My team just had this problem last night. We were driving the robot around for some testing, and about 3-4 minutes of driving it around on a cement area in the middle of our school, we noticed smoke from the motors. We checked it out and there was definitely smoke coming from the motors and a very strong smell of it. We have one large muffin fan mounted above each drill motor, although we noticed a large amount of escaped airflow, we thought this might be the problem, so today we are going to fabricate some air ducts. Does anyone else have any suggestions? We did not disassemble the motors and I do not believe there was any drilling on the chassis around the motors.
Also, we noticed that there was a lag with one wheel, so it skips three or four times at acceleration and then moves slower than the other wheel as we drive around. I know that the other wheel's gearbox is greased up, and this one's isn't. Does anyone know what else might cause this problem?

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2005 Las Vegas Regional Autodesk Visualization Award
2005 Las Vegas Regional #8 Seeded Alliance with 988 and 1505
2006 Southern California Regional #15 seed