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I tried l298n before but its output voltage wasn't high

so I use relay shield but it seems that the car can only go forward or stop

Can I control the speed and direction of dc motors?

  • Please can you expand on your question? What do you motors need V and A? – Code Gorilla Aug 17 '16 at 12:26
  • You can change the polarity of the power going to the motor using only a single DPDT relay. You'd need a second relay to turn the motor on and off. Using a relay to control speed will wear out the relay pretty fast. – Gerben Aug 17 '16 at 12:53
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Using a mechanical relay to control the speed is not a good idea. But you can control the directions.

I prefer you to use Solid state relays (SSR) to do this. Arrange 4 SSR as Hbridge and Use PWM to control the speed.

refer this

or you can use the devices like this which has direction control as well.

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Yes you can, but the easiest way is by using a "motor shield". There are more options than just L298N.

Are you sure it was the voltage that wasn't high enough, its normally the current (Amps)?

To do it with a relay you need to change the polarity of the feeds to the motor. You could do this with 2 relays both connected all the time, but if you close the wrong one, you will short everything. It would be better using a motor controller.

  • When I used l298n the output voltage was about 4.6V current was about 120~130mA – 黃銘賢 Aug 17 '16 at 12:34
  • the fast speed occurred when I connect 5V pin of arduino to the positive of motor and GND pin to the negative of motor I measured the current was about 120~130mA – 黃銘賢 Aug 17 '16 at 12:37
  • But I used the 9V battery to connect logic 5V of l298N ,the speed didn't increase. I am sure I connected I don't know why it didn't work – 黃銘賢 Aug 17 '16 at 12:40
  • Would this be better? learn.adafruit.com/adafruit-motor-shield-v2-for-arduino/… – Code Gorilla Aug 17 '16 at 12:42
  • 9V batteries can't provide a lot of power/current. – Gerben Aug 17 '16 at 12:55
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Most refer to relays when talking about mechanical devices which are either closed or open. If you arrange several in an H-bridge configuration, you can make you car go forward, stop and reverse. But controlling speed is not possible.

  • Ok thank you it seems the only choice is l298n – 黃銘賢 Aug 17 '16 at 12:33

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