🚀 go-pugleaf

In article <1993Jan27.043305.7387@sbcs.sunysb.edu> shane@cs.sunysb.edu
(Shane Bouslough) writes: 

>I've been thinking a lot about legs recently (don't we all? :-).
>If you're going to do a nice leg, say Brooksian, it seems like
>you'd need about one miniboard per. If you use 6 legs on your
>beastie, that's quite a few miniboards. Is that a good way to go?
>Or is something a bit more powerful a better idea?

In fact, this is just about what is done with Rod Brooks' robots:
there is a dedicated CPU per leg.  But, they use very small DIP CPU's
(maybe a 24-pin model), and surface mount motor controllers, so the
leg processor board is pretty small.  Also, it's kind of shaped like a
leg, long and skinny.

>Miniboards are such a nice "out of the box" solution, but a chain
>of them like that sure would suck down the juice.

The motor chips on the Mini Board are the "worst offenders"; they draw
about 30 mA each, even when not supplying power to a motor.  The CPU
itself only draws 20 mA.  If someone could find a more efficient motor
driver and paste it on to the Mini Board it wouldn't be too bad from a
power point of view.

	- Fred

In article <1993Jan27.043305.7387@sbcs.sunysb.edu> shane@cs.sunysb.edu (Shane Bouslough) writes:
>I've been thinking a lot about legs recently (don't we all? :-).
>If you're going to do a nice leg, say Brooksian, it seems like
>you'd need about one miniboard per. If you use 6 legs on your
>beastie, that's quite a few miniboards. Is that a good way to go?
>Or is something a bit more powerful a better idea?

I have been looking at this same problem (I have been designing a 6 legged
walking robot) and have come to the conclusion that the simplest/least expensive
solution is to use one of the dedicated stepper-motor controller chips.  At
about $10 a pop + $15 for a stepper motor, it will cost me only $75 per leg
(excluding the mechanicals).  Further, the each motor can be controlled by
2 bits (step and direction) thus allowing all 18 motors to be controlled by only
36 TTL outputs.

Mark Epperson

In article <1993Jan27.140858.29306@news.media.mit.edu>, fredm@media.mit.edu (Fred G Martin) writes:
|> In article <1993Jan27.043305.7387@sbcs.sunysb.edu> shane@cs.sunysb.edu
|> (Shane Bouslough) writes: 
|> 
|> >I've been thinking a lot about legs recently (don't we all? :-).
|> >If you're going to do a nice leg, say Brooksian, it seems like
|> >you'd need about one miniboard per. If you use 6 legs on your
|> >beastie, that's quite a few miniboards. Is that a good way to go?
|> >Or is something a bit more powerful a better idea?
|> 
|> In fact, this is just about what is done with Rod Brooks' robots:
|> there is a dedicated CPU per leg.  But, they use very small DIP CPU's
|> (maybe a 24-pin model), and surface mount motor controllers, so the
|> leg processor board is pretty small.  Also, it's kind of shaped like a
|> leg, long and skinny.


Actually, each leg on Attila and Hannibal has a dedicted 8751 on it that runs
three pwm servo loops, does sensor i/o, and communicates with the master
68000.  The only reason we really use this system is to save wiring.  With
20odd sensors per leg,  plus motors and power lines, we'd have needed
something like 40 wires per leg to do everything.  With the local micros, we
just have six (motor power/gnd, digital power/gnd, two wire serial
communications, the Signetics I2C in fact).  The 8751 boards have tiny FET
drivers for the motors--there are two boards piggy-backed, about 1.5 x 2
inches in size.


Were we to do it again, we'd definitely go with the Motorola parts--6811/16's
nand 683xx's, using the SCI bus.  The 6811's have much more flexibility, and
the communications bus is much faster.  Right now every bit is being used in
the I2C bus, and the 8751's are running a full load continuously (plus they
need a bunch of peripheral stuff for all the i/o).

6811 boards can be made pretty small too, at least as small as the 8751
boards we have (using surface mount parts).  Anita Flynn's "Squirt" robot has
a 6811 board on it that is just barely larger than the 6811.

: There are lots of lists of Electronics/Motor suppliers around, but
: what about other hardware? Aluminum stock for legs, chassis, etc?
: -Shane "I wanna build a critter" Bouslough

I am starting on a similar critter:  6 legs, 3 degrees freedom/leg,
6811.  I plan to use epoxy-fiberglass for structural components such
as the body and legs.  Strength to mass should be better than metal.
It is fairly easy to work with.  Repairs are easy.

I have been learning fiberglass fabrication by building a boat.  The
critter comes next.
--
  Allen C. Brown  abrown@cv.hp.com or hplabs!hpcvca!abrown or "Hey you!"
      Not representing my employer.
    I am not an actor, but I play one on television.