I’m completely new to robotics, but I want to play with some solenoids (I think)… so I’m looking for some recommendations on what to buy. I want to experiment with some haptic ideas, like feeling small taps/pressure on various body parts. My first thought was to get a bunch of cheap solenoids to play with. I noticed all the actuators are too expensive to buy a bunch for this, so solenoids look like they’re in the price range, and I’m looking for low push range, like 3-5mm. Hopefully they are quick/responsive? I found even cheaper ones on ebay: https://www.ebay.com/itm/12V-DC-Suction-Micro-Electromagnet-Spring-Push-Pull-Type-Rod-Solenoid-Magnet-4mm/153089629798?epid=7020120932&hash=item23a4da5e66:g:0gMAAOSwDZJbE~bJ I don’t know what sort of specs to check for when shopping besides the push/pull distance, so if there’s anything about responsiveness/pressure let me know. I’m a software engineer, and I’ve played with a raspberry pi once, so I’m confident I can figure out the technical with some documentation. I’ve got a PC running Windows 10 and I’m used to Visual Studio if that matters.
So, here’s what I’m looking for recommendations on:
-Any alternative components I should consider instead of solenoids? Cost is a big factor because I want a bunch of them.
-Which components would you recommend? Would the cheap solenoids I linked from ebay do the trick?
-What sort of controller or other device(s) do I need to operate several of these at once…like 10, 20, or even 50 of them independently? If that’s too many to do independent, one alternative would be something like 10 groups of 3-5 operating together.
I can help with the last question immediately. The others will have to wait.
To control the solenoids you need a single bit output port that can provide the amount of current the solenoid requires and a diode to damp the “inductive kickback.” If you don’t know what that is just ask.
Most port drivers on ANY computer can’t handle the amount of current a solenoid requires. But a single transistor or a “driver chip” such as a uln2803 can buffer the port and drive the solenoid.
What kind of computer do you want to control them from? If you want to use a PC I recommend some type of USB interface. And in that case I would recommend an Arduino.The arduino can drive around 15 or so on its own (with appropriate buffer chips added) and can easily be programmed to accept commands from the PC over the USB serial port. Some models of Arduino can handle many more, like the Mega. It is fairly simple to add some other chips, like a 74hc595 shift register that will then allow it to control as many as you like. Or you could just use multiple Arduinos.
If you are interested in the circuits required I can provide some links or draw up the diagrams myself. Do you know how to read schematic diagrams?
No, I don’t know what ‘a diode to damp the inductive kickback’ is.
Yes, planning on using my PC with Windows 10.
No, I haven’t read schematic diagrams, but I’m sure I could watch some youtube videos or find the right articles to guide me through reading them. That sounds helpful, thanks.
inductive kickback
When current flows through a conductor a magnetic field builds around the conductor. In a “coil” such as a solenoid or relay or motor, that field gets squished together and becomes quite large and strong. When the current is cut off, the magnetic field collapses and “tries” to maintain that current. Since that usually means the circuit is broken and current can’t flow, a very high voltage is generated that can ruin electronic components. That voltage is generated with a polarity that would keep the current flowing in the same direction, which means the voltage is normally opposite that was applied. The voltage will build until it is high enough to create a current path – through whatever: parts, air, or whatever. That is what we call “inductive kickback.” The actions of building and collapsing the magnetic field is what inductance means.
So, there are various ways to handle that kickback. Perhaps the most common, at least in hobby circuits, is to place a diode “across” the inductance (in parallel with it) so that when the voltage is applied current can’t flow (a diode only allows current to flow one direction.) So it has no effect when power is applied to the inductor. But when power is removed and the “induced” voltage, which is opposite, takes over, the diode acts as a short circuit across the inductance, limiting the voltage.
You really don’t need to worry too much about the technical details, but you do need to be aware of it and know how to deal with it.
Here is a link to a relay driving tutorial for Arduino. A relay is just a solenoid that pushes a switch, so just ignore the switching part of the tutorial and look at the circuit that drives the relay. That link uses pictorial diagrams instead of schematic diagrams.
For the number of devices you want to drive, I would highly recommend using the ULN2803 driver. It has all the transistors, resistors, and even inductive kick diodes for 8 drivers in a single 18 pin chip. It is common, cheap, and widely available. It is MUCH easier to use than individual transistors, too.
Now for some of your other questions …
I can’t think of any other device that would be cheaper. But there may be something.
The solenoids you linked should work find. They take quite a bit of power, but most solenoids do. By their nature, solenoids usually respond very fast. You can actually slow them down some and have them use less power by working on a lower voltage. A 12 volt solenoid will usually work fine on 9V or so if it doesn’t have to move much force. And it will use about 40% less power.
To drive that many solenoids you will need a big power supply. Each one takes 200 milliamps, so ten could take up to 2 amps worst case and 50 could take 10 amps. An old PC power supply would probably work well, or maybe even a laptop power supply.
