L293D Motor Driver Speed Problem

Other Hardware Motors, Mechanics, Power and CNC
1

Hi,
I'm having a bit of trouble with my latest project. It is a mini autonomous car that can maneuver around obstacles and stop when it gets too close to a wall. Everything works great, but the speed of the brushed DC geared motor is much lower than normal. I have been using a single transistor to control the motor's speed in one direction, but I wanted it to be able to have reverse, so I decided to use the l293D motor driver IC chip. I am not using the shield but using the chip itself. All of the car's electronics run off of a 3.7V lithium-ion battery. (I have a dc-dc booster to step 3.7V up to 5V for the Arduino and ultrasonic distance sensors.) The battery has been charged several times, and the voltage of the battery is normal. Do you guys have any thoughts on why the L293D may be lowering the speed of the motor? (If it is the driver, that is...)

Thanks in advance,
transistor_man

P.S. I don't know if these will help, but I have attached a few photos for reference:

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I can also provide the code I am using if that is helpful!

2

No surprise reading Your post.

That's good!

The main issue is the motor driver combined with the motor voltage.
Either go for a MOSFET based drive or make a separate motor supply of some 6, 7 volts.

3

What is the spec for the motor? Using an L293 You need to add some 2 to 4 volts more to use the motor capacity.

4

That's what 293s do.

5

Thanks for the quick reply! I thought about making a mosfet controller for it, but I found a few L293D driver's lying around so I decided to go for them. You are most likely correct about the voltage being supplied to the driver. I'll try a better supply for it. Here is a link to the motor I have: DC Gearbox Motor - TT Motor - 200RPM - 3 to 6VDC : ID 3777 : $2.95 : Adafruit Industries, Unique & fun DIY electronics and kits I didn't buy it off of Adafruit, but it is likely the same thing.

6

Well, yes. I know. It shouldn't be in this situation though.

7

I just read a little more on the L293 driver, and I think the input voltage is a bit too low.

8

The ancient L293 drops from 2V to over 4V across its Darlington output stage. The more the current that it passes the more the voltage drop.

Far better motor drivers are available at Pololu among many others.

9

The motor You have uses up to 6 volts. I suggest get a power supply of some 8 volts. Using 2* 3.7 volt accs giving 7.4 volt ought to work.
Designing Your own MOSFET driver might be easy if the motor only runs in one direction. Else, go for a ready built driver.
Anyway, You need to use a better motor power supply.

1 Like
10

Yes, I am aware of this, although I didn't realize that the drop was so big. Anyways, I used the driver I had lying around, but if I make a batter/different project, I will use some of Pololu's drivers.

11

I have 2 more li-ion batteries I will use. Thanks for the solution!

12

That's one way to go.

13

That's the second way to go.

Thanks for Your fast and serious replies!
We will be here for You.

1 Like
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