Different Types of Robots • Robot Arms (Fixed Robots) • Mobile Robots • Humanoid Robots • Legged Robots • Wheel Robots • 3 wheels • 2 Driver wheels, 1 Caster • 1 Driver wheel, 2 Casters • 4 wheels • Casters make diverse problems in the control of the robot
Wheel Robot Main Components • Main Components • Mechanics • Wheels • Driver Motor (s) • Power Transmission System • Electronics • Controller Board • Needing feedback from environment • Sensors We are now discussing some of the above topics
Different Types of Motors • DC Motors • You can simply control it • AC Motors • It’s difficult to be controlled but it can be used in high power applications • Servo Motors • You have complete control on the shaft angle
Different Types of Feed Back • Sensors • IR Sensors • Pressure Sensors • Light Sensors • Temperature Sensors • Encoder
Why do we use Power Transmission Systems? • To reduce Angular Velocity • To increase Torque P = (T . w) = cte. Different Transmission Systems • Gear • Hard manufacturing and adjustment • Pulley So w => T
Gear • Gears are used to change the speed and force of the motor. You can use gears to: • Speed up or slow down your robot. • Make your robot stronger or weaker. • There are many different types of gears • Spur Gear • Bevel Gear • Worm Gear • Rack & Pinion
Gear • Spur gears are wheels with teeth
Gear • Bevel gears mesh at right angles, so they change the direction of rotation.
Gear • Worm gears look like screws. They have many special properties.
Gear • Rack & pinion gears turn rotational motion into straight-line motion.
Where does all this “torque” come from? Consider a pair of gears that are meshed together. F A torque on this axle... …produces a force at the tooth. t r The moment arm is the radius of the gear. Remember: t = F x r
The force from the small gear’s tooth pushes against the large gear’s tooth. This creates an equal (and opposite) force in the large gear. This is Newton’s 3rd Law. F …and produces a larger torque on this axle. r t The force acts through this larger moment arm...
F1 = -F2 t1 r2 r1 t2 t1 = F1 x r1 t2 = F2 x r2 Analyzing the forces... • F1 = t1 / r1 • F2 = t2 / r2 • F1 = - F2 • t1 / r1 = -t2 / r2 • -t2 / t1= r2 / r1 The ratio of torques is the ratio of the gear radii. This is the gear ratio!
Idler Gear • An idler gear is a gear that is inserted between two other gears. Idler gears do not affect the gear ratio between the input and output gears. The gear ratio would be computed just the same if there were no idler gear.
Idler Gear • Recall that when using spur gears, the output axle rotates in the opposite direction as the input axle. • You can also use idler gears to change the spacing between the input and output axles • Remember, idler gears do not change the gear ratio
Gear The gear ratio of this gear box is 75 to 1 That means the last axle rotates 75 times slower than the first axle. It also means the last axle has 75 times the torque as the first axle.
Try this experiment. Have one person turn this wheel. And have another person try to hold on to this wheel.
Gears can increase the torque (and force) that they exert on something. This is known as mechanical advantage. torque increases BUT, it comes at a price. Do you know what it is?
2 D2 w2 w1 D1 1 C Belt Drives • Uses friction to transmit power Velocity Ratio: D1.w1=D2.w2
Belt Drive Basics Size Center Distance (center shaft to center shaft) Shaft Size for DR, can use NEMA frame Take-up/Installation Allowance DR DN Size Motor Nameplate
Belt Drive Basics 4” Speed-Down N 10” R 1750 rpm 10” R Speed-Up N 4” Speed Ratio = 2.5 700 rpm 4375 rpm Ratio always greater than 1
How to assemble our Robot • Here is our package
How to assemble our Robot • Bottom view of the robot
How to assemble our Robot • Sensor board assembly
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