Questions related to motor controllers

David_Sumo

Hello again, Summers almost over and its my last year of school, as leader of my schools robotics club, iv'e decided to build a large 20X20 cm sumo robot for the Canadian national robot games, powered by 2 basic stamp 2 micro controllers(the kind that comes with the premade sumobots :P). I spent last year exploring the possibility of using motor controllers so i can use DC motors. Although my H bridge motor controller i made didn't work well, it was fun learning. pic attached of it. A problem i always had with it though, is that i could never figure out how to get more power to my motors using an external power source, due to fear of the say, 16 volt battery blowing up my micro controller. :P

So this time around, im looking for a motor controller that would allow me to use an external power source, I've been looking at the L293D but im unsure as to if it can use external power, or how it would. Im also looking for better motors, hopefully ones that i can attach a nice little Dragon skin silicon wheel too.

if theres anyway you experts can help address some of the issues i have that would be great, thanks

Attached pic is my ghetto motor controller, i lost the schematics though. [noparse]:([/noparse]

Mike Green

The L293D is just a pair of 1/2 H-bridges that can be combined to form an H-bridge. You need to understand H-bridges first. There are some good articles in the Wikipedia. Do a web search for "wiki h-bridge", read the article, and look at the linked references.

Parallax also sells several different DC-motor controllers including their own HB-25 and one from Polulu. Look in Parallax's webstore under Accessories / Motor Controllers for information and links to documentation and sample code.

There are also several articles on motor control in the Nuts and Volts Columns. Click on the Resources tab on the main Parallax web page, then on Nuts and Volts Columns. That'll take you to the index where you can browse for the articles.

dev/null

Yes the L293D can have an external power supply. You connect V+ of the external source to pin 8, and have common ground for both power sources (pins 4,5,12,13). The L293D is suited for stepper motors. If you want to control DC motors, you need some sort of voltage controller or PWM signal in addition to the L293D. The best way to control DC motors is to use a PWM generator in addition to an H-Bridge where the PWM generator sends waves (triangle or square) through the bridge. If you use voltage control (lower and raise voltage say with a voltage divider/digital pot) a lot of power is dissipated in the circuit and not very effective.

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Don't worry. Be happy

David_Sumo

Thanks mike, i'll be ordering 2 of those HB-25's tonight. after reading about them they seem ideal for what i want! Plus 2 of them only use one I/O port, which means an extra set of LED lights or sensors [noparse]:D[/noparse]


I'll also look into what Dev/Null said for the sake of learning~ thanks. [noparse]:)[/noparse]