I have two motors that came with the Tamiya Twin Motor Gearbox kit. They are rated for 3V but I am running them off a 4 AA battery pack. I realize this isn't recommended, but I saw a post on Poulou that tested them and saw they would run for 5 hours straight at 6V.
When I connect both motors directly to the 6V source the motors are powered just like I tested them as. However, when they are controlled through the L293D they perform much worse. They are very inconsistent and will sometimes completely stop.
I thought it might have something to do with the constant changes in digital state I'm sending to them, but I tested them both
on high for 5 sec and I get the same result.
That L293 is a breadboarded circuit. We need a schematic drawn by hand that shows you how you connected the power for the arduino AND the motors and we need a voltage measurement taken on the arduino +5V power pin WHILE you are running those motors. A schematic of the L293 circuit is also necessary. that includes ALL components that are connected during that video.
That is the schematic I am using. I just measured the output at the 5V pin and it is indeed 5V. Pin 8 of the chip is reserved for the motor voltage, pins 1, 9 and 16 are for digital functions.
Measuring the voltage at pins at 3, 6, 11, and 14 I am getting varied voltage levels from 0.2 up to 2.5V, when I am expecting 6V.
The L293D H bridge is not suitable for those low voltage, high current motors. The L293D cannot provide the current required by those motors and is undoubtedly overheating. Also, the L293D "consumes" around 3 V at maximum current draw. If the battery voltage drops due to the high current, the remaining voltage will be too low to power the motor.
Pololu recommends use of a low voltage, high current motor driver, or to replace the motors with ones that require lower current. See http://www.pololu.com/product/61
jremington:
The L293D H bridge is not suitable for those low voltage, high current motors. The L293D cannot provide the current required by those motors and is undoubtedly overheating. Also, the L293D "consumes" around 3 V at maximum current draw. If the battery voltage drops due to the high current, the remaining voltage will be too low to power the motor.
Pololu recommends use of a low voltage, high current motor driver, or to replace the motors with ones that require lower current. See http://www.pololu.com/product/61
Current isn't too big a problem, these motors are 2.1A on stall, but much less in
normal operation.
The big issue is that L293's and other darlington-output H-bridges loose about 2.5V
and are a poor choice for a 3V motor. L293's always need good heatsinking
and fan cooling is a good idea, but lots of boards are sold without these, alas.
My personal recommendation would be choose 12V motors, then a L293D or L298
driver won't be totally inefficient, and your speed control will be much more positive
and you can run from a decent 12V battery.
jremington:
The L293D H bridge is not suitable for those low voltage, high current motors. The L293D cannot provide the current required by those motors and is undoubtedly overheating. Also, the L293D "consumes" around 3 V at maximum current draw. If the battery voltage drops due to the high current, the remaining voltage will be too low to power the motor.
Pololu recommends use of a low voltage, high current motor driver, or to replace the motors with ones that require lower current. See http://www.pololu.com/product/61
Current isn't too big a problem, these motors are 2.1A on stall, but much less in
normal operation.
The big issue is that L293's and other darlington-output H-bridges loose about 2.5V
and are a poor choice for a 3V motor. L293's always need good heatsinking
and fan cooling is a good idea, but lots of boards are sold without these, alas.
My personal recommendation would be choose 12V motors, then a L293D or L298
driver won't be totally inefficient, and your speed control will be much more positive
and you can run from a decent 12V battery.
I think we are on to something here. I have switched to the motors described by jremington and am seeing a slight increase of performance. Like Mark was saying, measuring voltage of the battery, then the output of the L293D, there is a loss of about 2.2V.
Would two 4 AA battery packs in series suffice for a 12V battery, or would a complete package be a lot better?
Also, I tried connecting a 4 AA battery pack with a half drained 9V battery in series (for a total of 10.5V), but the motors quickly stalled. Can someone give me any explanation of this? It seems contradictory to the use of a 12V battery.
