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Arduino Uno + Dagu 4 channel motor controller - power issues?

I have an Uno controlling a 4 channel Dagu motor controller with encoder support. Got this a month ago. (It's the red PCB version).

Although it works, I have read that I shall not power the motors before powering the control logic.

But does that really mean that if the controller voltage dies out in the field, and there's still juice in the motor batteries, the Dagu controller will burn ?

I saw OddBot said this might be the case, at least if you powered it up in the wrong order.

I have asked around on other forums and people seems to think this would be a rather dangerous design :D

People suggest that if this is truly the case, I could hook  up some kind of transistor circuitry to make sure motor power is cut if controller power is cut. At the moment, this is a bit above my electronics skills.

Can anyone confirm or deny that the Dagu board will burn if the controller logic voltage dies while the motor still has voltage ? (AFTER it has been powered up properly :)

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It is not really a good idea to have seperate batteries. If you must have seperate batteries then use a 5V regulator running from the motor batteries to feed your motor controller logic. Connect the grounds between the two sets of batteries but leave the +5V supplies seperate. The motor control logic uses almost no power so a standard LDO regulator will not get hot even if your dropping 12V down to 5V. You may actually need to wire up a power LED to make sure the regulators minimum current draw is being met.


Thanks for replying!

Let me try get this straight now: (electronics newb here, more of a code developer!)

Dagu board has two separate screw connectors, 5v for control logic and 9v for the motor.

My setup now:
Arduino gets power from 9V battery trough barrel jack.
Controller logic port gets 5v from Arduino.
Controller motor port gets 9v from the battery pack that came with the Rover 5.
5v and 9v GND's are not connected.

Are you saying it's best to power the Arduino from the 9v batteries in the Rover 5 instead ?
So that the Arduino 9v rail connects to motor power and 5v rail to controller power?

Or did you think i had a separate battery just to power the controller logic ? 

When i think about it, doesn't the Dagu board actually have selector pins to optionally power both motors and controller from the 9v input? (making the 5v control logic power connector unused)

regards, Kirk :)