MECHATRONICS EVALUATION EXAMS ALL
QUESTIONS AND ANSWERS SURE A+
✔✔Gears and Backlash - ✔✔- Gears trade speed for torque. In an RC servo motor, the
tiny motor inside spins incredibly fast, but the gear train slows that down into usable
speed while multiplying the strength.
- Backlash is the play between mating gear teeth. Its the tiny amount of free movement
before the teeth make contact.
✔✔Torque vs Speed Tradeoff - ✔✔- power is equivalent to torque * speed. If you want
one, you must give some up of the other.
- A low gear means that the motor spins many times to turn the output shaft once (think
of this as lowest gear on a bike, pedal a lot to move a little). High gear means that the
motor only spins a couple times before the shaft moves (think highest gear on a bike,
hard to pedal at first requires lots of torque but you go very fast)
✔✔Leadscrews and Ballscrews - ✔✔- Leadscrew is a simple threaded rod (think a long
bolt) that uses a nut to move a load. It relies on sliding friction. As the screw turns, the
threads of the nut slide along the threads of the screw, pushing the nut forward or
backward. It is self locking, quiet, and inexpensive, however, they're inefficient and wear
easily which increases backlash.
- Ballscrews use recirculating ball bearings inside the nut which relies on rolling friction.
Small steel balls roll between the screw threads and the nut, then loop back through a
return tube. It's like a ball bearing stretched out into a spiral. They're very efficient, offer
a high precision, and run cool since theres less friction. However, they're back-driving
(they can move backwards since the lack of friction), they cost more and require more
maintenance.
✔✔Bearings - ✔✔- Axial bearings support loads that act perpendicular to the shaft (like
a wheel on an axle). It uses balls or rollers between an inner and outer ring to let the
shaft spin freely.
- Thrust bearings support the loads that act parallel to the shaft along the axis.
- Linear bearings facilitate straight-line motion along a rail.
, ✔✔Encoders - ✔✔- Sensor device that can be used to determine the angular
orientation of a shaft
- Incremental encoders are the simplest. They only keep track of position. It only counts
"blips" or the positions its moved, but not the direction. It must home if it loses power.
- Quadrature encoders are basically two incremental encoders placed on two separate
tracks. This way, it can track direction and position. If A rises before B, the motor is
spinning clockwise. If B rises before A, the motor is spinning counter clockwise. Gives
four times the resolution of an incremental encoder. It also must home if it loses power.
- Absolute encoders provide a unique digital code for every single position of the shaft.
It often uses gray code where the sensor reads a unique binary string that corresponds
to one exact angle. Absolute encoders don't need to home.
✔✔IEEE 754 Floating Point Format - ✔✔Breaks up a floating point number into binary
data with three specific fields.
- sign bit (1 bit): determines if the number is positive (0) or negative (1)
- Exponent: determines the "scale" of the number
- Mantissa: stores the actual digits of the number (significand/fraction portion)
✔✔Data types - ✔✔- byte, word, long, ASCII/ANSI characters, strings
- Different data types store different amounts of bits
✔✔Parallel Processing - ✔✔- What is so special about the P2 Microcontroller
- Different processes can run simultaneously on different cogs each with independent
timers
- Helps to create smoother programs so not every event runs on one cog, overall faster
- Cog 0 (process 0) on the P2 controller is by far the fastest cog
✔✔Object-Oriented Programming - ✔✔- The marvel of modern programming, it's a way
to organize your code in such a way to increase it's reusability.
- What has lead to all the open source in popular coding languages over the past 20 -
30 years
✔✔Serial Peripheral Interface (SPI) - ✔✔- One of the ways digital information can be
sent back and forth between integrated circuit (IC) chips
- "Synchronous" Serial. It doesn't need to be precise and is incredibly simple to
implement. It's also very fast and very inexpensive
- When waking up the peripheral device, SPI has a chip select pin dedicated to
controlling each peripheral device. This is an inverted logic pin, so whenever the
controller wants to wake up the peripheral device, it sets the device's chip select pin to
be low and then sends or receives data to or from it.
