Let's Make Robots!

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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Thx for you reply, I will try to do what you said and will post a picture of the circuit if nothing helps.

But I already found one really weird and disappointing thing. The 5V out pin on my Arduino gives only 4.3V, the 3,3V pin gives sufficient 3,25V when powered from USB to PC cable. The 4,3V were measured WITHOUT any load applied and everything disconected from the board. The enable pin on the L293 requers 5V. Anyway the Arduino should give 5V out, whats going on ?

And btw, how do I when when the battery is dying? Is there any way to measure it etc?

 

Just opened up the motor housing and saw a weird yellow thingy: 

What is it and do I even need it ?

The yellow thingies looks like choke coils. They are used to supress electrical noise from the motor. The recommended input voltage for the Arduino is 7..12V. Powering the Arduino with 6V will supply the 5V output with less than 5V.

Hmm, if you look at the foto, the motor also has two small ceramic caps. Arent they supposed to filter tha noise out? I mean why additional choke coils?

Both, coils and capacitors build a better noise filter than the capacitor only filter, especially when using PWM. I would further recommend:

  • twist the motor wires together
  • keep motor wires as short as possible
  • keep motor wires away from any sensor wires

Here is the diagram about suppression of brushed DC motor

I was just thinking yesterday that those motors are probably going to make a grip of noise and how to proactively deal with it. I guess it's already taken care of, thx RF.

The Dagu RP5 tank platform has those on both motors. I just assumed. They're bigger than yours, but very similar. Perhaps someone can verify.

duh

This one is screaming "wiring" to me.

Double check everything, be sure that the + side of data power and motor power are not together. DO make sure your grounds are connected together. Double check the L293 for the enable pin, etc.

I think this is one, simple thing.

Everything is just as you said. Common ground with separate voltage 6V for the VSS and 5V for the enable pins. 

My guess is that your motors are drawing more current than your supply can provide. Because of Ohm's Law, when your current draw goes up your voltage will drop.

Once again, my knowledge is probably worth about 2 cents.