Solenoid Motor With Long Throw

This solenoid motor has an extra long throw to make it a more interesting display, and uses electronic switching instead of a cam and mechanical switch for longer life. The flywheel, connecting rod, and solenoid stand are 3D printed. The flywheel has a 625ZZ bearing to make for quieter, smoother operation. The motor runs from 5 volts to 12 volts; switching is done with a surface mount AO3400 N MOSFET with gate driven via P and N type bipolar transistors mounted on a postage stamp sized bit of perfboard. For detecting the right time to power the solenoid, a latching type hall effect sensor was used; a north magnet in the flywheel turns it on, while a south magnet turns the output off.

Base: 1/2" birch plywood, 3" x 8"

Screws: #4 pan head sheet metal screws for securing parts to wood base

1 ea. 625ZZ bearing, ebay

Plastic used in 3D printer: 1.75mm PLA- black

0- 80 screw x 1/2" and nut for connecting rod to solenoid plunger

M5 x .8 x 25mm screw for securing flywheel

Electronic parts:

Hall Effect sensor US1881LUA-AAA-000-BU from Mouser.com

2 ea. 1/8" x 1/8" cylinder magnets

2N2222 NPN transistor

2N3906 PNP transistor

2 ea. 1K SMT resistor

1 ea. 3.3 K 1/4 w resistor

1 ea. BYV 26E diode

AO3400 N MOSFET, SMT from ebay (100 for $2.50)

1 large red straw from Wendy's for solenoid bobbin

1 large black straw from McDonalds for solenoid bobbin

piece of paper cardstock for solenoid end pieces

#28 awg wire, approx. 300 feet

1/4" steel rod x 3" for solenoid core, hardware store

Cut the 1/4" steel rod to 3" long. Visit Wendy's and McDonald's to get straws that allow the rod to slide easily inside the straws. There is a slight diameter difference in the straws; one can fit inside the other, so they become stronger. A bit of super glue can be placed on the inner straw to hold it in place inside the other straw. Cut 2 ea 1/4" x 1" washers out of cardstock and glue them onto the straws to form a bobbin for the wire 1.5" long. Leave about 1/2" of the straw beyond the end of one washer, so that the straw (with steel rod inside) can be placed in the chuck of a cordless drill. Then wind approximately 300 feet of #28 awg wire onto the bobbin with the drill, leaving 6" of excess wire at the beginning and end of the coil.

Print the 3D solenoid bracket and mount to one end of the base. Drill a hole for the 0-80 screw in one end of the rod and file the rod end a bit so the rod can fit in the connecting rod small end and connect to the rod.

Remove the metal shields from the 625ZZ bearing with a fine flat blade screwdriver; pry the shields out. Dip the bearing in paint thinner to remove the bearing grease, dry, then lubricate with a light machine oil. 3D print the flywheel and press the bearing into the flywheel with a socket slightly smaller than the bearing outside diameter. Do not press on the inner bearing race. A vise will make pressing the bearing into the flywheel with the socket easier.

3D print the flywheel stand and mount to the base with screws after test fitting the connecting rod and solenoid positions. Assemble the flywheel onto the stand with the M5 x .8 screw. Test that the flywheel turns smoothly. Place a small washer on the end of the flywheel crank and use a screw to retain the connecting rod to the flywheel crank.

Make the electronic switch on a piece of perfboard. I used just the side with the holes since I wanted the board to lay flat against the base. Position the NPN facing down, and the PNP transistor facing up so that the emitters of the transistors can directly connect. Construct with reference to the photos and the circuit diagram. Place the magnets in the flywheel cutouts at the back of the flywheel as shown in the pictures. One magnet should be magnetic north, the other magnetic south; thus the latching Hall sensor will turn on when triggered with one magnetic polarity and turn off with the other magnetic polarity. Test the operation of the motor by holding the sensor near the magnets, while giving the flywheel a spin. The motor should operate best at one position; hot glue the sensor in that position to the stand.

The motor operates well from 6 volts to 12 volts, though lower voltages are better because the operation of the long throw crank can be better observed. Do not operate above 12 volts since the MOSFET gate isn't rated for more than 12 volts. A counterweight can be placed inside one of the flywheel cut outs to smooth the vibrations at higher speeds.