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My walkers -- an overview
Two takes to date
I've built 2-motor / 4-legged walkers from two designs to date:
- Protowalker
1 -- this walker design is an odd-looking thing, in
order to provide a number of different mechanical
configurations. The original idea was to build 2
identical units to allow side-by-side comparisons of
performance with various tweaks injected to one or the
other. Protowalker
is a basic 2-motor walker, but with a spring-loaded
"joint" between the two motors.
What I discovered early on was that putting a spring-loaded joint in the middle of a two-motor walker doesn't improve its walking efficiency, it keeps it from walking at all (the walker just sort of stands in place and does a bad imitation of the Hula). At some point in the future, I'll probably try out this idea again with a walker that has a hinge point further forward. Also note that Protowalker 1 has the majority of its weight (i.e., battery) toward the back of its body, so it needs some long rear legs to avoid dragging its rear feet.
In response to these issues, I designed a simplified version...
Protowalker 2 -- this has the same external configuration (i.e., length) as a Protowalker 1, just with no hinge (to simplify building it). This coincidentally gave me a bit more "deck" space to work with, so I laid the 9V battery down to improve (i.e., lower and move forward) its C.G. The geometry of the forward motor is still variable.
I've drawn up the parts for this walker, but haven't built one yet (I'm putting off study of that movable front motor for a while).
I then salvaged what I could from this walker, and built...
- ModWalker -- this takes its name from its modular design. The head, circuit, legs, and feet are all "swappable" for plenty of experimental flexibility.
All of these walkers are designed to allow for swap-out of various driving circuits. Accordingly, the walkers' circuits are implemented in two parts -- a "brain" card, and one or two "body" cards. Essentially a daughter card, the "brain" card contains the walker's core circuit (either a quadcore or master / slave bicores) and motor drivers. The "body" card(s) provide the power supply, structure, and some signal routing.
The interconnect
I use an 8-pin DIP
socket as interconnect between "brain" and "body" (here, the
socket is on the "brain" card, and the cable / pins are
connected to the "body" card). By doing things this way, I
can test my walkers with various combinations of "brain,"
legs, feet, etc. The assignment of pins on the interconnect
socket is shown here:
The brains
I've got all sorts of data on the "brain" circuits I'm
testing these walkers with elsewhere, but at a high
level:
- All provide sockets for timing resistors -- this
allows me to tinker with core timing, and play with
walker turning (via rear motor)
- All provide sockets for ICs -- this allows me to
tinker with IC families, and recover from "smoked"
ICs
- Later "brain" card designs provide sockets for IC power-filtering capacitors
The body
The "body" circuits are pretty straight-forward -- a 9V
rechargeable battery (which, of course, really puts out
7.2V), on / off switch, power regulation circuitry (to get
things down to 5V), and some drive power routing (since I'm
already using PCB
card as structure, why bother with wires?).
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