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View Full Version : Newbie, building a wheel bot.



AJ14
05-22-2012, 10:43 PM
I want to build a wheeled robot using a 24V 250Watt DC motor. I'm going to build the body out of plywood, but that's not the part I'm wondering about. I want to use a laptop and Wi-Fi to control the motor(stop and go, no speed variation.). I can easily write the programs using client/server side programming in Java, but I need to know how i can control the motor from a program. Will I need a Servo controller? I want to make it belt or chain powered to turn the axle. I have an idea of how all of this goes together, but I am not sure.

Thanks,

AJ

jwatte
05-23-2012, 07:15 PM
A typical "servo" controller controls hobby servos, that want a PWM control signal. The motor you have probably is nothing like that.

Instead, what you want is known as a "motor controller." For just on/off, you can use a simple relay; for forward/back, you can use two relays that switch between connections (to put one end of the motor to positive, and one to ground, or vice versa.) If you want speed control, relays won't let you run PWM (this is a different kind of PWM than servo control) for power control, so you'll need what's called an H-bridge, typically built out of a control IC and some high-power MOSFET switchers. Note that 24V / 250W counts as "big" in these circumstances, and thus will probably cost a little bit of money.

There's also the question of how you talk to the relay or H-bridge. There are USB I/O boards you can get. Or you can get something like an Arduino, and use a shield or just some wiring to the digital output pins of that device to in turn drive the external circuitry. (If you use an Arduino, you will additionally need a switching transistor to pull the coil on your relays, because they may use more power than available from the Arduino pins)

There are some relays here on Trossen: http://www.trossenrobotics.com/c/data-i-o-Relay-switching-boards.aspx
T (http://www.trossenrobotics.com/c/data-i-o-Relay-switching-boards.aspx)here are also various motor controllers: http://www.trossenrobotics.com/c/robot-motor-servo-controllers.aspx
J (http://www.trossenrobotics.com/c/robot-motor-servo-controllers.aspx)ust make sure that you get one that can switch > 24V and > 11A to drive your motor.
Perhaps the easiest start is to pick up this controller: http://www.trossenrobotics.com/p/sabertooth-dual-12A-motor-driver.aspx
A (http://www.trossenrobotics.com/p/sabertooth-dual-12A-motor-driver.aspx)nd some way to talk to that controller, if you don't have convenient GPIO pins on your receiver PC/Laptop. An Arduino Uno would do fine.