I built up the circuit at
As I didn't have any 74HC14 parts on hand I used a 74LS14 to see if I could get the circuit up and see how things worked.
I also used 220ohm pull-up resistors for the A & B signals (and tied all other inputs to +5vdc).
Checking voltages at various points to see if the circuit was good I found
+5vcd at both motor poles.
When I grounded B to start the motor it turned slightly and stopped, though if I gave it a hand start it would keep running.. I then noticed that Q2 was getting hot in a hurry.
I metered across the motor. Only getting about .5v. This is not what I expected.
I tried using the steering motor out of the same RC car. A much smaller motor.
Now when I ground A or B it runs the motor (reversing direction as expected) and I measure around 4v across the motor.
Both motors are causing my bench supply to jump from trivial amperage to around .3a when I make a connection.
Also when I hooked A & B both to Gnd with the intention of causing the motor poles to be low in the "off" state Q1 got hot in a big way very quickly.
I have a feeling this has to do with the motors "effective resistance". Unfortunately I really don't know how to figure this out for sure nor how to deal with it.
Looking for suggestions on what I am doing wrong and how I can fix it.
I have plenty of digital experience but anything analog always gets me.
Thanks, David