About this video
This build video shows how the negative side of the battery is wired to the center terminals of two single-pole, double-throw switches in a small robot. The switches reverse the polarity of the drive motors so the bot can back up. The builder strips and crimps stranded and solid wires without solder, wraps the joint with foil and tape, tests that power flows through the LED, and then hot glues the negative connection in place.
You'll be able to
- explain how two SPDT switches reverse motor polarity for a robot.
- describe how to make a tight, solder-free wire connection and why tightness matters.
- outline how to test the circuit before securing it with glue.
Key words
- SPDT switch
- A single-pole, double-throw switch that routes a common contact to one of two other contacts.
- Polarity
- Which terminal is positive and which is negative; reversing it reverses a motor's direction.
- Crimp connection
- A mechanical joint made by squeezing a wire tightly around a terminal, used instead of solder here.
- Stranded wire
- Wire made of many thin strands, which must be trapped and twisted carefully so none stick out.
- Hot glue
- A melted adhesive used here to hold the negative connection in place once it has been tested.
Transcript
So now we're going to connect the negative side of our battery to our switches. So we took a white wire and stripped about 3/4 of an inch of the insulation off of that wire. We're going to bend it and loop it through the center terminal in one of our switches, our single-pole, double-throw switches.
And we chose a white wire here because it stands out against the black AA battery housing, makes it a little easier to see. You can use really any color wire you want as long as it's copper or aluminum or something conductive. OK, so we're just crimping that wire against that terminal that comes out of our single-pole, double-throw switch.
And the wire is sticking straight up, and that's going to make it easier to connect to. So now we're trimming off the back end of the wire. And I actually trimmed it a little shorter than I probably should have so I would make the wire stick out about 1/2 an inch past the AA battery housing there at the end.
Now we're going to connect the two terminals of our switches, the two center terminals of our switches together. So in order to do this, we need to take about 1/2 inch of insulation off of two sides of our remaining white wire. And we're going to thread those wires again through the terminal blocks.
And so this wire is going through the center terminal block on the opposite switch that we've put. Now we're going to also strip the other end of the wire here off to make it easier to connect to the other side. So this is basically allowing us to provide a way to connect the negative side of our battery to our switches.
And these switches basically allow us to reverse the polarity of the motors causing the bot to backup up. So they are a very simple way of hardware programming the bot. OK, so we're just running our wire through there, and we want to loop it up. And again, we're going to take our needle nose pliers, and we're going to crimp that wire tightly in place so that we have a good firm electrical connection.
And it's really important that those connections are very tight because, since we're not using solder, the electricity won't flow if those connections aren't tight and so the bot won't perform like it's supposed to. So that wire is just a little bit long. So what I'm going to do is I'm going to take it and-- this one's come loose just a little bit here, so I'm going to crimp it down again on the other switch.
And then the wire that we just attached, it's a little bit long, so I'm going to-- instead of cutting it shorter, since I've already stripped it, I'm just going to loop it around. And then I'm going to twist it against that exposed wire, just like what we did with the LEDs and the resistors, twisting those two wires together.
And that'll allow us to have a good connection and spread the negative side of our battery to our switches. So we've got our negative black wire here, and we're going to trim it. And then we're going to strip it again. We'll strip probably about-- 1/2 to 3/4 of an inch of wire exposed is good.
It's always good to have a little bit extra wire there in case-- you just want to make sure that it is not too short. So again, this one's kind of tricky to strip because the installation is very soft, and so you kind of have to really work with it. But you don't want to pull too hard, or you'll, again, damage those strands.
And this is a stranded wire as opposed to a solid wire. So we're going to take those strands, and we are going to wrap them around our twisted-together wires. And that's going to allow us to connect the negative side of our battery to our switches and begin to build the rest of the circuit that we need to make the bot work.
So now we're going to twist the wires together. And it's kind of tricky because the stranded wire tends to spread out all over, so you have to work with it a little bit. And it's really important to keep all those stranded wires against the other two solid core wires because if you have a stray wire sticking out somewhere, it could cause a short or make a bad connection.
So we're just again twisting the wires together. And to do that really well, we want to use our needle nose pliers, and we're trying to get them as close together as possible. In order to trap those stranded wires, we're going to take a piece of-- a little piece of aluminum foil, and we'll wrap it around to the wires like we did for the LEDs.
And that just helps to prevent the stranded wire from sticking out somewhere it shouldn't and also helps to conduct electricity. Sometimes, it's hard to get the aluminum foil to stick to the switches, but you can do it-- or I should say stick to the wires there.
And then again, to hold everything together and insulate it, we're going to take a small piece of electrical tape about 1/2 an inch long, and we're just going to wrap it around that and squeeze it very tightly to make sure that we've got a good connection. Again, this is all about having really tight connections.
So what we're going to do is, before we finish anything else-- or before we glue anything else in place, we're going to test to make sure that we're getting power that flows. So now that we have our LED connected. The switch does work, so that indicates that, yes, the negative wire is working.
And so we'll try the other one too. Yeah. So we do have power flowing through that part of the circuit. So now what we can do is we can hot glue our negative side of the battery in place. Make sure to disconnect the resistors before you do that. So we're just going to take a little bit of hot glue here.
And, again, it's about half the size of a dime, a blob just enough to connect-- to cover over the connector. And we want to make sure that the hot glue flows completely around the wire. And that will help to hold it in place so that as we run our bot, it stays and doesn't pop out.
So now we're ready for the next step.
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