hi...
I have an L293D driver... I connect logic VSS from regulated 5V and the atmega8 too... the VS is connected through another 5V regulated voltage... it drives a little motor... but it doesn-t drive my tamiya box... everything is set up correctly and tested... why is this? when I measure the voltage on the motor pins it goes 4.95V and -4.95 every 5 seconds as it should go... but after I connect the motors and remove them, I measure again, I got 0.02 and -0.02... whats the problem?
Help us help you by
Help us help you by providing a clear picture of your setup and/or a schematic of how you have everything connected.
It sounds like you have a regulated 5V for the logic of the L293D and your atmega8. Then you run this through another 5V regulator to supply the motors through the L293D. Is this correct? There’s probably not enough voltage differential across your 2nd regulator to supply the current you need. Perhaps is works under no load, but as soon as you connect the motors…
Remember that the L293D drops some voltage as well.
I should ask what the stall
I should ask what the stall current or winding resistance is of the motor and the max current output of the 5v regulator to the motor is. The L293D can supply a maximum constant 1A of current. An L298N should do better if it is an issue with the power requirements of the motor. This little IC probably isn’t very sufficient for the stock FA-130 or whatever the motor is that comes with the Tamiya gearbox. For me the IC motor driver would overheat in a matter of about 10 seconds, but I was using a SN754410. All that being said the current bottleneck may be with the regulator, in which case try a big cap, a bigger regulator, or unregulated power.
Cheers
1A is the
1A is the regulator…
motor eats 470mAh at 3V
** this is the**
this is the schematic
electrolitic caps: 470uF
simple caps: 0.1uF
the switch is a button
Whats the stall current
Motor winding resistance? you have to overcome the stall current to get the motor turning. Someone correct me if I’m wrong. I bet the stall current is about 2 A on your motor.
Replacement motors
I recommend Solarbotics RM3 as Tamiya gearbox replacement motors ($1.99) which are nominal 6V:
http://www.pololu.com/catalog/product/604
I run these at 7V with good results.
I have a pair of GM2… but
I have a pair of GM2… but as I told… I can-t move even them… I use 1A regulator…
should I change it to 7806 for 6V and replace the tamiya motors with GM2 motors?
This little L293D peep gives
This little L293D peep gives 750mAh… 
so this can’t even drive a god damn tamiya box? why are they making this anyway? I need to get some L298N
You can see how they run
You can see how they run with 5V, or depending on your voltage input unregulated. I use rechargeable AA’s which have a lower voltage, so six of those can drive that motor well without regulation.
I tried with even two 9V
I tried with even two 9V batteries in series… which is… 18V by thw way… still nothing… just peeping motors… maybe the atmega should have some pins fried? I’ll try tomorrow with attiny2313 or when I’ll have the time
9V batteries are weak
9V batteries are weak current sources, could be part of the problem. There should be a datasheet for the 9V battery your using.
Why is VCC2 bypassed to GND
Why is VCC2 bypassed to GND but not connected to a power source?
Hi, IMHO VCC1 in the L293D
Hi, IMHO VCC1 in the L293D should use the same power sorce and ground as Atmega8 (5v) so you get the same logical levels on both chips.
VCC2 is the motor power and for the tayima should be around 3v. But L293D reccomends a minimum VCC2 equal to VCC1, being VCC1 higher than 4.5v. So, 5 V seems to be the reccomended minimum voltage in this scenario.
If using different power sources they must share ground.
Not shure if Atmega8 stands 8v for VCC, I´ve seen up to 5V in datasheets.
Hope this helps
CtC 
you are right… I’ll
CtC you are right… I’ll start testing soon… guess what… I have another DC controller board for L293D programmed correctly… the same thing… little motors run, biger don’t
ok made it on breadboard…
ok made it on breadboard… regulated 6V everywhere as needed… when I measure out1 and ou2… I got 3.6V… ok… as I connect the motors… nothing happen… I measured mA-s… I connected one pin of the motor to out 2, and between the other pin of the motor and out1 I put an ampermeter… 25mA… a bit low…
I second Ezekiel’s comment
I second Ezekiel’s comment (https://www.robotshop.com/letsmakerobots/node/23426#comment-55993). Why is VCC2 connected to ground via a capacitor instead of to a 2nd power source?
OK, I third the motion…
Why IS Vcc2 going to ground?
I think it was a mistake in
I think it was a mistake in the schematic, as the new one below is tied to Vcc with a capacitor to ground
