Is my circuit OK? (help a newbie out)

[chrisharris]

Hello

I recently bought a Rover 5 bot and hooked it up to an Arduino Mega 2560. It drives around pretty well on its own:

http://www.youtube.com/watch?v=9OVMwZeFF_8

However, I've never designed a circuit before and I'm concerned that I'm doing something wrong. The circuit is shown below. In particular I wonder if I need to put in resistors. The Rover 5 bot came with big black cylinders attached to the power-cords of the motors (blue arrow below). Someone told me they are actually inductors. I measure 3.5? across each 'motor-cylinder' pair. My battery is 9V. 9V/3.5? = 0.65A, which is well below the recommended peak current of the motors (2.4A). Voltage across the motors is 5.2V, which is also below recommended max (7.2V). So maybe I'm ok, but I'm sure there are things I don't know about that could improve my circuit and I'm still suspicious of the black cylinders, so I just thought I'd throw this up on the forum and hope for feedback. All comments and suggestions welcome!

[MarkT]

Hard to follow that diagram with the +9V rail at the bottom (power rail at top, ground at the bottom is the way to do this).

But yes, looks OK if you don't want reverse.  The cylinders are EMI suppression inductors from what I can find out, keep them.

If the TIP102 darlingtons get too hot then you should consider logic level MOSFETs of suitable rating.

[chrisharris]

Thanks!

I'll move the power source and sink around.

If the cylinders are EMI suppression inductors, does that mean I can take out the diodes? I only put them in to protect against power-spikes but they've been getting super-hot.

The transistors have been ok heat-wise but I'll keep an eye on them.

[Henry_Best]

Thanks!

I'll move the power source and sink around.

If the cylinders are EMI suppression inductors, does that mean I can take out the diodes?

No. They are still needed.

I only put them in to protect against power-spikes but they've been getting super-hot.

They're getting hot because they're zenner diodes! Replace them with 1N4002 or 1N4003 diodes.

[chrisharris]

thanks Henry_Best, I'll get some new diodes