Spout's reversing circuit and final assembly
About this video
This lesson shows how a single pole double throw (SPDT) lever switch reverses a motor by switching which battery and polarity feed it. Combining two such switches with a motor lets the Spout move forward, and either side can be bumped to back it up. The lecturer also explains how the paperclip lever extends the switch so it is easier to trigger.
You'll be able to
- explain what single pole double throw means in terms of poles and throws
- explain how an SPDT switch reverses a motor by changing the direction of current
- predict how a two-switch, one-motor circuit moves the Spout when either or both sides are bumped
Key words
- Single pole double throw (SPDT)
- A switch with one input contact that can connect to one of two output contacts, so it can select between two circuits.
- Pole and throw
- The pole is the common contact the current enters through; the throws are the two contacts it can connect to.
- Motor reversal
- Changing the direction of current through a motor so that it spins the other way.
- Polarity
- Which terminal is positive and which is negative; swapping the lead from red to black reverses the current direction.
- Lever switch
- A switch operated by a lever that can be bumped to change its contact position, here extended with paperclips for leverage.
Transcript
So this circuit combines the best of both worlds. We've got the forward and the reverse capability with this one because we added something called a "single pole double throw lever switch." It's called a "lever switch" because it's got a little lever here. And this is "single pole double throw" because there's one pole and two throws.
And that's the term for these electrical contacts here. We're going to go ahead and turn our switch on, which will let power flow. You can see the motor is spinning. And if we want to back the motor up-- we want it to go the opposite direction-- we can push on this switch.
And you can see it causes the motor to reverse. And what's happening is the contact inside that switch is switching from the red wire, which is the positive lead, to the black wire, which is the negative. That causes the power to flow the other direction. And if you're asking, how does it do that, well, it does that because it's flowing through only one battery at a time.
So it's going through this battery in this direction under normal circumstances. And then, when the switch is bumped, it goes and flows backwards through this battery. That causes the motor to flip back and forth. Now, if we take that and we combine it with another switch and another motor, we can make the Spout turn around and go back and forth in different directions.
OK. So this is the combination of all the previous circuits that we've talked about. We've got our lights, and our light switch circuit here. I believe that's this circuit. So you can see that the lights turn on when we turn that circuit. And then we have our motor circuit.
And we have our two single pole double throw lever switches here. Here's another example of what it looks like on the inside. You can see there. We basically extended the switch by just hot-gluing the paperclips on to the end, and that makes it easier for the switch to bump against the wall.
It also gives it some more leverage so it doesn't take quite as much force to get the switch to trigger. OK. Let's go ahead and turn it on. So you can see it's moving in this direction. It's moving forward. It'll be carrying Spout in the forward direction right now.
And then, if it gets bumped, you'll notice that, when this side gets bumped, this motor backs up. And then, if this one gets bumped, this motor backs up. Again, so what the switch is doing is it's switching the power flowing from one battery-- right now it's flowing from one battery in one direction-- switches it to the other battery that's flowing in the other direction and causes the motor to spin backwards, which means that Spout can back up.
If they both get hit, they both back up. So that's what's going on inside of Spout.
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