##### Shane Celis July 19, 2015 Jul 19, 2015 #mockup-monday

In this Mockup Monday, I review the Sunfounder Crawling Quadruped Robot Kit for Arduino. I’m not affiliated with Sunfounder. This review is my personal opinion.

# Assembly

This is a kit, so it does require some assembly. If you’ve done anything with an Arduino, this kit should be very easy for you to put together. If you haven’t, this kit is a great reason to try out Arduino. In the video I show some photos of the build and talk about some gotchas. Overall the kit was easy to put together like a big lego kit. It didn’t require any specialized tools. There is no soldering. It even comes with a small screwdriver. Although you might want a knife or a pair of scissors to help remove the adhesive that comes on the acrylic. It does not include that batteries, which are specialized, but I got four and a charger for cheap on amazon.

The servos attach to these little white discs which need to be screwed onto the acrylic. There are twelve discs and each one requires eight tiny screws. These screws are easy to torque the heads right off, so be gentle. This part of the build was admittedly tedious, but the rest went very smoothly.

An odd that happened was that it’s on while you assemble it at one point, so it flinches while you work on it. Kind of eerie.

I did have a little difficulty trying to get my Mac to see the Arduino Nanos. Turns out I needed this driver from Prolific. I informed Sunfounder about this, and they responded very quickly that they updated their documentation and download, which I thought was pretty impressive.

I do wish I had a chip extractor on hand because I think I damaged my Arduino Nano’s USB port on the transmitter by removing it clumsily. However, you can still burn a program onto an Arduino with a busted USB port if you have another Arduino handy. So I burned on the Remoter code and it’s working fine.

After assembly there’s a calibration step, which I was kind of relieved by because when I attached my servos, they weren’t all making the nice 90 degree angles that I was seeing in the documentation.

# Open Source

First let me say that I’ve been very interested in legged-robot kits. I’ve used virtual quadrupeds for research and I’m using them now in a video game I’m making. I’ve kept an eye on the Robugtix models for instance, which look like an excellent consumer robot. However, the fact that Robugtix’s software is proprietary and closed source means it’s of a limited use beyond its pre-programmed features. And to me programming a robot is more than half the fun.

One thing that differentiates Sunfounder’s kit is that all the code is open source. This is a huge benefit for people who want to get under the hood and tinker. Here’s just a for instance of some tinkering one might want to do: the default crawling code causes two legs to move even if you just tap the joystick up for a moment. Here’s a snippet of code that handles responding to the transmitter.

void loop() {

byte order;
while (1)   {
if (order > 0) {
Serial.print("Order:");
Serial.print(order);
Serial.print(" //");

if (order < 5)
if (!is_stand())
stand();

switch (order) {
case 1:
Serial.println("Step forward");
step_forward(1);
break;
case 2:
Serial.println("Step back");
step_back(1);
break;
case 3:
Serial.println("Turn left");
turn_left(1);
break;
case 4:
Serial.println("Turn right");
turn_right(1);
break;
...


Now if we want to have the remote control behave a little less “digitally” and behave more like an analog stick, we can dig into the step_forward() function. Maybe we’d change step from an integer to a floating point number. Not sure, but the most important thing is it’s not impossible.

/*
- go forward
- blocking function
- parameter step steps wanted to go
*/
void step_forward(unsigned int step) {
move_speed = leg_move_speed;
while (step-- > 0) {
if (site_now[2][1] == y_start) {
//leg 2&1 move
set_site(2, x_default + x_offset, y_start, z_up);
wait_all_reach();
set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
wait_all_reach();
...


Even if you’re not a programmer, having a open source kit is really important because this means this kit will get better with time. People will release new bits of code that will enable your robot to do new things! Open source products get better with time—not worse. I’m intent on making my robot controllable via a Leap Motion Controller similar to what I’ve done in Quadrapus Sumo.

# Results

Once I put the quadruped together, calibrated it, and loaded the code, I tried it out. You can see its near first run here:

I was very impressed with the quadruped’s performance. The gait matched what Sunfounder shows in their video and it works on both hard wood and carpet. The servos make pleasant hum-and-whine sounds—you know, like a real robot.

# Verdict

I highly recommend this kit. It’s an amazing deal. I purchased this kit from Sunfounder for about \$160, which seems like a steal. I’ve seen a quadruped chassis—i.e., minus brains, servos, and transmitters—cost that much. For some products the transmitter alone is nearly that much. The fact that this kit is open source just puts this way over the top. You could integrate distance sensors and make it walk around autonomously. And if you don’t, you can be sure that someone else will!

I, for one, welcome our four-legged Overlords.