Basics Drive Types Resources Torque Traction Mobility Speed - - PowerPoint PPT Presentation

 Importance  Basics  Drive Types  Resources  Torque  Traction  Mobility  Speed

The best drive train…

 is more important than anything else on the

robot

 meets your strategy goals  can be built with your resources  rarely needs maintenance  can be fixed within 5 minutes

 Know your resources  Decide after kickoff:

› Speed, power, shifting, mobility

 Use most powerful motors on drive train (usually)  Test early, with full weight, including destructive  Give software team TIME to work  Give drivers TIME to drive

 Speed (Measured in ft/sec)  Acceleration (Measured in ft/sec2)  Maneuverability (Measured in turning arc, degrees of freedom)  Turning Speed (measured in degrees/sec)  Traction (Measured in lb)  T

• rque (Measured in ft-lb)

 Weight (Measured in lb)  Cost (Measured by $ spent)  Efficiency (Measured in % Power)  Mobility (the ease with which the robot can be efficiently driven)  Controllability (Measured by rating – yuck)  Simplicity (Measured by time to fix, time to build)  Robustness (Measured by life time, # of impacts, force needed to

break)

The Standard in FIRST

Caster Driven Wheel

+ Easy to design + Easy to build + Light weight + Inexpensive + Agile

• Not much power
• Will not do well on ramps
• Less able to hold position
• Horrid traction

Motor(s) Motor(s)

Ziff 2.0

Chain

• r belt

Driven Wheels

+ Easy to design + Easy to build + Inexpensive + Powerful + Sturdy and stable 1 or 2 motors per side

• Not agile
• Turning is difficult
• Adjustments needed

Motor(s) Motor(s) Driven Wheels

The most standard drive train in FIRST

Icarus Carlson X

Driven Wheels

+ Easy to design + Easy to build + Powerful + Sturdy and stable + Many options Mecanum, traction

• Heavy-ish
• Costly-ish

Motor(s) Motor(s) Driven Wheels Motor(s) Motor(s)

Gearbox Gearbox

+ Easy to design + Easy to build + Powerful + Stable + Agile*

• Heavy **
• Expensive **

** - depending on wheel type

*2 ways to be agile A) Lower contact point

• n center wheel

B) Omni wheels on front or back or both + simple + easy + fast and powerful + agile 1 or 2 motors per side

Boris

Gearbox Gearbox

+ Powerful + Stable + Agile*

• HEAVY
• EXPENSIVE
• INNEFICIENT
• HORRID TURNING

*2 ways to be more agile A) Lower contact point on center wheel B) Omni wheels on front or back or both Benefits: Ability to go over things; high traction

Tank Tread Crab - Swerve Holonomic – Killough – Omni 3 wheel Mecanum Mouseball

Gearbox Gearbox

+ Powerful + VERY Stable

• NOT AGILE
• HEAVY
• Inefficient
• EXPENSIVE
• Hard to maintain
• Even worse

turning. For turning, lower the contact point on center of track wheel Benefits: Ability to go over things; even higher traction Will NOT push more than a well- controlled 6wd without major gearing-down 2-4 motors per side

 4 or 3 wheel drive

+ Simple Mechanics + Immediate Turning + Simple Control – 4 wheel independent

• No brake
• Minimal pushing power
• Jittery ride, unless w/ dualies
• Incline difficulty
• Max 50% Efficiency

+ Simple mechanisms + Immediate turn + Simple control – 4 wheel independent

• Minimal brake
• OK pushing power
• Expensive
• Heavy
• 67% Forward and reverse efficiency, 33%

sideways Has issues going up ramps

Thor

 High-traction wheels  Each wheel rotates to steer

+ No friction losses in wheel-floor interface + Ability to push or hold position + Simple wheels

• Complex system to control and

program

• Mechanical and control issues
• Difficult to drive
• Wheel turning delay
• Expensive
• Lots of machining required
• Minimum 5 motors (theoretically 4)

 One wheel steers  Various types  Lightweight  Fast  Non-standard › (design intensive)  Examples: › 16 in 2008 › 67 in 2005

Gearbox Gearbox

 More for fun!  Very maneuverable  Expensive, high-maintenance,

low pushing power

 Ackerman  Go Cart

+ Not many

• Complex system to control and program
• Going backward is interesting
• Complex to do well
• No real advantage in FIRST

 Torque = Force X Distance  Essentially, a measure of rotational force – how hard

the wheel turns

 Torque X Speed = Power  Controlled with gearboxes  Torque and speed have inverse relationship – if you

double the speed, you halve the torque

 Standard AndyMark Toughbox gearbox comes in

ratio 12.75:1

 Measured in Ft-Lbs

 CIM Motor:

› .25 ft-lbs of torque › 4614 RPM

 After Gearing Down:

› 3.18 ft-lbs torque › 362 RPM

 Static vs Dynamic

(^10% lower)

› Once you slip, you will slide easier › Design encoders into your system › Dynamic breaking & traction control

 Pushing force = Weight * m › m = friction coefficient

Normal Force (weight)

Static friction coefficients m = 0.05 = Self Lubricating Wheels (Lunacy anyone?) m = 0.1 = caster (free spinning) m = 0.3 = hard plastic m = 0.8 = smooth rubber, 80A durometer m = 1.0 = sticky rubber, 70A durometer m = 1.1 = conveyor treads

Pushing Force Traction

 Move x feet in any direction in a second  Generally speaking, the more mobile your robot

is, the less it can resist a push

Higher Mobility Higher Traction

 Robot mass is represented at one point  Mobility increases when Cg is low and centered  High parts = light weight  Low parts = heavy (within reason)  ROBOTS TIP! Battery motors pump, etc. Battery motors pump, etc. Ms Mobile Mr Fall Guy

 Game dependent  Stats for 2008 (very speedy year):

› max: 20 ft/sec › Controllable top speed: 15 ft/sec › Good pushing speed: 5 ft/sec

 Toughbox – 9 FPS

 Ground Interface (Wheels, Treads)  Shaft (Live, Dead)  Gears, Sprockets, and Pulleys  Chains, Belts, T

ensioners

 Bearings and Bushings  Gearbox  Motor  Sensors (encoders, counters)  Speed Controller

Provide propulsion in the forward and reverse

Omni Wheels

direction while allowing for easy sideways movements Rollers positioned at 45 degree angles from

Mecanum Wheels

wheel centerline, providing omnidirectional motion. Wheels paired with Roughtop or Wedgetop tread

Traction Wheels

material to make a strong and high-traction wheel.

Standard Wheels

 Live Shaft  Dead Shaft

Finally, the fun part!

 Thor’s First Steps  The Power of Traction Control  The Nonadrive

 Drive Trains are necessary and offer considerable

competitive advantage

 A well-built drive train offers flexibility, power, and

robustness

 A non-reliable or non-repairable drive base will turn

your robot into a boat anchor

 Good drive bases win consistently  Reliable drive bases win awards  Well-controlled, robust drive bases win

Championships

Andy Baker Brian Graham Mike Saunders