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Small DC Motors
• Plain motors: spin fast, low torque• Gear motors: spin slow, high torque• More voltage = more speed and more
torque• Less voltage = slows down, but torque
down• If spin too fast, bearings fail• If too much current, coil heats up and
melts
Speed (rpm)
Torq
ue (
oz-in
)
Motor complaintsStall too wimpy!
No-load spins too fast!
Solution: A transmission gets you on a new T-S curve
Speed (rpm)
Torq
ue (
oz-in
)
5:1 Transmission
Before: low torque, high speed
102
5
25
After: high torque at low speed
T2 = n*T1 v2 = (1/n)*v1
TO SLIDE OR TO ROLL?
Rolling elements: Low friction, complex, expensive
Sliding elements: Simple, high friction