FTC Mechanical design
considerations
2012 edition
by: Andrew Rudolph
What we’re going to talk about
the rules
manipulators
ideas
2012-2013 rules
You’ve already read them right?
rules
Only can use preformed robotics
components from:
• Lego
• Tetrix
• Matrix
matrix
•Designed to bring costs down of FTC overseas
•Designed off standard lego grid
•Different motors
•Different motor controllers
•Different Gears and wheels
•Possibly thinner metal
•Belt system
•CV Axles
•Check some of the offerings at:
•http://matrixrobotics.com
Observed at World Cmp
http://www.chiefdelphi.com/forum
s/showthread.php?t=106017
matrix
rules
• Only COTS (Custom Off The Shelf) items
allowed:
• Linear Slide
• Non-motorized Turntables and Lazy
Susan
• Lead screws and threaded rod plus
compatible nuts
• Servo Blocks
• #25 Chain and connector or half links
rules
• Unlimited in quantity or size of the following:
• Raw material available to all teams from standard
distributors
• Standard bearings or bushings
• Fasteners
• Rope, Cord, Cable, monofilament, …
• Rubber bands
• Latex tubing
• Zip ties
• Nonslip pad without adhesive backing
• Electrical solder, tape and any type of glue/cement
• Any COTS lubricant as long as it doesn’t get on stuff
materials
www.onlinemetals.com
Extrusions
• Readily available from many retailers
• Cut and drill with simple tools
• Strong and lightweight
• Most commonly 6061 Aluminum
• 7075 Aluminum for higher strength
www.8020.net
materials
• Readily available from many retailers
• Cut and drill with simple tools
• Or Water Jet, Laser Cut, CNC Break
for complex parts
Sheet metal
materials
• Lexan (NOT ACRYLIC) easy to find and
work with
• Bend with heat
• Lots of shapes and different mechanical
characteristics available
Polycarbonate
(lexan)
Plastics
Coroplast
Sintra
Teflon
Nylon
Delrin
HDPE
materials
You can now Rapid Prototype Parts!
You can now 3D print Parts!
ABS
Polycarbonate
PLA
Plastics
materials
Steel wire rope
Paracord
150 lb test = 0.56mm
diameter
Solid steel wire
Rope, cord, etc…
Braided fishing line
88725K33 @ McMaster for $2.68 for 3’
materials
Drill rod (tool steel rod)
Bushing
6338K311 @ McMaster for $0.75 ea!
Lubricants
Lead screw or
Acme screw
drive components
Shoulder Bolts
Linear Bearing
Lifts!
You mastered these last
year…right?
lifts
We saw them last year
lifts
What did we miss last year?
Precision lifting
Variable position lifting
Lifts go up
Lifts go down
lifts
• Short height, Wide base
• Lift over base
• Requires lots of power
• Lots of moving parts
• Difficult to synchronize two sides
• Difficult to lift from ground
• Difficult too have finite control
• Poor lateral loading
Scissor lift
lifts
FRC 343 circa 2000
Lead screw or Acme screw
lifts
• Simple to build
• Can move fast
• Can reach fore and aft
• Light weight
• Object orientation changes
• Strong Lateral load
• Lift outside base
• Object orientation changes
• Difficult to multi position
• Do not lift high
Single joint arm
lifts
• Lots of freedom
• keep lift inside or outside of base
• complex to build
• heavy
• Lots of motors
• Difficult to control
multi joint arm
lifts
• Simple to build
• Light weight
• Object orientation stays the same
• Lift outside base
• Lots of torque required at shoulder
Four bar linkage
lifts
• twice the weight of four bar
• Object stays the same
• Higher lift than four bar
• Lift outside base
• Lots of torque required at shoulder
• More joints to create friction and
wobbles
six bar linkage
lifts
• Straight lift
• multiple positions
• small footprint
• COMPLEX
• difficult to maintain
• high CG
Telescoping
lifts
Combine multiple mechanisms
hybrid
Ideas
General design practices
ideas
What tasks within my
strategy do I need to
perform?
Let strategy drive your
robot design, not the
opposite
Are you going to…
• acquire it?
• manipulate it?
• store it?
• lift it?
• position it?
• release it?
ideas
Think like a robot about
the game piece
What does the game piece look like from
the robots POV?
What are all the ways the game piece
could lay?
What is the most usable or stable
position?
How does the object react?
ideas
other design considerations
Maximize your “Acquisition Zone”
ideas
other design considerations
Alignment Devices
ideas
other design considerations
Make it easy to drive
ideas
other design considerations
Will stray objects interfere?
ideas
other design considerations
Keep your Center of Gravity (CG) low
ideas
other design considerations
Design is an iterative process
ideas
Some design mantras
Really, simple IS better.
You don’t have to prototype everything…
Just the parts you want to work.
Assume nothing.
Sometimes wild ideas lead to champions.
Celebrity Endorsed.