For a while I’ve been wanting a more capable Internet Enabled RC car, something that could go outside. Well, I finally got working the Wild Thumper I got a few weeks ago.

This is still very much a prototype

I initial tried controlling the motors with 3 L298Ns for each of the wheel pairs, but they overheated. So I tried a couple of other motor controllers, the ones that did the trick are a couple of BTS7960s.

Rated for high current, heating is simply not an issue

I ported the Nosy Monster code to work with them, and I improved several things,  mostly around smoothing controls. You can’t just start these motors are full power, you need you ramp up and down. This is to be mechanically gentle on the motors, but it also helps with piloting.

Outside!

We’re figuring out the wifi range around the house, it’s worst than I thought, well, for live streaming video at least.

Iterating on a case for the electronics

The suspensions are excellent, the motors could be beefier

More to come…

Every time I throw the Nosy Monster outside, it can’t handle even the best cut grass. The wheels just don’t cut it. So I finally splurged and got a Wild Thumper from SparkFun.

There’s a million things I’d like to do with it, and I don’t know how many I’ll get to. But at the very least, I’d love to have the vehicle able to go outside. WiFi goes pretty far around the house, and it so it would have a nice range of operation.

I’d love to set it up so random people on the internet can pilot it. Maybe via some sort of voting system.

I’d love for it to be energy autonomous with a solar panel.

And I’d love for it to be able to take some rain and snow.

The later is unlikely to happen, the rest very well may over time. Ultimately, this will be a better setup allowing for more development.

The Nosy Monster will remain in its current funny form. We’ll need to find a cool name for this new one, but I want to see what it looks like when it’s done first.

Quick points about this motor & driver

They are wonderfully cheap and extremely accurate due to 1/64 gearing. They move by 0.087890625° per step! However, the gearing is made of plastic and will wear out overtime, especially if moving heavy objects. Lastly the motors can become a little toasty if you work them hard.

Circuit

Fritzing

Code

#!/usr/bin/python3
import RPi.GPIO as GPIO
import time

in1 = 17
in2 = 18
in3 = 27
in4 = 22

# careful lowering this, at some point you run into the mechanical limitation of how quick your motor can move
step_sleep = 0.002

step_count = 4096 # 5.625*(1/64) per step, 4096 steps is 360°

direction = False # True for clockwise, False for counter-clockwise

# defining stepper motor sequence (found in documentation http://www.4tronix.co.uk/arduino/Stepper-Motors.php)
step_sequence = [[1,0,0,1],
                 [1,0,0,0],
                 [1,1,0,0],
                 [0,1,0,0],
                 [0,1,1,0],
                 [0,0,1,0],
                 [0,0,1,1],
                 [0,0,0,1]]

# setting up
GPIO.setmode( GPIO.BCM )
GPIO.setup( in1, GPIO.OUT )
GPIO.setup( in2, GPIO.OUT )
GPIO.setup( in3, GPIO.OUT )
GPIO.setup( in4, GPIO.OUT )

# initializing
GPIO.output( in1, GPIO.LOW )
GPIO.output( in2, GPIO.LOW )
GPIO.output( in3, GPIO.LOW )
GPIO.output( in4, GPIO.LOW )

motor_pins = [in1,in2,in3,in4]
motor_step_counter = 0 ;

def cleanup():
    GPIO.output( in1, GPIO.LOW )
    GPIO.output( in2, GPIO.LOW )
    GPIO.output( in3, GPIO.LOW )
    GPIO.output( in4, GPIO.LOW )
    GPIO.cleanup()

# the meat
try:
    i = 0
    for i in range(step_count):
        for pin in range(0, len(motor_pins)):
            GPIO.output( motor_pins[pin], step_sequence[motor_step_counter][pin] )
        if direction==True:
            motor_step_counter = (motor_step_counter - 1) % 8
        elif direction==False:
            motor_step_counter = (motor_step_counter + 1) % 8
        else: # defensive programming
            print( "uh oh... direction should *always* be either True or False" )
            cleanup()
            exit( 1 )
        time.sleep( step_sleep )

except KeyboardInterrupt:
    cleanup()
    exit( 1 )

cleanup()
exit( 0 )

Stuff you might need for this to run:

sudo apt-get update --fix-missing && sudo apt-get install python3-rpi.gpio

Results

This motor takes 5.625*(1/64)° per step, this means 2048 steps for 180°:

and 4096 steps for 360°:

One thing that is super cool about the driver board are the LEDs. Projects are always cooler with blinky LEDs, but these guys also help show what is actually going on inside the stepper, and can help you find issues. They are supposed to light up in sequence.

