Date: Mon, 14 Nov 2005 02:58:45 -0600 (CST)
Subject: motor control for steering motor is ok
X-UID: 104
Content-Type: IMAGE/JPEG; name="img2397.jpg"
Content-Type: IMAGE/JPEG; name="img2398.jpg"

I didn't get as far as I had hoped this weekend. However, it's likely that 
my original estimate of about a week for design and fabrication of the 
motor control circuits is correct. I should have a working motor control 
board in a few days. The stuff is working!

The small Mabuchi motor I picked up at Fry's spins under software control 
of the on-board computer. It can spin in either direction at variable 
speeds. The motor requires a duty cycle of 60% to 70%. That was 
unexpected. I'm guessing the inductive coils don't energize enough to 
overcome mechanical resistance without a high duty cycle. This means that 
my original design of an overvolted steering motor at a low duty cycle 
probably would not have worked.

I'm not using the full-size gear motor for robot steering as it has much 
higher current requirements. A breadboard can't support high frequencies 
or currents. That's why I'm using the small Mabuchi for testing. The 
Mabuchi is a brushed DC motor. I originally tried using a brushless 60 mm 
fan for testing. However, brushless motors have semiconductors inside to 
energize the coils in proper timing. I found that any sort of pulse width 
modulation confused the electronics inside the fan. The fan might move but 
it would never spin.

I also saw Mabuchi "solar motors". All of the documentation on the package 
is in Japanese but I think they operate at .5 and 1.5 volts. So 
low-voltage motors are available.

In img2397.jpg, note the tiny circuit board in the lower right hand 
corner. This is the electronic speed control from one of the Panasonic 
drills. Everything is surface mount. Yet, it's not so small as to be 
impractical for home fabrication.