Development of the #ShrimpBot
At this point I have built the base of the #ShrimpBot.
Both motors have been checked by connecting them directly to battery terminals.
I have soldered the jumper cables onto the motors & wrapped them in tape to keep them secure.
I now want to begin the breadboard circuit that will allow me to send a signal to the motors to turn them on & off, in effect steering the Bot.
In order to test the circuit I’m going to use a spare motor & just push the jumper cables through the wholes in the terminals.
I’ve also blue tacked a toothpick to the axle so its clearer in the video to see whether its turning.
I’m going to be using a modified version of the 3rd circuit from the Arduino Experiments kit to control the motors.
I can’t recommend the ARDX kit highly enough – its a bit expensive but an absolute MUST if you’re new to this stuff!
To begin you’ll need to take a Transistor (the black three legged fella) & a Resistor (the ceramic type thing with stripes on it).
The exact position of them along the board isn’t important (ie it doesnt matter if you use row 49,50 or 51) but they should create a T shape.
Also it’s important to check the Transistor is facing the right way – the flat side should be facing towards the Resistor.
The WHITE jumper cable is plugged in next to the Resistor & I’ve just blue tacked that down to make the photo clearer.
This WHITE cable will be the signal cable – it will be the wire that we send our signal down to tell the motor when we want it to turn.
I have also included a powerpack – I bought this one super cheap from radio Shack but you can get them at Maplin & online.
(I feel duty bound to give a word of caution here as I have had 2, that’s TWO ASDA batteries literally explode on me in the last 2 months –
I will include photos of the remains of them in a separate article – I’m told batteries should never explode but one went in the middle of a
lesson & I have 2 dozen year 8 pupils with frazzled nerves who will attest to how loudly the thing BANGed when it went!!!)
Although the two stages above look like a big jump in complexity all that I’ve really done is add the motor.
I’ve blue tacked the motor onto the corner of the breadboard. I’ve chosen to use RED as the positive/powerIN lead.
The wires allowing current out of the battery are BLACK & it connects right next to the WHITE signal pin.
The following diagrams make this clearer…
The circuit is essentially putting a tap on the outflow of the electricity.
The Transistor waits for a signal on the WHITE cable & if it receives one it allows current to flow from the BLACK wire
through the Transistor and on down the BLUE wire back to the negative terminal on the battery pack as can be seen here.
Now we need to work on putting a signal down the WHITE signal cable to tell the motor WHEN we want it to turn.
At this point I would have MUCH preferred to use the #Shrimp (other wordpress blogs deal with my use of the #shrimp)
However I took advice from Tim Moore of Accrington Academy & am using an Arduino in order to remove as many doubts from the circuit as possible.
The Arduino already has the Blink sketch uploaded onto it.
You can see this if you compare the two photos – on the left there is only the GREEN power led.
On the right photo (above the MEGA chip on the left) you can see the YELLOW pin 13 led is lit.
This means that pin13 is turning ON then OFF constantly.
We want to attach the white signal wire to pin13 so that the motor is prompted to turn ON then OFF.
Notice:- The white signal cable is being stretched down to plug into pin13.
IMPORTANT: The circuit above uses the Arduino’s 5V or 3V power pin as a substitute for the battery power pack. At present the battery power pack circuit doesn’t work. However I can create a working circuit using both the Arduino’s 5V AND 3V power pin but it’s too complex to show the theory of the circuit & I think it’s important for the pupils to see the understandable circuit implemented before giving them a more complex circuit.