I'm making a solenoid motor with a n-channel logic MOSFET to operate the solenoid. I'm having trouble controlling the MOSFET gate, which needs to be adjustable between about 4 to 15 Hz to turn the motor flywheel. I've used a 555 as an astable but it doesn't switch the MOSFET. Any help would be very useful. Thanks.

 

Can't help without a complete schematic of what you have.

 

What voltage? What MOSFET?

Some MOSFETs require 10V to turn on fully.

 

So I realised that the MOSFET was being switched too fast by the 555, and was buzzing rather than pulling.
The solution was to add a 4148 diode to the 555 between pins 6 and 7 to reduce the duty cycle, and keep both timing resistors the same, with R1 as a 50 k pot.

 

I meant the solenoid was buzzing, not the MOSFET

 

A rectifier across the motor may help, also a higher freq. PWM signal may work better?
How are you switching off for the return stroke?

 

You need a proper Commutator of some type,
( Mechanical-Switches might work, but an Optical/Interrupter setup will work best ),
rather than hoping that You can accidentally find a Frequency using your 555 Timing-Components,
that "might" get your Motor to continue to spin by it's self,
that is, after you manually spin it fast enough to get it started.

With a Commutator,
it will be possible for the Motor to start, and continue to run on it's own,
provided that the Solenoids are well designed,
and the overall friction in the Motor is not excessive.

A 555 is not the best way to do it.
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