Let's Make Robots!

Multiple power supplies, one way.

First off, I'm using a Pixaxe board.

Considering the juice that can be used by periphrials, I wanted to use it's ability to use multiple power supplies,
one for the board, and one for the "output devices". However, a small question, just to be sure:
 A SHARP sensor is NOT consiered an "output device" on the board, right? I think it's not, but making sure...

Anyhow, I wanted to run the motors up to their maximum 5v-6v capacity.
I was thinking of using 2 power sources, including a small solar pannel, on a parallel circuit to the battery,
then finally to the power pins on the board.

Now, my question is here, since I know little about solar panels:
Should I have something like a transister between the solar panel and the batteries in the parallel circuit,
so that  the voltage from the batteries don't wash back into the solar panel?

I want the power from the solar panel to travel through the battery,
then the battery and/or the solar panel to connect to the power pin,
BUT I do not want the power from the battery to go to the solar panel:
When it's dark, voltage would NORMALLY go there,
considering that it's not generating, but still on the circuit.

What would you recommend to only allow OUTGOING voltage to pass; OR
only allow the voltage to/from the solar panel IF it's generating power?

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Edited out, wrong thread >_<
(Can't find the delete button) 

Each individual cell is a diode.  Any diode will produce electricity if it is exposed to light.  That is one reason most diodes are enclosed in black plastic.  The voltage they produce has nothing to do with the forward voltage of the diode.  They are unrelated.  Voltage is not current.  The amount of current going through something is what causes heat, and heat is what will damage them.  If the battery can drain through the diodes, it can damage them.

The diode can go either on the positive or negative side, but the positive side is most common.  It goes in line with the power wire.  There is plenty of information about this on the web and I encourage you to look it up.  Make sure the diode can handle the full current of the panel.

Thanks for all the help!

If you could provide me a "what/why" for the diode information you're recommending I look up, that you'd think would help,
I'd be much appreciative! I have trouble sorting through information I don't yet know, and can't really learn new things unless it's related to something I already know (AKA I can't "memorize", I have to understand.

Appreciate all the feedback! 

let me back up a minute.  I want to clarify.  I made those posts last night and was in a hurry.  I was a bit over dramatic and slightly inaccurate.  In the first post, I should have said a solar CELL is just a diode.  You are correct, a solar PANEL has bunch of cells arranged in series or parallel or both.  But, the overall effect is essentially the same.  Also, the danger of damaging it is real, but I think it came across too strong.  Sorry about that.

Anyway, as for the diode, a good choice would maybe be a 1N5820, 1N5821, or 1N5822.  http://www.onsemi.com/pub_link/Collateral/1N5820-D.PDF

The difference between them is only the reverse voltage they can handle, being 20,30, or 40 volts, respectively.  The specified voltage should be somewhat more than your battery voltage.  If you use a 12V battery, any would work.  If the battery is more than 12 don't use 5820.  If more than 24 V don't use 5820 or 5821.  Other than that get whatever is easiest.  I made that choice for two reasons:  first they are common and easy to get.  Second, they can handle up to 3 amps (you didn't say how much current your panel can produce) and they have a low voltage drop, about 0.3 volts at low current, which helps with efficiency by minimizing loss.  A "standard" rectifier diode like a 1N4001 has about 0.6 Volt drop.

Thanks for the response.

But I wasn't asking how much power a SHARP takes, but rather if it's connecting to the same power source as the servos.

On the second note, I'm not worried about frying the solar panel, as to charge the battery would have to be a LOWER voltage, for it to even get charged by the solar panel. My concern, is because of how electricity works, I don't want to lose battery life by the batteries trying to travel into the solar panel, when it's not generating anything.

I know a lower voltage shouldn't blow it out, I just don't want to drain the batteries fast, the reason I'm using solar panels in the first place. So, when I get the parts, I'm going to try to put the recommended diode in there,
so the batteries only go where they need to: The servos. 

The solar panel is simply a diode, nothing more, nothing less.  The rated voltage is with a bright light shining on it.  With no light, it has zero volts, and the battery will discharge through it.  Consider what would happen if you connect a diode across a battery with nothing to limit the current.  It will burn up.  A very small battery, like a coin cell, doesn't present a danger since the large area of the diode could handle the max current it could provide.  But a battery big enough to run a robot can burn up a solar cell / panel rather quickly.  You need a charge controller or at least a diode in line to protect it.

How is a solar panel ONLY a diode? I know it can be made FROM diodes, but...?
My plans were to put the solar panel on a parallel circuit to the batteries, to the robot.
Then, the voltage wouldn't stack, and shouldn't burn anything, right?

Though, I do think I get what you're saying for the battery can maybe burn the solar panels.
I knew the voltage would go there if it's not producing, getting drained, which was my concern.
However, I thought that solar panels were made of many smaller cells, some parallel, some series, to increase voltage an wattage... So why would they fry from a battery, if they can get to be higher voltages in a series?

 And if that's the case, if I have the solar panels on a parallel circuit to the batteries, then robot:
I connect the diode on the return path (+) between the solar panels and battery, right? 

Sharp sensors are not output-they do take a little current but not on the level of a motor/servo. What you're describing otherwise is a diode to keep current from flowing the wrong way, but I wouldn't think it would be a big issue in the setup you're using. I don't think you have to worry about frying the solar panel. Just make sure you do your math so you don't start a battery fire or inadvertently drain the battery rather than trickle charge it.