What voltage are your motors?
Using step-up converters is a significant waste of power, especially in a portable, battery operated device. NOT RECOMMENDED.
I don't see any reason all the grounds should not be tied together, permanently.
Why one battery for the motor and the other for the Arduino? The Arduino will draw a tiny fraction of what the motors use. One battery will be exercised regularly while the other (identical?) battery will barely idle along without breaking a sweat. Not a very good use of expensive batteries.
The grounds are all tied together right now.
The Arduino + sensors + camera + servos + xbee or wifi draw a lot and take away from the motors, in otherwards I am at a point that with 1 battery it can't move. If you read the thread about the batteries you will see we decided to go with 2 batteries.
3.7v isn't enough for the Arduino. I need more then 5v. The step-ups worked well on my first tank robot. I need high capacity batteries.
I am using 2 Lithium-Ion 6Ah from Sparkfun.com
The motors are hobby 3v+. I could connect them in series, right now they are parallel. But from what I read it can cause some problems if 1 motor becomes under heavy load.
It would be nice if the motor controller had a separate connection for motor power. The other one I have from adafruit is that way. Its on the other tank robot, that unfortunately have had to borrow parts from. I could use the motor shield, but there isn't enough room and some of the pins overlap with the voice shield.
the TX>RX to motor controller is causing power across it.
the motor controller only dims a little, doesn't turn off unless I remove the TX wire.
That sounds pretty bizarre. Perhaps you need to explain what you mean by "causing power across it"? Something seems significantly wrong with your circuit to cause this kind of behavior.
Yeah I am not sure what is going on here. If I turn off the motor controller the Power LED on the motor controller is still lit dimly and the step-up has some power out.
I was trying to switch the ground with the TIP120
If you already have a motor controller handling the heavy current switching, it is still not clear why you think you need ANOTHER power switch??
Because the motor controller has its own power and I need to turn that off when the robot is off, otherwise it is always on.
I am using this motor controller: http://www.sparkfun.com/products/9571
It did work today, last night the NPN was getting too got to touch. Except tonight I didn't try running the motors.
I would think the PNP would get hot, I guess not.
What NPN was getting too hot? What PNP? I don't see those in your diagram anywhere? Transistors getting too hot, especially if you aren't feeding any significant loads (like motors), is a symptom of something very wrong with your power scheme.
The transistors I am using as a switch, see other post.
I would use the batteries in SERIES to create the 7V without using those power-wasting step-up converters. It would also equalize the load on the batteries and give them a more normal life expectancy. If you must charge them individually (vs a 7V charger), then use a switch or relay to convert between series connection (for operation ) to isolated access (for charging). Coincidentally, that same switch or relay would provide your safety cutoff functionality.
The chargers can't charge 2 cells only one. I haven't found one otherwise, and they wouldn't be a match set. See link to post about needing 2 batteries above. I need to be able to charge while the robot is powered. It will dock to charge and needs to still receive commands and such.
If you are using only one control output to the motor controller, it is not clear why a Mega2560 is used? Note that there are Arduino boards that are designed to run on 3.3V, so again, no step-up converter is needed and you will save much of the power stored in the battery.
Edit: A comprehensive power plan will also include planning on how things will work as the battery terminal voltage (and power) droop from exhaustion.
Because I left off all the stuff I haven't connected as it isn't part of this problem. I have lots of sensors and stuff. If you look at the diagram they are labeled there on the mega box. Figure 'H'.
Right now I am using a Xbee but the final design uses WiFi which draws a lot. As well as the camera/servos.
I hope this clears things up. This is my first large electronics project and hope to learn all this and get it running so I can play with code.
Thanks for all the input and help. I feel I am close to having a running robot. I do wish I could conserve power more as the idea is be able to run for days, hence the charging dock and possible supplemental power from solar.