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I'm modifying an RC car to use bluetooth. I use the L293D chip, and when I connect the motor to the chip, the car barely moves. If I connect the 9V battery directly to the motor, it moves the car well. I've used a voltmeter, and the chip does indeed output 9V, which seems really strange to me. If it outputs the right amount of voltage, how come the motor is barely moving? How do I solve this issue? My apologies if the schematic is difficult to read. That was my first schematic ever.

schematic

simulate this circuit – Schematic created using CircuitLab

JYelton
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faeophyta
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    Did you measure the voltage *while the motor was connected*? Or any other significant load? Sure, the open-circuit voltage may have been close to the battery voltage, but the output structure of the L293(D) guarantees that with any significant load, you'll lose anywhere from 2.6 to 3.6 volts across the drivers. – Dave Tweed Jul 24 '14 at 14:01
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    Yeah as Dave says, the output drivers of the L293D are Darlington pairs, on high and low side, meaning you drop at least 1.4V * 2 before the motor windings can see the voltage. The motor uses voltage and it's "motor constant" to relate input voltage to torque generated, so with a low input voltage, it's torque is probably just enough to turn the shaft/wheel of your RC car. – KyranF Jul 24 '14 at 14:50
  • You might want to read this http://electronics.stackexchange.com/questions/108686/what-h-bridge-drivers-are-preferred-for-applications-controlling-a-low-voltage-m – Andy aka Jul 24 '14 at 17:09
  • @DaveTweed, I'm using a 9V battery, and when I hold the rc car up without any load, it shows 2V. Is this normal/is there any way to fix this? – faeophyta Jul 24 '14 at 20:13
  • First, don't use a (small rectangular) 9v battery for motor loads. It's not designed for that. – Chris Stratton Jul 24 '14 at 20:54
  • @ChrisStratton, should I use 4 AA or AAA instead? – faeophyta Jul 24 '14 at 21:16
  • The capacity of AA cells would be much more appropriate, yes. But 4 may not be enough - you get a lot of loss from those bipolar bridges. Depending on what your motor needs you might want to you 6, 7, or 8 cells (or use a MOS bridge rather than a bipolar one) – Chris Stratton Jul 24 '14 at 21:27

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