BEAM From the Ground Up is a
The brain-bone connects to the
This section covers connecting the Nv
net to the motors. What follows is a low current
solution. High current motors and drives present a whole new
set of problems that you don't want to deal with right now.
Besides, the microcore
does its best when driving through a low gain system.
1: Rethinking the Nv
By now you should have familiarized
yourself with the basic 6 Nv microcore
circuit. But a little math and you'll notice
that with two motors and two directions each, 4
Nv's would seem appropriate. For basic walking
function only 4 of the 6 available Nv's are
needed in a two motor walker (although 6 makes
for a whole new set of behaviors), so rebuild
the basic circuit so you get this....
Have no fear the other two Nv's will be
The 74ALS245 is an Octal bus
transceiver designed for data transmission.
Well, we're going to use it to drive motors. If
you've chosen you motor / gear combination
properly then this won't be a problem. If you
dig up a TTL data book you'll see that the 245
has 8 bidirectional non-inverting amplifiers
each capable of driving 50 mA, a direction pin
(Dir) for selecting which way through the chip
and an enable pin (E).
If you tie the Dir pin to Vcc and the E pin
to ground, you can essentially think of the chip
as 8 active drivers going from left to right
like this graphic....
- A data book will show you more but for the
purposes of driving your legs this'll do......
Note that the ALS version has been found to
be the best for current, feedback, etc. CMOS
(HCT, HC, C) will work but they loose a little
in the feedback. They do consume less parasitic
power so for solar apps they are the better
If you are building a battery walker use ALS
wherever you can (contrary to what some people
will tell you you can still get them.... try
[Editor's note: the
74ALS245 will only work well with a supply
voltage of between 4.5 and 6.0 V -- unless your
source is within this range, you'd be well
advised to use a 74HC245
3: Ganging up for
If you've tested your motors you probably find
that they need a little more than 50 mA to do
anything useful [although this depends on
your motors -- see here,
Ed.]. And with a little math you'll see
that there are 2 drivers available for each Nv, so
gang them together like so....
The result is four drives capable of 100 ma
each. Good but not great....
So if you need more, double your output by
stacking a few chips...
So now you have a 4 Nv loop set up and a 4
channel driver set up. The next step is to glue em
together and add the motors. Kinda' like so...
5: Power Up
Power on the whole thing, stabilize the loop
(one process), and you
should get this:
If things aren't right change the motor polarity
on one of the motors and it should work.
6: Tuning for a