- Private road, only one car on it
✔✔I2C - ✔✔- For I2C, there are only ever two pins, a clock and a data pin. Each
peripheral device has a predetermined address such that when the controller wants to
"talk" to a particular device, it begins by "shouting" the name across the bus. That
QUESTIONS AND ANSWERS SURE A+
✔✔Gears and Backlash - ✔✔- Gears trade speed for torque. In an RC servo motor, the
tiny motor inside spins incredibly fast, but the gear train slows that down into usable
speed while multiplying the strength.
- Backlash is the play between mating gear teeth. Its the tiny amount of free movement
before the teeth make contact.
✔✔Torque vs Speed Tradeoff - ✔✔- power is equivalent to torque * speed. If you want
one, you must give some up of the other.
- A low gear means that the motor spins many times to turn the output shaft once (think
of this as lowest gear on a bike, pedal a lot to move a little). High gear means that the
motor only spins a couple times before the shaft moves (think highest gear on a bike,
hard to pedal at first requires lots of torque but you go very fast)
✔✔Leadscrews and Ballscrews - ✔✔- Leadscrew is a simple threaded rod (think a long
bolt) that uses a nut to move a load. It relies on sliding friction. As the screw turns, the
threads of the nut slide along the threads of the screw, pushing the nut forward or
backward. It is self locking, quiet, and inexpensive, however, they're inefficient and wear
easily which increases backlash.
- Ballscrews use recirculating ball bearings inside the nut which relies on rolling friction.
Small steel balls roll between the screw threads and the nut, then loop back through a
return tube. It's like a ball bearing stretched out into a spiral. They're very efficient, offer
a high precision, and run cool since theres less friction. However, they're back-driving
(they can move backwards since the lack of friction), they cost more and require more
maintenance.
✔✔Bearings - ✔✔- Axial bearings support loads that act perpendicular to the shaft (like
a wheel on an axle). It uses balls or rollers between an inner and outer ring to let the
shaft spin freely.
- Thrust bearings support the loads that act parallel to the shaft along the axis.
- Linear bearings facilitate straight-line motion along a rail.
, ✔✔Encoders - ✔✔- Sensor device that can be used to determine the angular
orientation of a shaft
- Incremental encoders are the simplest. They only keep track of position. It only counts
"blips" or the positions its moved, but not the direction. It must home if it loses power.
- Quadrature encoders are basically two incremental encoders placed on two separate
tracks. This way, it can track direction and position. If A rises before B, the motor is
spinning clockwise. If B rises before A, the motor is spinning counter clockwise. Gives
four times the resolution of an incremental encoder. It also must home if it loses power.
- Absolute encoders provide a unique digital code for every single position of the shaft.
It often uses gray code where the sensor reads a unique binary string that corresponds
to one exact angle. Absolute encoders don't need to home.
✔✔IEEE 754 Floating Point Format - ✔✔Breaks up a floating point number into binary
data with three specific fields.
- sign bit (1 bit): determines if the number is positive (0) or negative (1)
- Exponent: determines the "scale" of the number
- Mantissa: stores the actual digits of the number (significand/fraction portion)
✔✔Data types - ✔✔- byte, word, long, ASCII/ANSI characters, strings
- Different data types store different amounts of bits
✔✔Parallel Processing - ✔✔- What is so special about the P2 Microcontroller
- Different processes can run simultaneously on different cogs each with independent
timers
- Helps to create smoother programs so not every event runs on one cog, overall faster
- Cog 0 (process 0) on the P2 controller is by far the fastest cog
✔✔Object-Oriented Programming - ✔✔- The marvel of modern programming, it's a way
to organize your code in such a way to increase it's reusability.
- What has lead to all the open source in popular coding languages over the past 20 -
30 years
✔✔Serial Peripheral Interface (SPI) - ✔✔- One of the ways digital information can be
sent back and forth between integrated circuit (IC) chips
- "Synchronous" Serial. It doesn't need to be precise and is incredibly simple to
implement. It's also very fast and very inexpensive
- When waking up the peripheral device, SPI has a chip select pin dedicated to
controlling each peripheral device. This is an inverted logic pin, so whenever the
controller wants to wake up the peripheral device, it sets the device's chip select pin to
be low and then sends or receives data to or from it.
- Private road, only one car on it
✔✔I2C - ✔✔- For I2C, there are only ever two pins, a clock and a data pin. Each
peripheral device has a predetermined address such that when the controller wants to
"talk" to a particular device, it begins by "shouting" the name across the bus. That
