I am building a whiteboard CNC pen plotter for my classroom out of some old 3D printer parts, a Melzi board running Ramps 0.92 and Inkscape to generate the Gcode. I have the machine up and running but I need a solution to actuate the pen in and out. I want to use an electromagnet or solenoid to do this and I was thinking of running the solenoid off of the cooling fan header. I can use Gcode to turn the fan circuit off and on or control its speed via PWM. The system is a 12 volt system and I think the old 40mm fan was rated at 0.18 amps, 2 pin. I am wondering if a small solenoid could be powered by the fan circuit? If so, what ratings should I look for? Would a solenoid be a bad choice? Could I buy some magnet wire and wind my own electromagnet which could just pull the marker into the whiteboard? I don't need much movement out of the pen, just a few mm.
I know there are better solutions out there like using a servo or another stepper motor. I am avoiding the stepper motor because I am trying to keep the mass of the moving parts as low as possible. I would use a servo, but I really don't know a whole more than basic circuits. Is there an easy/cheap way to convert the two pin pwm fan signal to a servo signal?