From: "Jonathan Mills" <jwmills@moose.cs.indiana.edu>
Subject: Re: Stiquito, A Small Nitinol-Propelled Robot
Organization: Indiana University, Bloomington
Date: Mon, 28 Sep 1992 09:42:39 -0500

In article <TED.92Sep27215600@lole.nmsu.edu> ted@nmsu.edu writes:

>furthermore, with a 50 GRAM payload, it is going to be hard to put
>enough batteries on the beast to take more than a few steps.  

The payload may be underestimated.  Stiquito in its role as
Braitenburg Bug carries a 6-volt alkaline "J" battery, a handful of
2N2222 and 2N2907 transistors, resistors, capacitors, LEDs, and
cermet trimmers.  Two photo-transistors stand at the end of wire
stalks, and the sensor/controller package is mounted on a battery
case/styrene sheet circuit board that plugs into the top of the
robot.

Because the nitinol actuators are cycled roughly once a second,
and because current flows for only a small part of the cycle
time, the 180-250 mA drain for each leg does not run the battery down
that quickly.  After two weeks, during which the battery was used
for five or six hours intermittently, it can still power Stiquito.

I'll try a continuous walking test to see how long the J battery
will last.

The controller card I'm working on now will hold two Actel FPGAs, some
transistors, and a 9-volt cell.  Stiquito can carry it.


>tethered operations are more interesting.

Long tethers may add too much weight, especially if legs are used
with more than one degree of freedom.  Not that tethers can't be
made to work, but they might need to be hung from a stand.  How
about decoding serial input to the legs using a serial-in parallel-out
IC like a 74C164?  A low baud rate could be useful here.  Or, how
about IR LEDs to avoid the tether, off-loading control to a PC?


>people should also note the 10cm per minute walking speed.

Stiquito is definitely *not* a speed-demon.  If cockroaches moved
that fast, they'd be extinct.

Some possible approaches to increasing speed of legged
nitinol-propelled robots:

	- use higher temperature nitinol.  The Flexinol (tm)
	  in Stiquito has a transformation temperature of 70
	  degrees C.  The 90 degree C version relaxes faster,
	  allowing cycle times to be doubled or tripled. So
	  perhaps 20 or 30cm per minute is possible.

	- drive the leg with two actuator wires that oppose
	  each other, relying on them for recovery force instead
	  of the music wire leg.  The wires probably will not
	  last as long, but the cycle time could be increased
	  at the expense of power & stress on the nitinol.

	- pipeline multiple legs.  there is a lot of time in the
	  walking cycle when Stiquito's legs are doing nothing
	  but waiting for the next impulse, or relaxing after having
	  contracted.  Using a caterpillar gait (pairs of opposite
	  legs), one could pipeline their operation so that four
	  legs (out of say, 16) are thrusting.  The speed could
	  be increased, perhaps by a factor of three after wasted
	  motion is accounted for.  Of course, the controller is
	  more complex, and power consumption goes up.

Stiquito is fits into a niche I'd describe as low and slow.  For
faster operation, to carry heavy loads, to attach complex effectors...
a more traditional wheeled robot or more robust legged robot is
desirable.

But within its niche, what *can* you do with Stiquito?  I enjoyed
the post on walking CPUs.  What else can you think of?

Sincerely,
Jonathan