Let's Make Robots!

My Herbie photovore is whistling at me

Over the past couple days I constructed the 'Herbie' junkbot from MAKE (PDF here: http://cachefly.oreilly.com/make/mousey.pdf ). When I hit my 'on' switch I immediately start hearing a high-pitched whistle / squeal coming from the motor(s). When I read the voltages of them I get 0V on the left motor and ~8V on the right motor.

My LED, however, is nice and bright. I've checked and re-checked my solder joints and it all looks OK. I prototyped the circuit with the same parts on breadboard and had no problems (though I only used one of the motors, not both).

Any suggestions?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Shoot, I must have used too large motors. I used the smallest I had, but they still look bigger than the ones in the tutorial I am following. I was just hoping that they'd run, but not very fast.

My left motor has a resistance of about 40k, and the multimeter doesn't read anything on the second one, even on my highest setting, so maybe its resistance is much higher than it should be.

40kΩ is a huge resistance for any motor, it sounds like the reading's not coming out right.
Anyway if you want some smaller motors and you can't find any locally you might want to think about salvaging some. Broken CD/DVD players and cheap motorised toys are a great source of small, high-speed DC motors. If you find some that look more like the ones in the tutorial you're on the right track, but you can also use the short, round 'pancake' style motors that are common in similar sizes.

The LM386 can't handle a very big load, have you tried temporarily removing one of your motors again?

I'd suspect that either your motors are too power-hungry, or your circuit is oscillating rapidly due to feedback in the amplifier. If you have a multimeter can you please measure the resistance across the leads of one of your motors?

Bumping, because I still don't know how to fix my photovore :S