Robot Club - fourth session completed

Link to Preparing post details in the parts in the kits.: http://winkleink.blogspot.co.uk/2014/11/preparing-for-2015-after-school.html

Link to First session; http://winkleink.blogspot.co.uk/2015/01/robot-club-first-session-completed.html

Note; I did not post for the second session. There is a short summary in the Third Session post.
Link to Third session: http://winkleink.blogspot.co.uk/2015/01/robot-club-third-session-completed.html

This week we nearly had a full house.
Only 1 child missing due to illness.

The 4 who attended the previous week remember a lot of their work and code so were getting stuck into getting their robots to go around a corner.

I had a bit more fun getting drivers on enough school PCs to permit the Arduino Nano to be seen. It needs custom USB/Serial drivers that are not included by default.

The teacher who is ICT coordinator came in to see the session in full swing with robots spinning, or moving along the floor. With coding going on and due to plus and minus lines on the batteries being shorted a nice little display of black smoke and the lovely smell of burnt plastic.
No real harm done just a jumper wires plastic sleeving was melted.
I congratulated the child on making smoke as it's something we all do when we work with electronics.  They were kind of shocked.
It was great that the teacher had the same attitude so no harm done and no concern about burning down the school.
I tested their robot kit and Arduino. Nothing damaged, amazingly so did a little bit of rewiring and handed them back their robot to get working on again.

On of the kids who was in the previous session had a problem where their robot was pulling to the left.  These are small cheap kits so the motors aren't tuned and the wheels are small and have grip meaning they catch on the carpet.  Meaning they cannot reliably go straight.
We tried to fix it by turning the wheels in or our to change the resistance but no go so introduced that child to analogWrite.
A value of 235 seemed to make it all work perfectly. They had a nice straight running robot.

Once again the kids were not that eager to leave as they were perfecting their code and making it better.

At the end one of the girls who was being collected wanted to show her mother what she had done so she gave a great demonstration of her robot.  Holding down reset to stop it moving.
Set it up and let it go. She then explained the code she had made as well as giving details on some of the other parts we will be using.

Next week we will be using an input device. A small line following sensor. I will mark the edge of the room area with white paper providing a contrast with the blue flooring. The idea will be to detect the paper and make the robot turn.
This will be the first time the kids do inputs and will also require the introduction of the 'if' statement.

Looking forward to another productive session next Monday.

Arduino Compatible robot for £15

I was looking for a low cost way of building a vehicle controlled by an Arduino or Raspberry Pi and eBay once again came up with the solutions.

1 x Smart Robot Car Chassis Kit  - £7.60
1 x L298N - £1.86
1 x Arduino Compatible Pro Mini - £2.53

Total Cost: £11.99

The Smart Robot Chassis comes with 2 motors and wheels.  It comes with the encoding wheels for optical encoder to measure rotation, but without the electronics.

All the parts with chassis. 

The L298N is a Motor Driver Module

That's it on the right next to the battery pack

While the Pro Mini is a small Arduino compatible board that I previously blogged about programming (http://winkleink.blogspot.co.uk/2014/01/programming-arduino-pro-mini-16mhz-5v.html) and soldering the headers (http://winkleink.blogspot.co.uk/2014/01/soldering-up-pro-mini-arduino.html)

You need a USB to serial adaptor to program it. For this adaptor you have to solder a pin to the DTR and then attach that to the RST line on the Pro Mini when programming.

I built the Chassis and attached the L298N

All the parts

Bits for the front wheel mounting

Screw the spacers to the chassis

Attach the swivel wheel to the spacers.
Note nuts not in original picture

Parts for motor/wheel mount

Use small screws to attach pillars to chassis

Parts for connecting motors

Screw motor to the outside of the pillars.
Note: make sure to have motor connectors on the inside
for easy cable management

Add the encoder wheels if you want and the actual wheels

See in front of batter holder are the two holes where
the battery holder will be bolted to.
Use 2 of the slightly longer bolts for this.

All finished.  Still needed to solder the wires to the motors.

The L298N is then wired.

+ Battery to VCC and 5V on the L298Nand RAW on the Pro Mini. The L298N appears to be OK with 6V going to the 5V line. And the Pro Mini doesn't complain about the 6V from the batteries either.

As always connect all the GNDs together

Then for each motor connect Out1 and Out2 to one Motor and Out3 and Out4 to the other motor. Depending on which way around you do the connection will decide which way the motors spins, so if this is wrong you can either swap the wires or modify the code.

Then for control from the Pro Mini I connected

IN1 to 3

IN2 to 5

IN3 to 9

IN4 to 10

The eagle eyed will have noticed these are 4 of the PWM lines so in the future I can enable speed control by driving using PWM rather than digital.

Uploaded the following Sketch tot he Pro Mini and let it rip - see video at the bottom

// motor driver using PWM

int lb = 3;

int lf = 5;

int rb = 10;

int rf = 9;

void setup() {

  // put your setup code here, to run once:

  pinMode(lb, OUTPUT); 

  pinMode(lf, OUTPUT); 

  pinMode(rb, OUTPUT); 

  pinMode(rf, OUTPUT); 

  

  digitalWrite (lb, LOW);

  digitalWrite (lf, LOW);

  digitalWrite (rb, LOW);

  digitalWrite (rf, LOW);

}

void loop() {

  // put your main code here, to run repeatedly: 

  

    digitalWrite (lf, HIGH);

    digitalWrite (lb, LOW);

    digitalWrite (rf, HIGH);

    digitalWrite (rb, LOW);

    delay(1000);

    digitalWrite (lf, LOW);

    digitalWrite (lb, LOW);

    digitalWrite (rf, LOW);

    digitalWrite (rb, LOW);

    delay(1000);

    digitalWrite (lf, LOW);

    digitalWrite (lb, HIGH);

    digitalWrite (rf, HIGH);

    digitalWrite (rb, LOW);

    delay(600);

    digitalWrite (lf, HIGH);

    digitalWrite (lb, LOW);

    digitalWrite (rf, HIGH);

    digitalWrite (rb, LOW);

    delay(1000);

    digitalWrite (lf, HIGH);

    digitalWrite (lb, LOW);

    digitalWrite (rf, LOW);

    digitalWrite (rb, HIGH);

    delay(600);

}

All worked well.

Next I need to put in place a way of controlling it remotely.

The adventure continues.

Note: This chassis and L298N should also work with a Raspberry Pi. Need to be more careful with the power and a few other bits.