L293D DC motors speed issue

Hello,

I just finished my first Arduino project and I am facing a little issue.

I build a Buetooth RC car with 2 motors using the next parts:

-Arduino Uno.
-Motor driver shield for Uno L293D.
-Bluetooth module HC-05.

The car is generally functional and working as expected, however the motor spin is very slow, like 1 complete rotation every 2-3 seconds. I saw the capabilities of this motor and they are much higher than that. The motor supports max 6V and 300mA. The L293D can provide max values between 4.5V-36V and 600mA per each motor from what I saw in the technical specifications, so I suppose that the driver is not the issue.

For power supply I am using an external battery of 5V and 1A that is connected to my Arduino via USB. The motor shield is powered directly from Arduino (The jumper is included).
If I connect the motor directly to a 9V battery for example is working like a charm.

I attached the code that I’m using if it could help, however the issue I think is more like a power problem than a programming one.

If someone encountered situations like this, a little help would be appreciate it. I am new to Arduino and programming in general.
Please let me know if you require any more information from my side.

Thank you.

RC_Car_2Motors.ino (1.86 KB)

Look at the datasheet of the ancient (30+ year) L293D.
There is a typical H-bridge loss of 2.6volt@600mA.
That means that your need a ~8.6volt supply for a 6volt motor.
Now your motor will get 5volt-2.6volt= 2.4volt.
AFAIK Adafruit replaced their V1 L293D shield with a V2 model with modern low-loss mosfet drivers.

Leo..

Thank you for your answer.

I had no idea about the 2.6V loss on the L293D nor that it is that old. I checked the datasheet and it's not mentioned.
Is there any way of increasing the current output voltage of L293D to compensate for the 2.6V loss? maybe by using some transistors? (just asking). I don't really want to change the motor driver right now.

Thank you.

bogdan3220:
I checked the datasheet and it's not mentioned.

High-level output voltage: VCC2 – 1.4
Low-level output voltage: 1.2

The only solutions I can think of are a separate motor supply or a more modern H-bridge.
Two LiPo batteries in series, or six AA NiMH batteries will do the trick for your shield.
Go to pololu.com for mosfet motor drivers.
Leo..

Ok, I will try your suggestions.

Thank you.

An RC car's motors might take 10A - RC stuff is very high current, usually requires a suitable ESC
and LiPo pack to power it.

Wawa:
The only solutions I can think of are a separate motor supply or a more modern H-bridge.
Two LiPo batteries in series, or six AA NiMH batteries will do the trick for your shield.
Go to pololu.com for mosfet motor drivers.
Leo..

I used a pack of 6 AA batteries to power only the shield and it works like a charm.
Until I get a better motor driver, this will be the workaround solution.

I have only more question. I tried a few days ago the same thing, but with one 9V battery and it didn't worked. The motors weren't even spinning. How come a pack of 6 AA is so much better? They are supposed to be equal in voltage right ?

Thank you for your help.

A 9volt smoke alarm battery can’t supply enough current.
Battery voltage will collapse as soon as you connect the motors to it.
Leo…