Author Topic: Reduce number of hbridges?  (Read 2166 times)

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Offline anilgTopic starter

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Reduce number of hbridges?
« on: January 20, 2008, 01:41:20 AM »
I'm createing a robot car weighing around 1.5Kg powered by a lead acid 12v battery.

I'll now need 3 motors 2 to differential-drive the wheels, and one to run the pulley to pick up objects. I have access to 8 digita output lines... Vcc and Ground will be points on the 12V lead acid battery.

What is the minimum number of Hbridges I have to buy to control these 3 motors forward and backward? Any better plan than 3 different h-bridges?
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Offline Ro-Bot-X

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Re: Reduce number of hbridges?
« Reply #1 on: January 20, 2008, 01:51:11 AM »
Most of the H-bridges are dual, so you can controll 2 motors with them.
Make sure they can provide enough current for your motors!
To controll the motors, you need 2 pins from the mocrocontroller for each motor (6 pins total). Tie the Enable pin of the H-bridge to Vcc (+5V) and use the other 2 controll pins. If you use PWM, you can use an inverter gate (or tranzistor) from one controll pin to the other (on the H-bridge) and controll the motor with just one pin from the microcontroller. In this case, a 8bit PWM signal will make the motor rotate one direction for 0 value at max speed, stop for the 127 value, and rotate in the other direction at max speed for the 255 value. The value represents the ON time of the duty cycle.
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Offline anilgTopic starter

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Re: Reduce number of hbridges?
« Reply #2 on: January 20, 2008, 01:54:30 AM »
Quote from: Ro-Bot-X on January 20, 2008, 01:51:11 AM
Most of the H-bridges are dual, so you can controll 2 motors with them.
Make sure they can provide enough current for your motors!
To controll the motors, you need 2 pins from the mocrocontroller for each motor (6 pins total). Tie the Enable pin of the H-bridge to Vcc (+5V) and use the other 2 controll pins. If you use PWM, you can use an inverter gate (or tranzistor) from one controll pin to the other (on the H-bridge) and controll the motor with just one pin from the microcontroller. In this case, a 8bit PWM signal will make the motor rotate one direction for 0 value at max speed, stop for the 127 value, and rotate in the other direction at max speed for the 255 value. The value represents the ON time of the duty cycle.

Thanks for the reply.

hbridges (atleast the ones I saw) are kinda bulky. How do they stack up against L293D (www.solarbotics.com/products/l293d/)?
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Offline SmAsH

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Re: Reduce number of hbridges?
« Reply #3 on: January 20, 2008, 02:30:45 AM »
yea check out the $40 robot tutorial...they work well.


~smash
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