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From:   Jason E. Brown[SMTP:jebrown@CDC.NET]
Sent:   02 April 1997 17:27
To:     PICLIST@MITVMA.MIT.EDU
Subject:        Re: PIC's and PWM

At 07:49 PM 4/1/97 -0500, you wrote:

        I've been looking around and can't find any info on a 12c508 IC.
Got any pointers, the manufacturer, description etc... ???

12C508 is another form of the PIC microcontroller. It has 8 pins, 6 of =
which could be used as IO pins. See the Microchip www site for more =
info.

        I would be interested in ESC if I had a little more info on how =
they work,
what kind of input, etc..
They take an input pulse exactly the same as you would use to drive a =
servo. 1-2ms pulse width in 20ms cycle. 1.5ms pulse would normally be =
the off position of the ESC (it is adjustable), 2ms would be full on =
(also adjustable).

   I would also need to find 2 that were resonably
priced, 2 direction, and could handle about 40A CONTINUOUS!!! I have =
seen
The expensive ones handle higher currents and also have more things you =
can fiddle with such as response rates, current limiting curves, etc. =
The cheaper ones usually just let you set the off position and the full =
power position in relation to the incoming pulse widths. In the UK a 40 =
Amp ESC costs about 30 UK pounds, which is about 50 dollars.
all these little boxes rated at 140A and I just cant see how they can
handle that much current.  Unless RDS ON =3D .00004? :)

Some of the Speed controllers we use can handle MUCH more than 140 Amps =
peak, and certainly 40 to 80 AMPS continuous at 8.4 volts. The low RDS =
on needed is done by connecting several N-Channel FETs in parallel. Each =
FET has RDS on of about 0.04 ohms (BUZ11) to around 0.018 ohms (BUZ346).

        BTW the application is for remote control of a combat "robot" =
for robot
battles competitions.

        Of course, if I use one of these with servo pulse inputs, I will =
have to
make a servo driver for the autonomous parts of the "robot"
(which of course, have not been done yet) :)

Servos are nice small light-weight motors with gear boxes already =
supplied and have good positional control, they should be considered for =
small robots.

Kieran