I'm making a wearable device that interacts with the user by tactile sensation. So far I've been using coin motors, but that gets annoying if the device is active too often and really drains the battery life. I'm thinking that something better would be a small, button-like linear actuator. I'm thinking of something that looks like this
however instead of being a button, i.e. a pressure sensor, is actually an actuator, i.e. something that applies pressure as opposed to sensing it.
I tried looking it up online and on the forum, but no avail. Does anybody know if there's something like this around or how I could make something like this myself?
That kind of thing draws a lot of power. Do the maths. How much force do you want it to exert, how quickly, over what distance? You will get up to watts of power very quickly and that will drain your battery with a capacity measured in milliAh.
Solenoids seem like an obvious choice but they have to suck a lot of power to hold a constant force. A little tiny motor driving an even tinier worm screw doesn't need power to hold position but the mechanics are going to be so small and delicate nobody can touch it without breaking it.
A pump inflating a small air bladder can be made almost indestructable, but fitting that into such a small space will be a miracle.
You may want to look into shape-memory alloys. You can get ones that will change shape dramatically when the temperature of the metal changes. You just run some current through it to heat it. Turn off the current and it cools and goes back to the original shape. That solves most of the mechanical problems but you still have to supply enough power.
There are a ton of these miniature stepper motor powered linear actuators on eBay for ridiculously cheap:
I'm sure MorganS has a good point about them being fragile but maybe worth buying some to find out. At a grand total of $0.72 USD w/ free shipping for quantity 10 it's not a huge loss if it doesn't work for your application. I've been trying to come up with something I could use them for ever since seeing them.
MorganS wow thanks for the extensive discussion on the several alternatives! I don't really know how much force I'd like to apply, it should just be enough to be felt but not enough to be painful. I'm looking at the shape memory alloys, but I can't find anything that keeps a constant shape when it's cold and becomes soft when activated - as there's going to be 8 of these devices and only one or two active at any given time, I guess this is the behaviour I want. Do you think that something like this exists?
Pert I did see the stepper motors, but I'm not entirely sure of how to use them to apply pressure. I'm thinking that I could put a tiny metal plate thing around the plastic slider and a vescicle full of liquid between the plate and the motor. When the vescicle is squeezed, it will apply pressure. Do you think it would work/do you know if anybody has done something similar?
