack when a daughter card is mounted. If I'd made the "umbilical" about an inch longer, it'd make life much easier when I have a breadboard mounted on top.

Legs are mounted to the front and rear motors via junction strip cores (epoxied to the motor output gears), and feet are mounted to the legs via the same hardware. I've tried a few different leg shapes ('though all are made from coat-hanger wire), and have yet to settle on anything "final."

Right now, my "test feet" are just shirt buttons epoxied to junction strip cores, with rubber buttons for traction on flat surfaces (flooring, table tops, etc.).

ModWalker gallery -- click on image for larger JPG in a new window (note: large images are around 700 KBytes in size)

ModWalker (headless, "Walker 2:14:1" daughtercard) in profile

ModWalker with Walker 2:14:2 daughtercard
ModWalker (with Sharp IR proximity sensor head, "Walker 2:14:2" daughtercard)

ModWalker with Walker 2:14:2 daughtercard
ModWalker (with Sharp IR proximity sensor head, "Walker 2:14:2" daughtercard) in profile

ModWalker (headless) from above

Rear view (good view of power supply electronics on main board)
front motor mount thumbnail
Front motor mount
rear motor mount
Rear motor mount
foot detail thumbnail
Foot detail

For more information...

ModWalker is built on top of two Omron (Mac floppy eject) gear motors. I've written a full tutorial on how to modify these motors from their original form (to better work in BEAMbots) here.

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Copyright © 2001 Eric H. Seale