January Exam Flashcards
Two categories of bearing for the two types of mechanical motion
Three types of mechanical contact bearings
Three types of mechanical non-contact bearings
Linear, rotary
Sliding, flexing, rolling
Fluid film (hydrostatic)
Fulid film (hydrodynamic)
Two types of friction, equations for both
Static friction, kinetic/dynamic friction Fs = μ*F(N) μ = coefficient of static friction Fk = μ*F(N) μ = coefficient of kinetic friction F(N) = force downwards (m*g) Fs/Fk = force required to move object
Slide bearings: used for linear or rotary?
Where are they placed between?
Pros, cons
Both
Between shafts and housings
Pros: low noise, cheap, small
Cons: high friction, can be damaged from lubricants, stringent lubricant requirements
Special slide bearings: jewel bearings
Properties
Where are they used?
Low friction Thermally stable High hardness Bearing is stronger than shaft Watches, compasses, precision instruments
Sliding bearings in a linear application: pros, 5 of them
Self lubricating Low friction, noise Dust and shit doesn't stick to bearing Resists corrosion Light weight
Sliding bearing: dovetail linear slide
Pros, cons
Pros: adjustable tension
Precision defined by adjustment
Cons: regular maintenance
Undefined static friction
Application loading: what is is
Two types, which direction on a shaft they come from
Direction of forces on the bearings
Axial/thrust load: goes through shaft
Radial load: perpendicular to shaft
Rolling bearings: two types
What two grouping types for each of these are there
Spherical roller thrust bearings, tapered roller bearings: pros and cons
Ball or roller Can be classified as either radial or thrust/axial SRTB: Pros-help with misalignment Cons-expensive to produce TRB: Pros-cheaper to produce Cons-Doesn't help with misalignment
Needle radial bearings: applications and pros
Planetary gears
Universal joints
Constant mesh gears
Pros: low profile, lightweight, higher load capacity, cheap
Linear roller bearing-where sliding and rolling meet
Pros, cons
Pros: reduces risk of ‘Stick-slip’ (increased static friction due to angular forces)
Cons: expensive, bigger, more shaft damage
Slides: whats the ratio of length to width
Where should the F(pull/push) be on the slide?
1.6:1
As close to the centre line of mass as possible
Stepper motor equations: Whats pitch (definition)?
How to read a thread metric e.g. Tr, 12 x 3
Equation for number of motor steps?
P: distance between threads on a screw
Diameter of 12mm, pitch of 3mm
No. of steps = 306/( Step Angle) * Distance/Pitch
Stepper motor equations:
Relationship between travel time and step frequency
Equation for resolution
Travel Time = 1/Step Frequency
R = (Step angle*pitch)/360
Use for lead screw linear drives-think about stuff from lectures
For one revolution of a pulley, calculate distance travelled
Syringe driver, scissor action lift
Distance = Pitch * Number of teeth
Rack and Pinion: what is it, pros over belt
A rigid belt with a cog on an axel rotating along it
Pros: rigid, precise, easy to expand
Micro-stepping the stepper motor vs adding a gear box to the drive: pros and cons
MS: Pros-better resolution (256x)
Cons-torque, speed would decrease
GB: Pros-more torque, resolution would increase by gear box ratio
Cons-speed would decrease
Derailleur on a bike: what three tasks does it perform (the thing that sits on gears)
Controls chain/gear alignment
Limits range of lateral motion
Maintains a relatively constant tension on chain
Concentric and eccentric bearings: where is the shaft in both?
How to work out total offset using ‘e’ through 360°
CB: shaft at centre of the bearing
EB: shaft offset by value ‘e’, the eccentricity value
2*e
Eccentric bearings pros, cons
Pros: Can adjust for tension and remove gaps
Can adjust for wear and to counteract variance
Achieve higher motion accuracy
Cons: more expensive, set up required
Universal joint, cardan joint:
Use for both
What do they look like
What about velocity do you have to remember?
Change the axis angle of a rotational system-not for 90°
Pipe with a hinge in it
Pipe with two hinges in it
Velocity of output shaft isn’t same as input shaft unless they are aligned
Whats a Rzeppa joint used for
What effect does high and low belt tension have?
When an angle greater than 45° is needed
HBT: premature bearing wear
LBT: reduced accuracy and/or dislocation
Two ways to adjust a belt/pulley system
Adjustment distance for both
Linear and rotational tension adjustment L: slot distance R: 2*R(p)*sin(θ/2) R(p) = radius from pivot point θ = angle to move