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LA Robotics Club Message Board › Driving Servos

Driving Servos

Tony
user 2811262
Riverside, CA
Post #: 3
Mainly a question for Tim, since he is bring his magic box of goodies, but I figure I would post here since the answer could educate others as well

I have 4 servos. Based on what I saw @ http://hacker.instane...­, it looks like I will need a shield to drive them, or can they be driven without a shield?

Also, I noticed you have 2 shields:
L298N Motor Drive Board
Arduino L293D Motor Drive Shield

What is the difference between the two?

Thanks,

Tony

Chris J.
user 11772561
Redondo Beach, CA
Post #: 15
I think the L298N will handle higher amp output than the L293D. If your servo draws too much power it's going to start to get really hot.

I'm familiar with the Pololu shields and drivers. Basically the Shield is just a driver board with the pin outs setup to plug directly into the Arduino. If you just get a board then you'll have to run wires from each connection on it to the appropriate pins on the Arduino. Not super tough but definitely not as clean. Either way unless they are like 50mA I don't think you can plug them straight into the Arduino, they need something to power them.

If you do get a shield make sure that the analog and digital pins it uses on the Arduino aren't in use by something else. I got a dual motor driver shield that used about 8 different pins and some of them were already hardwired in my SD/Ethernet shield. The fix was to cut traces and run wires which really defeated the whole point of a shield vs. a board. So heads up on that.

Also the servo library uses Timer1 so make sure you aren't using it for anything else.
Tim L.
Tim_Laren
Granada Hills, CA
Post #: 7
Tony,

The Arduino L293D Motor Drive Shield has 4 full .6 Amp H-Bridges, It will drive 4 DC motors or two Steppers.

The L298N Motor Drive Board is not a shield but an external board that can be connected to the Arduino. It has two full 2 Amp H-Bridges, able to drive 2 DC motors or 1 stepper.

You mentioned Servos. Servos are basically a motor, gearbox and controller, all in one. Typically, the hobby type, have three wires. Most run on 6 Volts (5 Volts works well). They have three wires, + Voltage, Ground and signal. The signal is a stream of pulses, that the servo's rotation will be proportional to the width of the pulses. The cool thing about a servo is that pulse can be driven directly off the Arduino, but I recommend running the power off an external power pack, unless you are just playing and have only one connected at a time. Some servos can draw up into the Amps and our little regulator on the Arduino can only handle 1 Amp and the USB that most of us power our Arduino off of supports a very minimal 500 mA (.5 Amp).



Steppers, on the other hand, have 4 or 5 wires (some more). They are relatively stupid (Well dumb, we don't want to offend any of them) motors. Their wires are connected directly to the coils inside the motor. To make these motors move, you have to sequence voltage thru the coils in a specific order, one sequence goes clockwise and another goes counterclockwise. Also, one full sequence of the coils moves a very small amount. I have some steppers that are 64 steps per rotation and other that are 180. The other thing about steppers, you can keep them powered up and they resist rotation. Normal motors turn freely unless they are turning.

Martin777
user 3311364
Norwalk, CA
Post #: 13
If you're talking R/C Servo motors, you don't need high amp drivers.

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