Dan, I will take a pic of my solenoid, I use two with 48 ohm , they have 30 mm round , with an air core of 10 mm and #32 copper wire. They are a little hard to produce without a winding machine , but with paciente you can do it manually. The solenoids must be between magnets and three rounds of magnets as this magnet-solenoid-magnet-solenoid-magnet so when you input voltage to the solenoid it will repell itself from the magnets.Its more of a electromagnet constrution inverted and not properly a solenoid.It will not have ferrite or mild steel core , the only iron that i have is in the rolls and they are not even near the magnets or the solenoids