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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When do we get to see that ?

Looks awsome, I want one !!!

Awsome stuff Obi! 

Now I just need to make a robot that needs 48 servos :D

A serpent might be a good start, fun coding I imagine

How about a giant worm bot?!?

Add 48 pieces of rubber tubing and toss 'm all in a tight container: robot can of robot worms! Beautiful.

I serve you up fresh servo worms on a nice glass table and you want canned worms!

Even using micro servos that would need a very big can. I must admit it did remind me of a plate of gaH!

Thanks for tips, 1.I'm gonna try your code tonight and see if same. 2.Not quiet sure "grounds are not connected", do you mean the ground wire on shield connect to the mega?

I do not know how your I/O shield is configured. A simple test is to use a multi-meter to measure the resistance between the servo's ground and the processor ground. you should get a dead short.