A few things to know about the L298N

This is a rudimentary way to drive a stepper motor. You are activating the motor’s coils in sequence yourself to have it take steps. There exist cheap stepper drivers which only require 1 signal from the Pi to be instructed to execute a full step sequence.

There are 2 coils on a bipolar stepper motor, each with a + and a – side. As such, this method requires 4 pins from your Pi to drive the Motor Vs only 1 pin with a more advanced stepper driver. Equally true is that a more advanced stepper driver will require at least another pin for direction and they’ll usually have other pins for micro-stepping.

This method does not allow for micro-stepping, only full steps. This is fine enough for most applications.

Lastly, while the L298N method might appear less appealing because of the above points, I find it to be extremely robust (advanced stepper drivers can be very finicky). You can power your Pi or Arduino with it thanks to a 5V port (warning, it can only provide so many amps and a Pi running heavy processing will crash).

It can be used to drive 2 DC motors instead of 2 stepper coils of a bipolar stepper motor, and has 2 PWM pins to adjust power given to the motors. It’s a very versatile and enabling device to master. You’ll also learn a lot about how stepper motors work.

Finding your stepper motor coils

Documentation for electronics is often inaccurate, disparate, when it’s even available. It’s good to find or verify what wires you think your coils are on. To do so you can put an LED on 2 motor pins and spin it until it lights up. When it does, induction powered your LED so you know you are holding the 2 wires of a coil. The other 2 wires are obviously the other coil.

There is no good way I could find to verify which of a coil’s wire is positive or negative. In my trials, I found that it doesn’t matter for a bipolar stepper motor on an L298N. The worst that will happen is that your motor may turn in the other direction which is easy enough to fix by flipping wires.

Circuit

Fritzing

Code

[python]#!/usr/bin/python3
import RPi.GPIO as GPIO
import time

out1 = 17
out2 = 18
out3 = 27
out4 = 22

# careful lowering this, at some point you run into the mechanical limitation of how quick your motor can move
step_sleep = 0.002

step_count = 200

# setting up
GPIO.setmode( GPIO.BCM )
GPIO.setup( out1, GPIO.OUT )
GPIO.setup( out2, GPIO.OUT )
GPIO.setup( out3, GPIO.OUT )
GPIO.setup( out4, GPIO.OUT )

# initializing
GPIO.output( out1, GPIO.LOW )
GPIO.output( out2, GPIO.LOW )
GPIO.output( out3, GPIO.LOW )
GPIO.output( out4, GPIO.LOW )

def cleanup():
GPIO.output( out1, GPIO.LOW )
GPIO.output( out2, GPIO.LOW )
GPIO.output( out3, GPIO.LOW )
GPIO.output( out4, GPIO.LOW )
GPIO.cleanup()

# the meat
try:
i = 0
for i in range(step_count):
if i%4==0:
GPIO.output( out4, GPIO.HIGH )
GPIO.output( out3, GPIO.LOW )
GPIO.output( out2, GPIO.LOW )
GPIO.output( out1, GPIO.LOW )
elif i%4==1:
GPIO.output( out4, GPIO.LOW )
GPIO.output( out3, GPIO.LOW )
GPIO.output( out2, GPIO.HIGH )
GPIO.output( out1, GPIO.LOW )
elif i%4==2:
GPIO.output( out4, GPIO.LOW )
GPIO.output( out3, GPIO.HIGH )
GPIO.output( out2, GPIO.LOW )
GPIO.output( out1, GPIO.LOW )
elif i%4==3:
GPIO.output( out4, GPIO.LOW )
GPIO.output( out3, GPIO.LOW )
GPIO.output( out2, GPIO.LOW )
GPIO.output( out1, GPIO.HIGH )

time.sleep( step_sleep )

except KeyboardInterrupt:
cleanup()
exit( 1 )

cleanup()
exit( 0 )[/python]

Stuff you might need for this to run:

[bash]sudo apt-get update –fix-missing && sudo apt-get install python3-rpi.gpio[/bash]

This stepper motor is rated for rotating by 1.8° per step. This means that it takes 100 steps to rotate 180 degrees:

and 200 to do a full 360:

Power the Pi from the L298N?

As I alluded to earlier, the L298N comes with a 5V power output that is most convenient to power Pis and Arduinos as it allows you to eliminate one of the 2 power supplies to your system. Be advised that while it provides the right voltage, it does not provide enough amps to power a standard Raspberry Pi, and while it can power a Pi Zero, the later will not get enough power and crash if it works hard enough (having a camera and a live streaming server pushed it over the edge in my testing). It will power a Pi Zero on Wifi running Python which is enough for a lot of applications.

Here’s the circuit if you want to do this:

Fritzing