Let's Make Robots!

Driving up to 48 servos with a Spider controller

Controls more servos than you can fit on one robot :p
_48_servos_array.zip850 bytes

This tip/walkthrough will work with all Arduino Mega PCBs and their clones. I have found the instructions for the servo command to be a little vague so in this tip I will share my research.

The Spider controller is an Arduino Mega compatible PCB. Unlike the Arduino Mega the Spider controller was designed specifically to drive a large number servos. This made it ideal for this tip/walkthrough.

The Arduino servo library is capable of driving up to 48 servos. After a bit of experimenting I found that the servos can be assigned to any of the digital pins from D0 to D63. For those thinking that the digital pins only go to D53, analog pins A0 - A9 are digital pins D54 - D63.

For those who have never used the servo command before I will start at the beginning using the attached code as my example. The first line of the code "#include <Servo.h>" means that the instructions needed to generate the servo control signals will be included in the code to be uploaded to the microcontroller.

Before the setup() function you must define your servos same as you define your global variables. I've simply called my servos s00 to s47. You should name your servos with descriptive names to make your program easier to read.

The Servo command uses a timer for each 12 servos used starting with Timer 5. As these timers are also used for commands like PWM you need to plan your pin assignments to avoid conflicts.

1   to 12 servos use timer   5          disabling PWM on pins 44,45 and 46.
13 to 24 servos use timers 1&5       disabling PWM on pins 11,12,44,45 and 46.
25 to 36 servos use timers 1,4&5    disabling PWM on pins  6,7,8,11,12,44,45 and 46.
37 to 48 servos use timers 1,3,4&5 disabling PWM on pins 2,3,5,6,7,8,11,12,44,45 and 46.

Once you have defined your servos you need to attach them to the physical pins of the controller. In the setup() function you can attach your servos to any of your digital outputs. In my sample I have avoided digital pins 0 and 1 as they are used for serial communications. At this point even thought the servos have been attached to a pin they are not receiving any signals.

The first time you write to a servo using either the servo write() or writeMicrosecond() command the pin will be initialised and the servo will receive a control signal. depending on your application you may need to initialise the servos in the setup() function. In my example I initialise the servos in the loop() function.


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I only have code for a 12 DOF hexapod posted here: http://letsmakerobots.com/node/32854
This code is very easy to control and could be adapted for 3 DOF legs without too much effort. The simplest way is to make the knee joint copy the hip joint so that as the leg lifts up it also stretches outward. It's not true kinematics but it will get you moving quickly and easily.

The code has one variable for speed and another to specify what angle to travel at. A third variable makes the robot rotate clockwise or anti-clockwise.

waahhh...I'm so sorry for this very annoying comment. 

I thought this is my posted topic and replied hastily. 

I'm SO SORRY! I can't delete it. I dont know how. SORRY

So will there be an option to just get a board unpopulated or maybe the gerbers. And when will this beastie be available

The board is available from several distributors.

Looking at the back of the spider, it looks like ground and Vcc for the servo pins could be re-routed off-board from the back side.  With the USB to the right, looking at the back of the board, the top left corner looks like a bottle neck for ground and Vcc that could be severed, and soldered for off board (leave ground connected of course).

What do you reckon the likely cost of this will be, OddBot. Just an idea.

I can't say as it is up to the distributors. It should be roughly the same price as the Arduino Mega.

Whoa! For a moment I thought that the Dagu Spider controller pictured as part of the Quadruped Walking Robot kit was for sale for only $29.

However, further reading showed me that "Motor controller, microcontroller, batteries sold separately". I haven't found the controller for sale in the wild yet.

I was updating 2 post at once and accidently uploaded the picture to the wrong post.

No the QuadBot is just the chassis with 8 miniature servos. I need to send Robot Shop some good photos of the chassis.

Considering there are 8 servos in the kit, $29 is a fairly good price.

This is one sexy controller ! The video is Geekishly hilarious !