Please help review my Solar Racing Robot Circuit

[Mike odom]

yes, you will need a 5v regulator for your micro and sensor, or at least a way to limit it to 5.5V.

what are your motors rated at?

 

[brandon1213]

We were initially going to use a motor like this one: **broken link removed**

But I think that's going to be too small. What kinds of things should I be looking for when choosing motors? Our robot should be fairly light with the heaviest component being the PCB.

 

[Mike odom]

voltage and torque.

you want a motor that works at the voltage you are going to drive it with.
you want a motor with enough torque to drive the load you are driving.

A low voltage motor like the one you picked is a good choice, if it generates enough torque to drive your robot. The good thing about your micro is it'll run down to 1.8V. Your sensor board, however, may not work so well. There are probably logic chips on it that need the 5.0V.

We were initially going to use a motor like this one: **broken link removed**

But I think that's going to be too small. What kinds of things should I be looking for when choosing motors? Our robot should be fairly light with the heaviest component being the PCB.

Now, that motor might work. It would be a small light robot, though. A picture is worth a thousand words.... look at the bottom of the data sheet for the motor. There are your characterisics there. It lists the rpm, the current, and the stall current for 1.5V, 3.0V, and 5V. 3V@22mA, you could drive that with an opamp! The H bridge you are using, by contrast, can drive 600mA, or a motor 30x as big!

 

[brandon1213]

So, actually if I used a sensor that didn't need 5v e.g.,touch sensors, I could technically build a circuit without a voltage regulator as long as my solar cells outputted less than 5.5v with a load?

I wasn't really sure how to analyze the chart because there's such a huge difference between the free current and stall current. I was worried that the motors would be drawing something a little less than the 5v - 420mA stall current each? That would eat up my power pretty quickly.

Also is the RPM's listed just the rotations per minute? Because even free spinning, I can't believe that one of those motors can spin at 31,900 RPM with 5V. That's 532 rotations a second!

 

[Mike odom]

the stall current is what the motor will draw if you hold the shaft and don't let it spin. The nominal current is 32mA, but as you load the shaft, the motor will draw more current.

Believe it. It's small and will goooooooo.... how fast do you think harddrive motors spin? and that's loaded down!!!