The last twister I made had major issues with the gearing. I broke three gears because of it. I realized that it was time to make a better one; thus twister 2.0 was designed.
I didn’t want to gear up for a center UJ (inefficient), so I decided to put drive motors on the front as well as the back.
At first I was only planning to have 2 motor channels, but then decided to add another for a 3pt. hitch (which turned out to be a fasthitch). It ended up having 4 drive motors, plus the steering motor, as well as the hitch motor; a total of 6. The NXT only has 3 channels, and each channel is only supposed to power one NXT motor.
I could have used a second NXT as a motor controller using RS485, but I wanted big time driving power, and AA’s go kaput with a load like that. I decided to make a motor controller that could handle the current from all 4 driving motors. I considered using the NXT motor port for PWM and direction, but that would use up the only free motor channel. I ended up using a PICAXE 20X2 as an I2C slave to control the H-Bridge. I used a SN754410 1A Motor driver as the H-Bridge. 1A isn’t enough power, so I used both H’s (it has 4 half H’s total). I now get a rated 2A continuous power, and the IC doesn’t get more than slightly warm. Like I said earlier, AA’s just don’t have the juice I need to power 4 NXT motors like this, so I used a 7.2v 1500mah RC style battery pack. That thing can supply more than enough current, and lasts quite a while.
After I was done making the main vehicle, I decided to add a rear fasthitch blade. Because I still had one NXT motor port open, I used that to control the rotation of the blade.
In the end, it uses all three NXT motor ports for APR motor control, as well as my I2C motor controller for the drive motors. It now has 7 NXT motors altogether.