00100	                            CART HARDWARE

00200	
00300		The  cart is animated by three sets of motors, one motor pans
00400	the camera, one motor steers the front wheels and four  motors  drive
00500	the cart. The four drive motors always operate in unison.
00600	
00700		The  motors are controlled by six relays. Three relays switch
00800	the	power on and off, and three relays switch the polarity of the
00900	current.   Accordingly the cart can be commanded to drive forwards or
01000	backwards, to steer left or right, and to pan its camera clockwise or
01100	counterclockwise.
01200	
01300		The  Relays  in  their  turn  are controled by flipflops. The
01400	power relays are controlled by three retriggerible one shot flipflops
01500	called  the Action Bits.  The polarity relays are controlled by three
01600	regular flipflops (type D flipflops) called the direction  bits.  The
01700	direction  and actions bits may be set and cleared by radio commands.
01800	Naturely, Action bits being one shot delays, clear themselves after a
01900	tenth  of  a  second,  this  is so the Cart won't go very far without
02000	specific orders from the computer.
02100	
02200		The cart radio transmitter is located in the Kludge  Bay  and
02300	is  connected  to the PDP-6 via DACs numbered 51, 52, 53 and 54.  The
02400	voltage output of the DACs varies from zero to ten volts depending on
02500	a ten bit number. The DAC voltages control the spacing of five pulses
02600	that are transmitted to the cart. A Pentrad of pulses is  transmitted
02700	every 28 milliseconds, and the pulse spacing can be varied from about
02800	half a millesecond to 2.5 milliseconds.
02900	
03000		The Cart has a Radio Receiver which is connected to some  TTL
03100	logic.  The  logic interprets the pulse sequence as either a four bit
03200	command or as an error.  The error condition occurs if there are  too
03300	many  or too few pulse or if a single space is too short or too wide.
03400	If there are no errors short spaces are read as zero  bits  and  long
03500	spaces  are  read as one bits. If the 54-bit is a zero then the other
03600	three bits are strobed into their respective direction flipflops, and
03700	if  the 54-bit is a one then the three data bits are strobed into the
03800	action flipflops.
     

00100	COMMAND LOGIC
00200	
00300		The command logic contains thirteen bits of memory which is
00400	changed on clock pulses. The memory is in two for bit counters, a four
00500	bit shift register and and JK flipflop:
00600	
00700		4-bit	Command Data Shift Register
00800		4-bit	Pulse Width Counter
00900		4-bit	Pulse Serial Counter
01000		1-bit	Error bit.
01100	
01200		Input to the command logic is the Radio Pulse from the radio
01300	receiver interface and the clock pulses from the clock. Output from the
01400	command logic is the Action Bar Pulse, the Direction Pulse and three
01500	data bit levels Data-53, Data-52 and Data-51. All output goes to the
01600	Relay Register.
01700