Main controller for 16 * 16 array of servos.

[ChrisCross]

Hello,
For a digital art project I would like to control a 16*16 array of small servos with a raspberry pi. However I can't connect all 16 channel servo controllers directly to the pi, so my idea was to connect the pi to a main controller which controls the servo controllers, which finally control the single servos. Are there such a "main" controllers, that are suitable for my case and if so, which one should I choose. It should be able to work continuously for a couple of hours.
Thanks in advance
Chris

 

[Pommie]

Controlling 256 servos is not trivial. It they have a load on them then they could take a reasonably large current (anyone got a guess). Assuming 0.5 amp per servo gives 128A at 6V which is about 750 watts. The power requirements can be overcome. The signalling is a problem, how are your programming skills?

Mike.
Edit, how often do the servos change? All 256 every second or 1 every 5 mins?

 

[ChrisCross]

The servos should change very quickly. About every second. My programming is ok, however I didn't work a lot with hardware yet.
To give you a better understanding of what I am trying to build. It's a mechanical mirror, that processes the images of a camera in grayscale and displays them on the mirror. Like this.

 

[ChrisP58]

I don't have any personal experience with this board, but from reading the description, I think 16 of these board might meet your needs.

The pi would send motor info 1 channel at a time over it's I2C port. https://www.adafruit.com/product/815

This is the IC used on the board. https://www.nxp.com/products/power-...bit-pwm-fm-plus-ic-bus-led-controller:PCA9685

 

[ChrisCross]

I don't have any personal experience with this board, but from reading the description, I think 16 of these board might meet your needs.

The pi would send motor info 1 channel at a time over it's I2C port. https://www.adafruit.com/product/815

How would I connect these 16 boards to the raspberry pi? It has only one I2C port.

 

[gophert]

How would I connect these 16 boards to the raspberry pi? It has only one I2C port.

That's the cool thing about I2C,
- the daughter board has an address that the Raspberry pi can send down the pair of wires,
- if the address sequence is important to a particular chip, it opens its ears for the last bit to see if the pi wants to read from a register or write to a register (0 or 1).
- Then the register info is sent down the pair of wires by the pi, then
- if it was a write command, it's all over / if it is a read command, the pi waits for the byte associated with the register to be sent back up the pair.

You'll need a chip that can be assigned 16 different addresses if you want each to control 16 different plaques.


Alternatively, you can find an different number of combinations (1 chip that can control 256 plaques, or build a rostering system (16 x 16 with 8 pins with a "4-bit" in x "1 of 16 out."

 

[gophert]

Are these RC servos from the hobby store?

 

[ChrisCross]

Thank you for the explanation. I'll definitely have a look at I2C before, so that I really understand it. The servos are from here.

 

[ClydeCrashKop]

"6 address select pins so you can wire up to 62 of these on a single i2c bus, a total of 992 outputs - that's a lot of servos or LEDs"

 

[Pommie]

If you've not already bought the servos then it might be better to avoid metal gear servos due to noise.

Mike.

 

[gophert]

If you've not already bought the servos then it might be better to avoid metal gear servos due to noise.

Mike.

I think the noise would be a great feature of the kinetic art project.