@MarkT you said "A very common mistake you see is assuming the transistor's current gain applies to saturation - it doesn't. The current gain only applies in forward active mode, not saturation. This is presumably why 1k resistors were used in the instructable."
How should I calculate the correct resistors? I am willing to learn. Does your statements about transistors apply to MOSFET transistors or junction transistors or both?
I found these two datasheets for the FQP30N06L MOSFET:
I am not getting the voltage I wanted to see at the motor when I bread-boarded the circuit in the "FQP30N06L Mosfet with Arduino" diagram above. I am trying to decide what my troubleshooting steps should be - I may have built the circuit incorrectly, or I may need to modify the circuit to get what I want - or my transistors may be defective.