EYE ON NPI - Johnson Electric’s linear DC solenoids

Adafruit Industries

This week's EYE ON NPI is clicky-clacky with Johnson Electric’s range of linear DC solenoids (https://www.digikey.com/en/product-highlight/j/johnson-electric/linear-dc-solenoids) in various sizes and voltage ratings. Solenoids are a nifty type of motion control element - most folks think of motors or servos when thinking about motion control (and Johnson Electric does make motors too) but motors and servos are best used for rotation motion. You can convert them to linear motion but usually you need to gear them down a lot to get a reasonable torque - force conversion. Some use a rack-and-pinion mechanism (https://learn.adafruit.com/rack-and-pinion-bot/overview) or a drive/lead screw (https://en.wikipedia.org/wiki/Leadscrew). Solenoids provide a very easy to create a short but powerful linear force that is either on or off - you can't really be 'in the middle' of a solenoid actuation. Solenoids all work in the same basic way: there's a toroidal coil of copper that forms an electromagnet. (https://en.wikipedia.org/wiki/Solenoid) As current is passed through the coil, it pulls the ferrous slug into the coil with near-instant force. When the power is released, the electromagnet de-powers and the slug can move freely. In this sense, all solenoids are pull-type. Sometimes, there's a return-spring that will pull the slug out to 'reset it' - these are push-pull type (https://www.adafruit.com/product/413) - but most solenoids, including these from Johnson, don't have the spring. Usually, whatever the solenoid is installed in provides the return pressure. Most solenoids we've seen are rectangular style, which tend to be sort of 'candy bar' shaped. The Johnson solenoids are more 'pancake style' - with a flatter and wider design that has less requirements on depth. (https://www.digikey.com/en/product-highlight/j/johnson-electric/linear-dc-solenoids) Johnson makes a couple dozen of different solenoids with different voltages and sizes, we picked up two and one was about the size of a grape and the other the size of an orange. Common voltage ratings are 12V and 24V - the amount of current will vary with voltage since you still need the same amount of power per coil size. Usually the voltage is whatever the equipment is set up to provide. Note that solenoids require a lot of current, many amps whenever activating! Thankfully the power does not have to be very clean, so you can have a separate regulated supply just for your motion control. Finally, the Johnson Electric YouTube channel has a cool series of videos called "Interviews with Old Timers" where they interview employees that have been there for 50+ years, to hear what it was like when Hong Kong was first beginning to do manufacturing. (https://www.youtube.com/watch?v=JyzoR-XtR6M) There's some great historical information in there, we had a lot of fun watching them and looking at the old photos. Digi-Key stocks a full range of compact solenoids from Johnson Electric available for immediate shipment. (https://www.digikey.com/en/product-highlight/j/johnson-electric/linear-dc-solenoids) Be sure to check the datasheets for the specs and sizes, as there's quite a range in size/voltage/actuation force! We picked up 2024-1026-ND, a chunky 12V one (https://www.digikey.com/short/40dmhdhj), as seen in the EYE ON NPI video, it's a real beast. Whatever size you need, if you order from Digi-Key today , you can be electro-magnetting by tomorrow afternoon. See on DigiKey.com at https://www.digikey.com/short/40dmhdhj