Servo Motors

[mighty69]

anyone know the strongest (largest?) servo motors that can be used in conjunction with a Raspberry Pi? I'm working on some competitive robotics stuff and I need some more juice than the motors in the tutorial.

[adafruit_support_bill]

Most any RC servo should be controllable from the Pi if you power the servo separately.

[mighty69]

I'm currently trying to run two servos with the pi using the 16-channel driver. I have the driver powered by an external source and a 330 uF capacitor. For some reason when I run the Servo_Example module included with the Adafruit package, my pi freezes up. If I disconnect power it eventually comes back. suggestions?

[adafruit_support_bill]

Post a photo of how you have everything hooked up.

Brushed DC motors, such as the ones inside RC Servos, generate a lot of electrical noise that can cause problems with other circuits. Although most problems occur when the noise is conducted back through the power wires, it can also couple inductively. Try to keep your servos and associated wiring routed clear of your Pi.

[mighty69]

20140729_104256.jpg (805.24 KiB) Viewed 245 times

[adafruit_support_bill]

Using alligator clips on a header like that is very prone to short circuits. Worst-case, you can damage the GPIO pins on your Pi. But even a brief short could easily hang the i2c bus.

[mighty69]

so i swapped out the 'gator clips for some insulated quick connects and i'm still freezing the pi when i run both motors. one runs just fine.

[adafruit_support_bill]

i'm still freezing the pi when i run both motors. one runs just fine.

What power supplies are you using for the Pi and the servos?

[mighty69]

I have them separately plugged into a surge protector.

[adafruit_support_bill]

But what kind of supplies are they?

[mighty69]

120v AC via USB adaptors.

[adafruit_support_bill]

120v AC via USB adaptors.

There are many kinds of USB adapters. Most of which are not capable of reliably powering a Raspberry Pi. Please post a photo of the supplies and their current ratings.

[mighty69]

if the issue is only the supply, then i'm not overly concerned. I have some jumper leads in the mail and plan on wiring up AA rechargeable battery banks to power the motors. for the pi I'll be using a 5v/0.5a output portable power bank. the cables for the motors and pi are both awm 2725, 80 degrees C, 30v, VW-1, 28AWG/1p and 2c.

[mighty69]

the assembly seems to be working fine now that i'm using the insulated quick-connects in place of the 'gator clips, but I'm getting a considerable amount of walk from one of the motors. when i run only one motor then it creeps on the servoMax command, with two motors it's the second motor that walks on the same command.

[adafruit_support_bill]

The behavior you describe sounds suspiciously like a power problem. 0.5v is marginal for the Pi. They idle at 350-400mA and can easily exceed 700 - even without any peripherals attached.

I'm getting a considerable amount of walk from one of the motors.

Not sure what you mean by 'walk'. Is the servo not holding its position?