PDA

View Full Version : servo control



Let's Go!
09-22-2008, 07:24 AM
can the bs2 control a large servo, i.e. bigger than that shown at parallax, and if so what is the hookup recommendation? thanksˇ

Mike Green
09-22-2008, 08:03 AM
Almost all servos are controlled the same way, with a logic level signal consisting of pulses repeated roughly every 20ms, approximately 0.5ms to 2.5ms in width with the pulse width indicating the desired servo position or the servo speed and direction (for continuous motion servos). These pulses are the same regardless of the servo's size and the connections are the same. The only exception is a specific line of digital servos where this signal line uses high speed serial communications.

So, yes. The size of the servo doesn't matter. The hookup is the same.

A very large servo will draw more current than a small servo and the servo power supply and wiring has to be appropriate for the current needed.

Let's Go!
09-22-2008, 08:52 PM
mike, if i had a large servo, wouldn't i need to use, e.g., a large 12 volt battery, versus connecting it to the basic stamp, due to the current demands.



and if so, would i connect the servo red wire to the positiveˇ12v batt, connect the grounds of bs2 and 12v batt together, and send the pulse out of bs2 to the servo.ˇ thanks.

Mike Green
09-22-2008, 09:45 PM
The connections would be right, but the 12V would likely destroy the servo. In general, servos are made for a 4.8V to 7.2V supply. They'll handle a little bit higher voltage, like 7.5V, but higher voltages will shorten the life of the brushes in the motor and 12V will rapidly burn out the brushes.

allanlane5
09-22-2008, 10:35 PM
Don't confuse "Voltage" and "Amperage".

A powerful servo motor will take a LOT of amps (2, 3, 5, maybe 10) at 5 volts. Increasing the voltage will simply destroy the servo -- it's only designed to work at a particular voltage.

Now, there ARE DC motors designed for 12 volts. To interface to these you'll need an HPWM device, which will let you control speed and direction.

Post Edited (allanlane5) : 9/22/2008 5:13:35 PM GMT

Let's Go!
09-22-2008, 11:31 PM
thanks for the help