Robot power not enough

[Kontrolarge]

Hi to all

I made mutli functional robot car. I built 4 dc motor 3-6v motor L293 motor Driver arduino sensor shield hc sr 04 distance sensor arduino uno r3 and standart 6x1.5v battary. But there is a problem When i power it up on ground it doesnt move when it on air no ground it moved.

Where is the problem?   

[JimboZA]

Schematic?

[jscottb]

Power is a problem for most starting out in hobby robotics.  I will assume you are using 6 AA alkaline batteries for everything and the you have it running to the L293 and to the Uno as well. I will also assume you are not powering the L293 from the Uno.

Now...

The L293, though cheap, is a very power stealing H-bridge. The voltage drop is quite high vs newer controllers like the L9110 and many others.

Alkaline or Super Duty batteries are also a poor choices for a bot, especially a 4wd bot. They will not deliver the power you need, or if they do, not for very long.  NiMH or even NiCad rechargeables would be a better choice. 5 of them should power the motors fine.

I would also power the Arduino and motors with separate battery packs if you can. Just remember to have a common ground ref between the two.

4WD bots are also a pain to get moving, especially with the little yellow gear motors or other low torque motors. I usually ramp up the motors to the speed I want to drive at. This helps eliminate spin-out and gains max torque faster. You can do this by dividing up your max speed by say 4, and in a loop add that quotient to the speed and do a analogWrite with it on each iteration. At the end of the loop, do a final write of the max speed you wanted.

[JimboZA]

I will also assume you are not powering the L293 from the Uno.

There's nothing wrong with powering the 293 from the Arduino, surely?

[jscottb]

There's nothing wrong with powering the 293 from the Arduino, surely?

Chip, maybe, but not the motor power input.  I myself do not power the H-bridge chip from the controller.  I try not to anyway.

[MarkT]

You are best powering the logic supply of the L293 separate to the Arduino and use 10k
series resistors on the logic lines - then when the motor battery is offline or dead you don't
end up powering the motor from the Arduino 5V rail (the chip has unfortunate internal diodes
that allow this to happen, IIRC).

You are best off using a decent MOSFET H-bridge and not wasting half your power in the first
place!

[Kontrolarge]

Thanks for all your post.I am really happy to help my questions

[Kontrolarge]

There's nothing wrong with powering the 293 from the Arduino, surely?

there is no problem powering up L293

[MarkT]

What motors?  What is their stall current?  Multiply that by 4 (or 2 if using both channels) and I very
much doubt it will be less than the absolute maximum current for a L293.