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Questions about my hacked RC car arduino robot

Greetings everyone. I have an old RC car with 6V accumulator. Can I power my arduino board + the l293d motor driver from this accu without using any voltage regualtors? I read that arduino and 3 of the 4 pins on the l293d motor driver require 5V. 

The voltage requlator I have requires 2.5V more ie 7.5V, but the accu is 6V. More stupid questions will follow :D

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"accumulator" translated funny. No problem, happens all the time. Might just be that I don't recognize it here in the States.

Accumulator has got to be a battery pack? Maybe a voltage regulator or a ESC?

Thats funny, because accumulator is an english word from "to accumulate" and is a rechargable battery  - http://en.wikipedia.org/wiki/Accumulator_(energy)

And I want to add another question. In the datasheet of my 7805 voltage regulator it states that the recommended min. voltage should be 7V. I tested it with 6V and it gave sufficient 4.98V. What is the drawback ?

I got a simple answer for you. It will work, but not for long. The volt regulator says it needs 7v to work, in reality it will probably work as low as 5.5v or so. Probably not much lower than that. The 6v will work, but as the battery dies, there is not much "room" for it to die. If it started at 7.2v, you have 1.7 volts or so before you volt reg stops working. If you start at 6v, you only have to drop a little for the volt reg to stop working.

Don't forget --every time your motors start up or change direction, there is going to be a little surge in power. This little surge might be enough to pull the voltage down to a point where your microcontroller resets.

Check with the guys but you may just want to add a diode to that 6v pack to "shave off" a volt instead.

 

I was going to suggest that; use a 1N914 or some such diode with the usual 0.7V forward voltage. Put that in series before your ardu board and you'll get 6.0V - 0.7V = 5.3V.

Which Arduino board do you have, or did you build your own? I have a Mega clone and it is working just fine with the on-board regulator. I'm using 4xAA alkalines, which are currently providing less than 6V. The motors and everything else is working without a hitch.

If you are building your own, ditch the 7805 regulator and get yourself a Low Dropout (LDO) regulator. Those can supply the desired voltage with only 0.5V higher coming from the batteries. The LM294 is a good example. It provides 1A @ 5V output. You can run the motors and servos themselves directly from the batteries, so that doesn't count against the 1A.

You may want to check out the LMR Primer I put together. It includes a link to a great article by OddBot, Once you've decided on batteries, how do you regulate the voltage?  There are many other useful links for the beginner as well.

if you look at the L293d datasheet it can run as low as 4.5v, the ATmega microcontroller on the arduino can go even lower

Thank you all for your comments, it helped a lot. Now I have a more important issue. I hooked everything up just like you said using 470uF with 100Nf before and same caps after the voltage regulator. Also I have 4 100Nf caps on each L293 pin that goes to the motor.

Now to the issue. I "told" to both motors to go with 255 PWN wich shoould be 6V. What happens is that while the wheels are driving in the air everything is OK. As soon as the vehicle drives on the floor it slows very rapidly until it cant move. I did the voltage measurments and was astound. The setup is following: Arduino powers from the USB from the PC. Then we have 6V Battery-Switch-Power Regulator etc. If the Arduino is OFF and the switch is OFF I read 6.2V which is good. If I turn the switch on, so that the current can flow to the L293 motor driver while the Arduino is still OFF I read 5,7V. ! Just like that! The car is on the ground. If I now turn the arduino ON and the bot starts moving I read whipping 1.5V on the L293 motor output! If I then take the car from the ground the voltage raises to 4,7V which is better but still should be like 5,7V (well better 6,2V)

 

Now I still have the original electronics in the car and it drives flawlessly with a remote. Sorry for such a big post but I really dont know what to do.I can make a picture if it will help.

Are you using a 7805 regulator with the 6v battery?

Yea it kinda worked making 6V to 4.95V so I let it be. I will try to hook up the diode.